Annotation
Selection of supporting teeth for clamping fixation The supporting teeth for the arch prosthesis must meet the following requirements. First, they must be stable, have a well-defined anatomical shape and a sufficiently high clinical crown. When choosing supporting teeth, you need to carefully learn occlusal relationships. With close occlusal contact, it is very difficult, and sometimes impossible, to place a clamping support element in the figure - an occlusal patch - without disturbing the occlusal relationship. A similar situation may be the reason for using another tooth to place the supporting element, to create a special bed or cover this tooth with an artificial crown. The supporting teeth can have pathological mobility. In this case, they need to be splinted with a number of more durable teeth. When detecting chronic peri-vertebral foci of inflammation, they can be used to support only after filling the root canals. Parallelometry is the study of a model in a parallelometer to determine: 1) the way of insertion and removal of the prosthesis, that is, the search for the averaged parallelism of the teeth chosen for placement of supporting and exaggerating elements on them; 2) the boundary line (the support-retaining clamp is placed in a certain line with this line);
3) retention zone - deepening in the cervical part of the tooth (niche), where the retentive elastic part of the clamper is located. From the depth of the niche depends the length of the resting part of the shoulder, and accordingly - the type of the clasp and the design of the prosthesis. Since there is no parallelism between the supporting teeth of the patient, a special apparatus - a parallelometer - is needed to ensure that the prosthesis with a complex system of clamps can be easily applied and removed from the supporting teeth. At the heart of the structure of the parallelometer lies the principle of parallelism of perpendiculars, which are omitted on the plane. The apparatus consists of a base on which a stand is fastened around which the bracket rotates with movable devices adapted to fix the removable tools therein. With the help of these tools, the parallelism of the supporting tooth contours is determined and the wax, gypsum and other materials are cut when the working plaster model is prepared for duplication. In some designs, the hinged table for fixing the model is fixedly connected to the base, in others - the bracket with the stand is fixedly connected, and the latch is movable in the vertical direction. In these designs, the models are mounted on a hinged movable table.
Different types of parallelometers Basic rules of parallelometry: 1) the design of the clasp prosthesis should be determined after parallelometry; 2) the common clamping line, despite the fact that it is bent, should be parallel to the occlusal plane;
3) the prosthesis should transmit the chewing pressure along the tooth axis; 4) the prosthesis should rationally distribute the pressure that occurs during chewing, between the remaining supporting teeth and the alveolar bone. The best way to insert and remove a prosthesis should be considered such that when the prosthesis is easy, with a minimum of obstacles is imposed and removed from the supporting teeth. Possible ways of introducing the prosthesis: 1) vertical, at which there should be a good retention, since the prosthesis can be displaced during the opening of the teeth; 2) vertical right; 3) vertical left; 4) vertical rear; 5) vertical front.
Three methods of parallelometry are known, namely: 1) an arbitrary method; 2) method of determining the average inclination of longitudinal axes of supporting teeth; 3) method of choice. Arbitrary method Applied in the case of a minimum number of supporting teeth, the parallelism of their vertical axes and when the design of the clasp prosthesis is simple. Its essence lies in the fact that the model is mounted on the hinged table of the parallelometer in such a way that the occlusal plane of the tooth row is perpendicular to the analyzing rod. Bringing the graphite rod to each supporting tooth, delineate the boundary line, in relation to which the elements of the clamp are placed. At the same time, a part of the crown of the tooth that lies above the boundary line is used to locate the support parts of the clamper, and the one below the boundary line is used to locate the retentional part of the clamper.
Vibora Method During the fabrication of bug prosthesis with three or more support-retaining clamps, it is advisable to use a selection method. It is based on the result of the analysis of the position of the marginal line of supporting teeth and their surfaces (supporting and retaining teeth). Analysis shows that in most cases, on some teeth, there are better conditions for the location of the support parts of the clamper, and on others - for the retainers. If all the clamps performed equally well both the supporting and restraining functions, and all the supporting teeth took equal part in the redistribution of the load during chewing, one must find a slope of the model in which these zones would be sufficiently expressed on all supporting teeth. By
tilting the model, you can choose a more rational type of clamp for each supporting tooth and arrange its elements in the most advantageous in functional and aesthetic positions. To fulfill these conditions, a method is used to select the slope of the model in a parallelometer. Having fixed the model on the parallelometer table and having adjusted the "zero" position, when the analytical rod is installed perpendicular to the occlusal plane of the teeth, determine the degree of expression of the supporting and restraining zones for each supporting tooth. Method for determining the average inclination of longitudinal axes of supporting teeth according to Novak. This method involves two stages, the first is carried out without a parallelometer. For better orientation, the side plane of the model is marked with the number I, the back one - II. The direction of the longitudinal axes of each tooth is established with the help of pieces of wire 20 mm long (can be matches), which are fixed with sticky wax in the middle of the cutting edge or in the center of the chewing surface of the tooth. To the position of the wires coincides with the longitudinal axes of the teeth, each of them must be oriented along the crown of the tooth, looking at it alternately from the vestibular and oral sides. For the longitudinal axis of the tooth is a line that passes through the middle of the root and crown of the tooth. Since the root is not visible, then the definition of the axis of each of the teeth is carried out only on its crown. In the future, the projection of these axes is alternately manually applied with a pencil on both previously prepared planes (lateral and posterior). In Fig. 5 shows the projections of the axes of two supporting teeth - on the side surface of the model, designated as A and B. More often, the resulting projections are not parallel to each other and, when intersecting over the model, form an angle. The scheme of the slope of the projections of the longitudinal axes of the teeth and the formation of the angle is shown in Fig. 5 B. Novak suggests crossing them with two parallel lines, which are applied in such a way that the angles are equal to each other. These parallel lines should be applied as far apart as possible in order to increase the accuracy of further lines that divide the angle between the projections of the axes. The segments of both lines that run parallel are enclosed between the projections of the axes A and B, divided in half at the points O and OI, and connect the latter lines C, which halves the angle between the projection of the axes AI and BI (Figure 5c). Then on this surface of the model the projection of the longitudinal longitudinal axis of the tooth is applied. Conduct parallel lines between the directions CI and DI and find the desired directions of the longitudinal axes of all three supporting teeth in the first plane. Denote it with the letter EI (Figure 5d). A similar way is done on the back plane of the model. At the same time, the direction of the projections of the axes of the teeth is transferred first, which is marked already as AII and BDІІ.
CII is found between them. The direction of the projection of the longitudinal axis - on the back of the base of the model is marked as DІІ. Through the lines СІІ and DІІ, two parallel lines are drawn and the direction of all three supporting teeth is designated as E. By the EI and EІ directions found on mutually perpendicular planes (sagittal and frontal), the spatial orientation of the line is renewed, the projection of which on the indicated planes coincides with EI and EІІ. This line is the direction or route of insertion of the prosthesis. To determine it approximately at the center of the model stick a stick pin 3-4 cm long with sticky wax. Further orient the model in the hands so that if viewed from the side of plane I (lateral), then this pin was connected with the direction of EІІ, and on the side of plane II (Rear) - with the direction of EII (Figure 5e). In the repeated (control) survey, if necessary, correct the spatial position of the pin. The pin thus installed gives the direction of the insertion of the prosthesis. This concludes the first stage and the second begins, from the strengthening of the model on the parallelometer table.
Fig. 5. Novak's parallelometry method: a - is the projection of the axes in the sagittal plane; b - diagram of education an isosceles triangle; C - division of parallel lines in half; d - obtaining a common of all three projections; e - obtaining a common on the back side of the model; f -
installation of the pin according to the route of administration; g - the orientation of the model in the parallelometer. Tilting the table, combine the direction of the pin with the parallelometer shaft. Fix the found position of the model with a gypsum "spice-up": for this purpose a plaster is poured into the special mold and placed on its surface (until it hardens) the model in the found position (a special "adapter" can be used for this). The dental technician will later replace the analyzing rod of the parallelometer with a graphite one, apply the boundary lines (line of sight) to all supporting teeth. The described method has some disadvantages: the definition of the projection of the longitudinal axes of the teeth is done by eye, it is difficult to fix the wire with wax on each tooth, without taking into account the esthetic factor when locating the clasps. The boundary line is a line that is formed on the greatest convexity of supporting teeth with a certain slope of the model during parallelometry. Relatively to it the surface of the tooth is divided into two zones: between the outlined line and the occlusal surface - the support; Between the outlined line and the neck of the tooth - retentional, or restraining. There are five main types of boundary lines: Type I is typical when it is in the zone that is closer to the defect of the dentition, it starts in the middle between the cervical region and the anatomical equator of the tooth, and on the side that is removed from the defect, ends between the anatomical equator and the masticatory surface. Type II - atypical, passes contrary to type I, in the zone closer to the defect, begins midway between the anatomical equator and the masticatory surface, and on the side that is removed from the defect, between the cervical region and the anatomical equator of the tooth. The third type is diagonal, it is similar to the second type, but the extreme points of the line are located almost on the chewing surface and in the cervical area. ІV type - high location - the boundary line runs in the middle between the anatomical equator and the chewing surface of the tooth. V type - or the boundary line runs very low, along the cervical site, or very high, almost on the chewing surface. Each type of the boundary line shows its own type of clammer in the Neu system: І type of the boundary line - clamper number 1 (cl. Akker); ІІ type - a klamer № 4 (cl. Of rear action and back of rear action); III type - a clammer № 2, № 4, if premolar, then it is used with a long shoulder, and when a molar - a clasper № 5 (ring); ІV type - a klammer № 2 or a restoration crown;
V type - restoration crown. Determination of the depth of retention If you install the parallelometer rod so that it touches the equator to the tooth of the plaster model, which is mounted and fixed on the parallelometer table, a niche (groove) that forms around the tooth is formed between the core of the device and the crown of the tooth below the equator. During the construction of the clasps, this niche is used as the retentional surface of the tooth to accommodate the retaining parts of the arms of the clasps. Teeth with the same location of the equator may have a different degree of indentation. The zone of the depression is called the gap, which is limited by the device's rod, the tooth surface on the defect side and the gingival mucosa. These zones increase noticeably in the case of convergence of teeth. The depth of retentions is determined by special instruments-calibres-rods with different disc diameters: No. 1 - 0.25 mm; № 2 - 0,5 mm; № 3 - 0,75 mm. Each type of clamper corresponds to a rod for determining the place of the end of the retaining arm on the supporting tooth.
Using the caliber determine the location of the retaining part of the clamp shoulder The selected rod is strengthened in the collet device and closer to the model. Moving the rod upwards downwards, on the boundary line one chooses such position, when the rod-caliber and its measuring disk simultaneously come into contact, the support tooth falls. The place of contact of the disc with the tooth and is the place of termination of the shoulder of the clammer or its beginning.
Denoting the depth of the retention end of the clammer in this way with a pencil, you can start drawing a skeleton of the clasp prosthesis.