The manufacture of a clasp prosthesis begins with a detailed assessment of each case. The use of a diagnostic model improves planning efficiency.

Planning the design of the clasp prosthesis is:

1) in determining the route of insertion and removal of the prosthesis;

2) in the marking of the model to find the most convenient location of the clinical equator on the abutment teeth and the corresponding position of the clasps;

3) in determining the position of the arch in the palate and alveolar process of the lower jaw and other elements of the prosthesis (multi-link clasps, branches, processes, etc.).

All this as a whole makes it possible to apply a drawing of the frame of the future prosthesis to the model.

When planning a removable denture fixation system, two main objectives are pursued:

1) create a reliable attachment of the prosthesis during chewing and speech;

2) to ensure such fastening of the prosthesis, in which it would have the least effect on the abutment teeth and the mucous membrane covering the edentulous alveolar processes.

Of particular importance in solving these problems is a clear understanding of the biomechanics of a removable prosthesis, the effect of forces displacing the prosthesis: gravity, chewing pressure and traction.

The gravity of the prosthesis on the lower jaw is neutralized by the supporting teeth, the alveolar processes with the mucous membrane covering them. In this case, it helps to keep the prosthesis on the jaw. On the upper jaw, this force makes it difficult to attach the prosthesis and, under certain conditions, violates its stability. This is especially pronounced with bilateral end defects, when the base of the prosthesis, devoid of distal support, can sag or overturn under the influence of gravity.

Chewing pressure also helps to dislodge the prosthesis. Under the influence of sticky food, the prosthesis can move away from the prosthetic bed of both the upper and lower jaw. This increases the overturning moment due to the weight of the prosthesis. Its rotation takes place around the clasp line. Under the influence of chewing pressure, the prosthesis undergoes spatial movement in three planes - vertical, sagittal and transversal. Depending on the chosen method of fixation, the displacement of the prosthesis may prevail in any one plane. Its movement in other planes, as a rule, is less pronounced, but almost always takes place. This makes the nature of the displacement of the prosthesis under the influence of chewing pressure so complex that it requires detailed consideration under different clinical conditions depending on the type of removable prosthesis, the method of its fixation, the size and topography of the dentition defects, the nature and magnitude of atrophy of the edentulous alveolar ridge, etc.

Thus, the preservation of abutment teeth and the prevention of their functional overload during clasp fixation is an important problem. One of the ways to solve it is the correct location of the clasp line.

All supporting-holding clasps, their elements should be located strictly in relation to the clinical equator - the largest perimeter of the tooth, taking into account its inclination. The clinical equator coincides with the anatomical equator only when the longitudinal axis of the tooth is strictly vertical. Usually, due to the physiological inclination of the teeth, the line of the anatomical equator does not coincide with the clinical one. If the tooth is tilted orally, then the line of the clinical equator on the lingual side is shifted to the occlusal surface, and on the vestibular - it goes down to the gingival margin.

For the correct design of the clasps, it is important to determine the general clinical equatorial line of the dentition, which is also called the clinical equator, the prosthetic equator, the height of the contour, the guide line, the general sight line. E.I. Gavrilov was given a name that has become commonly used - the boundary line (demarcation).

The boundary line divides the tooth surface into support (occlusal) and retaining (retention, gingival). It cannot be called the equator, because does not coincide with it and, unlike it, changes position due to the inclination of the tooth: on the side of the inclination, it approaches the chewing surface, and on the opposite side, it moves away from it. The boundary line is revealed by means of parallelometry and serves as a guide for the location of the parts of the shoulder of the supporting-holding clasp.

PARALLELOMETRY

The route of insertion and removal of the prosthesis, as well as the boundary line common to all abutment teeth, in relation to which the elements of the support-holding clasp will be located, are determined using a parallelometer.

Parallelometer is a device for determining the greatest convexity of teeth on models of jaws, detecting the relative parallelism of the surfaces of two or more teeth or other parts of the jaw, for example, the alveolar ridge.

The device has a flat base on which a stand with a bracket is fixed at right angles. The bracket is movable in vertical and horizontal directions. The arm of the bracket is aligned with the rack at a 90 ° angle. There is a clamping device on the arm of the arm for interchangeable tools. This device allows you to move tools vertically.

Parallelometers

The set of tools includes:

A flat analyzer to determine the most advantageous position of the general survey (boundary line), and, consequently, the position of the clasps, which ensure the smooth introduction of the prosthesis and its good fixation;

A pin in which the leads are fixed with a collet to outline a line;

Retention pins: gauges? 1, 2 and 3; they differ in the diameter of the measuring disc: disc? 1 - 0.25 ml, disc? 2 - 0.5 ml, disc? 3 - 0.75 ml (with their help, the position of the ends of the holding arms of the clasps on the abutment teeth is determined);

Knife pins for removing excess wax after pouring undercuts.

The set also includes a table for fixing the models. The table platform is pivotally connected to the base, which allows you to tilt the model and bring them to the instruments at different angles.

All parallelometer designs are based on the same principle: for any displacement, the vertical bar is always parallel to its original position. This allows you to find points on the teeth located on parallel vertical planes.

The size of the supporting-stabilizing and retention zones on the tooth depends on the position of the general survey (boundary) line or the clinical equator, which, in turn, depends on the inclination of the model during parallelometry.

Basic rules for parallelometry:

1) the parallelometer makes it possible to determine the design of the clasp prosthesis;

2) the common clasp (boundary) line, despite the fact that it is curved, should be generally parallel to the occlusal plane;

3) the prosthesis, when fixing it in the oral cavity, must transmit the chewing pressure along the axis of the tooth;

4) the prosthesis should be designed so that it rationally distributes the chewing pressure between the remaining teeth and the alveolar processes.

Known three methods of parallelometry: arbitrary, the method for determining the average inclination of the longitudinal axes of the abutment teeth (Novak's method), the method of inclination of the model (selection method or "logical" method).

Arbitrary method... The model, cast from high-strength plaster, is placed on the parallelometer table so that the occlusal plane of the teeth is perpendicular to the lead shaft. Then a parallelometer lead is brought to each abutment tooth and a general sight line or clinical equator is drawn. The line with this method of parallelometry may not coincide with the anatomical equator, because its position will depend on the natural inclination of the tooth, therefore, conditions for the location of the clasps on individual teeth may be less favorable. This method of parallelometry is shown only with the parallelism of the vertical axes of the teeth, their slight inclination and the minimum number of clasps.

Method for detecting the average inclination of the long axes of the abutment teeth... The edges of the base of the model are cut so that they are parallel to each other. The model is fixed on the parallelometer table, after which the vertical axis of one of the abutment teeth is found. The stage with the model is installed so that the analyzing rod of the parallelometer coincides with the long axis of the tooth. The direction of the latter is drawn on the side surface of the model base. Next, the vertical axis of the second abutment tooth, located on the same side of the dentition, is determined and is also transferred to the lateral surface of the model. Then the resulting lines are connected by parallel horizontal lines, after dividing the horizontal lines in half, the average orientation axis of the abutment teeth is obtained. The middle axes of the teeth on the other side of the model are determined in the same way. The obtained middle axes are transferred to the free face of the model base with the help of the parallelometer analysis rod, and the middle axis of all abutment teeth is determined from them. Then the stage with the model is finally installed in the parallelometer. The analytical rod is changed to a graphite one and a survey line is drawn on each abutment tooth. When drawing, the end of the graphite rod should be at the level of the neck of the tooth. The disadvantage of the method lies in the duration, difficulty and probability of error in determining the general survey (boundary) line.

Selection method... The model is fixed on the parallelometer table. The stage is then positioned so that the occlusal surface of the model teeth is perpendicular to the evaluation rod (zero tilt). The latter is brought to each abutment tooth in turn and the presence and size of the supporting-stabilizing and retaining zones is determined. It may turn out that on one or several teeth there are good conditions for the location of the clasp elements, and on others - unsatisfactory. Then the model must be viewed at a different angle of inclination. From several probable inclinations, the one that provides the best retention zone on all abutment teeth is selected.

There are four main types of model tilt.: front, back, right side and left side.

When designing a clasp prosthesis this method allows you to take into account the requirements of aesthetics and the optimal degree of retention of the clasps. So, if the supporting-retaining clasps need to be placed on a group of teeth visible when smiling, then for reasons of aesthetics, it is advisable to bring the line of sight as close as possible to the necks of the supporting teeth. For this, the back tilt of the model is used, that is, the model is tilted back. The lateral inclination of the model is chosen to evenly distribute the degree of retention on the abutment teeth of both halves of the jaw.

So, for example, if in the horizontal position of the model it turns out that on the left lateral teeth the line of sight is located in the buccal surface along the necks of the teeth (due to the lingual inclination of the teeth), then it is advisable to tilt the model to the left in order to "raise" the sight line. The degree of lateral inclination of the model is determined by the sufficiency of the retention zone on the right lateral teeth.

Having fixed the movable table and the model placed on it in the selected position, a general overview line is drawn with a vertical pin with a lead.

Bringing the lead to each tooth so that its lower edge is located and moves along the level of the gingival edge, a line is drawn on the vestibular, oral and proximal surfaces of all teeth. Having removed the model with a table from the parallelometer stand, with a thin felt-tip pen or a soft pencil, they circle the resulting common equatorial line and proceed to planning the design of the clasps and drawing a drawing of the future prosthesis frame.

The common clinical equator is crossed only by the retention parts of the clasps. To determine the location of the retention part in the parallelometer, there is a special rod with a ledge - a retention degree meter (calibers 1, 2 and 3). The rod is fixed in the arm of the parallelometer and set so that it touches the clinical equator. At this point, the shoulder of the bar touches the point of the tooth below the clinical equator. Having passed the rod over the tooth, a notch is obtained, which indicates the line of location of the retention part, i.e. the point where the end of the holding clasp should be located: with the 1st degree of retention - 0.25 mm below the clinical equator, with the 2nd - by 0.5 mm and with the 3rd - by 0.75 mm.

The location of the line of the clinical equator on the crown after parallelometry, its relation to the occlusal and gingival parts of the crown determine the need to choose one or another type of support-holding clasp for each tooth. The choice of the type of clasp depends on the topography of the clinical equator and the area of the occlusal and gingival parts.

When planning the design of an arch prosthesis, the position of the abutment teeth in the dentition should also be taken into account. The displacement of the teeth to the medial, distal, buccal or lingual side makes it difficult to create their parallelism by grinding hard tissues, because fraught with opening of the tooth cavity or thermal damage to the pulp. In such cases, doctors often resort to their depulpation. Experience shows that pulping of teeth in order to create their parallelism when using an arch prosthesis should now be considered an extremely extreme measure. The correct choice of the design of the supporting-retaining elements after studying the models in a parallelometer dramatically reduces the indications for tooth pulping and covering them with crowns.

Special conditions arise with a significant vestibular inclination of the anterior group of teeth, when it is necessary to include splinting elements in the design of the prosthetic splint. The latter are sometimes impossible to apply due to a violation of aesthetics or the danger of difficult placement of the prosthesis. A favorable condition for the location of the claw-like processes is the presence of three and diastemas. Likewise, it is impossible to plan an arch prosthesis for the lingual inclination of the lower anterior teeth.

When planning the construction of a clasp prosthesis great importance has the appearance of a bite. So, with a deep, as well as deep traumatic bite, a multi-link clasp with splinting elements that will interfere with the closure of the teeth and the maintenance of the usual interalveolar height cannot be included in the design of the prosthesis. In patients with such a bite, it is necessary to find out the possibility of increasing the interalveolar height, and only after that, if indicated, can a cast palatine strip be applied, restoring the cutting-tubercular contact.

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Clasp prosthetics

Content

Introduction
1. Choice of design
Conclusion

Introduction

Clasp prostheses are removable prostheses. This is a design of replacement medical devices that allow you to completely restore biting and chewing food, while the pressure is distributed between the remaining teeth and the mucous membrane with the underlying bone tissue of the edentulous areas of the alveolar process.

Therefore, the chewing efficiency of such prostheses is close to the effectiveness of their teeth Clasp prostheses are used for prosthetics of extensive defects in the dentition, end defects, as well as for prosthetics for periodontitis.

There are many options for constructing clasp prostheses, they depend on the topography of defects in the dentition. The main feature of these types of prostheses is a metal frame and a base with artificial teeth.

The metal frame consists of an arc (an arc in German - clasp), sections for fixing the base and clasps of the supporting-holding type.

Compared to plate prostheses, clasp prostheses are much more compact, comfortable, and reliable.

Planning the design of an arch prosthesis consists, firstly, in determining the route of insertion and removal of the prosthesis, finding the most convenient location of the dividing line on the abutment teeth and, in accordance with it, the position of the clasps;

Secondly, in establishing the boundaries of the baseline, the position of the arch in the sky and the alveolar part of the lower jaw;

Thirdly, in the choice of the design of the supporting-holding elements of the frame (clasps, branches, processes, continuous clasp, indirect clamps, etc.) All this as a whole makes it possible to draw on the model a drawing of the frame of the future arch prosthesis.

clasp prosthesis dental arch

Before proceeding with planning the design of the prosthesis, a diagnostic model of the jaw is cast using an impression obtained with alginate masses.

1. Choice of design

The model is cast from high-strength plaster, dried and trimmed so that its base should be thick enough, at least 1.5 cm. The side walls are made parallel to each other and perpendicular to the base. The prepared model is examined in a parallelometer.

Parallelometer is a device for determining the relative parallelism of the surfaces of two or more teeth or other parts of the jaw, for example, the alveolar ridge. Many designs of parallelometers have been proposed, but they are based on the same principle, namely: when mixing, the vertical rod is always parallel to its original position. This allows you to find points on the teeth located on parallel vertical planes. The parallelometer is equipped with a set of rods: analyzing rods with discs of different diameters for measuring undercuts, a graphite rod for outlining the dividing line, a blade for removing excess wax.

Ways of insertion and removal of the prosthesis. By introduction, the movement of the prosthesis is called from the initial contact of its clasp elements with the abutment teeth to the tissues of the prosthetic bed, after which the occlusal linings are installed in their beds, and the basis is precisely located on the surface of the prosthetic bed.

The way to remove the prosthesis is defined as its movement in the opposite direction, i.e. from the moment of separation of the base from the mucous membrane of the prosthetic bed to the complete loss of contact of the supporting and retaining elements with the supporting teeth.

Several ways of inserting the prosthesis are possible, but the most convenient one should be chosen. The best way to insert and remove the prosthesis should be considered the one when the prosthesis is easily applied and removed, meeting a minimum of interference that cannot be excluded, and at the same time ensuring the same retention on each tooth. The route of administration depends on the location of the clasps, and the latter naturally affects the aesthetics. Therefore, a solution should be found in which less noticeable clasps are present and the shape of the front teeth is preserved. Given the aesthetic demands, sometimes you have to sacrifice other qualities, such as fixation.

There are countless ways to insert the prosthesis. All of them can be reduced to five options:

1) vertical, but at the same time there should be good retention, since viscous food can displace the separation of the teeth;

2) vertical right (movement goes slightly to the right of the true vertical);

3) vertical left;

4) vertical posterior;

5) vertical front.

The choice of the route of administration is not random, but is conditioned by certain circumstances.

These include interference with insertion and removal, undercuts of teeth and alveolar niches. It is necessary to choose a path in which there will be less interference, and the topography and dividing lines are most convenient for the location of the clasps. Consideration should be given to the fixation of the prosthesis during function. It is necessary that the clasps on the premolars were not noticeable, and the latter would have correspondence The study of the model of the jaw in a parallelometer aims to identify the dividing line of the tooth, i.e. a line dividing the surface into two parts: occlusal (supporting) and retention (retaining or cervical), and thereby simultaneously determine the route of insertion of the prosthesis. Between the dividing line and the gingival margin there is an undercut, that is, a zone that essentially allows the springy part of the clasp to provide retention of the prosthesis.

Determination of the dividing line of the abutment teeth helps to correctly distribute the clasp elements and at the same time find the most convenient way to insert the prosthesis.

2. Choosing the location of the arc (Bugel)

The arch of the prosthesis on the upper and lower jaw has a different configuration, thickness, width; its location depends on the anatomical features of the jaws and the topography of the dentition defects. The arc along its entire length should not touch the mucous membrane of the palate or the alveolar part. On the lower jaw, the arch is placed on the lingual side in the middle between the bottom of the oral cavity and the level of the gingival margin parallel to the mucous membrane of the alveolar part. In the manufacture of a clasp prosthesis replacing a group of chewing teeth, with the absence of distal supports, the arch should be unevenly spaced from the mucous membrane, and more in the lower section. This condition must be observed, since when the saddle-shaped part of the prosthesis is loaded, its subsidence occurs, which causes a small rotary motion arc and in the lower section it comes closer to the mucous membrane. The length of the arc depends on the size of the defect and its topography. In case of defects in the group of chewing teeth, the arc extends to the middle of the defect, where it is connected to the metal frame of the saddle-shaped part at an angle close to right. In the presence of additional defects in the group of anterior teeth, branches branch off from it for fixing artificial teeth. The shape of the arch in the section of the prosthesis on the lower jaw is more often semi-oval. The shape and topography of the arch of the upper jaw prosthesis have many variations. The simplest option - the arch passes across the palate at the level of the first molars, has in section the shape of the arch of the prosthesis on the lower jaw, but of greater width. IN last years more and more often they make a flattened arc with extended boundaries. Its slightly thickened middle is located between the first and second molars of the right and left sides. The course of the arc is not straight, but curved, somewhat resembling the letter 3, open to the group of the front teeth.

The retaining frame of the clasp prosthesis is used to fix the bases (saddles) made of plastic with artificial teeth. Depending on the defects in the dentition, there may be several of these areas.

3. Stages of manufacturing. Solid frame clasp prosthetics shape and color

The technological sequence in this case consists of the following stages:

1) obtaining a working model from strong gypsum (to save money, you can get a combined model) and an auxiliary model from ordinary gypsum;

2) study of the supporting teeth of the working model in a parallelometer and drawing a common equatorial line on them;

3) marking the pattern of the clasps on the abutment teeth;

4) drawing a drawing of an arc that holds parts of the base frame and the boundaries of the saddle parts;

5) applying an insulating layer to the areas where the arc and retaining parts are located;

6) modeling from standard wax blanks of the prosthesis frame;

7) installation of sprue pins;

8) removing the wax reproduction from the model;

9) installation of the reproduction on the foot cone and the gating system (branch channels);

10) applying the facing layer of the casting mold;

11) molding of the lost-wax model with refractory filling mixtures;

12) melting the wax, drying and firing the mold; 13) casting process; 14) removal of the gating system and processing of the frame; 15) the imposition of the frame on the working model and its refinement and polishing; 16) checking the accuracy of the fabrication of the frame in the clinic; 17) making a saddle-shaped part from wax and setting artificial teeth; 18) Replacement of wax with plastic, polymerization and processing of plastic. The study on the model of the crowns of the teeth, which the doctor has chosen as supporting ones, is carried out in accordance with the parallelometry technique. With the logical method, the model is fixed on the parallelometer table and its platform is placed horizontally. A pin-analyzer is sequentially brought to each crown and, drawing along the entire perimeter of the crown under study, the line of the clinical equator, the size of the occlusal and gingival parts are visually determined. If a retention zone is determined on each abutment tooth, then the analyzer pin is replaced with a pin with a lead and a line of the clinical equator is drawn. Then, with a pencil or felt-tip pen, necessarily different in color from the color of the lead, a drawing of the contours of the clasps and other parts of the metal frame is applied.

Having drawn the equator line, a drawing of all metal parts of the clasp prosthesis frame is applied. The position of the lower edge of the retention part of the clasp shoulder is determined using a pin - a retention measure.

For chrome-cobalt alloys with a clasp shoulder thickness equal to the thickness of standard wax blanks, it is better to use a retention of 0.5 mm. After drawing the pattern, they begin to prepare the model so that the arch and sections of the frame for fixing the base do not adhere to the mucous membrane. To do this, from a tin or lead plate with a thickness of up to 1.5 mm, the corresponding size and shape of the plane is cut out, squeezed according to the model and glued to it with universal glue. You can use an adhesive plaster, on which you should apply 1-2 layers of insulating varnish.

Then they begin to create a clasp system, having previously applied a thin layer of petroleum jelly to the teeth. The wax blank of the clasp, selected according to the size of the crown, is first pressed against the lateral surface of the tooth with the body of the clasp, then with an occlusal pad. The shoulders of the Acker clasp are positioned so that 2/3 (the stabilizing part) is located above the equator line, and the end third (retention part) is under this line, respectively, the groove drawn with a measuring pin. At the same time, they make sure that the transition from the stabilizing part to the retention part is smooth in width and thickness, gradually decreasing towards the end of the shoulder. After that, the anchor part of the clasp is bent to the frame and attached to it with an additional portion of wax.

Next, the molding and processing of the clasp prosthesis frame is carried out. It should be remembered that when fitting the frame to the working model, it is necessary

Apply it along the chosen route of administration. At the same time, it is not recommended to grind the retention parts of the clasp shoulder: it is permissible that they cut off part of the plaster of the crown, since there is elasticity.

The second method is the manufacture of a one-piece frame with its casting on a refractory model. It differs from the first in sequence. First, a working model is prepared, a copy of it is made from a refractory mass, a gating system is created and a refractory molding is performed.

4. Obtaining a refractory model

After parallelometry, drawing a drawing of the prosthesis frame and obtaining grooves indicating the location of the lower edge of the retention part of the clasp shoulder, a layer of refractory wax or moldin is applied to all areas of the working model that have undercuts. Then, in the parallelometer, using a pin-knife, the excess is smoothed out in all areas to a sheer cylindrical surface.

The prepared model is immersed in water for 2-3 minutes and a refractory working model is made.

A working model is placed on the tray of the duplicating cuvette and, if there are gaps, they are closed with any plastic material (mold, plasticine). The pallet is covered with a cuvette with 2-3 holes at the end. Previously, in a special device or in a vessel on a water bath, the hydrocolloid mass is heated, constantly stirring. The readiness of the mass is judged by its consistency and homogeneity: the mass should be free of lumps and its temperature should not exceed 55 - 60 ° C. At a mass temperature of 38-45 ° C, it is poured into a cuvette through one of the holes at the end. The mass hardens in air for 30-45 minutes, turning into a strong elastic gel. After that, it is necessary to place the cuvette under the stream cold water for 15-20 minutes, so that the inner masses also harden. Having removed the tray of the cuvette, a plaster working model is removed from the mass.

The shape obtained from the hydrocolloid mass is the exact shape for the refractory working model. From the side of the removed pallet, a standard cone is inserted into the center of the impression from the hydrocolloid mass and poured into it with a refractory mass ("Silamin", "Christosil-2"). These masses are prepared in accordance with the instructions. They have a small percentage of expansion during solidification (0.2%) and thermal expansion at a temperature of 500-700 ° C not less than 0.8%. Together with the volumetric expansion of super gypsum during solidification, this compensates for the shrinkage of the metal during its solidification.

All refractory masses require special heat treatment. Heat treatment at a temperature of 120-160 ° C is carried out for 30-40 minutes in an oven preheated to 40 ° C. The dried, uncooled model is placed in a molten (150 ° C) fixative for 30-60 s to impart strength and smoothness to the surface layers of the model.

After the refractory mass and the cuvette have cured, a duplicate mold is squeezed out through the filling holes. The refractory model is freed from the mass by layer-by-layer cutting.

On the refractory model prepared in this way, a drawing of the frame is applied, focusing on the drawing on the working plaster model, and the lower boundaries of the retention part are determined from the notches. Then the wax composition of the prosthesis is modeled. The gating system is created from wax arcuate curved blanks supplied to the thickest sections. The gating pins reduce to the existing hole in the model, formed during its casting with a standard taper.

5. Setting the teeth and making the bases of the clasp prosthesis

After making the frame of the prosthesis and checking it in the oral cavity, they begin to manufacture the bases. The previously applied insulation is removed from the working plaster model, models are made in the central occlusion using a wax base and occlusal rollers and plastering them into the occluder.

Place the frame on the model and check the evenness of the gap between it and the model. If at the same time a contact zone is found, then this area is grinded, controlling the uniformity of the arc thickness. After that, a softened wax plate is laid along the borders of the saddle part and, while the wax has not hardened, a slightly heated metal frame is placed on the model. The correctness of the imposition of the frame is judged by the tightness of fit of all occlusal linings, stabilizing parts of the clasp shoulders and by the position of the arc.

Two methods are used to replace wax with plastic. The first method: the framework with the wax composition is removed from the working model and plaster of paris at the base of the cuvette. At the same time, make sure that the wax of the saddle part is at the level of the edge of the cuvette, and the arch and clasps are completely covered with plaster.

According to the second method, the frame with the teeth is cast together with the working model. To prevent displacement of the frame at the time of pressing the plastic, it is necessary to cut off a 5 mm thick layer of gypsum on the working model in the area of the arc. When plastering into the base of the cuvette, the gypsum will pass into these areas and when it hardens it will reliably keep it from displacement.

Plastic forming, polymerization mode, finishing and polishing are not different from the conventional ones.

Conclusion

Loss of teeth (adentia) is a serious medical and social problem.

With adentia, the chewing function is impaired, which leads to various diseases gastrointestinal tract. With the loss of teeth, it is possible to change the appearance, proportion of the face and impairment of speech. Removal of even one tooth entails a number of problems due to the displacement of adjacent teeth with the resulting defect, which can cause improper closure and the ratio of the dentition when chewing, functional overload and diseases of the remaining teeth. This is a kind of "chain reaction", as a result of which, when one tooth is removed, there is a real risk of losing many teeth.

Thus, missing one or more teeth is not only a deterioration in chewing or a cosmetic problem. This is a real threat to the normal functioning of the entire dentition and the human body. This is a problem that requires timely and rational treatment, the purpose of which is to restore the anatomical integrity of the dentition and lost chewing functions.

Clasp prosthesis is the most reliable, expensive and convenient design.

In the manufacture of such prostheses, an accurate calculation and modeling of all elements of the prosthesis is performed.

An important advantage of the clasp prosthesis is that it does not cover the palate. This means that getting used to the clasp prosthesis is much faster, there is no change in diction, prosthetic stomatitis, activation of the gag reflex, there is no inconvenience when eating.

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Clasp prosthesis is a partial removable prosthesis, part of the basis of which is replaced by a metal arch (arch - bugel, hence the name). Clasp prostheses are also called supporting prostheses. The term "abutment dentures" / was introduced in 1924 by Kaiogouisch, who believed that every partial denture that transmits chewing pressure to the teeth with the help of clasps is a abutment denture.

There are still other names for clasp prostheses: arc, frame, skeletonized, which characterize their design features.

Historical data - Bryap (1906) was the first to connect two bridges with a transverse arch along the arch of the hard palate, which renew the defects of the lateral teeth. The archwire served as an additional fixation, was placed on the mucous membrane and often caused bedsores.

Since 1911, Kiespeitap has used an archwire to connect two symmetrically positioned bridges on the lower jaw.

These were the first prostheses with a combined supply of chewing pressure; they were made from gold alloys by soldering individual parts into a single block.

Clasp prosthesis design

Characteristic feature clasp prostheses is a combined method of transferring the chewing load through the teeth to the periodontal tissues and soft tissues that cover the edentulous alveolar processes. Clasp prosthesis consists of a metal frame on which plastic bases with artificial teeth are attached. The frame is formed by an arc with the connection of different types of clasps, sometimes springs, hinges and arcs, which are the supporting structure of the entire prosthesis.

The main part of the clasp prosthesis is the support-holding clasp, which provides a double way of transferring the chewing pressure. With the help of clasps, chewing pressure is distributed between the teeth and the mucous membrane of the alveolar processes.

Brief description of the main elements of clasp prostheses

1. Retention elements - devices that hold the prosthesis in its place during the movements of the lower jaw and prevent it from shifting in the vertical direction under the influence of its own weight, vertical and horizontal components of forces that arise during the act of chewing or as a result of food pressure. The retention of supporting prostheses is carried out using non-removable devices: clasps, attachments.

2. Elements that stabilize - serve to prevent the displacement of the prosthesis in the horizontal direction under the action of lateral loading.

They contribute to the distribution of the horizontal components of the force of pressure on the largest possible number of teeth that are left, thereby increasing the durability of the prosthesis. As elements that stabilize, continuous and multi-link clasps are used, as well as extended clasp shoulders, which are supporting-holding. The retention elements usually help stabilize the prosthesis during the chewing act.

3. Saddles - a saddle, or base, is a part of a supporting prosthesis, carrying artificial teeth and a lost part.

Requirements for clasps for clasp prosthetics:

1. Ensure fixation of the clasp prosthesis in the oral cavity.

2. Rationally distribute the chewing pressure between the abutment teeth and the mucous membrane
the shell of the alveolar processes.

3. The support-holding clasp should transmit the chewing pressure along the axis of the tooth.

4. For diseases of periodontal tissue should be applied

multi-link clasps with hook loops for teeth splinting.

5. The clasps should not overload the periodontal tissues and loosen the tissues.

Advantages of clasp prostheses over plate prostheses

1. Clasp prostheses transfer part of the functional load to
abutment teeth, due to which the pressure on the mucous membrane of the edentulous
areas of the alveolar ridge and the prosthesis is little immersed in the mucosa
shell and almost does not fall off.

2. The functional efficiency of clasp prostheses significantly exceeds the efficiency of plate prostheses and it reaches 70-80%.

3.Using the system of clasps, it is possible to regulate the distribution of vertical pressure between the abutment teeth and the mucous membrane of the alveolar process; it helps to reduce the functional load on the mucous membrane and the underlying bone tissue, which is important for slowing down the process of bone atrophy and maintaining the height of the alveolar processes.

4. Clasp prostheses do not violate diction, taste, temperature sensitivity of the oral cavity, do not injure the mucous membrane of the gums.

5. The arch prosthesis does not adhere to the necks of the teeth and does not harmful influence on their endurance.

6. Clasp prostheses have a splinting effect on the remaining teeth, and contribute to the preservation of the functional usefulness of the periodontal abutment teeth.

7. Clasp prostheses do not have a negative effect on the gingival margin, which is essential in the orthopedic treatment of periodontitis.

8. These prostheses help to reduce the harmful effect of the horizontal component of the forces that transmit pressure to the abutment teeth and to the alveolar processes.

9. Supporting prostheses are more hygienic than laminar ones.

Requirements for the functioning of removable partial dentures should restore aesthetic, chewing, speech and other functions of the oral cavity;

Clasp prostheses after the onset of full adaptation should restore chewing efficiency by 70-80%

Clasp prostheses should distribute the chewing load evenly, but on the periodontal tissue through the teeth and on the bone tissue through the mucous membrane of the prosthetic bed; - removable dentures should not loosen the abutment teeth; - clasp prostheses should not disturb the diction, taste, temperature and tactile sensitivity of the oral cavity, should not injure the mucous membrane of the gums;

Clasp prostheses should not violate the vertical components of the occlusion (increase or decrease the bite) and should not interfere with the movements of the lower jaw (lateral and anterior movements). There should be multiple multipoint contact in the central occlusion position; - in case of periodontal diseases, clasp prostheses should be splinted, which acts on the teeth that remain, and to help increase the functional endurance of the periodontal abutment teeth; - removable dentures should not have negative influence on the gum edge, which is important in the orthopedic treatment of periodontitis; - removable dentures should be well fixed and not balanced during chewing movements; - clasp prostheses should not interfere with the excursion of the soft tissues of the floor of the oral cavity.

Indications for replacing dentition defects with clasp prostheses.

Clasp prostheses are shown:

1. With distally unlimited defects with preservation of at least 6 teeth on the jaw.

2. With the included defects of the dentition, when the size of the defect is more than 3 teeth in the lateral area and more than 4 teeth in the frontal area.

3. With multiple included defects in the dentition.

4. With mobility of teeth (I, II degree as a result of periodontal disease);
A clasp prosthesis can not only combine individual groups of teeth into
functional blocks, but also eliminate functional overload (splinting elements).

The indications take into account the condition of the tissues of the teeth, the dental formula, the height of the crowns of the abutment teeth used for the clasps, the type of bite and the compliance of the mucous membrane.

For the implementation of clasp prosthetics, the following conditions are necessary:

1. In the area of the periapical tissues of the teeth that remained (especially those intended for clasps) there should be no pathological changes.

2 The fisura on the abutment teeth intended for occlusal overlays should be "deep.

3. The crowns of the abutment teeth should have more or less pronounced equators.

4. The dentition should have at least 5-6 adjacent teeth or teeth
must be positioned so that bridge prosthetics can be applied
create a marked position in the dentition (this requirement applies
mainly to the lower jaw).

5. The crowns of the abutment teeth that are used for clasping should not be low, and the roots should be of sufficient length.

6. Slight or moderate atrophy of the alveolar process.

The second, third and fourth conditions can be created in their absence using orthopedic interventions.

The choice of the design of the clasp prosthesis takes into account the type of defect, its length, the condition of the abutment teeth, the condition of the mucous membrane, the patient's age, the condition of the alveolar ridge, the type of bite, individual characteristics sick.

Taking impressions

Any prosthetics begins with an impression, the quality of the prosthesis itself depends on it. For each type of prosthesis, there are certain requirements for them. First of all, the use of this or that impression depends on the topography of the defects in the dentition.

For the manufacture of clasp prostheses, impressions have their own characteristics. So, in case of defects in the dentition, limited by the distal support, anatomical impressions, taken with well-chosen standard spoons, can be dispensed with. While in the case of defects without distal support, it is necessary to take functional impressions in order to obtain an accurate impression of the edentulous area, especially the distal area. Such an impression is taken with an individual spoon. The height and length of the spoon should be in such a way that you can get an imprint of the hard and soft tissues of the oral cavity to the neutral zone and the "A" line.

In cases where the degree of compliance of the mucous membrane of the prosthetic field is more than 0.8-1.5 mm, we use compression impressions according to known methods, if the mucous membrane is less compliant, we use unloading impressions.

Gypsum, "Sielast", "Tiodent", "Elastic" are used as an impression material, and thermoplastic materials are used for compression impressions. With the help of these masses, it is possible to obtain an accurate imprint of the hard and soft tissues of the oral cavity with all the smallest details of the relief of the mucous membrane, teeth, interdental spaces, fissures and retention points.

For the manufacture of the frame of the clasp prosthesis on the refractory model, we take two working impressions and one auxiliary, and if the clasp prostheses are made on both jaws, then four working impressions are obtained, two from each. This is necessary in order to use one model to study it in a parallelometer with subsequent duplication, and the second to determine the central occlusion, plastering it into the occluder and the final manufacture of the clasp prosthesis. When using silicone materials, you can limit yourself to one print, which can be used to cast two models.

Alginate materials are used for auxiliary impressions. They are not used to obtain working impressions in clasp prosthetics, as they shrink over 1.5% within an hour.

Ministry of Health of the Moscow Region

State budgetary educational institution

secondary vocational education

"MOSCOW REGIONAL MEDICAL COLLEGE №1"

Methodological development on the topic

"Planning the construction of a clasp prosthesis"

for teachers

for specialty 060203 "Orthopedic Dentistry"

Moscow, 2012

Specialty: 060203 "Orthopedic Dentistry"

basic education level

Developer: Kryuchkova O.Yu. - teacher of the highest qualification category, Moscow Regional Medical College No. 1

The methodological development on the topic "Planning the construction of a clasp prosthesis" was developed on the basis of the Federal State Educational Standard for the specialty of secondary vocational education 060203 "Orthopedic Dentistry", the basic level of education, and is intended for teachers as an aid to prepare for the lesson.

Explanatory note

Methodological development on the topic "Planning the construction of a clasp prosthesis" of the professional module "Making clasp dentures" was developed on the basis of the Federal State Educational Standard for the specialty of secondary vocational education 060203 "Orthopedic Dentistry", the basic level of education.

The methodological development contains a lecture summary, tasks in a test form with standards of answers and applications for independent work of students and is intended for teachers as a methodological aid to prepare for the lesson in the study of this topic. The development can also be used in lectures as part of a training and retraining program for dental technicians.

The purpose of studying this topic- training of a dental technician who knows modern methods of making dentures.

When studying the topic, the following PC and OK will be formulated:

PC 3.1. Knows how to make cast clasp dentures with a clasp fixation system.

OK 1. Understands the essence and social significance of his future profession, shows a steady interest in it.

OK 2. Knows how to organize their own activities, choose standard methods and ways of performing professional tasks, evaluate their effectiveness and quality.

OK 3. Can make decisions in standard and non-standard situations and be responsible for them.

OK 4. Knows and applies methods of searching and using information necessary for the effective fulfillment of professional tasks, professional and personal development.

OK 5. Has the skill of using information and communication technologies in professional activities.

OK 6. Can work in a team and in a team, communicate effectively with colleagues, management, doctors and patients.

OK 7. Can independently determine the tasks of professional and personal development, engage in self-education, consciously plan professional development.

OK 8. Knows how to organize a workplace in compliance with the requirements of labor protection, industrial sanitation, infectious and fire safety.

The main task of the teacher is the preparation of graduates for independent practical work as dental technicians.

The presentation of the topic is based on knowledge of previously studied disciplines: anatomy of human physiology with a course in biomechanics of the dentoalveolar system, dental materials science with a course in occupational health and safety, removable plate prostheses, fixed prostheses.

PLANNING OF THE STRUCTURE OF THE LUGAL PROSTHESIS

Relevance of the topic:

Currently, one of the urgent problems of prosthetic dentistry is the prosthetics of dentition defects using clasp prostheses. A competent assessment of the clinical situation underlies the correct choice of a rational design for the future clasp prosthesis.

The functional, technological and structural features of the clasp prosthesis determine the high accuracy of the fabrication of the frame with supporting-retaining elements, which are provided by the use of special methods for preparing the working model in a parallelometer for studying and marking the reliefs of the prosthetic field on working models (using parallel planes and lines).

After studying the topic, the student should know:

parallelometer device;

the value of parallelometry for correct fixation and stabilization of the prosthesis;

the value of parallelometry to determine the ways of insertion and removal of the prosthesis;

the value of parallelometry for the design of fixing elements;

the value of parallelometry for the distribution or redistribution of the chewing pressure on the abutment teeth, groups of teeth and underlying tissues of the prosthetic bed;

difference between the "boundary line" (line of sight) from the equator of the tooth.

The student should be able to:

to define the concepts of "boundary line" and "undercut";

draw the model in a parallelometer, plan the design of the prosthesis.

Questions to control the initial level of knowledge:

Anatomical and physiological features of the dentition with partial absence of teeth;

Anatomical structure of the tooth;

Definition of the concepts "anatomical equator of a tooth", "clinical equator of a tooth";

Definition of the concepts of "chewing pressure", "chewing efficiency";

Types of clasps, classification of clasps;

Organization of dental production for the manufacture of clasp prostheses;

Classification and properties of materials used in the manufacture of removable clasp prostheses.

The manufacture of a clasp prosthesis begins with a detailed assessment of each case. The use of a diagnostic model improves planning efficiency.

Clasp design planning the prosthesis is :

in determining the route of insertion and removal of the prosthesis;

Prosthesis insertion route- the movement of the prosthesis from the initial contact of its clasp elements with the supporting teeth to the tissues of the prosthetic bed, after which the occlusal linings are installed in their beds, and the basis is precisely located on the surface of the prosthetic bed.

Way of removal of the prosthesis- movement in the opposite direction, i.e. from the moment of separation of the base from the mucous membrane of the prosthetic bed to the complete loss of contact of the supporting and retaining elements with the supporting teeth.

The best by introducingandexcretion the prosthesis should be considered the one when the denture can be easily applied and removed, with a minimum of interference,

which cannot be excluded, and at the same time providing the same retention on every tooth.

2) in the marking of the model to find the most convenient location of the clinical equator on the abutment teeth and the corresponding position of the clasps;

3) in determining the position of the arch in the palate and alveolar process of the lower jaw and other elements of the prosthesis (multi-link clasps, branches, processes, etc.).

All this as a whole makes it possible to apply a drawing of the frame of the future prosthesis to the model.

When planning the fixing system of the removable thesis pursues two main tasks :

1) create a reliable attachment of the prosthesis during chewing and speech;

2) to ensure such fastening of the prosthesis, in which it would have the least effect on the abutment teeth and the mucous membrane covering the edentulous alveolar processes.

Chewing pressure also helps to dislodge the prosthesis. First, under the influence of sticky food, the prosthesis can move away from the prosthetic bed of both the upper and lower jaw. This pulling force increases the overturning moment due to the weight of the prosthesis. The rotation of the prosthesis takes place around the clasp line. Under the influence of chewing pressure, the prosthesis undergoes spatial movement in three planes - vertical, sagittal and transversal. Depending on the chosen method of fixation, the displacement of the prosthesis may prevail in any one plane. Its movement in other planes, as a rule, is less pronounced, but almost always takes place. This makes the nature of the displacement of the prosthesis under the influence of chewing pressure so complex that it requires detailed consideration under different clinical conditions depending on the type of removable prosthesis, the method of its fixation, the size and topography of the dentition defects, the nature and magnitude of atrophy of the edentulous alveolar process, etc.

All supporting-holding clasps, their elements should be located strictly in relation to the clinical equator - the largest perimeter of the tooth, taking into account its inclination.

Clinical equator coincides with the anatomical equator only with a strictly vertical position of the longitudinal axis of the tooth. Usually, due to the physiological inclination of the teeth, the line of the anatomical equator does not coincide with the clinical one. If the tooth is tilted orally, then the line of the clinical equator on the lingual side is shifted to the occlusal surface, and on the vestibular it goes down to the gingival margin.

For the correct design of clasps, it is important to determine the general clinical equatorial line of the dentition, which is also called the "clinical equator", "prosthetic equator", "contour height", "guide line", "general sight line". The most accepted name was given by E.I. Gavrilov - a boundary line (demarcation).

Boundary line divides the tooth surface into supporting (occlusal) and retaining (retention, gingival). It cannot be called the equator, since it does not coincide with it and, unlike it, changes its position due to the inclination of the tooth: on the side of the slope, it approaches the chewing surface, and on the opposite side, it moves away from it (Fig. 1).

The boundary line is revealed by means of parallelometry and serves as a guide for the location of the parts of the shoulder of the supporting-holding clasp.

The main types of location of the boundary line

1. Median - passes through the middle of the tooth from the vestibular and oral sides (Fig. 2a);

2. Diagonal - the descent of the boundary line to the neck from the side of the defect, close to the occlusal surface on the other side, and vice versa (Fig. 2.b, c);

3. High - in the vicinity of the occlusal surface (Fig. 2.d);

4. Low - the line runs at the level of the lower third of the crown (Fig. 2.e);

5.With dividing the crown of the tooth into occlusal and subgingival zones (as an option: near and far (Fig. 2.f).

Fig. one... Changing the position of the line of sight (boundary line) when changing the position of the egg-shaped object in relation to the diagnostic rod.

Fig. 2 Boundary line options: a — median line; b, c — diagonal; r - high; d — low;

e-near and far zones (separated by a vertical line).

The choice of the clasp is influenced by the position of the boundary line identified during parallelometry. Five main types of the boundary line are more common:

1. The boundary line runs in the middle of the approximal surface of the tooth and rises along the vestibular surface to the contact point with the adjacent tooth. Such an arrangement of the boundary line will make it possible to conveniently place Akker's supporting-holding clasp on the tooth.

2. The boundary line begins at the level of the contact point of the tooth from the side of the dentition defect and descends along the vestibular surface to the middle of the proximal surface at the adjacent tooth. In this case, clasps with long holding shoulders, Roach clasp, Bonigard clasp are shown.

3. Diagonal location of the boundary line on the abutment tooth. The boundary line runs at the chewing surface in the area of the dentition defect, crosses the obliquely vestibular surface of the abutment tooth and ends at the neck of the tooth on the opposite side. If this is a premolar, then a type 4 clasp (reverse action) is used, and if a molar - a ring clasp of Ney's classification. Both clasps have long shoulders, thanks to which they are elastic and easily pass the equator of the abutment tooth, providing good fixation of the prosthesis and the transfer of chewing pressure along the axis of the tooth.

4. When the teeth are abraded, a high location of the boundary line is observed, it runs at the level of the chewing surface. Such teeth require covering with artificial crowns to restore their anatomical shape.

5. A low outline of the boundary line is found in teeth that have the shape of a truncated cone. The equator runs at the level of the neck of the tooth. Such a tooth can only be used for a support clasp, otherwise it is necessary to restore its anatomical shape with a crown.

Parallelometry

The route of insertion and removal of the prosthesis, as well as the boundary line common to all abutment teeth, in relation to which the elements of the support-holding clasp will be located, are determined using a special device - a parallelometer.

Paral lelometer is a device for determining the greatest convexity of teeth on models of jaws, revealing the relative parallelism of the surfaces of two or more teeth or other parts of the jaw, for example, the alveolar process (Fig. 3).

Fig. 3 Parallelometer

The set of tools includes:

Flat analyzer to determine the most advantageous position of the boundary line, and, consequently, the position of the clasps, which ensure the smooth introduction of the prosthesis and its good fixation;

Fig. 4 Set of tools

A pin in which the leads are fixed with a collet to outline a line;

Pins measuring the degree of retention - calibers No. 1, 2 and 3; they differ in the diameter of the measuring disc:

Disc No. 1 - 0.25 ml,

Disc No. 2 - 0.5 ml,

Disc No. 3 - 0.75 ml (with their help, the position of the ends of the holding arms of the clasps on the abutment teeth is determined);

Knife pins for removing excess wax after pouring undercuts (fig. 4).

The set also includes a table for fixing the models. The table platform is pivotally connected to the base, which allows you to tilt the model and bring them to the instruments at different angles.

Classification of parallelometers

1.Standard - to perform general clinical and laboratory types works ( fig. 4 five).

Fig. 5 Standard parallelometer.

2. Special- to perform certain operations (fig. 6).

Fig. 7 Universal milling-parallelometric device.

Basic rules for paralleling:

1) the parallelometer makes it possible to determine the design of the clasp prosthesis;

2) the general clasp (boundary) line, despite the fact that it is curved, should, in general, be parallel to the occlusal plane;

3) the prosthesis, when fixing it in the oral cavity, must transmit the chewing pressure along the axis of the tooth;

4) the prosthesis should be designed so that it rationally distributes the chewing pressure between the remaining teeth and the alveolar processes.

Parallelometry methods

1. Arbitrary;

2. Method for determining the average inclination of the longitudinal axes of abutment teeth (Novak's method);

3. Method of inclination of the model (method of choice, or "logical" method).

Arbitrary method. The model, cast from high-strength plaster, is placed on the parallelometer table so that the occlusal plane of the teeth is perpendicular to the lead shaft. Then a parallelometer lead is brought to each abutment tooth and a general boundary line is drawn. With this method of parallelometry, the line may not coincide with the anatomical equator, since its position will depend on the natural inclination of the tooth, therefore, conditions for the location of the clasps on individual teeth may be less favorable.

This paralleling method is shown only when parallelinglability of the vertical axes of the teeth, their slight inclination and minia small number of clasps.

Method for detecting the average inclination of the long axes of the abutment teeth (Novak's method). The edges of the base of the model are cut so that they are parallel to each other. The model is fixed on the parallelometer table, after which the vertical axis of one of the abutment teeth is found. The stage with the model is installed so that the analyzing rod of the parallelometer coincides with the long axis of the tooth (Fig. 8).

Fig. 8 Novak's method.

The direction of the latter is drawn on the side surface of the model base. Next, the vertical axis of the second abutment tooth, located on the same side of the dentition, is determined and is also transferred to the lateral surface of the model. Then the resulting lines are connected by parallel horizontal lines, after dividing the horizontal lines in half, the average orientation axis of the abutment teeth is obtained. The middle axes of the teeth on the other side of the model are determined in the same way. The obtained middle axes are transferred to the free face of the model base with the help of the parallelometer analysis rod, and the middle axis of all abutment teeth is determined from them. Then the stage with the model is finally installed in the parallelometer.

The analytical rod is changed to a graphite one and a boundary line is drawn on each abutment tooth (Fig. 9)

Fig. 9

Alternative

The marking of the equator can also be carried out by overlaying an occlusal film using a measuring rod (Fig. 10).

Fig. 10

Note.

The disadvantage of the method lies in the duration, difficulty and probability of error in determining the general boundary (survey) line.

Selection method. The model is fixed on the parallelometer table. The stage is then positioned so that the occlusal surface of the model teeth is perpendicular to the evaluation rod (zero tilt). The latter is brought to each abutment tooth in turn and the presence and size of the supporting-stabilizing and retaining zones is determined. It may turn out that on one or several teeth there are good conditions for the location of the clasp elements, while on others they are unsatisfactory. Then the model must be viewed at a different angle of inclination. From several possible inclinations, choose the one that provides the best holding area on all abutment teeth (Appendix No. 1).

The main types of model tilt (fig. 11):

horizontal zero inclination: the axis of the diagnostic rod is perpendicular to the occlusal plane of the chewing teeth;

front;
left side;
right side.

Fig. 11. The position of the models in the parallelometer relative to the diagnostic rod.

When determining the route of insertion and removal of the prosthesis, it is most advisable to proceed from the topography of dentition defects:

In the absence of teeth in the distal regions (Kennedy class I) or in the anterior (class IV), the model should be tilted in the direction of the defect;

With the simultaneous presence of two or more defects in the anterior and lateral parts of the dentition, the model is tilted towards the defect, in the area of which sagging or less stability of the prosthesis is possible;

With a one-sided defect and the presence of a distal support (class III), it is advisable to tilt the model towards a more stable tooth to create the most favorable conditions for fixation on it;

In case of a class IV defect, the best fixation is provided by the front inclination of the model, and the rear one is expedient only for aesthetic reasons.

When designing a clasp prosthesis, the selection method allows you to take into account the requirements of aesthetics and the optimal degree of retention of the clasps. So, if the supporting-holding clasps must be placed on a group of teeth visible when smiling, then for reasons of aesthetics, it is advisable to bring the line of sight as close as possible to the necks of the supporting teeth. For this, the back tilt of the model is used, that is, the model is tilted back. The lateral inclination of the model is chosen to evenly distribute the degree of retention on the abutment teeth of both halves of the jaw.

If in the horizontal position of the model it turns out that on the left lateral teeth the boundary line is located on the buccal surface along the necks of the teeth (due to the lingual inclination of the teeth), then it is advisable to tilt the model to the left in order to "raise" the survey line. The degree of lateral inclination of the model is determined by the sufficiency of the retention zone on the right lateral teeth.

Having fixed the movable table and the model placed on it in the selected position, a general boundary line is applied with a vertical pin with a lead.

Bringing the lead to each tooth so that its lower edge is located and moves along the level of the gingival edge, a line is drawn on the vestibular, oral and proximal surfaces of all teeth. Having removed the model with a table from the parallelometer stand, with a thin felt-tip pen or a soft pencil, they circle the resulting general boundary line and proceed to planning the design of the clasps and drawing a drawing of the future prosthesis frame.

The common clinical equator is crossed only by the retention parts of the clasps. To determine the location of the retention part in the parallelometer there is a special rod with a ledge - a retention meter - gauges 1, 2 and 3. The rod is fixed in the arm of the parallelometer and set so that it touches the clinical equator. At this point, the shoulder of the rod touches the point of the tooth below the clinical equator (Figure 12).

Fig. 12

Having passed the rod over the tooth, a notch is obtained, which indicates the line of location of the retention part, i.e. the point where the end of the holding clasp should be located: with the 1st degree of retention - 0.25 mm below the clinical equator, with the 2nd - by 0.5 mm and with the 3rd - by 0.75 mm.

The location of the boundary line on the crown after parallelometry, its relation to the occlusal and retention parts of the crown determine the need to choose one or another type of support-holding clasp for each tooth. The choice of the type of clasp depends on the topography of the clinical equator and the area of the occlusal and retention parts (Fig. 13). And the size of the supporting-stabilizing and retention zones on the tooth, in turn, depends on the position of the general boundary line (on the inclination of the model during parallelometry).

Fig. 13. Different position and size of the retention zone depending on the severity of the equator and the inclination of the tooth : a, b — boundary line at zero slope, c — absence of conditions for retention; d, d-boundary line when the model is tilted; e-definition of the retention point.

The retention properties of the clasp depend on the following factors:

1. The type of clasp, namely the length of the shoulder. The longer the shoulder, the further from the line of sight it can be positioned.

2. Curvatures of the tooth surface: the more pronounced the curvature, the closer to the line of sight should be the retention shoulder of the clasp. Only elastic shoulders can approach the cervical area of the tooth.

3. Clasp thickness: the thicker the clasp, the less elastic it is and, therefore, the closer to the line of sight it should be.

4. Metal for manufacturing: the more elasticity the metal has, the less rigidity the clasp has and, therefore, it can be placed further from the boundary line.

When planning the design of an arch prosthesis, the position of the abutment teeth in the dentition should also be taken into account. The displacement of the teeth to the medial, distal, buccal or lingual side makes it difficult to create their parallelism by grinding hard tissues, since the opening of the tooth cavity or thermal damage to the pulp is possible. In such cases, doctors often resort to depulpation. Experience shows that pulping of teeth in order to create their parallelism when using an arch prosthesis should now be considered an extremely extreme measure. The correct choice of the design of the supporting-retaining elements after studying the models in a parallelometer dramatically reduces the indications for tooth pulping and covering them with crowns.

When planning the design of the clasp prosthesis, the type of bite is of great importance. So, with a deep and deep traumatic bite, a multi-link clasp with splinting elements that will interfere with the closure of the teeth and the maintenance of the usual interalveolar height cannot be included in the design of the prosthesis. In patients with such a bite, it is necessary to find out the possibility of increasing the interalveolar height, and only after that, if indicated, can a cast palatine strip be applied, restoring the cutting-tubercular contact.

Paralleling errors.

Ignorance of parallelometry leads to undesirable results:

Difficult fitting of the frame;

Incorrect definition of the clasp zone;

Break off the vestibular part of the clasp;

The topography of the support and retention zones is incorrectly assessed.

Difficult fitting of the frame

It occurs due to the fact that the isolation of the model was carried out incorrectly, i.e. the places of isolation have undercuts, which means that the teeth prepared for the clasps are not insulated in parallel. This makes it difficult to find the route of insertion of the prosthesis.

If the route of insertion of the prosthesis is not determined , then the clasps cannot clearly fulfill their functions. The isolation zone should be equal to "0" for all abutment teeth.

Incorrect definition of the clasp zone

Incorrect definition of the clasp zone, as a rule, leads to the fact that the clasp breaks during operation, or the frame is fixed on the abutment teeth with great tension.

Parallelometry gives a clear picture of the location of the clasp, since the clasp zone is measured from 0 to 25 microns. The clasp should be evenly thinned, then it works like a "whip" and 1/3 of the clasp should participate in the work.

If the parallelometry is carried out correctly, then the frame of the clasp prosthesis does not cause difficulties during fitting.

Breaking off the vestibular part of the support-holding clasp

This problem occurs due to the incorrect position of the clasp. Many technicians trace the model by eye, and therefore the clasp is positioned as bent. With this arrangement of the clasp, the working moment is very close to the occlusal patch. And as a result, that part of the clasp works where the maximum thickness is, i.e. the elasticity of the clasp is equal to "0". Sooner or later, material fatigue sets in, and the clasp will break off exactly at the point where the maximum load occurs.

The topography of the clasp support zone is estimated incorrectly.

The most common mistake is the complete or partial location of the continuous clasp on the teeth of the lateral group in the retention zone.

Conclusion:

From the above, we can conclude that clasp prosthetics is one of the most effective methods of prosthetics for partial loss of teeth. The manufacturing technology of such structures is complex and requires professional skills. Therefore, we study the technology of working with a parallelometer in theoretical and practical classes.

Knowledge of parallelometry methods guarantees high-quality manufacturing of the clasp prosthesis.

Control questions on the topic of the lesson:

Parallelometer. Basic structural elements. Work principles.

The value of parallelometry in clasp prosthetics.

Purpose of the parallelometer and its components.

Elements of the support-holding clasp, their functional purpose.

Parallelometry technique: arbitrary, selection method, graphic.

Advantages and disadvantages of the Novak method and the "choice" method

Ney's clasp system, the choice of clasps depending on the topography of the location of the boundary line.

Elements of the clasp prosthesis, which reduce the chewing pressure on the periodontium of the supporting teeth.

Measurement of the depth of the undercut (retention) zone.

The concept of the route of insertion and removal of the prosthesis.

Situational tasks

1. Dental formula of the patient

18 17 16 15 14 13 12 11 21 22 23 24 25 26 27 28

48 47 46 45 44 43 42 41 31 32 33 34 35 36 37 38

The preserved teeth are stable, have the correct anatomical shape, intact, high clinical crowns. The atrophy of the alveolar process is insignificant, the tubercle is of medium size, the vault of the palate is of moderate height. The attachment of the frenum of the tongue is high.

When designing a clasp prosthesis on the lower jaw, determine the rational location of the arch.

2. When studying the model in a parallelometer, a diagonal location of the boundary line (high in the nearby zone and lowered in the distant one) on the abutment teeth was revealed.

Suggest the type of clasp of the Ney system.

3. When studying the model in a parallelometer, on premolars, limiting end defects, and having a lingual inclination, a high location of the boundary line on the lingual surface and low on the vestibular surface of the teeth was revealed.

Select the design of the Ney system clasp for fixing the clasp prosthesis.

4. When studying the model in a parallelometer, a different location of the boundary line on the oral and vestibular surfaces of the tooth was revealed: on the oral - close to typical, and on the vestibular - diagonal.

Suggest the type of Ney system clasp for fixing the clasp prosthesis.

5. The patient has a partial absence of teeth.

Dental formula:

When studying the model in a parallelometer, the diagonal location of the boundary line on the models was revealed.

Suggest the design of the Ney system clasps for fixing the clasp prosthesis.

6. The patient's teeth are positioned correctly in the dental arch, stable.

Dental formula:

18 17 16 15 14 13 12 11 21 22 23 24 25 26 27 28

48 47 46 45 44 43 42 41 31 32 33 34 35 36 37 38

When studying the model in a parallelometer, a typical position of the boundary line was found on all abutment teeth.

Suggest the design of the clasps that are most effective for stabilizing and fixing the arch prosthesis under the given conditions.

Tasks in a test form to control knowledge.

Choose one correct answer:

1. The parallelometry method is based on

1) determining the boundary line

2) determining the vertical axis of the abutment teeth

3) the principle of parallelism of perpendiculars lowered to the plane

4) determining the vertical axis of inclination of the model

2. Parallelometry is carried out

1) when fitting and checking the frame of the clasp prosthesis in the clinic

2) when trying on a cast frame on a model in a laboratory

3) when checking the wax construction of the prosthesis in the oral cavity

4) when modeling the frame of the clasp prosthesis

3. On the base of the model for parallelometry lines are applied

1) overview (boundary)

2) the equator of the tooth

3) gingival margin

4) the longitudinal axis of the tooth

4. The part of the tooth crown surface located between the boundary line and the gingival margin is called

1) undercut zone

2) the occlusal area

3) safety zone

4) retention area

5. The area of the retention part of the shoulder

1) anatomical equator

2) gingival area

3) occlusal area

4) support zone

6. The boundary line serves to determine

1) the boundaries of the prosthesis

2) clasp designs

3) vertical axis of inclination of the tooth

4) design of prostheses in general

7. Measurement of the depth of the niche of the inclination of the tooth helps in choosing

1) the type of clasp of the Ney system

2) prosthesis design

3) ways of insertion and removal of the prosthesis

4) the location of the arc

8. The shaping of the undercut contributes to

1) creating a holding moment

2) creating parallelism of abutment teeth

3) the choice of the clasp

4) determining the location of the frame arc

9. The anatomical equator of the tooth coincides with the clinical

2) never

3) only with a strictly vertical arrangement of the longitudinal axis of the tooth

4) only when the model is tilted

10. The most important line in the arrangement of elements in the support-holding clasp is

1) longitudinal axis of the tooth

2) the line of the clinical equator

3) line of the anatomical equator

4) vertical line

11. For the manufacture of a clasp prosthesis, the working model is made of

1) beta modification of gypsum

2) alpha modification of gypsum

3) dental cement

12. The base of the working model for planning the clasp prosthesis during parallelometry must be high

1) 15 - 20 mm

2) 20 - 25 mm

3) 35 - 40 mm

4) 45 - 50 mm

13. The following number of incline types are possible on the parallelometer table.

14. The most advantageous position of the boundary line on the abutment tooth is

1) diagonal

2) high

4) coinciding with the equator of the tooth

15. The location of the tip of the fixing part of the support-holding clasp is determined using the parallelometer rod

1) graphite

2) analytical

3) index

4) undercut depth gauge

16. The retention area on the tooth surface is

1) equator

2) chewing surface

3) the cervical part of the tooth crown

17. The route of insertion of the clasp prosthesis is determined using

1) gnatodynamometer

2) rheograph

3) parallelometer

4) oscilloscope

18. The device used to determine the general clinical equator of the dentition is called

1) parallelometer

2) rheograph

3) gnatodynamometer

4) esthesiometer.

19. The retention part of the shoulder of the support-holding clasp is located

1) in the area of the equator of the crowns of the abutment teeth

2) in the area of the occlusal zone of the crowns of the abutment teeth

3) in the area of the gingival zone of the abutment crowns

20. General line drawn along the coronal parts of the teeth on the working model with parallelometry

1) undercut line

2) line of the anatomical equator

3) boundary gingival margin

Standards for answers

Independent work of students

1. Writing abstracts on topics:

"Device and types of parallelometers"

"Parallelometry"

"The value of parallelometry in clasp prosthetics."

2. Drawing the model. Definition of the "boundary line".

3. Creation of multimedia presentations.

4. Drawing up crosswords.

4.Work with educational and additional literature

5.Working with Internet resources

Homework

Mironova M.L. Removable dentures... M., 2009. P. 134–141, Abolmasov N.G. and other Orthopedic dentistry. M., 2008. S. 303–310; Denture technology / ed. M.M. Rasulova et al. M., 20011. S. 191-195.

Appendix # 1

Algorithm of measuring technique in a parallelometer (selection method).

Fig. 1. Measuring tool set

Determination of the route of administration

1. The model is firmly fixed on the model table. Using the measuring rod of the parallelometer, the general direction of insertion of the clasps is established.

2. Rotating the model from its original position, taking into account all abutment teeth ...

3. A position with a suitable undercut is found. As a result, the boundary line of individual teeth is determined.

4. The boundary line is the largest circumference of the tooth, based on the general direction of insertion for all abutment teeth.

The area below the equator is the retention area.

ALTERNATIVA A

The equator of the tooth is marked with a graphite rod.

ALTERNATIVE B

The equator can also be marked by applying an occlusal film using a measuring rod.

5. With the help of a measuring gauge, the deepest position of the retention arm is located in the retention area.

In this case, the gauge must be adjacent to the tooth.

Empirical values of undercuts

Clasp type Undercut (mm)

G-shaped 0.25-0.35

Clammer Acker 0.20-0.30

Reverse action clamp 0.25-0.40

Ring clasp 0.30-0.50

Note. When drawing, the end of the graphite rod (measuring rod) should be at the level of the neck of the tooth.

You can also use "Parameter 36045" - a tool for measuring the depth of undercuts.

Clasp marking

1. Now you can mark the position of the clasp, preferably with a graphite pencil, while taking into account the following:

2. Ideally, a third of the retention shoulder should be below, a third at the level and a third above the boundary line.

Appendix # 2

One of the popular methods for correcting various defects in dentistry is the installation of clasp prostheses. Their features, design varieties and rules of care will be discussed in the article.

What is clasp prosthetics?

A distinctive feature of the clasp is comfortable wearing, which is achieved due to the reduced volume and thickness of the base

- this is one of the types of removable structures, the basis of which is a metal arch with plastic fragments fixed on it, imitating the gum, and artificial teeth.

A clasp is a metal arch that repeats the shape of the jaw. The purpose of the prosthesis is to restore teeth, both in the upper and lower rows.

In addition to the metal base and imitating fragments, the structure has fixing elements that ensure a strong attachment of the arch in the oral cavity.

The orthopedic product represents worthy alternative removable lamellar and flexible nylon prosthesis.

A distinctive feature of the clasp is comfortable wearing, which is achieved due to the reduced volume and thickness of the base.

The basis of the clasp construction performs several functions at the same time:

connects artificial fragments of the gums and teeth;
gives support to the prosthesis;
stabilizes the position in the oral cavity.

When prosthetics of the lower row, the arch is located on the side of the tongue (at the midpoint between the bottom of the mouth and the level of the gum edge). The arch parameters are adjustable (made narrower or wider) so as not to create discomfort to the frenum of the tongue.

The denture for the upper dentition has a palatal bridge. It connects the saddle points of the structure and corrects the chewing load, bringing it as close as possible to the physiological one.

Varieties and design features

There are several types of clasp-type prostheses, the difference of which lies in the method of fixation:

On clasps- the design includes metal hooks that provide fixation of the product to the abutment teeth from both sides simultaneously. When installing, grinding of the abutment teeth is not carried out.
On attachments- the product has micro-locks that ensure reliable fastening. Due to their small size, the clips are almost invisible. When chewing, the load is distributed mainly to the support units.
On telescopic crowns- the prosthesis is fixed using special telescopes. These products are considered the most reliable, but the cost is very high, which is explained by the complex manufacturing technology and virtuosity of calculations. Before installing the structure, it becomes necessary to grind the abutment teeth, cover them with metal and polish. Only highly qualified specialists will be able to perform high-quality work (interaction between a dentist and a dental technician).
Splinting- the arch of the prosthesis exactly repeats the shape of the teeth, which ensures reliable fixation of the units. This factor determines the cases when the installation of the prosthesis is appropriate, namely the mobility of the teeth.

On telescopic crowns On attachments On clasps Splinting

Types of locks, lock fasteners

Clasps are produced for upper jaw in several versions, which differ mainly in shape:

ring;
horseshoe;
in the form of a transverse strip.

Clasp designs are considered the most common.

The varieties of this group differ in retaining elements:

Roach Clasps outwardly similar to T-shaped processes that extend from the arch of the frame and are located in the recesses. The products provide good hold, but the placement process is rather complicated.
Bonneville Clasps represent a group of cross-over structures. Crossing the occlusal surface across, they are placed on the vestibular and oral parts of the incisor (molar). Suitable for use when there is a gap between the teeth. The clasp completely fills it, which eliminates the accumulation of food debris.
Reichelman clasps They are distinguished by their transverse design and the presence of an occlusal lining in the form of a special partition.
Continuous clasp- the structure is presented from several links fastened together. The product is placed orally or vestibularly. The peculiarity lies in the tight fit of each link to natural teeth, which ensures a strong fixation.
Embrasure clasps- in fact, this is a kind of Bonneville clasps, but the two elements included in the design are directed in opposite directions. Products perform a stabilizing function, therefore they are often used for splinting.

Continuous clasp Embrasure clasp Clammer Bonneville Clammer Roach Clammer Reichelman

What are the parameters for selecting a variety?

To solve problems with loose teeth, a splinting prosthesis is more suitable.

Each type has a number of advantages, but the cast structure is considered the most reliable, therefore, when choosing the type of fastening, preference should be given to a solid product.

To solve problems with loose teeth, a splinting prosthesis is more suitable.

Its design is created in such a way that natural teeth are fixed in their natural position.

With prolonged exposure of the links to the units, the neck of the tooth is strengthened in the dentin. The same products are recommended for malocclusion. The stabilizing properties of the archwire make it possible to correct the defect during prolonged wear.

The locking structure is chosen with partial loss of teeth, when several units are missing in the row. And the clasp is appropriate to use when there are abutment teeth, which will redistribute the load on them during chewing.

Types of clasp prostheses

Dental prostheses are classified according to various criteria, including the type of material used in the production of an orthopedic product:

Types of clasp-type prostheses
Name	Description
Metal-free (quadrotti)	The main element of the prosthesis is made of polymer material, which makes it possible to use the structure for allergy sufferers.
Metal-containing	Various dental alloys are used for the manufacture of prostheses: titanium, chrome-cobalt, gold-platinum.
Plastic	The base is composed of acetal. This product is lightweight and comfortable to wear.
Sintered metal	In the process of manufacturing a prosthesis, a combination of metal and ceramic is used. This improves the aesthetic qualities of the prosthetic construction.

Element types

Support-retaining parts are of the following types:

solid - poured from a metal alloy:
composite - connected from several parts by soldering;
separate - first, wire elements are harvested, which are subsequently soldered together into a single structure.

Types of fasteners

All orthopedic prostheses in dentistry are divided into groups:

removable;
non-removable;
partially removable.

Clasp structures belong to the third group, since removal is carried out only to perform hygienic procedures. Patients easily cope with this task with one movement of the hand. There is no need to remove the denture at night.

When chewing food, emotional conversations and displays of joy (laughter), you do not need to worry about the reliability of the fixation. The prosthesis is firmly held in place by the mountings.

Clasp prosthesis with splinting

In the absence of a large number of teeth in a row, the patient is recommended to install a clasp prosthesis on implants

Prosthetics of teeth often reveal problems with soft tissues (periodontitis, periodontal disease).

As the inflammation progresses, the gum turns red and swells, a gap forms between it and the teeth.

In this case, a decision is made to install a splinting structure, which tightens the units, preventing them from loosening.

In the absence of a large number of teeth in a row, the patient is recommended to install a clasp prosthesis on implants.

Initially, the implants are implanted in those places of the gums where the support of the prosthetic structure is needed (in the complete absence of units, 4 implants are required, in other cases, 2 pieces are needed).

The operation is performed using a local anesthetic. After healing of soft tissues, a prosthesis is installed. For these purposes, the most suitable options are structures on attachments or beams.

On the upper jaw

Dentures for the upper jaw are made from openwork casting using durable medical alloys

Clasp prosthetics of the upper row is performed in the absence of one or more teeth.

If there is not a single tooth, 4 implants are implanted. The prosthetic structure at the location of the artificial teeth is fixed to the jaw, and the arch itself is fixed to the palate.

Among all types of clasp products, attachments and splinting prostheses are popular in the restoration of the upper jaw.

Clasps meet functional needs, but lose significantly in aesthetics. Therefore, they are rarely used for the top row.

Dentures for the upper jaw are made from openwork casting using durable medical alloys.

The connecting element (palatine membrane) does not cover the entire surface of the palate, which makes the habituation process quick and comfortable. The peculiarity of the upper jaw prosthetics lies in the more complex technique of performing the work.

Clasp prosthetics of the lower jaw is easier. The design of the prosthesis looks simpler, it lacks the palatal part. The abutment teeth, to which the product is fixed, take the entire load. All types of clasp prostheses are suitable for restoring the lower dentition.

Advantages and disadvantages

Experts highlight the following advantages of clasp-type prostheses:

even distribution of the chewing load over the entire jaw;
aesthetics, which is achieved by equipping the structure with tiny clamps;
comfortable wearing, which is ensured by the small size of the metal frame;
strength and reliability (metal arc can withstand regular and heavy loads, unlike polymer analogues).

The disadvantages of clasp structures may not appear if the preparatory work for installing the prosthesis and measurements are performed on high level... Most of the patients' complaints with complaints are related to errors in the calculations of the dentist.

As for the prosthesis itself, despite its strength, sometimes there are cases of broken locks. Such a defect cannot be repaired; it is necessary to replace the whole structure.

The high cost of the product is also attributed to the disadvantages, but it is quite justified. Casting process metal arc provides for the use of high-tech technology that requires high precision.

This ensures the strength and reliability of the prosthesis, hence the long service life, which fully pays off with comfortable wearing.

Prices

The cost of a clasp prosthesis is represented by a wide price range, which is explained by several factors:

An important role in pricing is played by the regional factor, the status of the clinic and the qualifications of the dentist.

Average prices for a clasp prosthesis (for 1 jaw):

clasp - 30,000-35,000 rubles ;
splinting - 45,000 rubles ;
on locks - 62,000-65,000 rubles ;
on telescopic crowns - 65,000 rubles.

Contraindications

There are restrictions on the installation of clasp prostheses.

They relate to such cases:

if the patient has a deep bite;
in the presence of pathological processes in soft tissues and on the oral mucosa;
when abutment teeth are absent or if they are low;
with severe jaw atrophy;
with a high location of the attachment point of the frenum of the tongue;
if there are inflammatory processes in the mouth;
when the bottom of the mouth is shallow;
with stubborn mucous membranes in the area of missing teeth.

A contraindication to the installation of an arched structure is the presence of an allergy to one of the components used in the production of the prosthesis, for example, to metal.

During the examination, the orthopedist may postpone the prosthetics for the following reasons:

due to pregnancy;
if the patient uses drugs;
during the period of the patient's treatment with the use of radiation therapy.

Installation of all types of prostheses becomes impossible with the following health conditions:

if the patient is diagnosed with mental disorders;
diabetes;
in the presence of problems with the respiratory system, proceeding in an acute form;
oncology;
exacerbation of diseases of the cardiovascular system.

Care, repair and service life

The process of caring for a clasp-type prosthesis is simple, but requires regular attention.

Throughout the day, bacteria accumulate in the oral cavity, which leads to the development of inflammation of the mucous membranes and the formation of an unpleasant odor.

At night, salivation decreases, as a result of which plaque appears on the teeth and structures.

Timely cleaning of the mouth with the use of special means: toothpaste and a brush, dental floss, rinse balm will help to get rid of complications.

So that the surfaces of the prosthesis do not wear out prematurely, it is better to acquire pastes of soft action (not aggressive). Once every six months, you should contact a specialist for the purpose of professional cleaning of the oral cavity, especially for coffee lovers, because the drink changes the color of artificial teeth (turn yellow).

The denture may break during wear. The reasons are different, but they are all provoked by a sharp mechanical impact on the structure. The possibility of repair depends on the severity of the breakdown of the product.

The main types of breakdowns include:

breakage of metal fasteners;
crack formation anywhere in the structure;
detachment of artificial teeth;
breakage of the lock part;
fracture of the prosthesis in two parts.

The service life of a prosthesis with proper care is 5-10 years.

Which prosthesis is better than clasp or nylon?

Both types of prostheses deserve attention, but the nylon construction is considered more modern. This is due to a number of factors: lightness, comfortable adaptation in the mouth and easy wearing, the absence of problems with the rubbing of soft tissues with individual nodes.

And nylon is easier to care for than metal. Although the chewing load is better distributed by the clasp-type product.

If we consider the main advantageous characteristics of nylon prostheses, then they outweigh the metal counterparts in the following indicators:

hypoallergenic;
flexibility, elasticity;
low probability of breakage;
the transparency of the material increases aesthetics.

There are not many disadvantages to nylon prostheses, but they are significant. For example, it is no longer possible to repair a broken product. And the price of new ones "bites".