With a concentrated external load (P = 35 kg),applied in the middle of the frame span (Fig. 1), the forces in the frame elements can be determined by the finite element method.

A qualitative picture of the support reactions is shown in Fig. 2, whichwhen exposed to an external concentrated force, they experience eccentric compression. Atimpact on the system of concentrated external load, crossbarexperiences eccentric compression.

If the load is applied in the center of the intermediate part of the bridge, then the entire structure and supporting tissues are loaded evenly, they are in the most favorable conditions. conditions, biostatic equilibrium is established and the periodontium responds to the chewing load with normal reactions. However, such conditions during the process of chewing food are observed extremely rarely. At the same time, it should be borne in mind that with an increase in the length of the intermediate part, its openwork or insufficiently elastic properties of the alloy, the body of the prosthesis can sag and cause additional functional load in the form of a converging inclination of the supporting teeth, which can contribute to the development of a local degenerative process in the periodontium.

The nature of the distribution and the magnitude of the chewing pressure, which falls on the intermediate part of the bridge and is transmitted to the supporting teeth, depends primarily on the application and direction of the load, the length and width of the intermediate part of the denture. It is important to know not only the reaction of the periodontium to the functional load of the supporting teeth, but also the distribution of elastic stresses both in the bridge itself and in the periodontal tissues of the supporting teeth.

It is necessary to consider various options for applying load to the bridge:

1. load in the middle of the intermediate part of the bridge, when the entire structure, as well as the periodontium, is loaded evenly and therefore finds itself in the most favorable conditions;

2. with an increase in the length of the intermediate part or insufficiently expressed elastic properties of the alloy, the intermediate part of the prosthesis can sag and cause additional functional overload in the form of a counter, or converging, inclination of the supporting teeth.

3. when a load is applied to one of the abutment teeth, both abutment teeth are displaced, and both supports are displaced in a circle, the center of which is the opposite, less stressed abutment tooth;

4. with a pronounced sagittal occlusal curve or with significant deformation of the occlusal surface of the dentition, when part of the vertical load is transformed into horizontal. Similar conditions arise when moving teeth are used as one of the supports;

5. vertical loads falling on the intermediate part of a bridge with one-sided support cause the abutment tooth to tilt towards the missing neighboring one. With lateral movements of the lower jaw during chewing, rotation of the supporting tooth occurs - a torque, which increases the functional overload of the periodontium.

6. with a one-sided support, which consists of two supporting teeth, when the supporting tooth adjacent to the artificial one is immersed in the alveolus. The second abutment tooth is subject to retractive forces.

The distribution of horizontal forces has distinctive features:

1. with a horizontal load applied to the middle part of the body of the bridge, the supporting teeth experience uniform pressure and transmit the load to the periodontium from the alveolar wall opposite to the application of force;

2. if pressure is applied to one of the supporting teeth, a displacement of this tooth occurs in a circle, the center of which is another supporting tooth with intact periodontium.

Basic principles for designing bridges:

1. the supporting elements and the intermediate part of the bridge must be on the same line;

2. when constructing a bridge, abutment teeth with a not very high clinical crown of the abutment tooth should be used;

3. The width of the chewing surface of the intermediate part of the bridge must be less than the width of the chewing surfaces of the teeth that are being replaced.

4. The amount of chewing pressure is inversely proportional to the distance from the point of its application to the supporting tooth. A completely opposite pattern is observed when constructing bridges with unilateral support. To reduce the functional overload of the supporting teeth, it is necessary to increase their number, avoiding the use of bridges with one-sided support and reducing the width of the chewing surface of the intermediate part of the prosthesis;

5. it is necessary to restore contact points between the supporting elements of the bridge and adjacent natural teeth;

6. competent design of bridges from the point of view of normal occlusion;

7. it is necessary to design such bridges that would best meet the requirements of aesthetics.

Indications for use in the orthopedic treatment of patients with dental defects with bridges and the choice of their design are determined mainly by the following factors: the size of the defect, its topography, the condition of the supporting teeth and antagonist teeth.

All patients who have dentition defects in the area of ​​the anterior or visible lateral teeth (premolars) require their replacement with dentures (usually bridges) not only for functional, but also for aesthetic reasons.

Federal State Budgetary Educational Institution of Higher Education

Department of Orthopedic Dentistry and Materials Science with a course in Adult Orthodontics

Essay

“Prosthetics with metal-ceramic bridges”

St. Petersburg, 2017

Introduction………………………………………………………………………………….3

1. Theoretical foundations of prosthetics with metal-ceramic bridges:

1.1 general characteristics bridges…………………………….5

1.2 Biomechanics of bridges……………………………………………………….

1.3 Basic principles of designing bridges………….13

2. Practical features of prosthetics with metal-ceramic bridges:

2.1 Indications for prosthetic bridges…………………

2.2 General features of manufacture and application……………………………..

Conclusion………………………………………………………………………..

INTRODUCTION

Metal-ceramic restorations are based on the principle of combining the strength and precision of a cast metal frame with the aesthetics of porcelain, allowing them to closely resemble, and in some cases surpass, natural teeth.

A metal-ceramic prosthesis consists of a cast metal part, or frame, that exactly fits the prepared tooth, and ceramics connected to it. The frame may be slightly larger than a thin thimble or distinctly resemble a cast crown with some of the metal removed. The damaged contours are restored with porcelain, which will hide or camouflage the metal frame, reproduce the desired shape and color and make the denture very similar to natural teeth. The metal frame in a metal-ceramic prosthesis is covered with three main layers of porcelain.

In this abstract I will consider metal-ceramic bridges.

1. THEORETICAL BASIS OF PROSTHETICS WITH METAL-CERAMIC BRIDGES.

1.1 GENERAL CHARACTERISTICS OF BRIDGES

Bridges are understood as structures that rest on teeth that limit the defect in the dentition. This is the most ancient type of prosthesis, which is confirmed by finds during excavations of ancient monuments and tombs. The United States of America is considered the birthplace of modern bridges, where they received the greatest development and distribution in the second half of the last century.

A bridge, resting on natural teeth, transfers chewing pressure to the periodontium. Most often, bridges rest on teeth located on both sides of the defect, that is, they have bilateral support. In addition, bridges with unilateral support can be used. In this case, as a rule, the supporting tooth is located distally in relation to the defect. For example, if a maxillary lateral incisor is missing, the canine tooth should be used for support rather than the central incisor. Unilaterally supported bridges are most often used when individual front teeth are lost.

To support bridges, artificial crowns (stamped, cast, combined, half-crowns, crowns on an artificial stump with a font) or inlays are used. In addition to supporting elements, the design of bridges includes an intermediate part located in the area of ​​the dentition defect.

According to the manufacturing method, bridges are divided into soldered, the parts of which are connected by soldering, and solid, which have a solid frame. In addition, the bridge can be made entirely of metal (all-metal), plastic, porcelain, or a combination of these materials (combined - metal-plastic, metal-ceramic).
For the manufacture of bridges, chromium-nickel, cobalt-chrome, silver-palladium alloys, 900-carat gold, acrylic plastics and porcelain are used.
The disadvantage of soldered bridges is the presence of solder, which consists of metals that cause intolerance in some patients - zinc, copper, bismuth, cadmium. Solid-cast bridges do not have this drawback.
Certain requirements are imposed on bridges, primarily regarding the rigidity of the structure. Relying on the teeth bordering the defect, the bridge performs the function of the removed teeth and, thus, transfers an increased functional load to the supporting teeth. Only a prosthesis with sufficient strength can resist it.
The aesthetic qualities of bridges are no less important. Increasingly, there are patients who do not want to have metal parts of the prosthesis visible when smiling or talking. Metal-ceramic structures are considered the best in this regard.

From a hygienic point of view, bridges are subject to special requirements. Here great importance has the shape of the intermediate part of the prosthesis and its relationship to the surrounding tissues of the prosthetic bed, the mucous membrane of the alveolar process, the gums of the supporting teeth, the mucous membrane of the lips, cheeks, and tongue. In the anterior and lateral parts of the dental arch, the intermediate part is not the same. If in the anterior section it should touch the mucous membrane without putting pressure on it (tangential form), then in the lateral section between the body of the prosthesis and the mucous membrane covering the edentulous alveolar process, there should be free space that does not interfere with the passage of chewed food products (washing space).

Shapes of the intermediate part of the bridge:

1 - tangent for front teeth

2 - hanging with high clinical crowns of teeth

3 - hanging with low clinical crowns of teeth

4 - saddle-shaped all-metal

5.6 - hanging with lining of the labial or labial-masticatory surface

7 - saddle-shaped with lining of visible surfaces - chewing and partially lateral artificial teeth of the lower jaw.
In the tangential form, the absence of pressure on the mucous membrane is checked with a probe. If its tip is easily inserted under the body of the prosthesis, it means that there is no pressure on the gum, and at the same time there is no visible gap that does not look aesthetically pleasing when smiling or talking.
In the lateral part of the dentition, by creating a washing space, they try to avoid food retention under the intermediate part of the denture, which can cause chronic inflammation of this area of ​​the mucous membrane. That is why the washing space is made quite large, especially in the lower jaw. On the upper jaw, taking into account the degree of exposure of the lateral teeth when smiling, the washing space is made slightly smaller than on the lower jaw, and in the area of ​​premolars and canines, which open when smiling, it can be minimized, even touching the mucous membrane. In each specific case, this issue is resolved individually.

In cross section, the shape of the intermediate part of the prosthesis resembles a triangle. In recent years, in connection with the introduction of highly aesthetic metal-ceramic structures, a proponent of using a saddle-shaped prosthesis body has emerged.
1.2 BIOMECHANICS OF BRIDGES
The nature of the distribution and the magnitude of the chewing pressure falling on the body of the bridge prosthesis and transmitted to the supporting teeth depends, first of all, on the place of application and direction of the load, the length and width of the prosthesis body. It is obvious that for living human organs and tissues the laws of mechanics are not absolute. For example, the condition of periodontal tissue depends on the general condition of the body, age, the local condition of the surrounding organs and tissues, the activity of the nervous system and many other factors that determine the reactivity of the body as a whole. However, it is important for the clinician to know not only the reaction of the periodontium to the functional overload of the abutment teeth bearing bridges, but also the distribution of elastic stresses both in the bridge itself and in the periodontal tissues of the abutment teeth.

If the functional load falls on the middle of the intermediate part of the bridge, then the entire structure and periodontal tissues are loaded evenly and therefore find themselves in the most favorable conditions.

However, such conditions during the process of chewing food are observed extremely rarely. At the same time, it should be borne in mind that with an increase in the length of the intermediate part or insufficiently expressed elastic properties of the alloy, the body of the prosthesis can bend and cause additional functional overload in the form of a counter or converging inclination of the supporting teeth.

In this regard, the functional overload is unevenly distributed in periodontal tissues, contributing to the development of a local degenerative process. Thus, to prevent possible changes in the periodontium of supporting teeth under bridges, the body of the prosthesis must be of sufficient thickness and not exceed the maximum length that prevents deflection of the metal in the area of ​​the dentition defect.

When a chewing load is applied to one of the abutment teeth, both supports are displaced along a circle, the center of which is the opposite, less loaded abutment tooth. This explains the tendency of the supporting teeth to diverge or diverge. Under these conditions, the functional overload is also distributed unevenly in the periodontal tissues.

If bridges are used with a pronounced sagittal occlusal curve or with significant deformation of the occlusal surface of the dentition, for example, against the background of partial loss of teeth, part of the vertical load is transformed into a horizontal one. The latter displaces the prosthesis sagittally, causing the abutment teeth to tilt in the same direction.
Similar conditions arise when moving teeth are used as one of the supports. However, in this case, the displacement of the prosthesis can reach critical values, aggravating the pathological condition of the periodontium.
Vertical loads falling on the body of a bridge with one-sided support are very dangerous for the periodontium. In this case, the functional load causes the abutment tooth to tilt towards the missing one nearby. In periodontal tissues there is also an uneven distribution of elastic stresses. In magnitude, these conditions significantly exceed those that develop in bridges with bilateral support. Under the influence of a vertical load falling on the body of such a prosthesis, a bending moment occurs. The supporting tooth tilts towards the defect, and the periodontium experiences a functional overload of an unusual direction and magnitude. The result may be the formation of a pathological pocket on the side of tooth movement and resorption of the hole at the root apex on the opposite side.
With lateral movements of the lower jaw during chewing, rotation of the supporting tooth occurs - a torque that aggravates the functional overload of the periodontium. The moments of torsion and bending are determined by the length of the body of the bridge, the height of the clinical crown of the abutment tooth, the length of the edge, the presence or absence of adjacent teeth, the amount of force applied and the state of the reserve forces of the periodontium. The likelihood of developing functional overload in the stage of decompensation can be significantly reduced by increasing the number and using a bridge with unilateral support in the case of defects of no more than one tooth in length.
When using an artificial tooth with one-sided support in the form of two abutment teeth, there is a predominant immersion in the alveolus of the abutment tooth adjacent to the artificial one. The other abutment tooth is under the influence of pulling forces. Thus, there is a kind of rotation of the prosthesis around the center located in the supporting tooth, bearing the artificial tooth. In this case, the difference in compression and stretching of periodontal tissues reaches quite large values ​​and can also have a detrimental effect on supporting tissues.
The distribution of horizontal forces has distinctive features. Intact dentition is most resistant to horizontal loads. This is due anatomical structure teeth and their roots, the position of the teeth on the alveolar process, the relationship of the dentition with different types of articulation, as well as the structural features of the upper and lower jaws. With the loss of teeth, the conditions for the distribution of vertical loads change. Thus, with a horizontal load applied to the middle part of the body of the bridge, the supporting teeth experience uniform pressure and transmit the load to the periodontium from the side opposite to the application of force from the alveolar wall.
If pressure is applied to one of the supporting teeth, especially when it is pathologically mobile, this tooth moves in a circle, the center of which is another supporting tooth with unaffected periodontium. The latter is thus subjected to rotation around the longitudinal axis.
1.3 BASIC PRINCIPLES OF DESIGNING BRIDGES
When designing bridges, certain principles should be followed. According to the first principle, the supporting elements of the bridge and its intermediate part should be on the same line. The curvilinear shape of the intermediate part of the bridge leads to the transformation of vertical and horizontal loads in rotation.

The load is applied to the most protruding part of the bridge body. If you draw a perpendicular to the straight line connecting the long axes of the supporting teeth from the point of the prosthesis body most distant from it, then it will be a lever arm that rotates the prosthesis under the action of the chewing load. The magnitude of the rotational forces is thus directly dependent on the curvature of the bridge body. Reducing the curvature of the intermediate part will help reduce the rotational effect of the transformed chewing load.
The second principle is that when constructing a bridge, abutment teeth with a not very high clinical crown should be used. The magnitude of the horizontal load is directly proportional to the height of the clinical crown of the abutment tooth. The use of abutment teeth with high clinical crowns and shortened roots is especially harmful for the periodontium.
In this case, there is a high probability of a rapid transition from a compensated form of functional overload to a decompensated form with the appearance of pathological mobility of the supporting teeth.
Similar conditions arise with atrophy of the alveolar process, when the height of the clinical crown of the tooth increases due to reduction of the intra-alveolar part of the root. At the same time, it should be borne in mind that with excessively low clinical crowns, the construction of a bridge is also difficult due to a decrease in rigidity and a decrease in the area of ​​contact of the body with the supporting elements. The connection is especially often destroyed in complete bridges.
The third principle suggests that the width of the chewing surface of the bridge should be less than the width of the chewing surface of the teeth being replaced. Since any bridge prosthesis functions due to the reserve forces of the periodontium of the supporting teeth, the narrowed chewing surfaces of the body reduce the load on the supporting teeth.
Moreover, when designing the body of the prosthesis, it is advisable to take into account the presence of opposing teeth and their type - whether they are natural or artificial. If the pressure is concentrated closer to one of the supporting ones due to the loss of part of the antagonists, then the body of the prosthesis in this place may be narrower than in other areas. Thus, the masticatory surface of the bridge prosthesis body is made narrower to avoid excessive functional overload, and the amount of narrowing in individual areas is determined individually in accordance with the characteristics of the clinical picture. An increase in the width of the chewing surfaces of the intermediate part of the bridge leads to an increase in the functional overload of the abutment teeth, not only due to an increase in the total area that receives chewing pressure, but also due to the appearance of rotational forces along the edge of the body of the prosthesis, going beyond the width of the abutment teeth.
The fourth principle is based on the fact that the amount of chewing pressure is inversely proportional to the distance from the point of its application to the supporting tooth. Thus, the closer the load is applied to the abutment tooth, the more pressure falls on this abutment tooth and, conversely, as the distance from the place of application of the load to the abutment tooth increases, the pressure on this abutment tooth drops. A completely opposite pattern is found when constructing bridges with unilateral support. The larger the size of the suspended artificial tooth, the more the adjacent abutment tooth is loaded.
To reduce the functional overload of supporting teeth, it is necessary to increase their number, avoid the use of bridges with one-sided support and reduce the width of the chewing surface of the prosthetic body.

The fifth principle is associated with the need to restore contact points between the supporting elements of the bridge and adjacent natural teeth. This allows the continuity of the dental arch to be restored and promotes a more even distribution of chewing pressure, especially its horizontal component, among the remaining teeth in the oral cavity. It is especially important to observe this principle with a well-defined sagittal occlusal curve, when horizontal loads transformed from vertical ones tend to tilt the abutment teeth in the mesial direction. A properly restored contact point will transfer some of the horizontal forces to the adjacent natural teeth. This helps maintain the stability of the supporting teeth and prevents their tilting in the mesial direction.
The sixth principle involves the competent design of bridges from the point of view of normal occlusion. There are two groups of patients. The first group includes patients whose prosthetic task is to restore correct occlusal relationships in the area of ​​the defect with careful modeling of the occlusal surface of the bridge, fitting into the patient’s existing functional occlusion. Here, first of all, care should be taken to prevent premature contacts, a decrease in the interalveolar distance and functional overload of the periodontium after prosthetics.
In the second group we include patients who need not only prosthetic replacement of a defect in the dentition with a bridge, but also a simultaneous change in the functional occlusion within the entire dentition. This may be necessary in case of partial loss of teeth, increased abrasion, periodontal diseases, anomalies of occlusion, complicated by partial loss of teeth, etc. What is common to all these pathological conditions is a decrease in the interalveolar distance. Thus, for the second group of patients, more complex prosthetics are required, taking into account changes in the occlusion of dentures.
The seventh principle: it is necessary to design such bridges that would meet the requirements of aesthetics to the maximum extent. For this purpose, the most aesthetically advantageous facing materials are used, and support elements and the intermediate part of the prosthesis are designed to ensure reliable fastening of the facing made of plastic, porcelain or composite material.

CHAPTER 2 PRACTICAL FEATURES OF PROSTHETICS WITH METAL-CERAMIC BRIDGES
2.1 INDICATIONS FOR PROSTHETIC BRIDGES
When determining the indications for prosthetics with bridges, one should keep in mind, first of all, the extent of the defect in the dentition - these can be small and medium defects and, less often, end defects. A special role is played by the requirements for abutment teeth. Planning of a bridge becomes possible only after a thorough clinical and paraclinical examination: in this case, it is necessary to pay attention to the size and topography of the defect, the condition of the teeth limiting the defect, and the periodontium, the condition of the edentulous alveolar process, the type of occlusion, occlusal relationships, the condition and position of the teeth that have lost their antagonists.
Of greatest importance is the periodontal condition of the supporting teeth, which limit the dentition defect. Stable teeth generally indicate healthy periodontium. Pathological mobility, on the contrary, is a reflection of profound changes in the tissues of the periodontium, the condition of which requires a particularly careful assessment. At the same time, it should be remembered that stable teeth that have signs of periodontal disease in the form of exposed necks, gingivitis, pathological gum and bone pockets require additional x-ray examination. The same applies to teeth that have fillings and carious defects, worn crowns, artificial crowns, and discoloration.
Diagnostic models are a good aid for assessing occlusal relationships and the position of abutment teeth.

Teeth with an average height of clinical crowns are ideal for bridge prosthetics. With high clinical crowns, the risk of traumatic occlusion in the stage of decompensation increases significantly. With low clinical crowns, the construction of a bridge prosthesis is difficult.
In addition, prosthetic bridges are greatly facilitated with correct occlusal relationships and healthy periodontium. The correct position of the supporting teeth, when their long axes are parallel to each other, is no less important. With deformations of the dentition, accompanied by tilting of the supporting teeth, which have lost their antagonists, the use of bridges becomes significantly more difficult.
As a support, the doctor often has to use teeth that have been treated for caries, pulpitis, and chronic apical periodontitis. The latter can serve as a support after careful filling of all root canals, provided that the clinical course is favorable and there is no history of exacerbation. Past periodontal diseases reduce its reserve forces and reduce the periodontal resistance to functional overload. When using bridges, it is quite large and can provoke an exacerbation of inflammation. That is why strict requirements are imposed on the quality of treatment of chronic apical periodontal diseases before prosthetics.
When determining the indications for prosthetics with bridges, the question of the number of supporting teeth with different sizes of dentition defect is important. An objective assessment of the periodontal condition is one of the main prerequisites for orthopedic treatment.

It is known that the ability of periodontal teeth to perceive a particular load can be measured not only using gnathodynamometry, which is characterized by large errors, but also by determining the size of the root surface.

As clinical observations show, socket atrophy is not always a reliable indicator of periodontal endurance. It is also necessary to take into account the degree of tooth mobility. Thus, periodontal endurance can most reliably be assessed from three positions: the degree of atrophy of the tooth socket, tooth mobility and the area of ​​their roots.
Based on this premise, when deriving conditional coefficients of periodontal endurance, we considered it appropriate to take the root area of ​​the lower central incisor as the smallest unit of endurance.
Considering the dependence of periodontal endurance on the degree of socket atrophy while maintaining the stability of the teeth, it is important to establish the magnitude of the reduction in the area of ​​the root, which approaches the shape of a cone. To carry out the corresponding calculations, the diameters of the necks and the lengths of the roots of permanent teeth according to V.A. Naumov were taken as the initial data. Comparison of these values ​​with the total area of ​​the roots made it possible to calculate the residual area of ​​the roots of the teeth with socket atrophy of 1/4, 1/2, 3/4, as well as to derive the values ​​of periodontal endurance for each degree of socket atrophy.

Until now, it was believed that the reserve forces of the periodontium decrease in proportion to the atrophy of the socket. At the same time, the anatomical feature of the roots of the teeth was not taken into account - an almost uniform narrowing from the neck to the tips of the roots. In addition, in accordance with the theory of the bilateral structure of the human body, it was conventionally believed that the periodontium of the teeth is capable of withstanding a double load, and the calculation of the remaining reserve forces was made based on the premise that when crushing food, half of the safety margin of the periodontium is used. This assessment of periodontal reserve forces is imprecise. Thus, the periodontium of the first permanent molars (37 kg) has the maximum endurance. At the same time, according to Schroeder, chewing boiled meat requires an effort of 39-40 kg. In addition, chewing pressure is distributed in direction (vertical and lateral) and, as a rule, acts on several adjacent teeth. Its extreme value exceeds the effort required to chew food. When compiling a periodontogram, there is no need to calculate the effort expended, for example, on biting or chewing food. It is important to assess the condition of the periodontium and its reserve forces both in individual teeth and in the dentition as a whole.
One of the most significant indicators of periodontal condition is the stability of teeth. With the appearance of pathological tooth mobility, the reserve forces of the periodontium disappear. Observations in the clinic show that in most patients, progressive atrophy of the sockets is accompanied by the appearance of pathological mobility of the teeth. But in some cases, for example, with developing primary traumatic occlusion, pathological mobility can occur without noticeable atrophy of the socket, and vice versa - despite advanced atrophy of the alveolar process in systemic and sluggish periodontal diseases of a dystrophic nature, teeth can remain stable for a long time and participate in chewing food. Thus, assessment of the periodontal condition should be carried out taking into account the degree of socket atrophy and pathological tooth mobility.
As gnathodynamometry data show, there is a fairly pronounced difference in the periodontal endurance of the teeth of the upper and lower jaws. Comparison of tooth root area confirms the existence of these differences in healthy periodontium. Apparently, this can be explained by the structural features of the jaws: the upper jaw is more airy and less adapted to perceive chewing pressure, while the lower jaw is more compact and has greater resistance to chewing pressure. The difference in the sizes of the surface areas of the roots, as it were, compensates for these anatomical differences and contributes to a more uniform distribution of chewing pressure on the jaw.
The state of periodontal reserve forces depends on many factors: the shape and number of roots; location of teeth in the dentition; the nature of the bite, age, previous general and local diseases, etc. In addition, the functional structures of the periodontium are hereditary, so the influence of the hereditary factor on the ability of the periodontium to adapt to the changed functional load cannot be denied.
So, the periodontal teeth have very limited capabilities, therefore, assessing the endurance of the periodontium and calculating the number of supporting teeth when planning the design of bridges should be carried out as follows.
For example, in the absence of two (first and second) molars of the lower jaw, the sum of the endurance coefficients of the healthy periodontium of the supporting teeth (35" and 38") is 4.0 units, and the sum of the coefficients of the extracted teeth (36" and 37") is 5.1. Periodontal endurance 38" is conventionally accepted as equivalent to 37". Thus, the supporting teeth find themselves in a state of functional overload, exceeding their endurance by 1.1 units. And this really does not contradict the idea arising from the theory of traumatic occlusion that any bridge prosthesis causes functional overload of the periodontium. However, its magnitude may vary. In the given example, the endurance of the supporting teeth is exceeded by 1.1 units. In other cases, this difference can be much greater. Thus, when three teeth are removed in the lateral part of the lower jaw (35,36,37), the sum of the periodontal endurance coefficients of the supporting teeth (34.38) will be 3.8 units, and of the removed teeth - 6.7. The difference is 2.9, that is, it is less (0.9) than the sum of the periodontal endurance coefficients of the supporting teeth. In this case, the functional overload of the periodontium is great, and there is a danger of acute traumatic occlusion in the stage of decompensation. As clinical observations show, the difference in the sums of periodontal endurance coefficients of abutment and extracted teeth should not exceed 1.5 - 2.0 units. As for mobile teeth, deprived of reserve forces, it should be assumed that the endurance of their periodontium, regardless of the degree of mobility, is zero. The use of such teeth as abutments without simultaneous splinting with other, stable teeth is contraindicated.
A special place in determining indications is occupied by bridges with unilateral support. The greatest danger to the periodontium of supporting teeth is the use of such structures to replace large molars. At the same time, it should always be borne in mind that when replacing end defects, such a bridge can be used in case of contraindications to the use of removable structures or provided that its antagonists are artificial teeth of the removable denture of the opposite jaw.

Absolute contraindications for the use of bridges are large defects limited to teeth with different functional orientation of periodontal fibers; relative contraindications are defects limited to mobile teeth with low clinical crowns; defects with supporting teeth that have a small reserve of periodontal forces (with high clinical crowns and short roots).
2.2 GENERAL FEATURES OF MANUFACTURE AND APPLICATION
Porcelain coating can be used not only in the manufacture of single crowns, but also bridges. Plastic, as a facing material for solid dentures, has a number of disadvantages. These, first of all, include the possibility of developing allergic reactions upon contact of plastic with both the soft tissues of the marginal periodontium (gum) and the adjacent areas of the mucous membrane of the lips, cheeks, tongue and toothless alveolar process. In addition, the connection of plastic with a metal frame, based on the creation of mechanical retention points, is not very strong. A comparison of the aesthetic qualities of plastic and porcelain indicates the undeniable advantage of the latter. Thus, porcelain coating has a number of undeniable advantages that give dentures special value.
When planning metal-ceramic bridges, special attention should be paid to the indications for their use. In this case, the following circumstances must be kept in mind. Firstly, when planning such prostheses, it is necessary to carefully study the possibility of covering abutment teeth with metal-ceramic crowns (we have discussed this issue in detail in the corresponding chapter). Secondly, a separate problem is determining the possibility of lining the intermediate part of the bridge with porcelain. To do this, it is necessary to assess the size of the interalveolar space in the area of ​​the dentition defect. It should be sufficient to design artificial metal-ceramic teeth with a beautiful anatomical shape and size. Thirdly, some authors consider medium defects, 2-3 teeth long, when using noble metal alloys, or medium and large defects, 2-4 teeth long, when using stainless steel alloys, as an indication for the use of such prostheses.
Other authors limit the use of metal-ceramic bridges to small and medium-sized defects with a length of 2-3 teeth. It is believed that increasing the length of the pontic may cause minor deformations leading to porcelain spalling. In addition, the length of the prosthesis is directly proportional to the height of the supporting teeth.

However, in this case, one should remember about possible deformation and its consequences. It is also useful to keep in mind the danger of excessive overload of the periodontium of supporting teeth in the case of applying large bridges using the method or using them not according to indications, for example, without increasing the number of supports in case of periodontal diseases. A thorough clinical and radiological assessment of the condition of the periodontium, supplemented by an assessment of its reserve forces, including using a periodontogram, allows a more accurate determination of the possibility of prosthetics with a metal-ceramic bridge. In addition, it should be borne in mind that this bridge design can be used with equal success to replace defects in both the anterior and lateral parts of the dentition.
The preparation of teeth is carried out according to known rules, taking into account the route of insertion of the prosthesis and the degree of deformation of the dentition, manifested in the inclination of the supporting teeth. A double impression will give the most accurate result. The working model is prepared according to the method of preparing a collapsible plaster model from high-strength gypsum. Abutment teeth must be covered with temporary crowns to prevent the prepared teeth from shifting towards the antagonists. With the help of temporary bridges, it is possible to protect the abutment teeth from the influence of the external environment and their displacement both in the vertical and in the mesiodistal direction.
When planning ceramic veneering of abutment crowns, one should take into account the type of occlusion, the depth of overlap of the anterior teeth, the height of the clinical crowns and their vestibulo-oral size. When veneering artificial crowns for lateral teeth, it is also necessary to keep in mind the degree of their exposure when smiling or talking. A strip of metal in the form of a garland above the neck of the tooth is left only on surfaces that are invisible for a simple examination of the oral cavity - palatal or lingual. However, in each specific case, a detailed plan is drawn up for the veneering of all elements of the bridge - the supporting parts and the body. The currently recommended sharp reduction in the area of ​​veneered surfaces must be carefully agreed with the patient in order to avoid conflict after prosthetics. The doctor's attentive attitude to possible ethical and psychological incompatibility prevents the occurrence of such a situation.
Modeling the intermediate part of the bridge is aimed at achieving the best aesthetic effect after prosthetics. As is known, there are two types of intermediate part: with or without a flushing space. If in the anterior parts of the jaws the tangent form is most often used, then in the lateral parts the solution may be different. Thus, when replacing missing premolars and the first molar of the upper jaw and a wide smile, the body of the prosthesis can have a tangent shape. On the lower jaw, in the lateral sections, an intermediate part with a washing space is more often used. However, in some patients this general pattern may be disrupted due to unusual clinical conditions: anomalies in the development of the jaws and alveolar processes, the height of the supporting or all teeth remaining in the oral cavity, the degree of exposure of the crowns of the teeth and alveolar processes when smiling, the length of the upper and lower lips, cross-sectional shapes of the edentulous alveolar process, etc. At the same time, when designing the body of a metal-ceramic bridge, one should strive to maximize the reproduction of the anatomical shape of lost teeth with occlusal relationships characteristic of each patient.
An obstacle to this is often the deformation of the occlusal surface of the dentition. Correcting it before prosthetics allows you to improve the quality of prosthetics and obtain a high aesthetic effect. Failure to comply with this rule leads to thinning of the metal frame and weakening of the entire structure of the metal-ceramic prosthesis. The shortening of the interalveolar distance is also the reason for the reduction in the height of the artificial pontic teeth. In this case, the surface of the prosthesis body facing the mucous membrane of the alveolar process may not be covered with porcelain and remain metal. This modeling makes it possible to make the frame of the intermediate part thicker, which provides it with the necessary rigidity.
When modeling the pontic, each tooth must repeat the anatomical shape of the one being restored, but be reduced in size by the thickness of a uniform porcelain coating. If a garland (collar) is modeled on the oral side, then it can be a continuation of a similar garland on the supporting crowns. Its dimensions and location are planned in advance when designing the entire prosthesis. Attention should be paid to the need to model the equator and tubercles. The absence of the latter, combined with the low height of the artificial teeth frame of the prosthetic body, can cause chipping of the porcelain coating. The transition of the garland into the rest of the frame, as well as the transition of the frame of the supporting crowns into the intermediate part of the bridge, should be smooth and not have sharp undercuts, sharp edges or protrusions.
The successful development of periodontology and modern implantology has led to the development of new techniques for preserving the alveolar ridge and surgically replacing its defects. New methods of soft tissue plastic surgery have influenced the shape of the perigingival surface of the pontic pontic.
Contrary to the traditional requirement to achieve minimal contact without pressure, currently, after plastic surgery, the connection of the PPJ is carried out with an oval gingival surface, maintaining direct contact and slight pressure on the underlying soft tissue throughout. With this design of the bridge body, very high aesthetic treatment results can be achieved.
If surgical preparation is undesirable or contraindicated, the method of choice for replacing small alveolar ridge defects is the use of pink ceramics.
The flushing shape of the pontic helps maintain soft tissue and periodontal health in a healthy condition with good hygiene of the supporting teeth. However, due to the distance from the alveolar ridge, a space is created where food debris accumulates. The functional, phonetic and aesthetic disadvantages of this design require its use exclusively in the area of ​​the lower lateral teeth.
In the absence of an alveolar ridge defect, a very good aesthetic result can be achieved using a saddle pontic. However, the extended area of ​​contact with the alveolar ridge prevents the removal of soft plaque. Clinical studies have shown that in 85% of cases such structures caused severe inflammation, even ulceration of the mucous membrane. Reducing the contact surface by creating a semi-saddle shape also did not provide a noticeable improvement in hygienic conditions with a concave gingival surface of the bridge body.
As already noted, the most common is the tangential form of PCHMP. The convex gingival surface, in point contact with the alveolar ridge, provides conditions for good hygiene and does not irritate the underlying soft tissue. However, often the individual contour of the alveolar ridge requires compromise solutions in order to prevent aesthetic, functional and phonetic deficiencies. Thus, in the presence of vertical atrophy of the alveolar ridge, the intermediate part looks unnaturally long and has black triangles due to the absence of gingival papillae. In this case, in addition to aesthetic problems, functional disorders appear due to the ingress of saliva and exhaled air into the vestibule of the oral cavity, as well as the accumulation of debris.

With an oval gingival surface, the PPMP provides extensive but area contact with soft tissues, simulating the natural transition of an artificial tooth into soft tissues. However, to achieve this effect, appropriate design of soft tissues is necessary. For this purpose, special methods have been developed that involve the design of the intermediate part, tooth extraction in the form of directed regeneration (immediate prosthesis technique), and plastic surgery in combination with orthopedic measures. Contact of the gingival surface of the PP with the mucous membrane suggests an increased readiness of the patient for oral hygiene, which should be assessed at the preparatory stage. Careful planning of PPMP is especially necessary for patients with a high smile line.
Surgical restoration of limited defects of the alveolar part of the jaw is carried out using various methods. These include guided bone regeneration using membranes, the introduction of autogenous bone, xenogeneic or alloplastic materials, and a combination of these. At the same time, the use of resorbable membranes allows one to avoid repeated surgical intervention. To restore alveolar crest defects with soft tissue, the following techniques are used: round stalked flap; onlay graft; subepithelial graft or connective tissue and its modifications.
Thus, surgical plastic surgery of local defects of the alveolar process can be a good help in solving orthopedic problems of prosthetics of dentition defects with bridges. Moreover, these methods can also be combined with implantation if the use of implant-supported bridges is planned.
The surface cleanliness of the cast frame largely depends on the accuracy of the gating system. Wax models of sprues and feeders are made from special casting wax (voskolit-2) with a diameter of 2-2.5 mm (for sprues) and 3-3.5 mm (for feeders). The sprues are installed in the thickest parts of the supporting crowns and artificial teeth of the intermediate part and connect them to a common feeder located along the dental arch.
The feeder is connected to the sprue cone using additional branches. It is useful to additionally install sprues of a smaller diameter (0.5 I mm) to remove air in thin places of the support crowns. The modeled wax reproduction of the prosthesis is carefully removed from the model and the production of a casting mold and subsequent casting of the frame begin.

The cast frame is sandblasted, removed from the sprues, and tested on a combined model. After this, the outer surface is processed with abrasive heads, bringing the thickness of the metal caps to 0.2-0.3 mm, and the intermediate part is separated from the antagonists by no less than 1.5 mm and no more than 2 mm. Violation of this rule leads to chipping of the ceramic coating. If casting defects are detected, the frame must be remade. An attempt to hide defects with ceramics also leads to destruction of the latter during the use of the prosthesis. The frame fitted to the model and prepared for ceramic coating is transferred to the clinic to check the accuracy of manufacturing.
When checking the frame in the oral cavity, you should first of all pay attention to the accuracy of the position of the supporting caps in relation to the marginal periodontium. The bridge framework must be easy to apply and positioned accurately in relation to the neck of the tooth.
The criterion for this, as a rule, is the minimum immersion of the edge of the cap into the gingival pocket (no more than 0.5 mm) in areas prepared without a ledge. Where the tooth is prepared with a shoulder, the edge of the cap should fit snugly against it. Difficult application of the frame can be a consequence of many reasons, the main of which are defects in the working model, deformation of the wax reproduction of the frame, shrinkage of the alloy during casting of the frame, inaccurate coating of the wax frame with the formation of air bubbles (especially on the inner surface of the cutting edge or chewing part of the crown), inaccurate preparation of abutment teeth. Consistently, excluding each of the possible causes, they achieve precise installation of the frame on the supporting teeth.
After applying the frame, the volume of the abutment teeth covered with metal caps and the artificial metal pontic teeth should be carefully assessed. If the frame occupies the entire volume, including that intended to accommodate the facing ceramic coating, you should first of all carefully evaluate the thickness of the frame in order to identify its possible increase. Another reason for such an error may be insufficient preparation of the supporting teeth. Making a bridge without correcting the mistakes made will lead to an increase in the volume of artificial teeth and supporting crowns of the prosthesis in comparison with adjacent natural teeth. The prosthesis will stand out among natural teeth and, instead of restoring aesthetics, will lead to its disruption. The correction consists of reducing the thickness of the frame of the supporting caps and cast artificial teeth of the intermediate part to the required size; if the thickness of the metal caps meets the requirements, it is necessary to carry out additional preparation of the supporting teeth and remake the frame of the bridge.
Occlusal relationships should be assessed especially carefully when inspecting the finished frame. General requirements involve creating a gap between antagonists of 1.5-2 mm in the position of central occlusion. In case of lateral and anterior occlusions, one should keep in mind the possibility of premature contacts of the frame with the antagonizing teeth. If found, they must be eliminated.
It is useful, after checking the metal frame, to again determine the central relationship of the jaws, since often the position of the frame on the supporting teeth is slightly different from its position on the working model. For the most accurate formation of the occlusal surface of a ceramic prosthesis, the position of the frame that it occupies in the oral cavity should be fixed.
When creating a ceramic coating on a bridge, first of all, the technology we described earlier, adopted for single crowns, is used. The differences concern mainly the intermediate part. Of particular importance for the aesthetic qualities of the prosthesis are the interdental spaces and the shape of the contact surfaces of artificial teeth adjacent to each other. To form them, after applying the dentin and enamel layers, separation is carried out with a modeling needle to the opaque layer. For the same purpose, a special separator varnish is used, which is applied to every second tooth. During subsequent firing, the varnish is applied in the reverse order. Particularly carefully in the bridge prosthesis is the cervical part of the artificial teeth adjacent to the mucous membrane of the edentulous alveolar process. This part of the tooth is of great importance for the overall appearance of the entire prosthesis. We mean, first of all, the shape and size of the cervical part, its overlap in relation to the alveolar process, the depth and width of the interdental spaces, and the inclination of the long axis of the artificial tooth.
Modeling of the chewing surface is carried out primarily from the point of view of restoring function, but the quality of restoring the anatomical shape is no less important. Thus, the occlusal surface of the paws must meet the most stringent requirements and, above all, correspond to the age-related characteristics of the microrelief in a given individual, ensure full chewing function and not have premature contacts with antagonizing teeth. The fulfillment of all these requirements is checked in the oral cavity. The finished prosthesis is carefully inspected, the quality of the ceramic coating and polishing of the metal garland is assessed. Before application, it is necessary to carefully examine the inner surface of artificial crowns. When applying dyes or correcting the anatomical shape, ceramic mass may get into the crowns, especially along the inner edge. Parts of it that are barely noticeable during examination can cause inaccurate or difficult application of the prosthesis. Using a shaped head of small diameter at low speeds of the drill, particles of the ceramic mass are ground off. The same is done with the oxide film covering the inner surface of the combined crowns. Only after such preparation is the prosthesis carefully applied to the supporting teeth. In this case, great forces should be avoided, as they can cause chipping of the porcelain coating if the prosthesis is not accurately fitted. It's about, first of all, about a possible excess of ceramic mass on the proximal surfaces of the abutment crowns, blamed on adjacent natural teeth. To detect this deficiency, carbon paper is inserted into the interdental space with the ink surface facing the ceramic veneer, and then a prosthesis is applied. If an imprint is detected, it is necessary to grind the ceramic in this place, preventing possible pressure on it when applying the entire prosthesis. The correction of the contact surfaces is repeated until the prosthesis is completely applied with visible contact of the crowns with the adjacent teeth. The patient’s lack of feeling of pressure from the prosthesis on the adjacent teeth indicates the accuracy of the correction of the abutment crowns. The final check of the prosthesis consists of clarifying the occlusal relationships for various types of articulation, as well as the shape and color of the artificial teeth.
The production of the prosthesis is completed, if necessary, by tinting the ceramic coating and glazing. In the oral cavity, the denture is strengthened with cement. The technique is simple and allows you to speed up the modeling process without condensing the ceramic mass and maintain constant humidity of the ceramic. Modeling begins with the vestibular surfaces, imitating the most striking features of the anatomical shape and color of the teeth. The palatal and lingual surfaces of the artificial teeth are then modeled, usually before the first firing. Layer-by-layer modeling should begin with the application of ceramic masses of a denser consistency (opaque masses). Subsequent layers should be less dense, not displacing the first layer. A thinner consistency is used for incisal masses. The density of the ceramic mass before application can be ensured using a special “liquid N, Ivoclar”.

When making large bridges, it is recommended to adhere to the following sequence. At the first stage, the front teeth are modeled (first firing), at the second, the chewing teeth are modeled and the front teeth are corrected (second firing), and at the third, the chewing teeth are corrected with possibly necessary correction of the front teeth (third firing). This sequence, according to the author, allows the use of layer-by-layer application of ceramics as the easiest way to speed up modeling, maintain constant humidity of the ceramics and avoid condensation of the ceramic mass.
When modeling a multilayer ceramic coating using intensely colored porcelain powders to create deep effects, it is necessary to provide for the following: since a layer of ceramic is applied taking into account its subsequent shrinkage during the firing process, a shift in individual color characteristics inherent in the initial application may occur; correction of the anatomical shape by applying additional portions of porcelain can also cause displacement or loss of individual details of the color effect; When the layers of ceramic coating condense, a blurring of individual fine details of reproducible features may occur.

CONCLUSIONS
A bridge as a treatment must meet the requirements of toxicology, technology, aesthetics, hygiene and function.

The requirements of toxicology come down to the use of materials that, while possessing anti-corrosion properties, are at the same time non-toxic, do not cause allergies, do not irritate the oral mucosa, do not combine with saliva and do not change its properties.
Certain requirements are imposed on bridges, primarily regarding the rigidity of the structure.

Relying on the teeth bordering the defect, the bridge performs the function of the removed teeth and, thus, transfers an increased functional load to the supporting teeth. Only a prosthesis with sufficient strength can withstand it. From a hygiene point of view, bridges have special requirements.
Here, the shape of the intermediate part of the prosthesis and its relationship to the surrounding tissues of the prosthetic bed, the mucous membrane of the alveolar process, the gums of the supporting teeth, the mucous membrane of the lips, cheeks, and tongue, are of great importance.
In the anterior and lateral parts of the dental arch, the intermediate part is not the same. If in the anterior section it should touch the mucous membrane without putting pressure on it (tangential form), then in the lateral section between the body of the prosthesis and the mucous membrane covering the edentulous alveolar process, there should be free space that does not interfere with the passage of chewed food products (washing space).
BIBLIOGRAPHY
1. Abakarov S.I. Modern designs fixed dentures - St. Petersburg Foliant - 2000. - 105 p.

2. Alabin I.V., Mitrofanenko V.P. Anatomy, physiology and biomechanics of the dental system. – M., 2002. – 241 p.

3. Budylina S.M., Degtyareva V.P. Physiology of the maxillofacial region. – 2000. – 352 p.

4. Voronov A.P., Lebedenko I.Yu. Orthopedic dentistry. - M.: Medicine, 1997 – 210 p.

5. Mironova M.L. Removable dentures: a textbook for medical professionals. colleges and schools. – GEOTAR-media, 2009. – 456 p.

6. Kopeikin V.N., Mirgazizov M.Z. Orthopedic dentistry. - M.:

Medicine, 2001.

7. Kopeikin V.N., Dolbnev I.B., Dental prosthetic technology. - M.: Medicine, 1997. - 178 p.

8. Kurlyandsky V.Yu. Ceramic and solid fixed dentures. - M.: Medicine, 1998 – 100 p.

9. Pogodin V.S., Ponomareva V.A. Guide for dental technicians - M.: Medicine, 2001. - 127 p.

10. Savchenkov Yu.I., Pats Yu.S. Physiology for the dentist: a textbook. – 2000. – 90s.

11. Handbook of dentistry / Ed. V.M. Bezrukova. - M.: Medicine, 1998.

Basic structural elements of bridges.

Basic principles of designing bridges. When designing bridges, certain principles should be followed. According to first principle, the supporting elements of the bridge and its intermediate part must be on the same line. The curvilinear shape of the intermediate part of the bridge leads to the transformation of vertical and horizontal loads into rotating ones. The load is applied to the most protruding part of the bridge body. If you draw a perpendicular to the straight line connecting the long axes of the supporting teeth from the point of the prosthesis body most distant from it, then it will be a lever arm that rotates the prosthesis under the action of the chewing load. The magnitude of the rotational forces is thus directly dependent on the curvature of the body of the bridge. Reducing the curvature of the intermediate part will help reduce the rotational effect of the transformed chewing load.

Second principle is that when constructing a bridge, abutment teeth with a not very high clinical crown should be used. The magnitude of the horizontal load is directly proportional to the height of the clinical crown of the abutment tooth. The use of abutment teeth with high clinical crowns and shortened roots is especially harmful for the periodontium. In this case, there is a great danger of a rapid transition from a compensated form of functional overload to a decompensated form, with the appearance of pathological mobility of the supporting teeth. Similar conditions arise with atrophy of the alveolar process, when the height of the clinical crown of the tooth increases due to a reduction in the intra-alveolar part of the root. At the same time, it should be borne in mind that with excessively low clinical crowns, the construction of a bridge is also difficult due to rigidity and a decrease in the area of ​​contact of the body with the supporting elements. Particularly often the connection is destroyed in soldered bridges.

Third principle suggests that the width of the chewing surface of the bridge body should be less than the width of the chewing surfaces of the teeth being replaced. Since any bridge prosthesis, as already noted, functions due to the reserve forces of the periodontium of the supporting teeth, the narrowed chewing surfaces of the body reduce the load on the supporting teeth.

Fourth principle is based on the fact that the amount of chewing pressure is inversely proportional to the distance from the point of its application to the supporting tooth. Thus, the closer the load is applied to the abutment tooth, the greater the pressure falls on this abutment tooth, and, conversely, with increasing distance from the place of application of the load of the additional abutment tooth, the pressure on this abutment tooth drops. A completely opposite pattern is found when designing cantilever prostheses. To reduce the functional overload of supporting teeth, it is necessary to increase their number, avoid the use of cantilever dentures and reduce the width of the chewing surface of the prosthetic body.

Fifth principle associated with the need to restore contact points between the supporting elements of the bridge prosthesis and adjacent natural teeth. This allows the continuity of the dental arch to be restored and promotes a more uniform distribution of chewing pressure, especially its horizontal component, among the teeth remaining in the oral cavity. It is especially important to observe this principle with a well-defined sagittal occlusal curve, when horizontal loads transformed from vertical ones tend to tilt the abutment teeth in the mesial direction. Correctly restored by the supporting elements of the bridge, the contact point will transfer part of the horizontal forces to the adjacent natural teeth. This helps maintain the stability of the supporting teeth and prevents their tilting in the mesial direction.

Sixth principle provides for the competent design of bridges from the point of view of normal occlusion. In this case, two groups of patients can be distinguished. The first group includes patients whose prosthetic task is to restore occlusal relationships in the area of ​​the defect with careful modeling of the occlusal surface of the bridge, fitting into the patient’s existing functional occlusion. Here, first of all, care should be taken to prevent premature contacts, reduce the interalveolar distance and functional overload of the periodontium after prosthetics.

The second group includes patients who need not only prosthetics, but also a simultaneous change in the functional occlusion within the entire dentition. This may be necessary in case of partial loss of teeth, increased abrasion, periodontal diseases, anomalies of occlusion complicated by partial loss of teeth, etc. What is common to all these pathological conditions is a decrease in the interalveolar distance. Thus, the second group of patients requires more complex prosthetics, taking into account profound changes in the occlusion of the dentition.

Seventh principle: it is necessary to design such bridges that would meet the aesthetic requirements to the maximum extent. For this purpose, the most aesthetically advantageous cladding materials are used, and support elements and the intermediate part of the prosthesis are designed to ensure reliable fastening of the cladding made of plastic, porcelain or composite material.

When designing bridges, certain principles should be followed. According to first principle the supporting elements of the bridge and its intermediate part are on the same line. The curvilinear shape of the intermediate part of the bridge leads to the transformation of vertical and horizontal loads into rotating ones. The load is applied to the most protruding part of the bridge body. If you draw a perpendicular to the straight line connecting the long axes of the supporting teeth from the most distant point of the prosthesis body, then it will be a lever arm that rotates the prosthesis under the action of the chewing load. The magnitude of the rotational forces is thus directly dependent on the curvature of the bridge body. Reducing the curvature of the intermediate part will help reduce the rotational effect of the transformed chewing load.

Second principle is that when constructing a bridge, abutment teeth with a not very high clinical crown should be used. The magnitude of the horizontal load is directly proportional to the height of the clinical crown of the abutment tooth. The use of abutment teeth with high clinical crowns and shortened roots is especially harmful for the periodontium. In this case, there is a great danger of a rapid transition from a compensated form of functional overload to a decompensated form, with the appearance of pathological mobility of the supporting teeth. Similar conditions arise with atrophy of the alveolar process, when the height of the clinical crown of the tooth increases due to contraction within the alveolar part of the root. At the same time, it should be borne in mind that with excessively low clinical crowns, the construction of a bridge is also difficult due to rigidity and a decrease in the area of ​​contact of the body with the supporting elements. Particularly often the connection is destroyed in soldered bridges.

Third principle suggests that the width of the chewing surface of the bridge body should be less than the width of the chewing surfaces of the teeth being replaced. Since any bridge prosthesis, as already noted, functions due to the reserve forces of the periodontium of the supporting teeth, the narrowed chewing surfaces of the body reduce the load on the supporting teeth. Moreover, when designing the body of the prosthesis, it is advisable to take into account the presence of opposing teeth and their type - whether they are natural or artificial. If the pressure is concentrated closer to one of the supporting teeth due to the loss of part of the antagonists, then the body of the prosthesis in this place may be narrower than in other areas. Thus, the masticatory surface of the bridge body is made narrower to avoid excessive functional overload, and the amount of narrowing in individual areas is determined individually, in accordance with the characteristics of the clinical picture. An increase in the width of the chewing surfaces of the intermediate part of the bridge leads to an increase in the functional overload of the abutment teeth, not only due to an increase in the total area that receives chewing pressure, but also due to the appearance of rotational forces along the edge of the body of the prosthesis, going beyond the width of the abutment teeth.

Fourth principle is based on the fact that the amount of chewing pressure is inversely proportional to the distance from the point of its application to the supporting tooth. Thus, the closer the load is applied to the abutment tooth, the greater the pressure falls on this abutment tooth and, conversely, as the distance from the place of application of the load to the abutment tooth increases, the pressure on this abutment tooth drops. A completely opposite pattern is found when designing cantilever prostheses. The larger the size of the suspended artificial tooth, the more the adjacent supporting tooth is loaded.

To reduce the functional overload of supporting teeth, it is necessary to increase their number, avoid the use of cantilever dentures and reduce the width of the chewing surface of the prosthetic body.

Fifth principle associated with the need to restore contact points between the supporting elements of the bridge and adjacent natural teeth. This allows the continuity of the dental arch to be restored and promotes a more even distribution of pressure, especially its horizontal component, among the remaining teeth in the oral cavity. It is especially important to observe this principle with a well-defined sagittal occlusal curve, when those transformed from a vertical horizontal load tend to tilt in the mesial direction. A contact point correctly restored by the supporting elements of a composite prosthesis will transfer part of the horizontal forces to the adjacent natural teeth. This helps maintain the stability of the supporting teeth and prevents their tilting in the mesial direction.

Sixth principle provides for the competent design of bridges from the point of view of normal occlusion. In this case, two groups of patients can be distinguished. The first group includes patients whose prosthetic task is to restore occlusal relationships in the area of ​​the defect with careful modeling of the occlusal surface of the bridge, fitting into the patient’s existing functional occlusion. Here, first of all, care should be taken to prevent premature contacts, reduce the inter-alveolar distance and functional overload of the periodontium after prosthetics.