Prosthetics of dentition defects 6 semester

Fixing the framework of the clasp prosthesis Before examining the finished frame of the arch prosthesis in the oral cavity, the doctor examines it on a plaster model. First of all, it is necessary to clarify the correspondence of the frame parts to the picture, which is depicted on the plaster model. Pay attention to the length of the arms of the clamps, the location of the occlusal overlays, the position of the branches, the arches, and so on. Clarity of the arrangement of individual elements with respect to the supporting teeth and toothless portions of the jaws; The location of the arcs, check the gap between them and the surface of the model, its uniformity and magnitude will indicate the quality of the frame. Pay attention to the quality of its processing, the surface structure of the metal after casting - the presence of pores, shells, casting defects, smooth transition of individual parts into each other. We pass to the examination of the framework in the oral cavity: we impose a skeleton according to the way of its introduction to the prosthetic bed. If it is not superimposed, then it is possible to change the way of introduction. Or metal on the frame got into the zones of undercuts, we find them with the help of carbon paper and carefully grind it. And also a possible variant of the deformation of the carcass in the treatment after casting. We estimate the adherence of the framework to the tissues of the prosthetic bed. We examine the support-retaining clamps: we pay attention to their location and fixation of the frame, which should be well fixed, removed with a little effort and also installed in the oral cavity. Be sure to check the gap between the arch, the frame of the saddle parts and the mucosa of the prosthetic bed. The ratio of the arc on the lower jaw to the bridle of the tongue, for this, after the imposition of the carcass in the oral cavity, we ask the patient to raise his tongue upward.
It is possible to detect the balancing of the carcass after its superimposition. Reasons: inaccurate imprint, deformation of the impression when casting the model, damage to the working model, shrinkage of the carcass after casting, deformation of the carcass during processing. You need to try to fit the frame by identifying areas that interfere with the overlap. If the doctor's actions do not lead to improvement when applied, then the frame needs to be altered. In this visit you need to make a choice of the color of artificial teeth.
 
Application of an arch prosthesis The doctor received the bugly prosthesis carefully examines. Checks the quality of processing, grinding and polishing of metal parts, as well as plastic ones. We check for the presence of a rounded edge of the prosthesis base, the quality of the inner and outer surfaces. On the outer surface, we evaluate the polymerization quality of the plastic (absence of pores, treatment of artificial gums, polishing of the surface). On the inner surface, we estimate the accuracy of the representation of the relief of the prosthetic bed, the presence of pores. When the doctor does not detect previously noted deficiencies, then we turn to the check in the oral cavity. We impose according to the way of insertion of the prosthesis. Correctly made prosthesis should be easily applied, well fixed, accurately restore occlusal relationships, fit tightly to the tissues of the prosthetic bed and do not balance. If the prosthesis does not overlap, then you need to establish the cause. First we put the copy paper under the denture and find out the places that prevent the imposition. Using a milling cutter remove excess plastic and again check the prosthesis in the oral cavity. Sometimes when melting wax on plastic, a test shift may occur, as a result of loosely fastening the frame, then some of the places in the frame may interfere, which are also checked with copying paper and cutting burs. If the balancing did not decrease, fixing the prosthesis did not improve, then such a prosthesis needs to be altered. Again, we check the fit of individual parts of the prosthesis to the tissues of the prosthetic bed. Then we check for occlusal relationships with different movements of the lower jaw using articulatory paper. A physician should seek multiple occlusal contacts between artificial teeth and between artificial and natural teeth. You can check the accuracy of the fit of the plastic base to the mucous membrane of the toothless portion of the alveolar process. Check with the help of the curing silicone mass. On the correct fit will be a thin, even layer of polymerized silicone mass. If there is an uneven surface of the mass, then it is necessary to remove the impression of the corrugating impression mass for carrying out the relocation by laboratory means. The patient should definitely give recommendations. In the first days of use, the prosthesis should not be removed within a day, only for hygiene measures. If
the patient feels discomfort during the use of the prosthesis or if the pain appears, then the patient removes the prosthesis, and 2-3 hours before going to the doctor to dress, to accurately diagnose the injury. The patient can eat almost any kind of food except hard (nuts and other). It is necessary to constantly maintain hygiene not only the oral cavity but also the prosthesis. To warn that the patient does not try to correct or sharpen the prosthesis with his own hands. In case of a breakdown, consult a doctor. The recommended period of use is about three years. Usually the period of adaptation in patients to prosthetic prosthetic devices is very rapid, as this type of prosthesis restores chewing efficiency by 98.4%.
 
The technology of manufacturing a solid-cast skeleton of a clasp prosthesis with a removable wax reproduction from the model.
After studying the model in parallelometry and drawing the framework of the clasp prosthesis, it is modeled using a silicone matrix. The process of preparation of the wax skeleton of a clasp prosthesis for casting it from metal and casting itself is as follows. The model on which the prosthesis is made should be of increased strength, because it models the elements of the skeleton of the clasp prosthesis with further replacement with metal, as well as their fitting. Combined models are manufactured for this purpose. Such models consist of a combination of solid gypsum, amalgam, cement, low-melting metal or plastic and gypsum. To obtain a combined model using low-melting metal in a gypsum print, it is necessary to fill the areas with a low-melting metal. They are covered with a roller from a moldin height of 5-6 mm. For a strong connection of the metal part with the gypsum base, use metal loops. One end is dipped in the molten alloy, the second - in the gypsum base of the model. The molten metal is filled with sections isolated by the mold. After cooling the metal, the mold is removed and the second half of the model is cast by conventional gypsum. Before modeling the arc and saddle parts, the model must be prepared. Areas where the arc and saddle parts will be covered with tin foil, burglar wax or adhesive plaster of appropriate thickness: under the arc - 0.3-0.5 mm, the surface of the toothless alveolar process - 1,5-2 mm. Simulation without gaskets can lead to the immersion of the arch of the manufactured prosthesis in the mucosa of the prosthetic bed. Modeling of the elements of the skeleton of the clasp prosthesis is carried out by using standard wax blanks or using special Formicant silicone matrices. To do this, the matrices are washed with boiling water and, using a heated spatula attached to the wax stick, fill the corresponding grooves of the matrix with molten wax to the level of its surface. Cut with a sharp spatula wax residues and release the wax reproduction.
After that, oil the surface of the teeth and the model and place in accordance with the drawing wax elements - first the arc and its branch, and then the clamper. After modeling the wax cage, the gates and sprue block are installed, the wax reproduction of the skeleton of the clasp prosthesis is removed, placed on the sub-cone cone and covered with a facing mass. After drying this layer, the gate block is covered with a cuvette and molded with a refractory mass. Dry and warm the cuvette in the muffle furnace, the wax is poured out. The mold is heated to 800 ° C. and filled with molten metal. After cooling, the frame is freed from the molding material and the sprue. By this method prostheses of simple designs with a minimum number of supporting teeth are manufactured, provided they are parallel. However, during the removal of the wax reproduction of the skeleton of the clasp prosthesis, the model always generates its deformation, especially in the area of the support-u-trivial clasps, whose shoulders go under the boundary line to the retention zone. After casting the frame, the shoulders of the clambers will have to be bent with forceps, which leads to the deformation of the clas- mers, and sometimes to their breaking off. Milling technology
Milling technology refers to a complex (complex) area in combined technology. Milling technology describes a method (method) for creating and introducing individual, parallel or conical fitings inside a tooth or tooth row. It arose because of the desire to meet the aesthetics and, if possible, achieve the axial load of the teeth, without creating an unnecessary burden on the periodontium. When we recall the technology of milling in the everyday life of the technique, we usually talk about individually created restraining and support elements, for example, a ring telescope, a full telescope, or a RS attachment (groove-shoulder attachment). BEGO Milling machine Paraskop M (Parascope M)
On the basis of the device is fixed the stand (frame), on which the movable bracket is mounted. The parascope M is driven by a micromotor, and its spindle can be moved by means of precisely driving three dimentional hinges. The pedal with the help of el. The magnet fixes the position of the micromotor. For replacing working tools, built-in collet clamps. Also, the device has a magnetic fixing of the model table, switching the left rotation to the right and adjusting the depth of the micrometer screw for drilling. The micromotor is adjustable up to 30,000 rpm. He does not need a service and has constant power every time he switches the speed.
Milling In the industry, milling is the process of processing the outer and inner surfaces of workpieces by the method of excision with the help of special cutting tools, called milling cutters. The essence of milling is not to create shavings, but
high-quality products on time and also economically. This is a mechanical cutting of objects by cutting tools that rotate around their axis.
 
Wax milling The main condition for an impeccable, almost definitive milling of wax is the fully modeled anatomical shape of the crown. Only then can we be sure that we will not go beyond the form and will have minimal metal losses during the next milling of the metal. Only in this way it is possible in the future to integrate the vestibular side lining into anatomical shape. Surface treatment is also possible with scrapers (scraper), but the advantage is provided by treating the wax with rotary tools. Since a small pressing force is needed here and a possible deformation is prevented in advance.
 
The technology of manufacturing solid brass prostheses on refractory models from cobalt-chromium alloys.
 
Without dwelling on the historical aspect of the gradual improvement of the technology of this labor-intensive process, which requires high qualifications of its performers, we will consider the technique of manufacturing an arch prosthesis at the present level, in particular, the casting of prosthetic frames on refractory models. The essence of this method is that the simulation of the wax reproduction of the framework and its casting from metal is carried out directly on the ceramic model. This technology prevents deformation of the wax reproduction and makes it possible to cast as accurately as possible the prosthetic bed, which in turn allows the incorporation into the prosthesis design of an unlimited number of supporting and supporting elements that ensure a rational distribution of the masticatory pressure, fixation and stabilization of the prosthesis. In addition, in the case of casting on a refractory model, the last time of casting expands and thereby compensates for the shrinkage of the metal during its cooling. The use of cobalt-chrome alloys for the casting of skeletons makes it possible to make them thin, delicate and at the same time sturdy.
 
Preparing the model for duplication The laboratory stage of manufacturing the arc prosthesis begins with the receipt of two working and auxiliary models. After examining the model in a parallelometer, drawing on the supporting teeth of the boundary line and the depth
of retention, a drawing is made on the model of the structure of the prosthesis frame. Next, a super-gypsum model is prepared for duplication to make a refractory copy, on which the frame will be modeled and cast. Preparation is that all the intervals between adjacent teeth, as well as part of the surface of the teeth between the necks and the boundary line, are poured with refractory wax or hardened by a mold or gypsum. On the supporting teeth fill niches (undercuts) only from the defect of the tooth row from the neck to the boundary line. If the retentive part of the clamber's shoulder on the supporting tooth is accurately placed on Ney's recommendation between the tooth's neck and the boundary line-lay a plate of refractory wax and cut it along the lower edge of the shoulder of the support-retaining clamp. On the lower edge of the shoulder on the tooth will remain a step that will go to the refractory model. GP Sosnin recommends a groove on the lower edge of the shoulder of the clammer with a sharp scalpel, which will pass to the refractory model and will be a guide for the location of this part of the clammer's shoulder. Pour wax gaps and retention points on the model, proceed to overlapping pads. The arc and the base mesh should not lie against the mucosa of the prosthetic field. These gaskets are made from clasp wax, tin or lead plates. The thickness of the pads under the net should be 1.5-2 mm - depending on the height of the supporting teeth, the type of bite. The thickness of the gaskets for the hyoid arc should be 0.5-1.5 mm, depending on the individual features of the relief of the alveolar process and the compliance of the mucosa. Pads for the palatine arch have a thickness of 0.3-0.5 mm. After selecting the plates of the required thickness and shape, they cover the model according to the skeleton drawing. Plates are strengthened with universal glue. If there are no such plates, you can use an adhesive plaster, which is glued with 1-2 layers of glue. The thickness of the gaskets in this case is regulated by the number of layers of the leucoplasty. Plates should be of uniform thickness, smooth and fit tightly to the model. After that, the model is strengthened on the table of the parallelometer in the position in which the boundary line was applied to the supporting teeth. In the collet device, fix the knife rod and rotate the table with the model, cut off the wax residues, the mold or gypsum up to the boundary line. These same teeth at the level of the boundary line are betrayed by parallelism, which is important for obtaining a high-quality refractory model.
 
Duplication of gypsum model
 
The masses for duplication should meet the following: - be elastic so that the model can be easily removed from the print; - be strong at breaking; - to have minimal shrinkage; - be resistant to chemicals; - be inert to the materials from which refractory models are made; - do not lose its properties in case of repeated use; - have a low melting point; - have a simple manufacturing technology. For duplication, reverse (reverse) hydrocolloid masses based on agar-agar (gelin, dentokol, perflex, virogel, veneer, etc.) or polyvinylchloride (PVC) are used. Recently, duplicating masses based on silicone (sillex, virosyl, etc.) and polyester rubber are widely used. Making an impression of helium. The model prepared for duplication is strengthened in a special cuvette, which consists of a base and a lid with three holes to fill the mass. The model is strengthened in the center of the base of the cuvette by a moldin or plasticine in order to obtain an impression with walls of uniform thickness. Mass "Gelin", cut into small pieces, put in an enamel, glass or porcelain vessel with a lid in which a thermometer is mounted. The vessel is put on a water bath (water is brought to a boil). Gelin is heated gradually, about 60 minutes. The heating temperature is 80 ° C. The mass is forbidden to heat above 90 ° C, because it will lose its properties and become unsuitable for obtaining impressions. The melted mass of "Gelin" is removed from the water bath and gradually cooled to a temperature of 48-50 ° C, stirring occasionally. The model for duplication is dipped for 5-10 minutes. In cold water to remove air bubbles from it and saturation with moisture. At the same time check the tightness of the fit to the model of the pads. The model with the base is removed from the water and blown with compressed air (to remove residual water). On the base of the cuvette, a lid is applied, and a melted mass is poured into one of its openings with a thin stream. When it appears in all the holes in the cover of the cuvette, complete the fill. Weight freezes 30-40 minutes. At room temperature. In order for the mass to freeze faster, after 15 minutes. After pouring the mass of the cuvette is dipped in a dish with cold proton water. The frozen mass becomes elastic, jelly-like, well cut with a knife. From the cuvette remove the base (bottom), the mass around the model is cut with a knife and slowly remove the model from the hydrocolloid print. The impression should be precise, smooth, shiny.
If the casting channels-gates pass through the base of the model, then in the impression the cone is fixed and the refractory model is manufactured. It must be manufactured immediately, to avoid shrinkage and deformation of the impression. The technology of obtaining impressions for all hydrocolloid masses is similar. The company BEGO (Germany) for duplication uses the masses "Virogel", "Virodubl", "Virozil" and special equipment. E.Ya. Vares (1992) proposes the use of impression elastic masses for the production of duplicate impressions. Impressions can be obtained in conventional standard cuvettes, but it is better to use the duplicated syringe cells developed by him (DShK). The set of DShK consists of a set of paired rings with a diameter of 40, 60 and 90 mm, a clamping ring, as well as a molding extension. This technique has a lot of positive. With the help of it you can duplicate all the varieties of models, because the duplicating form is thin and flexible enough, it's easy to bring out the model from it even if there are significant retention points. According to V.P. Stocking and co-authors, synthetic masses for dubbing are better in their properties than hydrocolloid ones based on agar-agar. The authors found that all the masses that are used to obtain impressions, after a while, decrease in size. This negatively affects the production of precise skeletons of clasp dentures in the case of casting on refractory models. So, the impression from the mass of "Gelin" becomes less than the standard immediately after its production by 0.4%, after 30 minutes. - by 0.7%, and after 60 minutes. - by 1%, in 24 hours - by 2.2%. It is known that the hydrocolloid masses slowly solidify at room temperature. Therefore, to accelerate the freezing according to the instructions, it is suggested that they be cooled with water. But after such cooling the impression becomes less than the standard. Given the above, it is understandable why the impression should be cast immediately after it is received. In addition, due to different thicknesses of the impression, the shrinkage will be different in different areas and this will lead not only to a reduction of the model, but also to its deformation. Polyvinylchloride mass allows during the duplication of models - to achieve high accuracy and stability, deviation in relation to the size of the impression from polyvinylchloride mass from methanol was 0.19%. The impression accurately repeats the standard, and during storage in the open air practically does not change its size. Multiple repartition of the mass does not actually change its properties. One impression can be cast several ceramic models, if there was a shortage. Impression of polyvinylchloride mass is elastic and strong. Thus, polyvinylchloride masses
more meet the requirements for duplicating masses and have irrefutable advantages over agar. The disadvantage of polyvinylchloride mass is only the high temperature of melting. On the print, it is possible to produce refractory models only from strong materials, otherwise the model will collapse during removal from the imprint. Modern industry produces a significant amount of synthetic materials that can be used to make duplicating masses.
 
Production of a refractory ceramic model The technique of casting skeletons of bronze prostheses on ceramic models has two advantages. First, there is no danger of deformation of the wax carcass reproduction during removal from the model and preparation for casting. Secondly, it is possible to compensate for the foundry shrinkage of the alloy by expanding the refractory model during the heating process. To compensate for casting shrinkage during casting on a refractory model, the ability to double expansion of quartz oxides during the heating process is used. It depends on such factors: expansion according to the law, after which all the bodies are expanded during heating; The ability of quartz oxides in the process of heating to transfer from one state to another, which is accompanied by a noticeable expansion and increase in the volume of the model. Accurate gravy can be obtained if the model uses a material that expands during heating The amount of shrinkage of the alloy, and then decreases during cooling to the previous dimensions. Such material is quartz, plasticized with ethyl silicate. Silicon oxide can be found in three alotrope forms: quartz, tridymite, cristobalite. Quartz, or ordinary natural quartz sand, has an L-shape. During heating to 573 ° C it acquires a B-shape. This is accompanied by an increase in volume. Transformations of the second form of quartz - cristobalite - occur at a temperature of 180-270 ° C, while a greater increase in volume is observed. The transformation of tridymite is not accompanied by an increase in volume, because it is not used as a molding mass. The volume of quartz is affected not only by its variety, but also by the size of the grain composition of the molding mass. The degree of thermal expansion is affected by the amount and type of fluid taken to mix the mass. MM Garner and co-authors (1962, 1969) note that the less liquid in the molding mass, the more it expands. The volume is also affected by refractory additives. So, if magnesium oxide is added to the molding material, then under the influence of temperature it will expand to a greater extent.
In 1933, Prenge and Mouwood were the first to propose a molding mass for the production of a refractory model for casting a clasp prosthesis. This technique is still used today. In our country, the first attempt to use the above-mentioned method of manufacturing prosthesis was made by M.I. Til. The technology was only for stainless steel casting. But then it turned out that stainless steel is unsuitable for the production of solid brass prostheses. R.M. Yurchak and coauthors (1969) proposed the molding mass "Silamin". This is a refractory mixture of fine grinding, which contains phosphate compounds. The mass of white color is released in a glass jar with ground glass stopper or plastic lid. On the lid put on a paper cap, which is then poured with melted paraffin. The weight is chemically resistant, hygroscopic, fireproof (1700 ° С). Mix in water. The beginning of hardening - after 7-10 minutes, and the end - 50-60 minutes. The coefficient of thermal expansion at a temperature of 800 ° C is 1.4%. To make a model, the powder is thoroughly mixed in a jar and poured into a rubber cup. To determine the amount of powder, multiply the mass of the dry gypsum model by 1.7. On average, one model requires 100-120 g of powder. To him, according to the instruction, add 14 ml of water. Vigorously stirring with a spatula, mix the powder with water to complete moistening for 1 min. On the vibration table, put a cuvette with an impression and fill it with small portions of mass. At the same time, the wet powder turns into a paste, which fills all the slits of the impression. In order to obtain a dense model with a smooth surface, it is necessary, during filling the impression, to smooth the spatula with a spatula, which are formed on the surface. Filling the form lasts 2-3 minutes, and then the shape is left on the vibration table for another 4-6 minutes. To compact the model and increase its expansion, the model must be cured under vacuum conditions, which helps to remove air and compact it. After 10-12 minutes. After the beginning of kneading the mass, when there is no longer a surface of the model to glow wetly, carefully remove the cone and leave the mold on the table for 43-45 minutes. - until completely solidified. From the beginning of mixing to full hardening, 55-60 minutes pass. Leave the model in the impression after full hardening is not recommended. The model with an otter is removed from the cuvette, and carefully cut the hydrocolloid mass with a knife so as not to damage it, free the model from the imprint. Dry in the air for 15-20 minutes, and then in a drying oven at a temperature of 180-200 ° C - 30 minutes. The dried warm model is dipped for 1 minute. In wax heated to a temperature of 150 ° C. The remains of the wax are shaken from the model and cooled, and then swept with a soft brush and proceed to the modeling of the clasp prosthesis.
The mass of "Christosil" consists of fireproof powder cristobalite, which has in its composition of phosphate compounds. Powder is hygroscopic, white, soluble in water. The beginning of hardening - in 5-7 minutes. Finally hardens after 40 minutes. The thermal coefficient of volumetric expansion at a temperature of 900 ° C is 1.4%. The mass is kneaded on hydrolysed tetrasilicate, which is prepared by mixing 55 ml of ethylsilicate - 32 from 36 ml of 96% ethyl alcohol and 16 ml of 1% hydrochloric acid solution. After 5 minutes. The active solution is used (VS Pogodin, VA Ponomareva, 1983). To prepare the mass take 100 g of powder and add 25 ml of hydrolysed tetraethylsilicate. The mass is thoroughly mixed, and in small portions it is filled with an impression in the cuvette, which is mounted on a vibration table. To increase the density of the model, a vacuum device is used. After 40 minutes. The model will become firm. After release from the impression and drying, it is fixed in paraffin at a temperature of 150 ° C for 1 minute. Weight "Christosil-2" - white powder, hygroscopic, soluble in water. The composition of the powder includes cristobalite, magnesium oxide, ammonium phosphate. Mix the mass on the water. The beginning of hardening - in 5-7 minutes. From the beginning of cooking. Finally hardens after 40-45 minutes. During the heating to 700 ° C, the expansion ratio is 1.4%. These masses contain phosphate compounds, on which the strength and expansion of the model depend during the hardening process. To duplicate the model, the hydrocoloid masses "Gelin" and "Dentacol" are used. Fill the duplicate print with masses on the shaker table. According to the instructions, the mass of "Silamin" is compacted on a vibration table for 6-8 minutes. Refractory models made by all rules are not strong enough, they can not always be cleaned of helium without breaking a tooth. At the same time, the outer surface of the base of the model will be much stronger than the working surface. This circumstance can be explained by the fact that during the vibration 6-8 min. The mass is considerably stratified. Large and heavier particles of mass settle in the lower layers of the model, and small and light ones settle in the upper layers. In this case, the amount of liquid in which the phosphate compounds are dissolved is increased in the upper layers of the model. Therefore, in the model after the crystallization of the phosphate compounds after prolonged vibration, the upper layers (the base of the model) are stronger than the lower (working surface). The crystallization of the upper and lower layers will be different, and this will lead to deformation of the model. Therefore, in the case of the production of refractory models from "Silamin" and "Christosila", it is not recommended to carry out vibration of the mass for longer than 1 min. The strength of refractory models is influenced by such phenomena as the adsorption of liquid from the molding mass
by helium. This reduces the strength of the contact layer of the model. To avoid this, the impression copy must be coated with ethyl silicate before the model is obtained, which has hydrophobic properties. The masses "Silamin", "Christosil", "Christosil-2" do not sufficiently compensate for shrinkage, they are not very strong even after drying and fixing the models. The use of ethylsilicate-32 for "Christosil" increases the strength of the model, but a significant amount of liquid (over 25 ml per 100 g of powder) can lead to significant shrinkage of the model during crystallization and drying. The amount of liquid can significantly affect the expansion of the model during heating. One way to increase the accuracy of casting dentures is to reduce the amount of fluid in the molding mass. Reduce the amount of bonding liquid (in case of hydrolysed ethylsilicate-32) Because of the low silicon content of the diooxide that is involved in the process of joining quartz particles, it is impossible, because less quantity of it can not bind the powder. Considering the shortcomings of the above-mentioned masses, V.A. Ozerov and E.M. Lyubarsky (1964) proposed a mass of "Bugelit", in which for binding is ethyl silicate-50-pexane. The composition of the mass includes: cristobalite sand (З0-40%), cristobalite in the form of dust (20-50%), quartz in the form of dust (20-40%). The powder is mixed with ethylsilicate-50-pexane. For solidification use a solution of caustic sodium (17-18% of the weight of the filler). Pecsan take 5-10% of the weight of the filler. The powder is resistant to air and does not lose its properties throughout the year. Take 18-25 ml of ethyl silicate per 100 g of powder. Mass is prepared on a vibration table, stirring constantly. The otipisk is filled in small portions. After vibration for 2-3 minutes. The vibrating table is turned off, and the surface of the model is smoothed and sprinkled with quartz sand. Cure the mass begins in 3-5 minutes, completely hardens after 40-50 minutes. After 40-50 minutes. The model is carefully released from the imprint, cutting it into pieces. The model is dried in air, and then in a drying oven at a temperature of 40 to 200 ° C, after which, in the hot state, the whole surface of the model is covered with a thin layer of ethyl silicate. After the model dries, this operation is repeated twice more. Fix the model in melted paraffin or wax, heated to 150 ° C. Models from the mass "Bugelit" are much stronger. І.Н. Krivenko, O.I. Marchenko and V.P. Stocking (1965) proposed a recipe for the molding mass, the
filler of which consists of quartz sand of different grinding. The composition of the mass includes the same amount of marshalite and quartz sand. For greater expansion of the model during heating, magnesium oxide is added to the composition of the mass. The bonding liquid is highly concentrated ethylsilicate50-pexane, and promotes the solidification of diethanolamine in a 1-2% solution of acetone. The thermal expansion coefficient of the model at 900 ° C is at least 1.61.8%. To prepare the model, take 50 g marshalite and 50 g quartz sand, 5 g magnesium oxide and all this is poured into a rubber cup. After thorough mixing, 16-18 ml of ethyl silicate-50-phexane is added to the mixture and again mixed well. Then the hardener is added to the mass, constantly mixing it. The mold is placed on a vibrating table and the impression is filled in small portions. After filling the vibrating table is turned off and the base of the model is sprinkled with quartz sand. The hardened model is freed from the impression and dried in air at a temperature of 20 ° C for 60 minutes, and then in a drying cabinet, raising the temperature to 200 ° C for 30 minutes. The model after that becomes sturdy, smooth, suitable for drawing a skeleton pattern on it, and also for modeling the skeleton of a clasp prosthesis. V.S. Fleis, M.I. Pyasetsky, S.I. Krishtab (1983) proposed a molding mass that sufficiently compensates for the shrinkage of KCS and can easily be made in the conditions of any dental laboratory. The composition of this mass includes: quartz sand (36.2%); Expanded clay in the form of powder (7.9%); Magnesium oxide (3.7%); Acetone solution of triethanolamine (7.9%); Polyethoxysiloxane-53 (8.3%); Quartz in the form of dust (37%). The mass compensates for the shrinkage of the alloy by 1.6-1.8%, which is a high index for the masses that the industry produces. Models made of this mass have a high hardness, good gas permeability, a smooth surface that ensures accuracy and a smooth surface of the casting of the prosthesis. The advantage of this mass over others lies in the fact that, having pre-prepared parts, it is possible to prepare a mass and obtain a refractory model as often as necessary, regardless of the mass available on the market. The model is also suitable for carrying out parallelometry and applying a pencil sketch of the clasp prosthesis to its surface. It is very strong and convenient for modeling the wax casing of the clasp prosthesis.
 
Simulation of the clasp prosthesis Before modeling the frame on the refractory model, the pattern is transferred from the gypsum model. Then the refractory model is covered with one layer of fine clay wax, well heated in water. This makes it possible to cover the entire surface of the model densely, than it achieves the adherence of the waxy
composition of the frame to the model, greater its strength. This reduces the shrinkage of wax. To model the frame of the prosthesis, wax "Formodent" is used. Silicone matrix should be rinsed with boiled water to remove wax and dust residues. The spatula is heated on the distiller and, holding it above the cavity of the arc or clamper form, a wax stick is applied to it, so that the melted wax slowly flows into the cavity until it is filled to the level of the surface of the matrix plate. Then gently cut off the excess wax above the level of the plate and, quietly, bending the silicone plate, remove the wax preform from the groove. The finished parts are folded in a box in layers, and, so that they do not stick together, restate with paper. To model the frame, wax blanks are selected, which correspond to the dimensions of the teeth, the shape of the clamp, and the size of the dentition defect. The selected parts are heated under an electric lamp before applying them to the model. Then the parts become plastic and cover the surface of the model well: the workpiece can not be heated on an open flame, because the thickness of the parts will be uneven. Simulations are performed carefully, accurately, without any assumptions for processing. All the elements are modeled so that the zones have the form of a finished part. Details, which account for the greatest load, should have the same thickness and be strong. The finished wax parts obtained by the matrix can immediately be applied to the model and crimped along the carcass pattern until the wax is plastic. Simulation of the framework must begin with the support-retaining clamps. In addition to blanks, wax yarns with a diameter of 0.8-1 mm can be used. The wax blank of the clamper is first pressed against the side of the tooth by the body of the clammer on the side of the defect of the tooth row, then the occlusal cover is pressed against the occlusal cavity on the chewing surface of the tooth. The shoulders of the Akera clamper are placed in such a way that the 2/3 (stabilizing part) lies above the boundary line, and the end parts (retention) under it, in accordance with the step on the supporting tooth. It is necessary to watch, that the shoulders gradually narrowed and thinned to the edge. The part of the clasp that lies on the supporting part of the tooth should be thick and have a semicircular cut. The shoots of the clasps are directed towards the basal grid or arc. Then the model is placed on the arc from a wax half-oval shape with a width of 4-5 mm. Subsequently, it is expanded by adding a modeling wax to a plate of clasp wax along the boundaries of the arc pattern, to the desired dimensions. Baseline grids should have a ledge, which they connect to the arc. This ledge is formed due to the smaller thickness of the mesh. It allows to create a gradual transition from the metal of the carcass arc to the base plastic and thus prevents the formation of
cracks and peeling in it. Wax details are connected with each other by melted wax. This avoids dangerous stresses in the wax structure of the frame. Wax for the modeling of the clasp prosthesis should be plastic, sticky, with minimal shrinkage and a small ash content.
 
Variants of location of the clasp prosthesis on the prosthetic bed The dimensions and position of the arc depend on the jaw, on which it is located, the type and localization of defects in the dentition, the shape and depth of the palatine slope, the shape of the alveolar portion, the mucosa of the prosthetic bed. The arc must repeat the configuration of the hard palate or the alveolar part of the jaw. On the upper jaw, the arch is made broad (8-10 mm) and flat, 1.5-2 mm thick, semi-oval in shape with rounded edges. The most rational is its location on the border between the middle and posterior third of the sky 10-12 mm anterior to the blind palatine fossae or at the level of the first permanent molar. With a flat sky the advantage is represented by a thin, but wider arc. With a high sky, the arc, on the contrary, can be thicker and therefore already. With a pronounced emetic reflex or the presence of the palatal torus, the arch has in the middle part the sky or in its front part. When the arc is located in the anterior part of the palatal slope, it is made wider and finer in the form of a narrow metal base. In some cases, especially when a combination of defects in the dentition in the anterior part with defect in the lateral, a metallic basis in the anterior part of the palatine slope can be combined with an arch that will be located at the level of the first molar. In addition, given the property of compliance of the mucous membrane of the prosthetic bed, the arch is raised above it by approximately 0.5-1 mm to prevent the formation of pressure sores. The annular arc is the most rigid structure. It is necessary in cases where anatomical formations are an obstacle to the application of an individual arc (a wide and long palatal torus). On the lower jaw, the arch is made (4-6 mm) and thicker (2-2.5 mm), placing it on the ligamental slope of the alveolar part in such a way as not to restrict the movement of the frenulum of the tongue. Here it also has a flat-convex cross-sectional shape, repeating the configuration of the alveolar part of the jaw by its flat surface. The arc is located 1 mm above the bottom of the hyoid fold at the maximum displacement upwards. The location of the arc on the slope of the alveolar part depends primarily on its height, the location of the attachment of the frenum of the tongue and the shape of the ramp. At a high alveolar part, the arch is located in its middle third, with a short one - the arch should be raised as high as possible, having its upper edge,
retreating approximately 1 mm from the gum level. With a very short alveolar part, when the distance between the bottom of the sublingual transitional fold and the gingival margin is less than 6 mm, there is a risk of injury to the bridle. This is an indication for changing the design of the prosthesis, that is, in this case, an advantage is provided, for example, by a prosthesis with a metal base in the form of a tongue plate or by applying a so-called tubercular arch, ie a metal strip that is located only on the lingual surface of the lower incisors. If the lingual ramp of the anterior part of the alveolar part of the lower jaw is pear-shaped, the lower edge of the lingual plate is located at the level of the most convex part at the beginning of the undercut zone. When determining the location of the arc on the slope of the alveolar part of the jaw, attention should be paid to its shape. In the canopy, first of all, it is necessary to take into account the length of the ramp, which depends on the severity of the alveolar part. When the mucous membrane of the toothless part of the alveolar ridges is compliant, when the sagging parts of the arch prosthesis may sag under the effect of the masticatory pressure, the arc can be submerged into the mucosa and injured by its lower edge. Therefore, the distance between the arc and the mucosa can be increased to 1.5-2 mm. When the steep slope of the alveolar part is taken into account, the degree of development of the alveolar part is taken into account, since the displacement of the arc occurs parallel to the surface of the mucosa. In this case, the arc is located at a minimum distance from the mucous membrane (0.5-1 mm), since its displacement can occur only in the vertical plane parallel to the ramp of the alveolar process. The most uncomfortable form of the alveolar ram is pear-shaped, under which an undercut appears, which limits the portion of the alveolar process to place the arch. The arc should be located above the maximum convexity of the ramp and be at least 0.5 mm from the mucous membrane. The frame of the saddle parts of the arch prosthesis is a grid or lattice, which, like the arc, should be 1.5-2 mm away from the mucosa and serve as a device for strengthening the base material. Between the arc and the frame of the saddle part it is necessary to create a so-called limiter of the basis, which has the form of a step and allows to prepare the place of transition of the arc into the saddle part of plastic in the form of an even surface.
 
Structure of the molding system To ensure the free access of molten metal to the mold, it is necessary to build a casting-feeding system correctly. To do this, a hole in the base of the model is filled with a wax stick with a diameter of 6-8 mm and proceeds to build a sprue
feeding system. The springs are a wire made of wax, after melting of which there are channels in the investment mass, with which the molten metal in the crucible or casting bowl of the flask comes into shape. Wax castles can be round or rectangular with a thickness of 0.8-4.5 mm. The industry produces gates in the sets "Voskolit". Gates of the desired diameter can also be made from waste wax on a special device that resembles the apparatus of "Parker". Such a device makes it possible to make gates with a diameter from 0.8 to 6 mm. They must be smooth, so as not to cause the appearance of vortices in the flow of molten metal, which adversely affect the quality of the casting. Since the crystallization of the metal starts from the periphery of the casting, this is not accompanied by a decrease in the volume of the solidifying metal. In order to obtain a homogeneous casting, it is necessary that the crystallization process of the metal takes place with a constant supply of additional molten metal to fill the voids that are formed during the hardening of the metal. If this does not happen, then in the middle of the casting there will be so-called shrinkage shells, which will weaken the casting. To prevent this at the springs near the part, a "clutch" in the form of a wax ball is installed, which is 3-4 times more than casting. When the gates are thick and short, the "muff" is not installed. For the casting of clasp prostheses on the refractory models, a cruciform, vane and single-channel gating systems are used. Cross-shaped sprue system is used for the manufacture of complex designs of prosthetic bridges. For the construction of a sprue system, rectangular springs are taken in the form of wax strips 3-4 mm wide and 0.8-1.5 mm thick. One end is attached at the arc-to-grid connection site, the second end is attached to the wax gate, which is fixed in the base hole of the model. Other gates are attached at one end to the middle of the arc, multi-link clasp, other parts of the frame. The second end of the gates is connected to the main gate, which passes through the base of the model. The number of gates depends on the complexity of the prosthesis. The winged gating system consists of arcuate-curved springs 3-1 mm in diameter, which are connected to the main gate at the base of the model with the elements of the prosthetic framework. The number of gates also depends on the complexity of the construction of the prosthesis. The bend of the springs makes it possible to fill the mold without reducing the movement of the metal and to reduce the stress in the alloy during its cooling. The single-channel gate system is formed by a gate 5-6 mm thick, which is attached to the cone with a thick end. Its second end, thinning to 3-4 mm, is attached to the frame of the prosthesis on one side. On the opposite side of the frame to the cone, attach a wax filament 1 mm thick - for the escape of gases. The
gate is strengthened in the direction of rotation of the model during the pouring of the alloy. In addition to these sprue systems, you can use others. During the construction of any runner system, the gates must be attached so that they can be easily separated from the cast frame without damaging it. After the construction of the sprue system, the waxy composition of the frame is treated with a tampon moistened with eucalyptus or other oil to smooth the surface of the carcass, eliminate chipping and unevenness. The residual oil is removed with acetone or ether and the smooth surface of the carcass is fixed. Then the skeleton of the prosthesis is washed in a solution of soap powder. Soap foam is removed by a stream of compressed air and proceeds to applying a refractory mass to the skeleton of the clasp prosthesis.
 
Molding materials For the production of solid braided prosthesis on refractory models from cobalt-chromium alloys, refractory masses "Silamin", "Kristasil-2", "Bugelit", "Stomaform", the masses of VP Chulka and PS Flisa are used. Foreign firms offer masses "Viroplyus", "Virovest", "Kerafayna", "Sakast", "Kermigold", etc. For casting skeletons of clasp prostheses made of precious metals, the masses "Aurit", "Sylaur", "Expectant". Molding masses "Siolit", "Formolite", etc. are used for casting prostheses without models. Since the refractory model is produced by filling with a molding mass of negative duplicated form, the latter should not be reduced. However, the masses after cooling give an insignificant shrinkage (0.40.5%). The refractory model of the molding mass must completely compensate for the hard shrinkage of the alloy, expand sufficiently during heating and be gas permeable to compensate for shrinkage and prevent the formation of gas pores. The weight of the refractory model should not be sintered to the surface of the metal, to recreate a smooth casting surface. The refractory model expands during hardening in a duplicating form and in a muffle furnace at a certain temperature. Thus, the precision of casting a metal frame depends on two types of expansion of the model: during hardening and Heating, i.e., from the total expansion expansion of the molding material. Compensatory expansion of molding materials, which are used for the manufacture of prosthetic bridges from KHS, range from 1.2-1.6%. Consequently, a properly selected set of basic and auxiliary materials, adherence to the technology of manufacturing solid-cast clasp prostheses makes it possible to produce them practically accurate.
 
Formation of the skeleton of the clasp prosthesis
 
To form a model with a skeleton of a clasp prosthesis in the flask, the same refractory mass should be taken from which the refractory model was made. The wax reproduction of the frame and the sprue system are covered with a liquid investment molding compound, it can be conveniently mixed in small portions (10-15 g) several times and applied to the frame with a brush, holding it over the model, and hand touching the vibrator. During vibration, the mass easily drains from the brush, filling the cracks, holes. This helps to avoid defects in the casting of the skeleton of the clasp prosthesis. Approximately 40-50 g of weight is used to cover one frame. After the mass has dried, the model is fixed on a special stand or cone and a suitable flask is selected. In the middle it is lined with plates of clasp wax or asbestos. The opoku is fixed on a support or a cone and poured with wax, so that the molding mass does not flow out. According to the instructions, the stock is prepared and poured into a flask, which is mounted on a vibrating table. Seal the mass at an average intensity of vibration. After hardening of the foaming mass, the flask is heated, the stand or cone is removed, the wax is waxed and heat treated. Modern molding masses allow casting of prosthetic frames on refractory models by an unprofitable method. In this case, plastic molds are used for forming, which are easily removed from the muffle after the mass has hardened. Form the frame, as in the first case. Due to the shape of the muffle during thermal processing, obstacles with respect to expansion disappear, and this makes it possible to get the casting more accurately. For the application of the refractory layer on the prosthesis frame and the gating system, it is also possible to use marshalite mixed with hydrolyzed tetraethylsilicate. The hydrolysis of ethylsilicate is carried out by adding to 105 ml of ethylsilicate 105 ml of ethyl alcohol and 45 ml of distilled water acidified with 0.20.3% hydrochloric acid solution (0.5 ml of water with 1-1.5 ml of acid with specific gravity of 1, 19). The mixture is constantly shaken. When the temperature reaches 45 ° C, add another 75 ml of ethyl silicate, continuing to shake. Wait until the temperature decreases and the ethyl silicate becomes transparent. The resulting ethyl silicate is left for 24 hours. After that, prepare the mixture: 3 parts marshalite and 1 part ethylsilicate. She is covered with a skeleton of a clasp prosthesis: put on a skeleton with a brush or pour it from a spoon. After applying a layer of mass, the frame is sprinkled with dry quartz sand. The model with a refractory layer applied to the frame is dried for 30 minutes. In air, and then set the model in a desiccator for 10 min. For drying in pairs of ammonia. To form ammonia vapors, 0.4 liters is poured onto the bottom of the desiccator. 20% ammonia solution.
After drying of the refractory layer in the desiccator, the model is ventilated for 10 minutes, and then a second layer of refractory mass is applied. For the second layer, the refractory mass must be slightly lighter than the first. The technique of applying the second layer is the same as for the first one. After that, pick up the flask, wipe it with paper from asbestos and install it on a stand or cone. The formation of the flask is carried out with dry quartz sand with two wet plugs. To do this, the flask is mounted on a shaker and filled with a layer of wet sand moistened with a 50% aqueous solution of liquid glass and compacted. Then fill the flask with dry quartz sand to the edges, compact it with vibration. The top layer of sand is moistened with a 50% aqueous solution of water glass with a thickness of 10-15 mm, the flask is dried in air for 10-16 minutes, and then the wax is melted, heating it in a muffle furnace. When the wax is completely melted and burned, the flask is transferred to a second muffle furnace with a programmed control, heated to 200 ° C. Correct heat treatment of the mold ensures accurate casting of the clasp prosthesis.
 
Melting the metal and pouring it into shape For melting metal, different melting units can be used. This is an oxygenacetylene device, or autogen, a voltaic arc apparatus, high-frequency and electroslag casting installations. For casting on refractory models, the first two machines should not be used, because during the melting of metal by these devices, a lot of carbon gets into the metal, some components burn out, because this process takes place in an external medium and the metal combines with the oxygen of the air. This leads to a change in the structure of the alloy. The best consequences for casting dentures on refractory models are provided by high-frequency and electroslag casting plants. The principle of the operation of foundry plants, with the exception of electroslag, is described in different textbooks, therefore we will only consider the technology of casting with the electroslag method. High-frequency casting plants are considered to be the best for today, but the zones also have certain drawbacks. While they are expensive, they require constant engineering supervision. Therefore, for small dental laboratories, they are not costeffective.Централизовано их использование также не всегда дает желательные последствия.
In the conditions of district, rural dental laboratories, it is best to use an electroslag melting apparatus. Equip it is not difficult, it is inexpensive and easy to use. In 1961, the Institute of Electric Welding. E.O. Paton developed a technology for obtaining steel and alloys of special quality (electroslag remelting of metal). Based on this development, the Department of Orthopedic Dentistry of the Poltava Dental Institute developed a method for melting steel for dental purposes. Its essence consists in remelting the electrodes from steel in a medium of molten synthetic slag. Melting of metal in the slag environment allows to obtain high quality casting, because the molten metal passes through the slag and is cleaned of impurities. The slag protects the metal from oxidation and prevents the elimination of alloy components from the alloy, which can not be achieved by melting in high-frequency installations. The study testified that the physicochemical properties of casting, which is obtained at electroslag installations, are better than those obtained at highfrequency melting plants. The installation consists of a metal cabinet that does not have side walls. On the basis of the cabinet, a steam generator and a stand with a glass for the flask are mounted. On the front wall of the cabinet there is a window with a protective light filter. The cover of the steam generator is connected by a rod, which is fixed to the back wall of the cabinet. The steamer is lowered onto the flask by means of a foot pedal connected by a pull rod. Moving the steam generator in the opposite direction is carried out by a spring. The steamer in form resembles a metallic glass. It is filled with moist asbestos or clay. The model with a frame and sprue system is strengthened on a special cone covered with a thin layer of wax. This cone is slightly different from those cones that are used for other methods of casting. On the cone, you can install one, two or three models with scaffold prosthetic skeletons. Models in this case should be placed on the cone at an angle of 180-120. Thus, in one ovary it will be possible to cast not one, but two or three skeletons of bugly prostheses, which is economically very viable. But refractory models should not have a very high base. Then the diameter of the flask will not be too large. Opoku is formed in the usual way. After melting the wax in the refractory mass, there remain a deep gating bowl and a conical primary riser. The opoku is heated to 800-900 ° C and kept at this temperature for 20-30 minutes. Then the flask is removed from the muffle furnace for the period of the metal melting. The main riser is closed with a device, a special valve with a spring of nichrome, so that slag does not enter the channels. The spring is made of nichrome wire with a
diameter of 0.6-0.8 mm (6 turns). The valve is manufactured on a special matrix of marshalite with ethyl silicate or from "Stomaform". When the mass begins to solidify in the matrix, a spring is inserted into the valve in the middle and dipped into 5 turns. The flask with the valve is placed in the installation cup and the synthetic slag ANF-1 or ANF-6 (6-8% of the weight of the metal to be melted) is poured into the spout. Slag includes calcium fluoride, aluminum oxide, titanium oxide, etc. Slag conducts current and has a large resistance. Due to the large resistance during the passage of current, the slag melts, melting the metal electrodes. In a dry state, the slag does not conduct a current, therefore, so that the current passes, a few drops of saturated sodium hydroxide solution are applied to the surface of the slag. In these drops of solution, electrodes made of cobalt-chromium alloy (for other types of casting - stainless steel) are introduced at a short distance from each other. If there are no special electrodes, then they are prepared from standard blanks that the industry produces, welding them. The electrodes are fixed in special holders. The electrodes are supplied with voltage from a conventional welding machine (voltage 45-60 V, current 60-80 A) through the holders. Since the slag has a large electrical resistance, it quickly heats up, melts, reaching a temperature of 1700-1800 ° C, as a result of which the electrodes are melted. The electrodes of different diameters (8-18 mm) can be melted, changing the voltage and current. Molten metal drips down through the slag to the bottom of the sprue bowl, while cleaning from non-metallic particles. Having welded a sufficient amount of metal, the electrodes are removed from the slag bath while turning off the current. Press the pedal lowering the steam generator, and a glass of steam generator tightly covers the gate bowl. The surface of the slag bath in the gating bowl has a temperature above 1000 ° C, because a large amount of steam appears in the steam generator and a pressure of 10-12 atm is created. The pressure is transferred to the liquid slag, which is contained above the molten metal, which, in turn, presses on the valve and causes it to drastically shift to its extreme position in the riser. The molten metal fills the riser and along the channels - the entire shape. After 3-4 minutes. After pouring the metal, the flask is immersed in cold water and gradually cleared of refractory mass and casting. If the flask was formed with quartz sand with two wet plugs, then destroy the plug and pour out sand from the flask. The prosthesis frame after this has a small hardness and plasticity, it is easy to machine and fit on the gypsum model with less time spent on these operations. After processing and polishing to provide a framework of high hardness, endurance and storage of elasticity, the carcass is heat treated at 760 ° C for 15 minutes. With further gradual cooling in the muffle furnace.
To prevent deformation of the prosthetic framework, it is thermally treated on a refractory model or dipped in sand. Alloys of metals In our country, the cobalt-chromium alloy (KHS), "Bugodent", as well as the alloys "Metost", "Plastocrist", "Kerakrist", "DBP-7", "DBP-8" are used for the production of solid braided prosthesis. Foreign firms produce cobalt-chrome alloys: Vitalium, Ticonium, Viptan, Vizil, Vironit, Virokast, Vironium and others. Gold-platinum and silver-palladium alloys are used to make bug prosthesis very rarely, because they are expensive and have unsatisfactory physicochemical properties. Most often, alloys based on cobalt and chromium are used for the fabrication of prosthetic bridges. They are strong enough, firm, springs, elastic, give a relatively small shrinkage. Cobalt-chrome alloy: the basis of this alloy is cobalt (66-67%), has high mechanical properties, chromium (26-30%), gives the alloy a hardness and increases the anti-corrosion resistance. With a chromium content of more than 30%, a friable phase forms in the alloy, which degrades the mechanical properties and cast properties of the alloy. Nickel (3-5%) increases ductility, viscosity, malleability of the alloy, increasing its technological properties. According to the requirements of the international standard, the chromium, cobalt and nickel content in the total mass of the alloy must be at least 85%, which ensures high corrosion properties, prevents the occurrence of oxidation-reduction reactions in the oral cavity, regardless of saliva composition and the influence of various factors. The introduction of more chromium and cobalt into the composition of the alloy reduces its shrinkage by 1.8-2%, which makes it possible to apply the technology of manufacturing prostheses, which completely compensates for shrinkage and ensures the accuracy of the product dimensions. Chrome, silicon and other components provide high hardness of the alloy, which greatly complicates the processing of products. But the use of precision casting methods on molded or prefabricated models from modeling materials does not require complex processing of cast dentures or parts and correction of them in the oral cavity. The physical and chemical properties of alloys depend on the nature and quantitative content of the alloying elements in them. KHS is characterized by high casting and technological properties, has good fluidity and low shrinkage, resistant to corrosion. Do not overheat the alloy more than 100 ° C after reaching the melting point. A more significant increase in the melting temperature promotes an increase in shrinkage, the formation of a coarse-grained structure, a decrease in other mechanical properties, and an anti-corrosion resistance. During the casting of complex thin-walled structures, KCS must be poured into a mold that needs to be
heated to 900 ° C. This helps maintain a good flow of molten mass, moving it through the channels of the mold and provides possible compensation of shrinkage during the crystallization of the alloy, since the heated form is increased in size as a result of thermal expansion. Despite the fact that the thermal expansion of the material from which the mold is made and the shrinkage of the KHS are different, if the casting material is properly selected and the casting regime is observed, it is possible to obtain an absolutely exact casting (without shrinkage), since it is not necessary to compensate for all shrinkage (1,8-2%), but only that part of it that occurs from the beginning of crystallization to complete cooling of the alloy. CCC is poorly stamped, soldered, bent and amenable to other mechanical influences, which are aimed at changing the shape of the product, therefore, it is not used for the manufacture of brazed and stamped products. The melting point of the alloy is 1450-1490 ° C. Gold alloy 750 pts: melting point is 1064 ° C. Pure gold has high ductility and ductility, and also small shrinkage. An exact gold sample can only be determined by chemical analysis, solutions that contain nitric and hydrochloric acid, or chlorine gold, are used as reagents.  The alloy of 750 samples consists of 75% gold, 8.3% silver and 16.7% copper. It is used for the manufacture of parts of removable structures of prostheses (clasps, arches). By reducing the percentage of copper in the alloy, 5-10% cadmium is introduced, which significantly reduces the melting temperature of the alloy. Such an alloy is used as a solder for joining individual parts of the prosthesis, which are made of gold from higher samples - 900 and 916. Some of the gold alloys contain up to 8% platinum. At the same time, their hardness, strength and elasticity are significantly increased. Such an alloy is characterized by a small shrinkage coefficient. It is used for making clasp prostheses, clasps, pins and others. Shrinkage of metal alloys Shrinkage is a reduction in body size when passing from a molten state to a solid state or from a warmer to a less heated state. Distinguish volumetric and linear shrinkage. Volume shrinkage - reduction in body volume. Linear shrinkage - reduction of body dimensions in a straight line (along the length and width). The degree of shrinkage of the material is characterized by the ratio of the reduced volume of the product to its initial volume and is expressed as a percentage. The reduction in body volume when it is cooled by 1 ° C is called the shrinkage factor. When manufacturing dentures, account should be taken of the shrinkage of the materials that are used. To better match the size of the prosthesis that is being manufactured, materials that have a small shrinkage are selected for the extent of the defects in the dentition. They also apply
such manufacturing techniques and methods of processing products that most densely compensate for the shrinkage of the material.
 
Methods of metal melting, which are used in the manufacture of skeletons of arc prostheses For melting of metal it is possible to use different melting plants: oxygenacetylene apparatus, autogen, apparatus of voltaic arc, high-frequency and electroslag casting installations. For casting on refractory models, the first two methods of melting metal should not be used, because during the melting of metal by these apparatuses, a lot of carbon enters the metal, some alloying components burn out, in addition, the process takes place in an external medium and the metal combines with air oxygen. This leads to a change in the structure of the alloy. The best results for casting bugelite prostheses on refractory models are provided by high-frequency and electroslag casting plants. Electroslag remelting of metal is important. This method of obtaining a special quality steel was developed in 1961 in the Institute of Electric Welding. E.O. Paton. Based on this development, the Department of Orthopedic Dentistry of the PMSI developed a method for melting steel for dental purposes. Further development of research in this direction was carried out at the Department of Orthopedic Dentistry of the PMSI (now UMSA). The essence of this method is the remelting of electrodes from KCS in a medium of molten synthetic slag (ANF-6). Melting of metal in the slag environment allows to obtain high quality casting because the molten metal passes through the highly active molten slag and is cleaned of impurities. Slag cleans the metal of nonmetallic impurities, as well as from oxygen, hydrogen, nitrogen, sulfur, phosphorus and prevents the alloy from alloying out of the alloy, which can not be achieved by melting in high-frequency installations. The study testified that the physicochemical properties of casting, which is obtained on electroslag installations, are better than those obtained at highfrequency melting plants. Compensation of shrinkage of metal at the ESR is solved due to the fact that the metal becomes thicker, as it is released from non-metallic inclusions, which leads to a significant decrease in the degree of shrinkage of the metal.
 
Treatment of the skeleton of the clasp prosthesis. Two methods are used to clean the molded framework of the clasp prosthesis from the refractory mass: 1) mechanical (the casting is cleaned of the refractory mass on the sandblasting unit); 2) chemical (use potassium or sodium hydroxide).
Pour in a stainless steel beaker to half the potassium hydroxide and put in a glass casting. Heat until the hydroxide melts, that is, up to 360 ° C, and boil for 2 to 3 minutes. After this, the casting is taken out of the beaker and immersed in cold water in a second metal beaker, cleansing of the refractory mass. To clean the casting from the hydroxide, it is immersed in bleach and boiled for 1-2 minutes, and then washed in running water. The surface of the casting after these treatments becomes clean. Chemical cleaning must be carried out in a fume hood with the ventilation included in a special device. Work should be in gloves and goggles. It is forbidden to dip wet casting into molten potassium because the water evaporates instantly on the casting surface and steam sprays the hydroxide, which can lead to injury. The springs are separated from the skeleton of the clasp prosthesis by a special cutting disc, which is strengthened on the grinding motor. The processing of the skeleton of the clasp prosthesis is carried out with abrasive wheels, heads, burs. They remove the remains of the gates, smooth the irregularities, blunt the sharp edges of the frame. At the same time, ensure that the relief and the thickness of the carcass surface, which is adjacent to the teeth and mucous membrane, are preserved. To smooth the surface of casting rubber elastic grinding wheels are used. After this treatment, the skeleton of the clasp prosthesis is tried on and adjusted to the working model from the super-gypsum. The fitted frame on the model is transferred to the clinic to check the design, fitting it in the patient's mouth. After that, the prosthesis is finally ground and polished with the help of fillets, hard brushes and pastes on the grinder. The skeleton of prosthetic braces has many hard-to-polish places, so it is better to polish them electrolytically. For this purpose, a cathode (stainless steel plate measuring 76x38x0.8 mm) is placed in a porcelain vessel with a capacity of 120 ml with a height of 50 mm. The anode is the skeleton of the prosthesis. An electrolyte is poured into the vessel (1-1.5 liters), consisting of: ethyl alcohol (120 ml), distilled water (120 ml), orthophosphoric acid (120 ml), ethylene glycol (540 ml), sulfuric acid (120 ml ). During the preparation of the solution, sulfuric acid is added to ethylene glycol. The current source is the 24V BC-24 rectifier with a current strength of up to 6 A. For polishing, the skeleton of the clasp prosthesis is fixed to the anode at a distance of 40 mm from the cathode, a current of 2 A is applied, returning the frame from time to time around the axis. The polishing period is 10-15 min. After polishing the frame is removed from the electrolyte and washed under running water. To improve the aesthetic appearance, the clasp prosthesis frames can be coated with nitrite titanium and gold. Fast durable gilding is made with a special liquid. This does not require the preparation of the frame. The liquid for gilding
has a high chemical resistance, economical, the process of degreasing the surface occurs simultaneously with the gilding. It can be performed on a ready clasp prosthesis. The last step in the laboratory production of an arch prosthesis is the placement of artificial teeth, which is performed after the carcass inspection in the clinic by an orthopedic physician. The setting of artificial teeth on a wax basis is performed under the control of the occludator or articulator, by the classical method. The technology of wax replacement for plastic does not differ from that used in manufacturing, partial removable prosthesis.
 
Duplication of gypsum model
 
The masses for duplication should meet the following: - be elastic so that the model can be easily removed from the print; - be strong at breaking; - to have minimal shrinkage; - be resistant to chemicals; - be inert to the materials from which refractory models are made; - do not lose its properties in case of repeated use; - have a low melting point; - have a simple manufacturing technology. For duplication, reverse (reverse) hydrocolloid masses based on agar-agar (gelin, dentokol, perflex, virogel, veneer, etc.) or polyvinylchloride (PVC) are used. Recently, duplicating masses based on silicone (sillex, virosyl, etc.) and polyester rubber are widely used. Making an impression of helium. The model prepared for duplication is strengthened in a special cuvette, which consists of a base and a lid with three holes to fill the mass. The model is strengthened in the center of the base of the cuvette by a moldin or plasticine in order to obtain an impression with walls of uniform thickness. Mass "Gelin", cut into small pieces, put in an enamel, glass or porcelain vessel with a lid in which a thermometer is mounted. The vessel is put on a water bath (water is brought to a boil). Gelin is heated gradually, about 60 minutes. The heating temperature is 80 ° C. The mass is forbidden to heat above 90 ° C, because it will lose its properties and become unsuitable for obtaining impressions. The melted mass of "Gelin" is removed from the water bath and gradually cooled to a temperature of 48-50 ° C, stirring occasionally.
The model for duplication is dipped for 5-10 minutes. In cold water to remove air bubbles from it and saturation with moisture. At the same time check the tightness of the fit to the model of the pads. The model with the base is removed from the water and blown with compressed air (to remove residual water). On the base of the cuvette, a lid is applied, and a melted mass is poured into one of its openings with a thin stream. When it appears in all the holes in the cover of the cuvette, complete the fill. Weight freezes 30-40 minutes. At room temperature. In order for the mass to freeze faster, after 15 minutes. After pouring the mass of the cuvette is dipped in a dish with cold proton water. The frozen mass becomes elastic, jelly-like, well cut with a knife. From the cuvette remove the base (bottom), the mass around the model is cut with a knife and slowly remove the model from the hydrocolloid print. The impression should be precise, smooth, shiny. If the casting channels-gates pass through the base of the model, then in the impression the cone is fixed and the refractory model is manufactured. It must be manufactured immediately, to avoid shrinkage and deformation of the impression. The technology of obtaining impressions for all hydrocolloid masses is similar. The company BEGO (Germany) for duplication uses the masses "Virogel", "Virodubl", "Virozil" and special equipment. E.Ya. Vares (1992) proposes the use of impression elastic masses for the production of duplicate impressions. Impressions can be obtained in conventional standard cuvettes, but it is better to use the duplicated syringe cells developed by him (DShK). The set of DShK consists of a set of paired rings with a diameter of 40, 60 and 90 mm, a clamping ring, as well as a molding extension. This technique has a lot of positive. With the help of it you can duplicate all the varieties of models, because the duplicating form is thin and flexible enough, it's easy to bring out the model from it even if there are significant retention points. According to V.P. Stocking and co-authors, synthetic masses for dubbing are better in their properties than hydrocolloid ones based on agar-agar. The authors found that all the masses that are used to obtain impressions, after a while, decrease in size. This negatively affects the production of precise skeletons of clasp dentures in the case of casting on refractory models. So, the impression from the mass of "Gelin" becomes less than the standard immediately after its production by 0.4%, after 30 minutes. - by 0.7%, and after 60 minutes. - by 1%, in 24 hours - by 2.2%. It is known that the hydrocolloid masses slowly solidify at room temperature. Therefore, to accelerate the freezing according to the instructions, it is suggested that they be cooled with water. But after such cooling the impression becomes less than the standard. Given the above, it is understandable why the
impression should be cast immediately after it is received. In addition, due to different thicknesses of the impression, the shrinkage will be different in different areas and this will lead not only to a reduction of the model, but also to its deformation. Polyvinylchloride mass allows during the duplication of models - to achieve high accuracy and stability, deviation in relation to the size of the impression from polyvinylchloride mass from methanol was 0.19%. The impression accurately repeats the standard, and during storage in the open air practically does not change its size. Multiple repartition of the mass does not actually change its properties. One impression can be cast several ceramic models, if there was a shortage. Impression of polyvinylchloride mass is elastic and strong. Thus, polyvinylchloride masses more meet the requirements for duplicating masses and have irrefutable advantages over agar. The disadvantage of polyvinylchloride mass is only the high temperature of melting. On the print, it is possible to produce refractory models only from strong materials, otherwise the model will collapse during removal from the imprint. Modern industry produces a significant amount of synthetic materials that can be used to make duplicating masses. Production of a refractory ceramic model The technique of casting skeletons of bronze prostheses on ceramic models has two advantages. First, there is no danger of deformation of the wax carcass reproduction during removal from the model and preparation for casting. Secondly, it is possible to compensate for the foundry shrinkage of the alloy by expanding the refractory model during the heating process. To compensate for casting shrinkage during casting on a refractory model, the ability to double expansion of quartz oxides during the heating process is used. It depends on such factors: expansion according to the law, after which all the bodies are expanded during heating; The ability of quartz oxides in the process of heating to transfer from one state to another, which is accompanied by a noticeable expansion and increase in the volume of the model. Accurate gravy can be obtained if the model uses a material that expands during heating The amount of shrinkage of the alloy, and then decreases during cooling to the previous dimensions. Such material is quartz, plasticized with ethyl silicate. Silicon oxide can be found in three alotrope forms: quartz, tridymite, cristobalite. Quartz, or ordinary natural quartz sand, has an L-shape. During heating to 573 ° C it acquires a B-shape. This is accompanied by an increase in volume.
Transformations of the second form of quartz - cristobalite - occur at a temperature of 180-270 ° C, while a greater increase in volume is observed. The transformation of tridymite is not accompanied by an increase in volume, because it is not used as a molding mass. The volume of quartz is affected not only by its variety, but also by the size of the grain composition of the molding mass. The degree of thermal expansion is affected by the amount and type of fluid taken to mix the mass. MM Garner and co-authors (1962, 1969) note that the less liquid in the molding mass, the more it expands. The volume is also affected by refractory additives. So, if magnesium oxide is added to the molding material, then under the influence of temperature it will expand to a greater extent. In 1933, Prenge and Mouwood were the first to propose a molding mass for the production of a refractory model for casting a clasp prosthesis. This technique is still used today. In our country, the first attempt to use the above-mentioned method of manufacturing prosthesis was made by M.I. Til. The technology was only for stainless steel casting. But then it turned out that stainless steel is unsuitable for the production of solid brass prostheses. R.M. Yurchak and coauthors (1969) proposed the molding mass "Silamin". This is a refractory mixture of fine grinding, which contains phosphate compounds. The mass of white color is released in a glass jar with ground glass stopper or plastic lid. On the lid put on a paper cap, which is then poured with melted paraffin. The weight is chemically resistant, hygroscopic, fireproof (1700 ° С). Mix in water. The beginning of hardening - after 7-10 minutes, and the end - 50-60 minutes. The coefficient of thermal expansion at a temperature of 800 ° C is 1.4%. To make a model, the powder is thoroughly mixed in a jar and poured into a rubber cup. To determine the amount of powder, multiply the mass of the dry gypsum model by 1.7. On average, one model requires 100-120 g of powder. To him, according to the instruction, add 14 ml of water. Vigorously stirring with a spatula, mix the powder with water to complete moistening for 1 min. On the vibration table, put a cuvette with an impression and fill it with small portions of mass. At the same time, the wet powder turns into a paste, which fills all the slits of the impression. In order to obtain a dense model with a smooth surface, it is necessary, during filling the impression, to smooth the spatula with a spatula, which are formed on the surface. Filling the form lasts 2-3 minutes, and then the shape is left on the vibration table for another 4-6 minutes. To compact the model and increase its expansion, the model must be cured under vacuum conditions, which helps to remove air and compact it. After 10-12 minutes. After the beginning of kneading the mass, when there is no longer a surface of the model to glow wetly, carefully
remove the cone and leave the mold on the table for 43-45 minutes. - until completely solidified. From the beginning of mixing to full hardening, 55-60 minutes pass. Leave the model in the impression after full hardening is not recommended. The model with an otter is removed from the cuvette, and carefully cut the hydrocolloid mass with a knife so as not to damage it, free the model from the imprint. Dry in the air for 15-20 minutes, and then in a drying oven at a temperature of 180-200 ° C - 30 minutes. The dried warm model is dipped for 1 minute. In wax heated to a temperature of 150 ° C. The remains of the wax are shaken from the model and cooled, and then swept with a soft brush and proceed to the modeling of the clasp prosthesis. The mass of "Christosil" consists of fireproof powder cristobalite, which has in its composition of phosphate compounds. Powder is hygroscopic, white, soluble in water. The beginning of hardening - in 5-7 minutes. Finally hardens after 40 minutes. The thermal coefficient of volumetric expansion at a temperature of 900 ° C is 1.4%. The mass is kneaded on hydrolysed tetrasilicate, which is prepared by mixing 55 ml of ethylsilicate - 32 from 36 ml of 96% ethyl alcohol and 16 ml of 1% hydrochloric acid solution. After 5 minutes. The active solution is used (VS Pogodin, VA Ponomareva, 1983). To prepare the mass take 100 g of powder and add 25 ml of hydrolysed tetraethylsilicate. The mass is thoroughly mixed, and in small portions it is filled with an impression in the cuvette, which is mounted on a vibration table. To increase the density of the model, a vacuum device is used. After 40 minutes. The model will become firm. After release from the impression and drying, it is fixed in paraffin at a temperature of 150 ° C for 1 minute. Weight "Christosil-2" - white powder, hygroscopic, soluble in water. The composition of the powder includes cristobalite, magnesium oxide, ammonium phosphate. Mix the mass on the water. The beginning of hardening - in 5-7 minutes. From the beginning of cooking. Finally hardens after 40-45 minutes. During the heating to 700 ° C, the expansion ratio is 1.4%. These masses contain phosphate compounds, on which the strength and expansion of the model depend during the hardening process. To duplicate the model, the hydrocoloid masses "Gelin" and "Dentacol" are used. Fill the duplicate print with masses on the shaker table. According to the instructions, the mass of "Silamin" is compacted on a vibration table for 6-8 minutes. Refractory models made by all rules are not strong enough, they can not always be cleaned of helium without breaking a tooth. At the same time, the outer surface of the base of the model will be much stronger than the working surface. This circumstance can be explained by the fact that during the vibration 6-8 min.
The mass is considerably stratified. Large and heavier particles of mass settle in the lower layers of the model, and small and light ones settle in the upper layers. In this case, the amount of liquid in which the phosphate compounds are dissolved is increased in the upper layers of the model. Therefore, in the model after the crystallization of the phosphate compounds after prolonged vibration, the upper layers (the base of the model) are stronger than the lower (working surface). The crystallization of the upper and lower layers will be different, and this will lead to deformation of the model. Therefore, in the case of the production of refractory models from "Silamin" and "Christosila", it is not recommended to carry out vibration of the mass for longer than 1 min. The strength of refractory models is influenced by such phenomena as the adsorption of liquid from the molding mass by helium. This reduces the strength of the contact layer of the model. To avoid this, the impression copy must be coated with ethyl silicate before the model is obtained, which has hydrophobic properties. The masses "Silamin", "Christosil", "Christosil-2" do not sufficiently compensate for shrinkage, they are not very strong even after drying and fixing the models. The use of ethylsilicate-32 for "Christosil" increases the strength of the model, but a significant amount of liquid (over 25 ml per 100 g of powder) can lead to significant shrinkage of the model during crystallization and drying. The amount of liquid can significantly affect the expansion of the model during heating. One way to increase the accuracy of casting dentures is to reduce the amount of fluid in the molding mass. Reduce the amount of bonding liquid (in case of hydrolysed ethylsilicate-32) Because of the low silicon content of the diooxide that is involved in the process of joining quartz particles, it is impossible, because less quantity of it can not bind the powder. Considering the shortcomings of the above-mentioned masses, V.A. Ozerov and E.M. Lyubarsky (1964) proposed a mass of "Bugelit", in which for binding is ethyl silicate-50-pexane. The composition of the mass includes: cristobalite sand (З0-40%), cristobalite in the form of dust (20-50%), quartz in the form of dust (20-40%). The powder is mixed with ethylsilicate-50-pexane. For solidification use a solution of caustic sodium (17-18% of the weight of the filler). Pecsan take 5-10% of the weight of the filler. The powder is resistant to air and does not lose its properties throughout the year. Take 18-25 ml of ethyl silicate per 100 g of powder. Mass is prepared on a vibration table, stirring constantly. The otipisk is filled in small portions. After
vibration for 2-3 minutes. The vibrating table is turned off, and the surface of the model is smoothed and sprinkled with quartz sand. Cure the mass begins in 3-5 minutes, completely hardens after 40-50 minutes. After 40-50 minutes. The model is carefully released from the imprint, cutting it into pieces. The model is dried in air, and then in a drying oven at a temperature of 40 to 200 ° C, after which, in the hot state, the whole surface of the model is covered with a thin layer of ethyl silicate. After the model dries, this operation is repeated twice more. Fix the model in melted paraffin or wax, heated to 150 ° C. Models from the mass "Bugelit" are much stronger. І.Н. Krivenko, O.I. Marchenko and V.P. Stocking (1965) proposed a recipe for the molding mass, the filler of which consists of quartz sand of different grinding. The composition of the mass includes the same amount of marshalite and quartz sand. For greater expansion of the model during heating, magnesium oxide is added to the composition of the mass. The bonding liquid is highly concentrated ethylsilicate50-pexane, and promotes the solidification of diethanolamine in a 1-2% solution of acetone. The thermal expansion coefficient of the model at 900 ° C is at least 1.61.8%. To prepare the model, take 50 g marshalite and 50 g quartz sand, 5 g magnesium oxide and all this is poured into a rubber cup. After thorough mixing, 16-18 ml of ethyl silicate-50-phexane is added to the mixture and again mixed well. Then the hardener is added to the mass, constantly mixing it. The mold is placed on a vibrating table and the impression is filled in small portions. After filling the vibrating table is turned off and the base of the model is sprinkled with quartz sand. The hardened model is freed from the impression and dried in air at a temperature of 20 ° C for 60 minutes, and then in a drying cabinet, raising the temperature to 200 ° C for 30 minutes. The model after that becomes sturdy, smooth, suitable for drawing a skeleton pattern on it, and also for modeling the skeleton of a clasp prosthesis. V.S. Fleis, M.I. Pyasetsky, S.I. Krishtab (1983) proposed a molding mass that sufficiently compensates for the shrinkage of KCS and can easily be made in the conditions of any dental laboratory. The composition of this mass includes: quartz sand (36.2%); Expanded clay in the form of powder (7.9%); Magnesium oxide (3.7%); Acetone solution of triethanolamine (7.9%); Polyethoxysiloxane-53 (8.3%); Quartz in the form of dust (37%). The mass compensates for the shrinkage of the alloy by 1.6-1.8%, which is a high index for the masses that the industry produces. Models made of this mass have a high hardness, good gas permeability, a smooth surface that ensures accuracy and a smooth surface of the casting of the prosthesis. The advantage of
this mass over others lies in the fact that, having pre-prepared parts, it is possible to prepare a mass and obtain a refractory model as often as necessary, regardless of the mass available on the market. The model is also suitable for carrying out parallelometry and applying a pencil sketch of the clasp prosthesis to its surface. It is very strong and convenient for modeling the wax casing of the clasp prosthesis. Simulation of the clasp prosthesis Before modeling the frame on the refractory model, the pattern is transferred from the gypsum model. Then the refractory model is covered with one layer of fine clay wax, well heated in water. This makes it possible to cover the entire surface of the model densely, than it achieves the adherence of the waxy composition of the frame to the model, greater its strength. This reduces the shrinkage of wax. To model the frame of the prosthesis, wax "Formodent" is used. Silicone matrix should be rinsed with boiled water to remove wax and dust residues. The spatula is heated on the distiller and, holding it above the cavity of the arc or clamper form, a wax stick is applied to it, so that the melted wax slowly flows into the cavity until it is filled to the level of the surface of the matrix plate. Then gently cut off the excess wax above the level of the plate and, quietly, bending the silicone plate, remove the wax preform from the groove. The finished parts are folded in a box in layers, and, so that they do not stick together, restate with paper. To model the frame, wax blanks are selected, which correspond to the dimensions of the teeth, the shape of the clamp, and the size of the dentition defect. The selected parts are heated under an electric lamp before applying them to the model. Then the parts become plastic and cover the surface of the model well: the workpiece can not be heated on an open flame, because the thickness of the parts will be uneven. Simulations are performed carefully, accurately, without any assumptions for processing. All the elements are modeled so that the zones have the form of a finished part. Details, which account for the greatest load, should have the same thickness and be strong. The finished wax parts obtained by the matrix can immediately be applied to the model and crimped along the carcass pattern until the wax is plastic. Simulation of the framework must begin with the support-retaining clamps. In addition to blanks, wax yarns with a diameter of 0.8-1 mm can be used. The wax blank of the clamper is first pressed against the side of the tooth by the body of the clammer on the side of the defect of the tooth row, then the occlusal cover is pressed against the occlusal cavity on the chewing surface of the tooth. The shoulders of the Akera clamper are placed in such a way that the 2/3 (stabilizing part) lies above the boundary line, and the end parts (retention) under it, in accordance with the step on the supporting tooth. It is necessary to watch, that the
shoulders gradually narrowed and thinned to the edge. The part of the clasp that lies on the supporting part of the tooth should be thick and have a semicircular cut. The shoots of the clasps are directed towards the basal grid or arc. Then the model is placed on the arc from a wax half-oval shape with a width of 4-5 mm. Subsequently, it is expanded by adding a modeling wax to a plate of clasp wax along the boundaries of the arc pattern, to the desired dimensions. Baseline grids should have a ledge, which they connect to the arc. This ledge is formed due to the smaller thickness of the mesh. It allows to create a gradual transition from the metal of the carcass arc to the base plastic and thus prevents the formation of cracks and peeling in it. Wax details are connected with each other by melted wax. This avoids dangerous stresses in the wax structure of the frame. Wax for the modeling of the clasp prosthesis should be plastic, sticky, with minimal shrinkage and a small ash content.
 
Variants of location of the clasp prosthesis on the prosthetic bed The dimensions and position of the arc depend on the jaw, on which it is located, the type and localization of defects in the dentition, the shape and depth of the palatine slope, the shape of the alveolar portion, the mucosa of the prosthetic bed. The arc must repeat the configuration of the hard palate or the alveolar part of the jaw. On the upper jaw, the arch is made broad (8-10 mm) and flat, 1.5-2 mm thick, semi-oval in shape with rounded edges. The most rational is its location on the border between the middle and posterior third of the sky 10-12 mm anterior to the blind palatine fossae or at the level of the first permanent molar. With a flat sky the advantage is represented by a thin, but wider arc. With a high sky, the arc, on the contrary, can be thicker and therefore already. With a pronounced emetic reflex or the presence of the palatal torus, the arch has in the middle part the sky or in its front part. When the arc is located in the anterior part of the palatal slope, it is made wider and finer in the form of a narrow metal base. In some cases, especially when a combination of defects in the dentition in the anterior part with defect in the lateral, a metallic basis in the anterior part of the palatine slope can be combined with an arch that will be located at the level of the first molar. In addition, given the property of compliance of the mucous membrane of the prosthetic bed, the arch is raised above it by approximately 0.5-1 mm to prevent the formation of pressure sores. The annular arc is the most rigid structure. It is necessary in cases where anatomical formations are an obstacle to the application of an individual arc (a wide and long palatal torus).
On the lower jaw, the arch is made (4-6 mm) and thicker (2-2.5 mm), placing it on the ligamental slope of the alveolar part in such a way as not to restrict the movement of the frenulum of the tongue. Here it also has a flat-convex cross-sectional shape, repeating the configuration of the alveolar part of the jaw by its flat surface. The arc is located 1 mm above the bottom of the hyoid fold at the maximum displacement upwards. The location of the arc on the slope of the alveolar part depends primarily on its height, the location of the attachment of the frenum of the tongue and the shape of the ramp. At a high alveolar part, the arch is located in its middle third, with a short one - the arch should be raised as high as possible, having its upper edge, retreating approximately 1 mm from the gum level. With a very short alveolar part, when the distance between the bottom of the sublingual transitional fold and the gingival margin is less than 6 mm, there is a risk of injury to the bridle. This is an indication for changing the design of the prosthesis, that is, in this case, an advantage is provided, for example, by a prosthesis with a metal base in the form of a tongue plate or by applying a so-called tubercular arch, ie a metal strip that is located only on the lingual surface of the lower incisors. If the lingual ramp of the anterior part of the alveolar part of the lower jaw is pear-shaped, the lower edge of the lingual plate is located at the level of the most convex part at the beginning of the undercut zone. When determining the location of the arc on the slope of the alveolar part of the jaw, attention should be paid to its shape. In the canopy, first of all, it is necessary to take into account the length of the ramp, which depends on the severity of the alveolar part. When the mucous membrane of the toothless part of the alveolar ridges is compliant, when the sagging parts of the arch prosthesis may sag under the effect of the masticatory pressure, the arc can be submerged into the mucosa and injured by its lower edge. Therefore, the distance between the arc and the mucosa can be increased to 1.5-2 mm. When the steep slope of the alveolar part is taken into account, the degree of development of the alveolar part is taken into account, since the displacement of the arc occurs parallel to the surface of the mucosa. In this case, the arc is located at a minimum distance from the mucous membrane (0.5-1 mm), since its displacement can occur only in the vertical plane parallel to the ramp of the alveolar process. The most uncomfortable form of the alveolar ram is pear-shaped, under which an undercut appears, which limits the portion of the alveolar process to place the arch. The arc should be located above the maximum convexity of the ramp and be at least 0.5 mm from the mucous membrane.
The frame of the saddle parts of the arch prosthesis is a grid or lattice, which, like the arc, should be 1.5-2 mm away from the mucosa and serve as a device for strengthening the base material. Between the arc and the frame of the saddle part it is necessary to create a so-called limiter of the basis, which has the form of a step and allows to prepare the place of transition of the arc into the saddle part of plastic in the form of an even surface. Structure of the molding system To ensure the free access of molten metal to the mold, it is necessary to build a casting-feeding system correctly. To do this, a hole in the base of the model is filled with a wax stick with a diameter of 6-8 mm and proceeds to build a spruefeeding system. The springs are a wire made of wax, after melting of which there are channels in the investment mass, with which the molten metal in the crucible or casting bowl of the flask comes into shape. Wax castles can be round or rectangular with a thickness of 0.8-4.5 mm. The industry produces gates in the sets "Voskolit". Gates of the desired diameter can also be made from waste wax on a special device that resembles the apparatus of "Parker". Such a device makes it possible to make gates with a diameter from 0.8 to 6 mm. They must be smooth, so as not to cause the appearance of vortices in the flow of molten metal, which adversely affect the quality of the casting. Since the crystallization of the metal starts from the periphery of the casting, this is not accompanied by a decrease in the volume of the solidifying metal. In order to obtain a homogeneous casting, it is necessary that the crystallization process of the metal takes place with a constant supply of additional molten metal to fill the voids that are formed during the hardening of the metal. If this does not happen, then in the middle of the casting there will be so-called shrinkage shells, which will weaken the casting. To prevent this at the springs near the part, a "clutch" in the form of a wax ball is installed, which is 3-4 times more than casting. When the gates are thick and short, the "muff" is not installed. For the casting of clasp prostheses on the refractory models, a cruciform, vane and single-channel gating systems are used. Cross-shaped sprue system is used for the manufacture of complex designs of prosthetic bridges. For the construction of a sprue system, rectangular springs are taken in the form of wax strips 3-4 mm wide and 0.8-1.5 mm thick. One end is attached at the arc-to-grid connection site, the second end is attached to the wax gate, which is fixed in the base hole of the model. Other gates are attached at one end to the middle of the arc, multi-link clasp, other parts of the frame. The second end of the gates is connected to the main gate, which passes through the base of the model. The number of gates depends on the complexity of the prosthesis. The winged gating system consists of arcuate-curved springs 3-1 mm in diameter, which are connected to the main gate
at the base of the model with the elements of the prosthetic framework. The number of gates also depends on the complexity of the construction of the prosthesis. The bend of the springs makes it possible to fill the mold without reducing the movement of the metal and to reduce the stress in the alloy during its cooling. The single-channel gate system is formed by a gate 5-6 mm thick, which is attached to the cone with a thick end. Its second end, thinning to 3-4 mm, is attached to the frame of the prosthesis on one side. On the opposite side of the frame to the cone, attach a wax filament 1 mm thick - for the escape of gases. The gate is strengthened in the direction of rotation of the model during the pouring of the alloy. In addition to these sprue systems, you can use others. During the construction of any runner system, the gates must be attached so that they can be easily separated from the cast frame without damaging it. After the construction of the sprue system, the waxy composition of the frame is treated with a tampon moistened with eucalyptus or other oil to smooth the surface of the carcass, eliminate chipping and unevenness. The residual oil is removed with acetone or ether and the smooth surface of the carcass is fixed. Then the skeleton of the prosthesis is washed in a solution of soap powder. Soap foam is removed by a stream of compressed air and proceeds to applying a refractory mass to the skeleton of the clasp prosthesis.
 
Molding materials For the production of solid braided prosthesis on refractory models from cobalt-chromium alloys, refractory masses "Silamin", "Kristasil-2", "Bugelit", "Stomaform", the masses of VP Chulka and PS Flisa are used. Foreign firms offer masses "Viroplyus", "Virovest", "Kerafayna", "Sakast", "Kermigold", etc. For casting skeletons of clasp prostheses made of precious metals, the masses "Aurit", "Sylaur", "Expectant". Molding masses "Siolit", "Formolite", etc. are used for casting prostheses without models. Since the refractory model is produced by filling with a molding mass of negative duplicated form, the latter should not be reduced. However, the masses after cooling give an insignificant shrinkage (0.40.5%). The refractory model of the molding mass must completely compensate for the hard shrinkage of the alloy, expand sufficiently during heating and be gas permeable to compensate for shrinkage and prevent the formation of gas pores. The weight of the refractory model should not be sintered to the surface of the metal, to recreate a smooth casting surface. The refractory model expands during hardening in a duplicating form and in a muffle furnace at a certain temperature. Thus, the precision of casting a metal frame depends on two types of expansion of
the model: during hardening and Heating, i.e., from the total expansion expansion of the molding material. Compensatory expansion of molding materials, which are used for the manufacture of prosthetic bridges from KHS, range from 1.2-1.6%. Consequently, a properly selected set of basic and auxiliary materials, adherence to the technology of manufacturing solid-cast clasp prostheses makes it possible to produce them practically accurate.
 
 
Formation of the skeleton of the clasp prosthesis
 
To form a model with a skeleton of a clasp prosthesis in the flask, the same refractory mass should be taken from which the refractory model was made. The wax reproduction of the frame and the sprue system are covered with a liquid investment molding compound, it can be conveniently mixed in small portions (10-15 g) several times and applied to the frame with a brush, holding it over the model, and hand touching the vibrator. During vibration, the mass easily drains from the brush, filling the cracks, holes. This helps to avoid defects in the casting of the skeleton of the clasp prosthesis. Approximately 40-50 g of weight is used to cover one frame. After the mass has dried, the model is fixed on a special stand or cone and a suitable flask is selected. In the middle it is lined with plates of clasp wax or asbestos. The opoku is fixed on a support or a cone and poured with wax, so that the molding mass does not flow out. According to the instructions, the stock is prepared and poured into a flask, which is mounted on a vibrating table. Seal the mass at an average intensity of vibration. After hardening of the foaming mass, the flask is heated, the stand or cone is removed, the wax is waxed and heat treated. Modern molding masses allow casting of prosthetic frames on refractory models by an unprofitable method. In this case, plastic molds are used for forming, which are easily removed from the muffle after the mass has hardened. Form the frame, as in the first case. Due to the shape of the muffle during thermal processing, obstacles with respect to expansion disappear, and this makes it possible to get the casting more accurately. For the application of the refractory layer on the prosthesis frame and the gating system, it is also possible to use marshalite mixed with hydrolyzed tetraethylsilicate. The hydrolysis of ethylsilicate is carried out by adding to 105 ml of ethylsilicate 105 ml of ethyl alcohol and 45 ml of distilled water acidified with 0.20.3% hydrochloric acid solution (0.5 ml of water with 1-1.5 ml of acid with specific gravity of 1, 19). The mixture is constantly shaken. When the temperature
reaches 45 ° C, add another 75 ml of ethyl silicate, continuing to shake. Wait until the temperature decreases and the ethyl silicate becomes transparent. The resulting ethyl silicate is left for 24 hours. After that, prepare the mixture: 3 parts marshalite and 1 part ethylsilicate. She is covered with a skeleton of a clasp prosthesis: put on a skeleton with a brush or pour it from a spoon. After applying a layer of mass, the frame is sprinkled with dry quartz sand. The model with a refractory layer applied to the frame is dried for 30 minutes. In air, and then set the model in a desiccator for 10 min. For drying in pairs of ammonia. To form ammonia vapors, 0.4 liters is poured onto the bottom of the desiccator. 20% ammonia solution. After drying of the refractory layer in the desiccator, the model is ventilated for 10 minutes, and then a second layer of refractory mass is applied. For the second layer, the refractory mass must be slightly lighter than the first. The technique of applying the second layer is the same as for the first one. After that, pick up the flask, wipe it with paper from asbestos and install it on a stand or cone. The formation of the flask is carried out with dry quartz sand with two wet plugs. To do this, the flask is mounted on a shaker and filled with a layer of wet sand moistened with a 50% aqueous solution of liquid glass and compacted. Then fill the flask with dry quartz sand to the edges, compact it with vibration. The top layer of sand is moistened with a 50% aqueous solution of water glass with a thickness of 10-15 mm, the flask is dried in air for 10-16 minutes, and then the wax is melted, heating it in a muffle furnace. When the wax is completely melted and burned, the flask is transferred to a second muffle furnace with a programmed control, heated to 200 ° C. Correct heat treatment of the mold ensures accurate casting of the clasp prosthesis.
 
Melting the metal and pouring it into shape For melting metal, different melting units can be used. This is an oxygenacetylene device, or autogen, a voltaic arc apparatus, high-frequency and electroslag casting installations. For casting on refractory models, the first two machines should not be used, because during the melting of metal by these devices, a lot of carbon gets into the metal, some components burn out, because this process takes place in an external medium and the metal combines with the oxygen of the air. This leads to a change in the structure of the alloy. The best consequences for casting dentures on refractory models are provided by high-frequency and electroslag casting plants.
The principle of the operation of foundry plants, with the exception of electroslag, is described in different textbooks, therefore we will only consider the technology of casting with the electroslag method. High-frequency casting plants are considered to be the best for today, but the zones also have certain drawbacks. While they are expensive, they require constant engineering supervision. Therefore, for small dental laboratories, they are not costeffective.Централизовано их использование также не всегда дает желательные последствия. In the conditions of district, rural dental laboratories, it is best to use an electroslag melting apparatus. Equip it is not difficult, it is inexpensive and easy to use. In 1961, the Institute of Electric Welding. E.O. Paton developed a technology for obtaining steel and alloys of special quality (electroslag remelting of metal). Based on this development, the Department of Orthopedic Dentistry of the Poltava Dental Institute developed a method for melting steel for dental purposes. Its essence consists in remelting the electrodes from steel in a medium of molten synthetic slag. Melting of metal in the slag environment allows to obtain high quality casting, because the molten metal passes through the slag and is cleaned of impurities. The slag protects the metal from oxidation and prevents the elimination of alloy components from the alloy, which can not be achieved by melting in high-frequency installations. The study testified that the physicochemical properties of casting, which is obtained at electroslag installations, are better than those obtained at highfrequency melting plants. The installation consists of a metal cabinet that does not have side walls. On the basis of the cabinet, a steam generator and a stand with a glass for the flask are mounted. On the front wall of the cabinet there is a window with a protective light filter. The cover of the steam generator is connected by a rod, which is fixed to the back wall of the cabinet. The steamer is lowered onto the flask by means of a foot pedal connected by a pull rod. Moving the steam generator in the opposite direction is carried out by a spring. The steamer in form resembles a metallic glass. It is filled with moist asbestos or clay. The model with a frame and sprue system is strengthened on a special cone covered with a thin layer of wax. This cone is slightly different from those cones that are used for other methods of casting. On the cone, you can install one, two or three models with scaffold prosthetic skeletons. Models in this case should be placed on the cone at an angle of 180-120. Thus, in one ovary it will be possible to cast not one, but two or three skeletons of bugly prostheses, which is economically very viable. But refractory
models should not have a very high base. Then the diameter of the flask will not be too large. Opoku is formed in the usual way. After melting the wax in the refractory mass, there remain a deep gating bowl and a conical primary riser. The opoku is heated to 800-900 ° C and kept at this temperature for 20-30 minutes. Then the flask is removed from the muffle furnace for the period of the metal melting. The main riser is closed with a device, a special valve with a spring of nichrome, so that slag does not enter the channels. The spring is made of nichrome wire with a diameter of 0.6-0.8 mm (6 turns). The valve is manufactured on a special matrix of marshalite with ethyl silicate or from "Stomaform". When the mass begins to solidify in the matrix, a spring is inserted into the valve in the middle and dipped into 5 turns. The flask with the valve is placed in the installation cup and the synthetic slag ANF-1 or ANF-6 (6-8% of the weight of the metal to be melted) is poured into the spout. Slag includes calcium fluoride, aluminum oxide, titanium oxide, etc. Slag conducts current and has a large resistance. Due to the large resistance during the passage of current, the slag melts, melting the metal electrodes. In a dry state, the slag does not conduct a current, therefore, so that the current passes, a few drops of saturated sodium hydroxide solution are applied to the surface of the slag. In these drops of solution, electrodes made of cobalt-chromium alloy (for other types of casting - stainless steel) are introduced at a short distance from each other. If there are no special electrodes, then they are prepared from standard blanks that the industry produces, welding them. The electrodes are fixed in special holders. The electrodes are supplied with voltage from a conventional welding machine (voltage 45-60 V, current 60-80 A) through the holders. Since the slag has a large electrical resistance, it quickly heats up, melts, reaching a temperature of 1700-1800 ° C, as a result of which the electrodes are melted. The electrodes of different diameters (8-18 mm) can be melted, changing the voltage and current. Molten metal drips down through the slag to the bottom of the sprue bowl, while cleaning from non-metallic particles. Having welded a sufficient amount of metal, the electrodes are removed from the slag bath while turning off the current. Press the pedal lowering the steam generator, and a glass of steam generator tightly covers the gate bowl. The surface of the slag bath in the gating bowl has a temperature above 1000 ° C, because a large amount of steam appears in the steam generator and a pressure of 10-12 atm is created. The pressure is transferred to the liquid slag, which is contained above the molten metal, which, in turn, presses on the valve and causes it to drastically shift to its extreme position in the riser. The molten metal fills the riser and along the channels - the entire shape. After 3-4 minutes. After pouring the metal, the
flask is immersed in cold water and gradually cleared of refractory mass and casting. If the flask was formed with quartz sand with two wet plugs, then destroy the plug and pour out sand from the flask. The prosthesis frame after this has a small hardness and plasticity, it is easy to machine and fit on the gypsum model with less time spent on these operations. After processing and polishing to provide a framework of high hardness, endurance and storage of elasticity, the carcass is heat treated at 760 ° C for 15 minutes. With further gradual cooling in the muffle furnace. To prevent deformation of the prosthetic framework, it is thermally treated on a refractory model or dipped in sand. Alloys of metals In our country, the cobalt-chromium alloy (KHS), "Bugodent", as well as the alloys "Metost", "Plastocrist", "Kerakrist", "DBP-7", "DBP-8" are used for the production of solid braided prosthesis. Foreign firms produce cobalt-chrome alloys: Vitalium, Ticonium, Viptan, Vizil, Vironit, Virokast, Vironium and others. Gold-platinum and silver-palladium alloys are used to make bug prosthesis very rarely, because they are expensive and have unsatisfactory physicochemical properties. Most often, alloys based on cobalt and chromium are used for the fabrication of prosthetic bridges. They are strong enough, firm, springs, elastic, give a relatively small shrinkage. Cobalt-chrome alloy: the basis of this alloy is cobalt (66-67%), has high mechanical properties, chromium (26-30%), gives the alloy a hardness and increases the anti-corrosion resistance. With a chromium content of more than 30%, a friable phase forms in the alloy, which degrades the mechanical properties and cast properties of the alloy. Nickel (3-5%) increases ductility, viscosity, malleability of the alloy, increasing its technological properties. According to the requirements of the international standard, the chromium, cobalt and nickel content in the total mass of the alloy must be at least 85%, which ensures high corrosion properties, prevents the occurrence of oxidation-reduction reactions in the oral cavity, regardless of saliva composition and the influence of various factors. The introduction of more chromium and cobalt into the composition of the alloy reduces its shrinkage by 1.8-2%, which makes it possible to apply the technology of manufacturing prostheses, which completely compensates for shrinkage and ensures the accuracy of the product dimensions. Chrome, silicon and other components provide high hardness of the alloy, which greatly complicates the processing of products. But the use of precision casting methods on molded or prefabricated models from modeling materials does not require complex processing of cast dentures or parts and correction of them in the oral cavity.
The physical and chemical properties of alloys depend on the nature and quantitative content of the alloying elements in them. KHS is characterized by high casting and technological properties, has good fluidity and low shrinkage, resistant to corrosion. Do not overheat the alloy more than 100°C after reaching the melting point. A more significant increase in the melting temperature promotes an increase in shrinkage, the formation of a coarse-grained structure, a decrease in other mechanical properties, and an anti-corrosion resistance. During the casting of complex thin-walled structures, KCS must be poured into a mold that needs to be heated to 900°C. This helps maintain a good flow of molten mass, moving it through the channels of the mold and provides possible compensation of shrinkage during the crystallization of the alloy, since the heated form is increased in size as a result of thermal expansion. Despite the fact that the thermal expansion of the material from which the mold is made and the shrinkage of the KHS are different, if the casting material is properly selected and the casting regime is observed, it is possible to obtain an absolutely exact casting (without shrinkage), since it is not necessary to compensate for all shrinkage (1,8-2%), but only that part of it that occurs from the beginning of crystallization to complete cooling of the alloy. CCC is poorly stamped, soldered, bent and amenable to other mechanical influences, which are aimed at changing the shape of the product, therefore, it is not used for the manufacture of brazed and stamped products. The melting point of the alloy is 1450-1490°C. Gold alloy 750 pts: melting point is 1064°C. Pure gold has high ductility and ductility, and also small shrinkage. An exact gold sample can only be determined by chemical analysis, solutions that contain nitric and hydrochloric acid, or chlorine gold, are used as reagents.  The alloy of 750 samples consists of 75% gold, 8.3% silver and 16.7% copper. It is used for the manufacture of parts of removable structures of prostheses (clasps, arches). By reducing the percentage of copper in the alloy, 5-10% cadmium is introduced, which significantly reduces the melting temperature of the alloy. Such an alloy is used as a solder for joining individual parts of the prosthesis, which are made of gold from higher samples - 900 and 916.    Some of the gold alloys contain up to 8% platinum. At the same time, their hardness, strength and elasticity are significantly increased. Such an alloy is characterized by a small shrinkage coefficient. It is used for making clasp prostheses, clasps, pins and others. Shrinkage of metal alloys Shrinkage is a reduction in body size when passing from a molten state to a solid state or from a warmer to a less heated state.
Distinguish volumetric and linear shrinkage. Volume shrinkage - reduction in body volume. Linear shrinkage - reduction of body dimensions in a straight line (along the length and width). The degree of shrinkage of the material is characterized by the ratio of the reduced volume of the product to its initial volume and is expressed as a percentage. The reduction in body volume when it is cooled by 1°C is called the shrinkage factor. When manufacturing dentures, account should be taken of the shrinkage of the materials that are used. To better match the size of the prosthesis that is being manufactured, materials that have a small shrinkage are selected for the extent of the defects in the dentition. They also apply such manufacturing techniques and methods of processing products that most densely compensate for the shrinkage of the material. Methods of metal melting, which are used in the manufacture of skeletons of arc prostheses For melting of metal it is possible to use different melting plants: oxygenacetylene apparatus, autogen, apparatus of voltaic arc, high-frequency and electroslag casting installations. For casting on refractory models, the first two methods of melting metal should not be used, because during the melting of metal by these apparatuses, a lot of carbon enters the metal, some alloying components burn out, in addition, the process takes place in an external medium and the metal combines with air oxygen. This leads to a change in the structure of the alloy. The best results for casting bugelite prostheses on refractory models are provided by high-frequency and electroslag casting plants. Electroslag remelting of metal is important. This method of obtaining a special quality steel was developed in 1961 in the Institute of Electric Welding. E.O. Paton. Based on this development, the Department of Orthopedic Dentistry of the PMSI developed a method for melting steel for dental purposes. Further development of research in this direction was carried out at the Department of Orthopedic Dentistry of the PMSI (now UMSA). The essence of this method is the remelting of electrodes from KCS in a medium of molten synthetic slag (ANF-6). Melting of metal in the slag environment allows to obtain high quality casting because the molten metal passes through the highly active molten slag and is cleaned of impurities. Slag cleans the metal of nonmetallic impurities, as well as from oxygen, hydrogen, nitrogen, sulfur, phosphorus and prevents the alloy from alloying out of the alloy, which can not be achieved by melting in high-frequency installations. The study testified that the physicochemical properties of casting, which is obtained on electroslag installations, are better than those obtained at highfrequency melting plants. Compensation of shrinkage of metal at the ESR is solved
due to the fact that the metal becomes thicker, as it is released from non-metallic inclusions, which leads to a significant decrease in the degree of shrinkage of the metal. Treatment of the skeleton of the clasp prosthesis. Two methods are used to clean the molded framework of the clasp prosthesis from the refractory mass: 1) mechanical (the casting is cleaned of the refractory mass on the sandblasting unit); 2) chemical (use potassium or sodium hydroxide). Pour in a stainless steel beaker to half the potassium hydroxide and put in a glass casting. Heat until the hydroxide melts, that is, up to 360°C, and boil for 2 to 3 minutes. After this, the casting is taken out of the beaker and immersed in cold water in a second metal beaker, cleansing of the refractory mass. To clean the casting from the hydroxide, it is immersed in bleach and boiled for 1-2 minutes, and then washed in running water. The surface of the casting after these treatments becomes clean. Chemical cleaning must be carried out in a fume hood with the ventilation included in a special device. Work should be in gloves and goggles. It is forbidden to dip wet casting into molten potassium because the water evaporates instantly on the casting surface and steam sprays the hydroxide, which can lead to injury. The springs are separated from the skeleton of the clasp prosthesis by a special cutting disc, which is strengthened on the grinding motor. The processing of the skeleton of the clasp prosthesis is carried out with abrasive wheels, heads, burs. They remove the remains of the gates, smooth the irregularities, blunt the sharp edges of the frame. At the same time, ensure that the relief and the thickness of the carcass surface, which is adjacent to the teeth and mucous membrane, are preserved. To smooth the surface of casting rubber elastic grinding wheels are used. After this treatment, the skeleton of the clasp prosthesis is tried on and adjusted to the working model from the super-gypsum. The fitted frame on the model is transferred to the clinic to check the design, fitting it in the patient's mouth. After that, the prosthesis is finally ground and polished with the help of fillets, hard brushes and pastes on the grinder. The skeleton of prosthetic braces has many hard-to-polish places, so it is better to polish them electrolytically. For this purpose, a cathode (stainless steel plate measuring 76x38x0.8 mm) is placed in a porcelain vessel with a capacity of 120 ml with a height of 50 mm. The anode is the skeleton of the prosthesis. An electrolyte is poured into the vessel (1-1.5 liters), consisting of: ethyl alcohol (120 ml), distilled water (120 ml), orthophosphoric acid (120 ml), ethylene glycol (540 ml), sulfuric acid (120 ml ). During the preparation of the solution, sulfuric acid is added to ethylene glycol. The current source is the 24V BC-24 rectifier with a current strength of up to 6 A. For polishing, the skeleton of the clasp prosthesis is
fixed to the anode at a distance of 40 mm from the cathode, a current of 2 A is applied, returning the frame from time to time around the axis. The polishing period is 10-15 min. After polishing the frame is removed from the electrolyte and washed under running water. To improve the aesthetic appearance, the clasp prosthesis frames can be coated with nitrite titanium and gold. Fast durable gilding is made with a special liquid. This does not require the preparation of the frame. The liquid for gilding has a high chemical resistance, economical, the process of degreasing the surface occurs simultaneously with the gilding. It can be performed on a ready clasp prosthesis. The last step in the laboratory production of an arch prosthesis is the placement of artificial teeth, which is performed after the carcass inspection in the clinic by an orthopedic physician. The setting of artificial teeth on a wax basis is performed under the control of the occludator or articulator, by the classical method. The technology of wax replacement for plastic does not differ from that used in manufacturing, partial removable prosthesis.