Annotation

The problem of the relationship of tissues and organs of the oral cavity with materials intended for the manufacture of dental prostheses and orthodontic appliances is one of the main problems in the clinic of prosthetic dentistry. It is known that tissues and organs of the oral cavity are in dynamic equilibrium with balanced biochemical processes that preserve the structures of tissues and support their function.

Currently, in the manufacture of prosthetic structures, acrylic plastics are the most widely used (up to 98% of dentures worldwide are made of acrylic plastics, whose strength is insufficient under conditions of varying mechanical loads, and the thermoregulation of oral tissues under them). Technological properties of acrylic plastics do not require expensive equipment. However, according to most experts, plastics have a number of significant drawbacks: the presence of residual monomer in the cured base (with the correct polymerization mode, hot-curing plastics contain 0.5%; quick-hardening - 3.5% of residual monomer), which leads to toxic-allergic reactions, impaired microflora of the oral cavity, the development of blastomatous growth in the tissues of the prosthetic bed. In addition to the disadvantages of acrylates can be attributed to the low modulus of elasticity, which leads to an increase in the deformation of the basis of the prosthesis under load and leads to changes in the underlying soft and bone tissues of the jaw. A number of technological drawbacks should also be noted: to obtain a product with sufficiently high strength properties, it is necessary that the polymer + monomer mixture is polymerized under conditions in which the highest polymer density is achieved.

These conditions include:

1) the optimal ratio of components of the mixture;

2) full maturation of the plastic test before molding;

3) the creation and strict maintenance of the temperature mode of polymerization;

4) maintaining the necessary pressure inside the form.

An analysis of the literature has shown that considerable material has been accumulated to identify and solve the problems of intolerance and toxicity of removable dentures made from acrylates. But the frequent cases of true allergy to components of acrylic plastics require finding ways to prevent it.

Improvement of basic acrylic plastics goes in several ways:

1. changing the properties of acrylates depending on the modes of polymerization;

2. Introduction to acrylic compositions of chemicals that change the properties of plastics;

3. application to the surface of various substances;

4. The study of the physicomechanical properties of plastics in various ways.

One of the ways to prevent undesirable effects on the organs and tissues of the prosthetic acrylate bed is 5. creation of new materials. The increasing interest of modern clinicians is attracted by the problem of the biocompatibility of the dental materials used. Currently, the requirements for the manufacture of dental prostheses are not only in the restoration of the dental system in the functional and aesthetic terms, but also the maximum preservation of the tissues of the prosthetic bed for successful re-prosthetics.

Interest in the production of removable prostheses from thermoplastic materials - as a promising technological and aesthetic solution - has been steadily growing in recent years. Attention specialists deserve molded monomer-free polymers with extremely high levels of elasticity, strength and aesthetics. The bases of such removable structures are manufactured by injection thermal casting technology. Acrylic plastics containing polymethyl methacrylate gradually take the place of acrylic base materials based on methyl methacrylate. Representatives of non-monomer materials based on acrylic plastics: Flexite MP (USA) Acry-free (Israel), The.r.mo Free (San Marino), Fusicril (Italy), Polyan (Germany), Villacryl SP, Villacryl H Plus, Villacryl H Rapid (Zhermack).

The most widely used in dentistry are such brands of thermoplastics as “Dental D” (Quattro Ti, Italy) and “T.S.M. Acetal Dental "(Pressing dental, Italy) based on polyoxymethylene, Valplast, (Flexite, USA), Flexy-Nylon (Israel) based on nylon, LIPOL (prof. Vares E.Ya., Ukraine) based on polypropylene. Studies have shown that flexible prostheses contribute to the rapid adaptation of patients, but their chewing effectiveness is inferior in comparison with laminar and byugelny removable dentures.

Polyurethanes are a class of polymers whose common generic feature is the presence in the main chain of more or less regularly alternating urethane groups. From the point of view of the indicator “residual monomer”, a polyurethane system has a priory advantage over acrylates due to its exhaustion before the end of the hardening process. Polyurethanes also belong to thermoplastic molding base materials, but the casting process is different (“free casting”). Representatives of polyurethane base materials: Dentalour and Pentalur (Research Institute of Rubber and Latex Products, Russia).

Material "Valplast" is a polyamide-12, has several shades of pink, elastic, transparent. This material, the bases of which are made injection system.

Nylon prostheses are shown:

1. with intolerance to metallic inclusions, reactions to the monomer;

2. when the preparation of abutment teeth is excluded;

3. patients with traumatic occupations (army, Ministry of Internal Affairs, firefighters, rescuers), athletes;

4. if necessary, high aesthetics (dento-alveolar clasps are almost not noticeable).

Stages of manufacturing a prosthesis of nylon (for example, material "Valplast")

1. Removal of impressions with alginate mass for the least compression impact on the mucous membrane of the prosthetic bed or with silicone materials designed to remove impressions for removable prosthetics.

2. Immediate casting of models from gypsum not lower than the third class using a vacuum mixer and a vibration table. If necessary, a functional impression - the production of the model is made from medical plaster with the subsequent receipt of an individual spoon.

3. Fixation of the bite or the ratio of the jaws. In the first case, with a fixed bite height, it is possible to use silicone clamps. In the second case, it is necessary to make a waxy bite template with which to determine the central ratio of the jaws.

4. Determination of the color of artificial teeth.

5. Preparing the model for duplication and the actual duplication. This stage involves the choice of the design of the prosthesis, the study of models in the parallelometer, blocking of undercuts and technological zones of tolerance. The nylon prosthesis uses dento-alveolar clasps that do not have a dislocating action on the abutment teeth. These clasps rely on the cervical area of ​​the tooth, leaving the mucosa without touching it, eliminating the formation of pressure sores. The task of the dental technician in preparing the model for duplication is to make an admission in this area, the flow of its boiling wax strictly along the border of the future prosthesis. In the case of a wrong clearance of the clasp's abutment zone (processing it with wax that goes beyond its boundaries), a gap is formed on the finished prosthesis between the clasp and mucous membrane, where food residues will fall during operation. Bone protrusions, places of ablation, anatomical defects, etc. are also treated with boiling wax. All other undercuts formed by the teeth and mucous are blocked with wax in the parallelometer, based on the approximate route of insertion of the prosthesis (elastic material allows minor errors). Klammers should be crescent-shaped and, if possible, not located on the frontal teeth. Duplication can be done with duplicate masses, like Hilin, or silicone masses for duplication. The latter are preferable because of the clarity of the resulting form. The cuvettes and procedures for preparing for the duplication process do not differ from those commonly known for the manufacture of refractory models. The difference lies only in the material, poured into the resulting form. We use the fourth grade plaster, we get the master model, the duplicated model is also cast from the fourth grade plaster, we get the working model.

6. Design wax composition. Split up the duplicated model. Draw on the working model with a pencil design of the prosthesis. We make modeling of the wax composition of the prosthesis, the production of artificial teeth. It is necessary to make the teeth diatorial for better fixation in the prosthesis.

7. Checking the wax composition of the prosthesis in the mouth.

8. Replacing wax on nylon. The cuvette consists of two main components, one of which is wider than the other, with circular holes in the center for plaster casting and threaded connections for four mounting bolts. On the inside of each part there is a cavity, which repeats the form of the model's cap, for plastering a wax composition into it. On the back of the cavities are the halves of the gutters of the injection opening. Before plastering, pour the edges of the wax composition with hot wax to the model, cut off all the plaster teeth, soak the model for 5-7 minutes in cold water. For plastering, you should use a plaster not lower than the third class. Before pouring gypsum, treat both internal cavities of both halves of the cuvette with vaseline oil. Gypsum is made into the wide part of the cuvette, where the wax composition is placed after the gypsum, oriented so that it is located as close as possible to the back side of the cap to the injection channel groove and immersed in the gypsum to the wax modeling line. It is necessary to achieve a smooth surface without undercuts and locks, using lint brushes and running water. After curing, proceed to the manufacture of gating system.

9. Gating system - a channel through which liquid heated nylon will flow into the cuvette. Gates are made of base wax heated in warm water. Excess trimmed with a scalpel.

10. Gypsum second part of the cuvette. Pre-placed the first part of the gating system in cold water for 10-15 minutes. We install the second half of the cuvette into place, attract it with two bolts diagonally. Fill the plaster. Give the plaster to harden.

11. Digestion of wax. After the plaster has set, loosen the bolts 2 turns. Soak the cuvette in boiling water for about 7 minutes, loosen the bolts, remove the wax from the cuvette, the gypsum surface is covered with release paint, blow through with compressed air. The cuvette is assembled, tightened with four bolts diagonally to avoid skewing.

12. Injection. The material is produced in a factory sealed package of five seamed almine cartridges with granulated Polyamide-12. An injection window is planned on the rolled side - a breakthrough point through which the material enters the cell. Nylon is injected in a pneumatic dental injection system. The heating temperature of the cartridge is 287.7 ° C, the warm-up time is 11 minutes, the holding time under pressure is 3 minutes, the pressure in the system is 8 atm.

13. After the cell has cooled down, it is unpacked. The prosthesis is processed in an ultrasonic bath with a solution to remove gypsum, the gate is cut off with a hard-alloy cutter, and fitted on the master model. The prosthesis is machined with one-piece diamond cutters, rubber polishers, burrs are removed with a scalpel.

14. Polishing of the prosthesis is carried out using a hairbrush and polishing powder for acrylic plastics at low revs, then with a large fabric disc at low revolutions with Advanced Technologies paste, for glossy polishing is completed with Mirror Shine paste. After polishing, the prosthesis is again subjected to ultrasonic cleaning with a soap solution for 10 minutes, then rinsed with running water.

An alternative to molded thermoplastics are removable dentures, manufactured by thermoforming (for example, ProForm). The technique involves the use of a vacuum molder in the dental laboratory. Consumables - thermoplastic plates (laminates) of various thickness and material. The combination of certain laminates with acrylic plastic, which has the same modulus of elasticity as the thermoplastic base, is called the Pro-flex system.

Последнее изменение: Воскресенье, 11 ноября 2018, 18:38