Preparation of teeth for a crown. Preparation for metal-ceramic crowns Preparation of a tooth for a cast crown

Classifications of cast crowns:

1. By design features:

a. full crowns;

b. telescopic crown element;

c. element of the locking system for fixing removable structures of dentures;

d. element of the beam system for fixing removable structures of dentures.

2. By appointment:

a. Recovery;

b. support-fixing;

c. preventive;

d. splinting.

They are made by casting from metal alloys used for dental work. Cast metal crowns are used mainly on the chewing group of teeth.

metal alloys are macroscopic homogeneous systems consisting of two or more metals with characteristic metallic properties. In a broad sense, alloys are any homogeneous systems obtained by fusion of metals, non-metals, oxides, organic substances.

castingcalled obtaining castings of the necessary parts of the prosthesis by pouring molten metal into a mold.

Advantages of cast metal crowns over stamped crowns:

1. More accurately restore the anatomical shape of the teeth, occlusal contacts and contact points;

2. Create favorable conditions for the formation of optimal functional occlusion;

3. Have higher strength;

4. Provide a snug fit of the inner surface of the crown to the stump of the tooth;

5. The edge of the crown fits snugly against the ledge, eliminating the traumatic effect on the tissue of the marginal periodontium.

Stages of manufacturing cast metal crowns:

First clinical stage (first visit to the patient) involves:

· Anesthesia (more often, infiltration anesthesia is performed, or preparations begin without anesthesia).

· Odontopreparation of a tooth under a cast metal crown.

· Obtaining working and auxiliary impressions with silicone and alginate materials.

First laboratory stage includes:

· Production of a working collapsible model from class IV supergypsum and an auxiliary model from class III plaster.

· Production of wax bases with occlusal rollers.

Second clinical stage (second patient visit):

· Determination and registration of central occlusion or central relation of teeth.

Second laboratory stage includes:

· Comparison of models in the position of central occlusion or central relation of the jaws.

· Plastering models in an occluder or articulator.

· Preparation of the model of the prepared tooth stump.

· Wax crown modeling.

· Preparation for casting and casting crowns from metal alloys.

· Machining and fitting of a cast crown on a working collapsible model.

Third clinical stage (third visit to the patient) involves:

· Evaluation of the quality of the cast metal crown.

· Fitting the crown in the oral cavity.

When evaluating the quality of a cast metal crown, attention is paid to its compliance with all clinical and technological requirements, to the fit of the inner surface of the crown to the ledge and stump of the tooth. After a visual inspection, the crown is fitted on the abutment tooth and the quality of its manufacture is re-evaluated. To fit a cast crown, a corrective silicone impression material, liquid carbon paper or a layer of marker varnish is applied to its inner surface. Then the crown is placed on the stump of the tooth. Imprints on the stump of the tooth or signs of a sternum marker on the inner surface of the crown correspond to areas that prevent the imposition of a cast crown on the tooth, which are subject to correction with special cutters. In case of errors in the manufacture of the crown, which cannot be corrected, the crown must be redone.

Third laboratory stage - Grinding and polishing crowns.

Fourth clinical stage (also the patient's third visit)

· Fixation of an artificial crown on the tooth with a fixing material.

Odontopreparation of a tooth under a cast metal crown

Features of odontopreparation of a tooth for a cast metal crown are due to the volume of hard tissues removed - at least 0.3 - 0.5 mm from all surfaces of the tooth crown; the need to give the tooth stump the shape of a truncated cone with a small angle of convergence of its walls; the obligatory formation of a round ledge in the cervical area.

Scheme of odontopreparation of the tooth:

· Separation and preparation of contact surfaces with preliminary formation of a ledge;

· Preparation of the chewing surface or cutting edge;

· Preparation of the vestibular and oral surfaces with the preliminary formation of a ledge;

· The final formation of the ledge;

· Smoothing the edges and corners of the transition from one tooth surface to another.

Odontopreparation of the tooth begins with the separation of the contact surfaces. Contact surfaces are prepared from the chewing surface or cutting edge to the top of the interdental papilla. The cutting tool is not brought to the edge of the gingival papilla by approximately 0.5 mm and at this level a ledge 0.3–0.5 mm wide is preliminarily formed at a right angle to the vertical axis of the tooth. The contact surfaces of the tooth are given a taper with a convergence angle of not more than 5 - 7 0 .

The chewing surface or cutting edge is prepared to a depth of at least 0.5 mm with the maximum repetition of their anatomical shape, keeping the shape of the tubercles and deepening into the area of ​​grooves and natural pits.

The preparation of the vestibular and oral surfaces of the tooth begins with the creation of vertical marking grooves. To do this, use marker burs with a diameter of 1.0 mm, allowing you to control the depth of preparation. In the cervical region, horizontal grooves are formed, which are connected to ledges on the contact surfaces of the tooth. The hard tissues of the tooth are removed to the depth of the marking furrows, preliminarily forming a ledge on the vestibular and oral surfaces. The walls of the tooth are tapered with a convergence angle of not more than 5 - 7 0 .

The ledge is finally formed by smoothing the edges and corners of the transition from one tooth surface to another. To form a ledge, end diamond burs or cylindrical burrs with a diameter of the working part of the tool corresponding to the width of the ledge are used. The ledge may be formed above the gum, at the level of the gum, or below the gum. The optimal ledge angle for cast crowns is 135 0 to the longitudinal axis of the tooth.

In conclusion, diamond finishing burs smooth out the edges and corners of the transition from one tooth surface to another.

Requirements for a tooth stump prepared for a cast crown:

· The stump of the tooth should be in the shape of a cone;

· Convergence angle of contact surfaces - 3 0 ;

· The gap between the stump of the tooth and the antagonist teeth is 0.3 - 0.5 mm;

· Preservation of the relief of the chewing surface or the cutting edge of the tooth stump;

· Absence of protruding areas on the vestibular and oral surfaces;

· The location of the ledge above, at the level or below the level of the gingival margin;

· The ledge width is 0.3 - 0.5 mm;

· Smooth transition into each other of all surfaces of the tooth stump.

Production of metal-plastic crowns by casting a metal part

Metal-plastic crowns made by casting a metal part, according to their design features, are full crowns, and they can be an element of telescopic systems. By appointment - restorative, supporting, fixing, prophylactic, splinting, estatic crowns. The metal base of the crowns is made by casting from various dental alloys. In comparison with the combined crown according to Belkin cast metal-plastic has significantly higher functional and aesthetic performance

First clinical stage (first patient visit) includes

· Anesthesia;

· Odontopreparation of a tooth under a cast metal crown with a plastic lining;

· Obtaining working and auxiliary impressions with silicone and alginate materials;

· Choice of plastic cladding color.

If necessary, determine and record the central occlusion.

First laboratory stage suggests:

· Production of a working collapsible model from class IV supergypsum and an auxiliary model from class III plaster;

· Production of wax bases with occlusal rollers.

Second clinical stage (second visit of the patient) - determination and registration of the central occlusion or the central ratio of the jaws.

Second laboratory stage includes:

· Comparison of models in the position of central occlusion or central ratio of the jaws;

· Plastering of occluder or articulator models;

· Preparation of the prepared tooth stump model;

· Modeling the metal frame of a wax crown;

· Application of retention elements on the vestibular surface of the wax crown;

· Preparation for casting and cast framework crowns made of metal alloys;

· Machining and fitting of a cast crown frame on a collapsible model.

Third clinical stage (third visit of the patient) includes:

· Evaluation of the quality of the manufactured frame of a cast metal crown;

· Fitting a metal frame in the oral cavity.

Third laboratory stage includes:

· Polishing of the metal frame;

· Insulation with varnish of the vestibular surface of the metal frame to prevent metal from showing through the plastic lining;

· Modeling of the vestibular surface of the crown;

· Plastering the crown into a cuvette with the vestibular surface up;

· Obtaining a counterstamp of a plaster imprint of the vestibular surface of the crown;

· melting of wax;

· Preparation of plastic dough;

· Forming plastic dough in a cuvette;

· polymerization of plastics;

· Processing, grinding crowns.

Fourth clinical stage (fourth visit of the patient) involves:

· assessment of the quality of the manufactured crown; pay attention to the correspondence of the color of the plastic veneer to the color of natural teeth;

· fit of the crown in the oral cavity.

If errors were made at the previous clinical or laboratory stages, the doctor performs a crown fitting to eliminate correctable errors. If the errors are uncorrectable, the crown must be redone.

Fourth laboratory stage – grinding and polishing of plastic lining.

Fifth clinical stage (also the fourth visit to the patient) - fixing the artificial crown on the tooth with a fixing material.

Production of metal-ceramic crowns

Metal-ceramic crowns according to their design features are full crowns. In addition, they can be an element of telescopic, locking and beam systems for fixing removable dentures. By appointment - restorative, supporting, fixing, prophylactic, splinting crowns. A metal-ceramic crown consists of a cast metal cap and a ceramic coating. The advantages of metal-ceramic crowns are due to the combination of functional qualities of cast constructions with high aesthetic and biological properties of ceramics.

On first clinical stage(first visit to the patient) carry out:

anesthesia

· odontopreparation of a tooth for a ceramic-metal crown;

· obtaining working and auxiliary impressions with silicone and alginate materials;

· choice of color for ceramic cladding.

If necessary, determine and record the central occlusion.

First laboratory stage

Porcelain crowns

Plastic crowns

Stamped metal crown

Solid metal crown

Solid metal crown with veneer

III. Issues studied previously: 1. Tooth preparation for stamped crown. 2. Requirements for artificial crowns.

II. Targets:

: 1. Make a diagram: Indications and contraindications for the manufacture of a solid metal crown. 2. Compile a thematic dictionary on the topic (at least 20 words).

3. Make a table: Clinical and laboratory stages of manufacturing a solid metal crown.

4. Make a table: Advantages and disadvantages of a solid metal crown compared to a stamped metal crown.

IV. Tests.

1. Indications for the use of a solid metal crown: 1. Children under 16 with live pulp. 2. Support element for orthodontic appliances. 3. With pathological abrasion of hard tissues of the teeth. Answer 2. The number of clinical and laboratory stages in the manufacture of a solid metal crown compared to a stamped crown: 1. Less 2. More 3. Remains unchanged Answer 3. The alloy used in the manufacture of a solid metal crown:

4. What impression masses are used in the manufacture of a solid metal crown: 1. Thermomass 2. Silicone 3. Alginate Answer

5. Thickness of solid metal crown (mm): 1. 0.3 - 0.5 2. 0.8 - 1 3. 1.5 - 2 Answer 6. Contraindications to the manufacture of a solid metal crown: 1. Mobility of teeth of the 3rd degree 2. As a supporting element of a bridge prosthesis 3. Children under 16 years old with live pulp Answer 7. The disadvantages of a solid metal crown include: 1. Low aesthetics 2. High strength 3. Less traumatic Answer 8. The advantage of cast crowns compared to stamped ones: 1.1 2.3 3.5 Answer

9. Advantages of a one-piece cast metal crown: 1. Accurate reproduction of the relief of the anatomical shape 2. Tight fit in the cervical area 3. Poor aesthetics Answer 10. When preparing a tooth for a solid metal crown, a stump is created: 1. With parallel walls 2. In the form of a truncated cone 3. With preserved tooth equator Answer 11. When preparing a tooth in the manufacture of a solid metal crown, a ledge is not created: 1. On the first premolars of the upper jaw 2. On the first premolars of the lower jaw 3. On teeth with a narrow neck Answer 12. The first clinical step in the manufacture of a cast metal crown is: 1. Taking an impression 2. Fitting the crown 3. Odontopreparation Answer

13. When preparing a tooth for a solid metal crown, the walls should: 14. The first laboratory step in the manufacture of a solid metal crown is: 1. Preparation of the tooth and taking an impression 2. Making a collapsible model and waxing 3. Polishing the crown Answer 15. A collapsible plaster model consists of: 1. Silicone impression mass and super plaster (alpha fraction) 2. Silicone impression mass and ordinary plaster (beta fraction) 3. Super plaster and ordinary plaster. Answer

Lesson number 14.

Topic: Preparation of a tooth for a cast crown with a lining (metal-plastic, metal-ceramic). Types of ledges, their shapes, location, method of creation. Requirements for a properly prepared tooth in the manufacture of a combined crown.

Issues studied previously: 1. Tooth preparation for stamped crown. 2. Tooth preparation for a cast crown. 3. Classification of artificial crowns. 4. Requirements for artificial crowns.

II. Targets:

III. Task for independent work on the topic under study: 1. Draw up a diagram: Indications and contraindications for the manufacture of a cast crown with a lining (metal-plastic, metal-ceramic). 2. Compile a thematic dictionary on the topic (at least 20 words).

3. Make a table: Clinical and laboratory stages of manufacturing a cast crown with a lining (metal-plastic, metal-ceramic).

4. Make a table: Advantages and disadvantages of a cast metal crown with lining (metal-plastic, metal-ceramic).

IV. Tests.

1.Indications for the use of metal-ceramic crowns: 1. Prosthetics of teeth with live pulp in adolescents 2. Low, small or flat clinical crowns of teeth with thin walls 3. In case of allergy to plastic facings of fixed dentures Answer 2. Contraindications to the use of metal-ceramic crowns: 1. The presence of artificial crowns made of metal alloys that do not meet aesthetic requirements 2. With pathological abrasion of hard dental tissues 3. Severe periodontal disease Answer 3. Ceramic-metal crown refers to: 1. Combined 2. Non-metallic 3. Metallic Answer

4. When preparing a tooth for a metal-ceramic crown, grinding of the hard tissues of the tooth should be: 1. Intermittently without cooling 2. Intermittently with cooling 3. Remove the burr from the tooth as little as possible Answer

5. When preparing for a ceramic-metal crown, the creation of an excessive taper of the tooth stump causes: 1. Periodontal trauma 2. Weakening of fixation 3. Difficulty in applying a prosthesis Answer 6. Making temporary plastic crowns on teeth prepared for metal-ceramic crowns is necessary for: edges on the ledge 2. Splinting of teeth in case of periodontal disease 3. For the convenience of modeling the frame of the metal-ceramic crown Answer 7. When preparing a tooth for a ceramic-metal crown, the ledge is located: 1. Around the entire perimeter of the neck of the tooth 2. From the vestibular surface 3. From the oral and contact surfaces Answer 8. When preparing a tooth for a ceramic-metal crown hard tissues grinding on (mm): 1.0.2 - 0.3 2.0.5 - 1 3.1.5 - 2.0 Answer 9. Creation of a ledge in the manufacture of a metal-ceramic crown is necessary for: 1. Removal of an accurate impression 2. Uniform distribution of the load through an artificial crown on the root of the tooth 3. Prevention of periodontal diseases Answer 10. What type of ledge does not exist when preparing for a metal-ceramic crown: 1. 135* angle 2. 90* angle 3. Ditch shoulder Answer 11. The sequence of tooth preparation for a metal-ceramic crown: 1. Bringing the cervical ledge to a predetermined level - 2. Preparation of the vestibular and oral surfaces - 3. Separation of contact surfaces with shortening of the crown part - 12. When preparing a tooth for a ceramic-metal crown, do not use tools: 1. Separating discs 2. Diamond heads 3. Carbide heads Answer

13. When preparing a tooth for a ceramic-metal crown, the walls should: 1. Be parallel 2. Converge at an angle of 5-9 degrees 3. Converge at an angle of 12-15 degrees Answer 14. Causes of decementation of a metal-ceramic crown can be: 1. Excessive shortening of the tooth 2. Poor quality casting 3. Deformation of the two-layer impression Answer 15. Can a ceramic-metal crown be a support for an orthodontic construction: 1. Yes 2. No 3. At the discretion of the doctor Answer

16. Method for modeling a cast frame of a metal-ceramic crown at the 1st laboratory stage: 1. Applying wax to the model using modeling tools 2. Making 2 caps from a polymer film of different thicknesses 3. Lowering a plaster column into heated wax with subsequent modeling in relation to the size of a natural tooth: 1. Equal 2. More by 10-15% 3. More by 20-30% Answer 18. Alloy used in the manufacture of metal-ceramic crowns: 1. Cobalt-Chromium Alloy 2. Stainless Alloy 3. Titanium Alloy Answer

19. In the manufacture of a metal-ceramic crown, the ceramic mass is applied to: 1. Stamped cap 2. Cast cap 3. Platinum cap Answer

20. The composition of the porcelain mass does not include: 1. Feldspar 2. Quartz 3. Monomer Answer 21. To achieve adhesion of ceramics to the metal surface of the frame, it is necessary to carry out: 1. Sandblasting and degreasing the carcass 2. Degreasing the carcass and making the oxide film 3. Sandblasting, degreasing the carcass and making the oxide film Answer 22. The thickness of the cast cap in the manufacture of a metal-ceramic crown must be at least: 1. 0.1 mm 2. 0.3 mm 3. 0.5 mm Answer

23. A collapsible plaster model is cast in the manufacture of a crown: 1.Stamped 2.Plastic 3.Cermet Answer 24. Error leading to chipping of the ceramic mass from the cast frame: 1. Incorrect core preparation 2. Excessive number of firings 3. Contamination of the framework Answer 25. Method for modeling a cast frame of a metal-ceramic crown: 1. Applying wax to the model using modeling tools 2. Making two caps from a polymer film of different thicknesses 3. Lowering the plaster column into a bath with heated wax, followed by its modeling Answer 26. When firing porcelain mass, in addition to high-temperature exposure, use: 1. Pressure 2. Vacuum 3. Centrifugation 27. To reduce internal stresses in the coating during the manufacture of a metal-ceramic crown should be the same: 1. The firing temperature of all layers of the ceramic mass 2. The thickness of the ceramic mass 3. The thickness of the platinum cap Answer

28. When modeling the framework of a metal-ceramic crown, wax is used: 1. Lavax 2. Modevax 3. Voskolit Answer 29. The final laboratory stage of manufacturing a metal-ceramic crown is: 1. Fitting on the model 2. Final firing 3. Glazing Answer 30. The method of firing porcelain mass in the manufacture of metal-ceramic crowns:

31. Indications for the use of a metal-plastic crown: 1. Dental prosthetics with living pulp in adolescents 2. Low, small or flat clinical crowns of teeth with thin walls 3. Pathological abrasion Answer 3 2. Contraindications to the use of a metal-plastic crown: 1. The presence of artificial crowns made of metal alloys that do not meet aesthetic requirements 2. With pathological abrasion of hard dental tissues 3. Severe periodontal disease Answer 3 3. Disadvantages of a metal-plastic crown in front of a stamped crown according to Belkin: 1. The cast frame of a metal-plastic crown is more rigid than a stamped one 2. The cast frame is made in the form of a cap that tightly covers the tooth stump 3. The need to prepare a larger volume of hard tooth tissues Answer

34. Advantages of a metal-plastic crown over a stamped crown according to Belkin: 1. For a cast crown, the tooth is prepared with a ledge, which reduces the effect of plastic on the periodontium 2. The method of attaching plastic veneers is more reliable 3. Aesthetic advantages Answer

35. In the manufacture of a metal-plastic crown, the connection of plastic with a cast frame is carried out due to: 1. Formation of an oxide film 2. chemical compound 3. Formation of retention points with balls Answer 3 6. Contraindications to the manufacture of a metal-plastic crown: 1. Severe periodontitis 2. Splinting for periodontal disease 3. Supporting element of small bridges Answer 3 7. Material for the manufacture of a metal-plastic crown: 1. Thermomass 2. Plastic "Ftorax" 3. Plastic "Sinma" Answer 38. Making temporary plastic crowns on teeth prepared for metal-plastic crowns is necessary for: 1.Creating contact points 2 Taking a more accurate impression 3. Protecting the tooth from chipping Answer

39. When making a metal-plastic crown, it is desirable to take an impression: 1. Gypsum 2. Alginate mass 3. Silicone mass Answer 40. When preparing a tooth for a metal-plastic crown, a stump is created: 1. With parallel walls 2. In the form of a cone 3. With preserved tooth equator Answer 41. In the manufacture of a metal-plastic crown, hard tissues are ground to (mm): 1. 0.2-0.3 2. 1.3-1.5 3. 2.0-2.5 Answer 42. The first clinical stage in the manufacture of a metal-plastic crown is: 1. Choosing the color of the resin 2. Fitting the crown 3. Odontopreparation Answer

43. When preparing a tooth for a metal-plastic crown, the walls should: 1. Be parallel 2. Converge at an angle of 5-7 degrees 3. Converge at an angle of 12-15 degrees Answer 44. The mode of plastic polymerization in the manufacture of a metal-plastic crown does not include the stage: 1. Sandy 2. Viscous 3. Rubbery Answer 45. Method of polymerization of plastic in the manufacture of a metal-plastic crown: 1. Vacuum 2. Pressure 3. Curing oven Answer

One of the frequent procedures in prosthetics is the preparation (turning) of teeth. It is done under, veneers and other types of removable or non-removable structures.

Some patients want to know in advance what is this procedure and what you need to mentally prepare before visiting the dentist. Let's talk about the nuances of grinding healthy and pulpless teeth and the various requirements for this process.

What it is?

During orthodontic treatment, in some cases, it is necessary to grind off part of the hard tissues in order to create the desired shape of the tooth, level the surface and fit it to the crown. Only when a good junction of natural and artificial materials is achieved, the tight fit of the structure is achieved and the normal protection of the tooth from damage and infection is ensured.

More recently, this procedure caused panic fear in patients, as it was too painful, lengthy and laborious. Today, the latest developments, high-precision and high-quality instruments for the doctor's work, as well as good painkillers are available in dentistry. All this significantly reduces the time of manipulation and provides the patient with relative comfort.

Tooth preparation is necessary in the following cases:

• when installing a crown;
• for fixing removable dentures;
• for the purpose of fixing the "bridge";
• under veneers;
• at ;
• for fixing special tabs, etc.

But each of these options has its own requirements and features of the procedure, which the doctor should be aware of. The most important thing for the patient is the choice of a good specialist who knows how to adequately select the method of turning, performs manipulations with high accuracy and is able to prevent the occurrence of any complications after the procedure.

Separately, it is worth mentioning the painful sensations. If anesthesia is used during the preparation process and the patient does not feel anything, then after the effect of the anesthetic has ended, the following problems may be encountered:

• When a vital unit was processed, that is, a living one, with a pulp, too much tissue could be removed, which is why the teeth hurt after preparation. They react painfully to hot, cold and sour foods due to the resulting. To eliminate such symptoms, you need to consult a doctor and he will install a temporary cap to protect the treated tooth.
• Sometimes, to improve access during work, the specialist moves the gum with special threads. As a result, after the procedure, the patient complains that he has swollen mucous membranes, there is swelling and soreness. This is considered normal and goes away on its own in a day or two. To alleviate the condition, you can rinse at home with decoctions of herbs or saline.
• Much more serious is the following situation - when pain appear a few days after the procedure. Such pain indicates the onset of pulpitis or periodontitis. Therefore, as soon as possible, you need to consult a doctor for professional help.

Teeth preparation methods

There are various options for treating the surface of the enamel under the installed prosthesis:

1. Ultrasound - the main principle of this method is the presence of high-frequency vibration of the instrument and the absence of direct contact with the hard tissues of the tooth. At the same time, the tip does not press on the enamel, does not overheat it and does not affect the pulp in any way. The entire procedure for the patient is painless and safe. The appearance of chips or microcracks is also excluded.
2. The laser is considered one of the most better ways impact due to impulses of a special apparatus. Everything happens as follows - under the influence of a laser beam, the water in the dental tissues heats up and gradually destroys the integrity of the enamel in small volumes. And a special water-air mixture immediately cools the breakaway particles, which ensures the safety of the procedure, but makes it possible to achieve a quick result. The device works silently and does not deliver to the patient any discomfort. Thanks to the non-contact method, it is possible to prevent damage to the enamel, the appearance of chips and cracks, as well as the heating of deep tissue layers. What is especially valuable is that the instrument works silently and does not frighten anxious patients.
3. Tunnel turning - in this case, a special turbine device is used, with which you can adjust the maximum accuracy of the preparation. In this case, the diamond or metal tip works at different speeds, due to which it is possible to remove a minimum of enamel, leaving most of the tissue to protect the pulp. But here you need to monitor the condition of the device, because as it wears out, it begins to overheat the tooth, causing harm to it. If the actions of the doctor are illiterate and inaccurate, then the mucous membrane is also damaged.
4. Air-abrasive preparation - due to a mixture of abrasive powder fed under high pressure, there is a grinding of the tooth to the desired shape and size. Fine tissue destruction due to this dust occurs safely and without any pain. Also, thanks to this, you can save a large amount of healthy surfaces, preventing damage, chips, cracks and overheating. The procedure takes place in a short time and is quite simple for the dentist.
5. Chemical exposure - in which active substances, mainly acids, capable of destroying hard tissues in a short time. The doctor can only remove the softened parts and give the desired shape to the tooth. True, for the patient, this method turns out to be long in terms of waiting, but absolutely painless. In this case, there is no overheating, no exposure to terrible tools, no mechanical damage to the surface, which many like more than all other available methods. Even anesthesia or anesthesia is not used, because it is not required.

To make a high-quality fixation of the crown, you need to remove carious cavity and other types of destroyed tissue. And only after that to give the remains of the tooth the correct, often beveled and smooth shape for an accurate fit of the future product.

Varieties of ledges when turning

For high-quality and reliable fixation of the crown for a long period, the doctor must make not only a convenient shape of the prepared tooth, but also create certain ledges. They are a prerequisite for turning units and can be of various types:

• Knife-edge - the most common, the width of which is 0.3-0.4 mm. It is more often used for surface treatment for the installation of a solid metal crown and involves a certain inclination of the tooth.
• A grooved rounded shape (chamfer) - 0.8-1.2 mm wide, makes it possible to preserve natural healthy tissues as much as possible. It is chosen for metal-ceramic products.
• Shoulder ledge (shoulder) - they grind out a width of at least 2 mm and at the same time depulpation is still required. It turns out not the most economical type of turning, in which the unit is destroyed as much as possible. But, in this way, high aesthetic performance is achieved when fixing any structures.

If the doctor forgets to make the necessary ledge, then the crown will not fit snugly against the tooth surface, which will lead to the rapid development of secondary caries and other diseases. Indeed, in this case, there is a gap, a space between the product and the enamel. Clogged pieces of food that cannot be cleaned out quickly lead to infection of the tissues, due to which the tooth is destroyed, and the structure will still have to be removed for re-treatment.

Turning for crowns

It is a protective cap for the affected tooth, prevents the development of caries, prevents infection from entering weakened tissues and completely restores the integrity and functionality of the smile. IN modern dentistry popular types of crowns:

• metal - cast, stamped or ceramic-metal based on a solid frame, but with an aesthetic lining to match the color of natural fabrics;
• ceramic, porcelain - the most accurate and pleasant appearance, completely repeat the natural series;
• – especially strong and durable constructions;
• plastic - less reliable, but the cheapest, more suitable as a temporary measure;
• metal-composite - combined options, where plastic elements are used only for the front visible part.

There are the following features of turning teeth for crowns:

1. In order not to damage adjacent units, processing for solid metal products starts from the side surfaces and is removed up to 0.3 mm.
2. If it is required to install cermet, then in addition to preparation, depulpation is also needed. Removal of tissues occurs up to 2 mm on each side, and the ledge is selected according to the type and shape of the selected design. Very important point is the presence of roughness on the main surface, which will ensure a strong fit of the product.
3. When fixing a porcelain crown, you need to grind the tooth in the shape of a cylinder or cone. The ledge should be rounded and immersed in the gum by 1 mm. This is the only way to achieve a strong and reliable installation for a long period of time.
4. When preparing for a zirconium product, it is required to create a clear border of the ledge of the shoulder or rounded shape. The frontal units are treated with a maximum of 0.3 mm, and the chewing side requires tissue removal up to 0.6 mm.

Under veneers

A separate type of turning is the processing of a tooth for the installation of veneers - aesthetic overlays that cover only the frontal visible part of the smile. Most often, they are chosen for their manufacture, which fully fulfills its aesthetic functions.

In this case, the correct preparation greatly affects the density and reliability of fixation of each element. Having paid a large amount for a high-quality product, not a single patient wants it to come off just because of the illiterate actions of the dentist.

The following order is maintained here: first, the vestibular surface is treated, then the lateral parts of the tooth are ground, and only if necessary, the cutting edge and the palatal zone are prepared, although this is generally not required.

When removing hard tissues on the anterior surface, it is important to consider the dimensions of future plates. To accurately maintain the required volumes, the doctor makes recesses and, when completely grinding, focuses on them, aligning the entire treated area accordingly.

Also in this process, the sides deserve special attention: in the first option, interdental contact points are preserved, then it is possible to preserve the overall integrity of the row and its stability; the second method of processing involves bringing the boundaries of the ledges to the lingual side, that is, the inner one, which provides the best aesthetic performance when installing products.

Tabs

This partial dentures, which are needed in the presence of large defects in hard tissues. The following forms are distinguished:

• inlay (Inlay) - tubercles of the teeth remain intact and are not damaged;
• onlay (Onlay) - replace the internal slopes;
• overlay (Overlay) - completely cover at least one of the tubercles;
• pinley (Pinlay) - differ in an additional element - a pin and affect all the protrusions;
• stump tabs - serve to support a heavily damaged tooth, they are made in the form of a metal pin.

For good fixation of the product, it is necessary to create side walls parallel to each other. They help to introduce the finished structure, evenly and accurately fix it at the desired depth.

The doctor must adhere to the following rules when performing manipulations:

1. The cavity is prepared in such a way as to achieve an optimal shape with smooth walls. Angles and slopes are unacceptable, except perhaps in minimal volumes.
2. The side parts of the surfaces pass into the bottom at an even angle. It is necessary to achieve a uniform distribution of the chewing load for better stability and long-term operation of the product.
3. It is important to maintain sufficient dimensions of the remaining tissue that covers the pulp of the tooth. In adult patients, this is at least 0.6 mm, and in children - 1.4 mm. This is the only way to talk about full protection nerve endings from external aggressive influences.
4. If the creation of a complex cavity for the insert is foreseen, then it is desirable to additionally prepare the fixation points for its strong fixation.
5. To maintain high-quality marginal contact of a metal prosthesis with dental tissues, a bevel is formed at an angle of 45⁰ and not less than 0.5 mm wide.
6. But when using fragile materials, such as ceramics, such bevels are not provided at all.

Prostheses

In orthodontics, tooth turning is also needed for a strong fixation of various prostheses. Some of them are removable (, nylon,), others are permanent (bridges, implants). Preparation is necessary only in cases of installation of bridge options. All the rest involve other fixation systems that do not require the removal of healthy tissues.

Since "bridges" are very similar to crowns, only designed to restore more affected units in a row, hard tissue turning is done in the same way as for crowns.

When splinting

Splinting involves fixing the dentition, preventing them from loosening. It is needed when chronic forms periodontal disease and other gum diseases, when healthy teeth may fall out. In dentistry, the following options for their fixation are used:

• - made of metallic materials, and immersed vertically in hard tissues;
• beam - attached to the outer teeth with crowns and look like metal constructions, laid in furrows on the lingual part of the row;
• insert tires - made of polymer tape, are also fixed on internal surfaces.

For splinting, it is necessary to preserve healthy tissues to the maximum extent, therefore, turning is carried out with minimal removal of enamel. Sometimes, however, depulpation of individual units is required.

Dissection in childhood

For the treatment of milk teeth, dentists try to do without unnecessary manipulations that damage thin enamel. In addition, children are very afraid of various devices and tools with which the preparation is performed. There are also anatomical features in the structure of children's teeth, which the doctor must foresee when deciding whether to turn under the crown or not.

Most often they try to use any alternative methods treatment, so as not to injure hard tissues that are not fully formed, and at the same time the psyche of the child.

If turning and installing a crown on baby tooth, then they try to choose the least painful - the chemical version of their treatment. In this case, it is enough to remove only the area affected by caries.

Video: tooth preparation procedure.

Additional questions

Is it possible to do without turning?

Unfortunately, no matter how high modern technologies, nevertheless, it is not yet possible to get rid of the preparation stage when installing crowns and other dental structures. Doctors have not come up with any alternatives to the strong fixation of such products.

Cost of procedures

How much does the stage of turning the tooth cost? The price in each case will differ depending on the intended manipulations. In most clinics, it is included in the cost of general procedures for preparing the dentition for prosthetics or veneers.

The modern level of prosthetic technology allows to maintain and even improve the advantages of suture crowns, significantly reducing the time spent on their manufacture. Using precision investment casting or refractory casting methods, it is possible to cast crowns from inexpensive alloys that will cover the clinical neck, restore proximal contacts in diastemas, and have an occlusal surface of a given thickness.

It is advisable to use single cast crowns on chewing teeth with a decreasing bite, as well as as supports for one-piece cast bridges.

Solid crowns can be veneered with porcelain and resin.

Clinical interventions for cast crowns have certain features.

The preparation of a tooth for a cast crown should provide:

• a) the shape of the truncated cone of the natural crown of the tooth;
• b) the presence of a ledge in the area of ​​the clinical neck with a depth of up to 0.3 mm;
• c) the gap between the occlusal surface of the prepared tooth and the chewing surfaces of the antagonist teeth is at least 0.4 mm.

Performing this work, you must adhere to the following sequence.

1. Prepare the contact surfaces in such a way that they have a slight but uniform slope towards the occlusal surface, and ledges up to 0.3 mm deep (proximal shoulders) are formed in the interdental spaces at the gum level.

2. With a lenticular stone from the oral and vestibular sides, a recess of 0.3 mm is made along the clinical neck. From this recess, further preparation is made along the longitudinal axis of the tooth of the tissues hanging over it with the help of cylindrical stones. This completes the provisional preparation of the ledge and all surfaces of the tooth, except for the chewing one.

3. When starting the preparation of the chewing surface, it is necessary to decide what thickness it should be. The thickness of this part of the crown depends on anatomical features tooth, pain during preparation and the relationship of the prosthetic tooth to the prosthetic plane.

On incisors, there is no need to thicken the occlusal surfaces by more than 0.3-0.35 mm, while on chewing teeth, the thickness of the occlusal facets is adjusted to 0.4-0.45 mm. The preparation of devitalized teeth, if there are no inflammatory phenomena in the periapical tissues, is less painful, and therefore the chewing surface can be easily ground off by 0.5-0.7 mm, which significantly lengthens the time of using the crown.

Due to the fact that cast crowns are denser than stamped crowns and practically do not spring, all prepared surfaces must be carefully ground with paper abrasives, because even burrs invisible to the eye can become an obstacle to fitting a cast crown.

4. The last and very important stage in the preparation of teeth for cast crowns is the deepening of the ledge into the physiological pocket. In a cast crown, the edges do not cover the neck of the tooth, but rest against the cervical ledge, which guarantees high marginal accuracy. It is this circumstance that allows, within acceptable limits, without risking injuring the round ligament, to deepen the cervical ledge, which is a kind of foundation for cast crowns.

Recessed shoulder crowns blend harmoniously with the tooth socket, which is very cosmetically advantageous, and their high marginal accuracy without mucosal contact has clinical advantages. Such crowns do not injure the gums, are securely fixed on natural teeth, and prevent food from entering the physiological pocket.

The deepening and final formation of the ledge is carried out using special burs that have a working notch only at the end (end burs). Such burs do not injure the mucous membrane hanging over the ledge. For greater safety, before the preparation of the ledge, the mucous membrane must be moistened with adrenaline hydrochloride or a ligature to move the gum away from the clinical neck of the tooth. To prevent the bur from sliding off the ledge, the work is carried out on dry tissues with well-centered tools.

The classic option for obtaining an impression after preparation with a ledge involves the use of a custom-made ring and thermoplastic mass (see "Ring Impressions"). In this case, it is possible to obtain an accurate imprint from a ledge, which is located deep in the physiological pocket.

Modern silicone impression masses can greatly simplify this manipulation. Using them, you can achieve good results with proofreading prints. When it becomes necessary to take an impression of several adjacent or separated teeth, it is more expedient to use two-layer impressions (stens, sielast).

On the resulting impressions, the ledge and other surfaces of the prosthetic tooth should be clearly printed. When taking occlusal impressions Special attention should pay attention to the correct ratio of antagonistic teeth in a state of central occlusion.

The quality of the fit of a cast crown largely depends on the cleanliness and accuracy of the casting of the inner surface. If from the outside it is possible to relatively painlessly grind off the metal that prevents the crown from being fitted along the bite, then it is dangerous to do this inside the crown, since it can violate the accuracy of its fit to the ledge. Therefore, only clearly visible protrusions can be ground inside, which are an obvious consequence of poor casting.

In all other respects, fitting and fixation of cast crowns is carried out according to the same scheme and taking into account the same clinical requirements as for stamped crowns.