Turning of teeth for crowns is solid metal. Rules for the preparation of a tooth for a plastic, cast, metal crown. What is turning for?

Often, in order to restore the dentition, a preparation for a stamped crown is used. In other words, the necessary part of the tissue is removed from the damaged tooth so that the crown fits well on it. This procedure is done under general anesthesia.

When is this procedure used?

It is mandatory to prepare a tooth for a stamped crown. It is important to do this so that it fits perfectly to the tooth surface. To this end, it is important to observe the following rules:

• grind the convex parts of the tooth when they plan to install a cast crown on it so that the installation is easy and without consequences;
• take into account the thickness of the future prosthesis so that it does not cause discomfort;
• during processing, it is important to carefully remove the affected tissues, so the design will last a long time, and the patient will be insured against secondary caries.

Peculiarities

Consider the main features of the preparation:

1. It is important to start work from the side surfaces so that adjacent teeth are not damaged, while approximately 0.3 mm of the surface is removed.
2. When installing a metal-ceramic crown, the nerve must be removed from the tooth. Then it is processed and a ledge is made.
3. The ledge for a porcelain crown should be approximately 0.1 mm, and the stump should be in the shape of a cone or cylinder.
4. For a crown made of plastic, processing is also done similar to processing for a porcelain product.
5. The ledge for a stamped crown should be from 0.2 to 0.3 millimeters, while the tooth is shaped into a cylinder. The thickness of the tooth will be individual for each patient.

How does turning happen?

At the very beginning of the procedure, the patient is given anesthesia. If it is meant to work with the teeth of the vital group, anesthesia is not used, except when it is necessary to move the gums with a special thread.

Before the procedure, it is best to take an x-ray. With its help, the dentist will see all the features of the structure of the dental organs and possible deviations.

It is also important to take into account the anatomical features of the patient's teeth and the response of soft tissues to the preparation procedure.

What materials are used?

They make stamped metal structures. They can be coated or not. As a coating, noble materials are usually used: silver and gold. Gold is used much more often.

In Soviet times, stamped crowns were mainly used without coating, and the demand for them was significant.

To date, products obtained by stamping are used by patients with little financial capacity. After all, they are much cheaper than ceramic and porcelain structures.

Preparation methods for a cast crown

To date, dentists use the following types of turning:

• turning by means of ultrasound;
• laser processing;
• tunnel preparation for a stamped cap;
• air-abrasive method;
• chemical processing.

Consider the features of each technique:

1. Ultrasonic grinding has such positive aspects as the minimum pressure exerted on the dental tissues, while the tissues do not overheat, because during the procedure there is minimal heating, the procedure takes place without pain, chips and cracks do not form on the pins, there is no adverse effect on the pulp.
2. Laser treatment involves the use of pulsed lasers. The procedure is silent, safe, passes quickly enough, the tooth tissues do not heat up, there is no pain, there is no risk of infection, the pins are not subject to chips and cracks.
3. Tunneling involves the regulation of the speed of work carried out through special installations. You can use different tips. It is very important that the equipment used is in proper order, because the result of the treatment depends on it. When using a worn tool, the tissues can overheat, leading to further destruction of the dental organ. An important advantage of this technique is that you can control the amount of layer that needs to be removed. Before the procedure, it is important to apply anesthesia to avoid pain. There is a risk of injury during work.
4. The air-abrasive method of preparation is quite simple, fast and absolutely painless. With it there is no effect on the nerve bundle. It is also important that with this method of tooth treatment, most of its living tissues are preserved.
5. Chemical treatment involves the use of special chemicals that soften damaged tissue. The disadvantage of this method is its sufficient duration of treatment. This type of treatment is especially often used for children. The advantages of this treatment are the absence of thermal tissue burns, pain, minor injuries and psychological discomfort, because the drill does not work, which many patients are afraid of.

What are the concessions?

The main condition for attaching a crown to a tooth is its turning with a ledge.

The absence of a ledge violates the standards of prosthetics, because in this case there will be no necessary tight fit of the crown to the dental organ, which can lead to serious complications.

The ledges are different in relation to the type of crown. Consider the main types of ledges:

1. Knife-shaped - the most common type. Its width is 0.3-0.4 mm. They are used for preparation for a solid cast structure, as well as for grinding inclined teeth.
2. A rounded grooved ledge with a thickness of 0.8-1.2 millimeters is made under the ceramic-metal crown.
3. The most expensive preparation will cost with a shoulder ledge. In this case, the tooth nerve must be removed. The width of such a ledge is equal to two millimeters. With it, the crown is attached most tightly, and the artificial tooth looks more aesthetically pleasing.

Nuances in the manufacture and installation

Consider the basic rules that are important to follow in the manufacture and installation of stamped structures:

1. After installation, the crown should fit snugly against the tooth surface. With a wide product, irritation and displacement of the gingival tissue, as well as its atrophy, are possible. But there will still be a gap between the tooth and the crown, so it is filled with a special cement composition, which gradually dissolves over time.
2. The product should not go into the groove more than 0.3 mm. With greater immersion, the formation of an acute form of marginal periodontitis is possible.
3. The product must fully restore both the chewing function of the dental organ and its full functionality.
4. It is important that the crown comply with all the anatomical features of the tooth. It is necessary to have all hillocks and equators.
5. When contacting the opposite tooth, it is important that the interalveolar height is not exceeded, otherwise injury may occur.

Does the patient feel pain during treatment?

Grinding the tooth takes place under anesthesia, so there is no pain. But when the anesthesia wears off, pain can be felt, both in the tooth and in the gum.

Causes of pain:

• when too much cover is removed;
• when the gums are pushed back (in this case, a special thread is used), the tooth may hurt for a couple of days;
• if pain is detected some time after the treatment procedure, an inflammatory process may begin in the tooth.

Contraindications

On a note: Contraindications to the use of stamped products are: bruxism, increased tooth wear, severe destruction of the tooth crown or subgingival destruction, foci of chronic infection of the periapical tissues.

Stamped crowns are not much different from other prostheses. They must meet the following requirements:

• restore a tooth, taking into account all its anatomical properties;
• fit snugly against the tooth neck of the tooth and sink into the groove between the tooth and the gum no more than 0.2-0.3 mm;
• restore contacts with adjacent and opposite teeth.

For the manufacture of stamped structures, stainless steel sheets are used. Of these, caps are stamped in the form of a cylinder, of different diameters (sleeves).

Also, composite compounds and plastics are used to modify stamped products.

Indications for installation

Stamped products are used in situations such as:

• the need to restore a tooth that has a defect in its crown;
• installation of a clasp prosthesis on a healthy tooth, in order to protect it from stress and harmful effects;
• when installing a bridge prosthesis on a tooth as a protective element of the supporting dental unit;
• the need to protect children's milk teeth, which have begun to collapse.

Positive and negative qualities

The advantages of stamped products are:

1. Low cost, significantly inferior to the price of ceramic-metal products and approximately similar to the price of plastic products.
2. Simplicity of design.
3. Short production time.
4. The ability to apply in cases in which the use of other methods of prosthetics is complicated.

Negative qualities:

1. The cement fixing the crown dissolves over time.
2. It is possible to develop caries if the crown does not fit snugly against the dental organ, and pieces of food accumulate in the gap formed.
3. The alloy used for manufacturing is not very strong, so the crown is gradually subjected to abrasion.
4. Lost tooth functionality is not fully restored.

How to take care of these crowns?

With a stamped crown installed, the patient should follow all the basic rules of oral hygiene, as usual. The most important thing is to do it regularly and carefully.

The main features of care:

• you need to brush your teeth twice a day, using a brush and paste;
• after each smoking and eating, including snacking, it is important to rinse your mouth or brush your teeth;
• Dental floss is used to remove food debris from interdental spaces.

It is important to remember that 3 months after the installation of the prosthesis, you need to visit a doctor who will examine and evaluate the condition of the product. Then trips to the dentist should be made regularly every three months in order to avoid complications, for example, the appearance of caries under the crown.

How long do stamped products last?

The service life of crowns made by stamping is small, about two to three years.

Some doctors insist on their annual replacement, since during this time a gap may appear between the product and the tooth, into which food debris will fall, which can damage the structure of the tooth.

Price

How much a stamped product will cost depends on its composition and coating.

Consider the prices for the main types of such products:

1. Metal product - 1500 rubles;
2. Coated crown - 1700 rubles;
3. A product lined with plastic material - 1900 rubles;
4. Lined crown with spraying - about 2100 rubles;
5. A product with a clasp design - 1800 rubles, with a coating - 2000 rubles.

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 this procedure is and what they need to mentally prepare for 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 end of the action of the anesthetic, you may encounter the following problems:

• When a vital unit was treated, that is, a living unit 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 appears 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. Laser - is considered one of the best methods of exposure 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 cause any discomfort to the patient. 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. At the same time, 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, supplied under high pressure, the tooth is grinded 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 are used, 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 the 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, the following types of crowns are popular:

• 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 in appearance, completely repeat the natural row;
• – 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 structure. A 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

These are partial dentures that 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. Only in this way can we talk about the full protection of 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 necessary for chronic forms of periodontal disease and other gum diseases, when healthy teeth can 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 extreme teeth with the help of crowns and look like metal structures laid in the grooves 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 some alternative methods of treatment so as not to injure hard tissues that are not fully formed, and at the same time the child's psyche.

If turning and installing a crown on a milk tooth is required, then they try to choose the least painful - the chemical version of their processing. 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 are, it is still not 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.

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:

· Making 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 the 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 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 the 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

Anastasia Vorontsova

Preparation or turning of teeth for crowns is one of the stages of prosthetics, which is the removal of hard tooth tissues in order to prepare its surface for fixing the structure.

Until recently, the preparation procedure was quite painful and lengthy.

Thanks to modern anesthetics and the perfection of instruments, the time of the procedure has been reduced.

Do teeth always grind

Unfortunately, this stage of prosthetics is mandatory.

In order for the crown to be properly fixed on the tooth, it must be in contact with it as much as possible.

• But the natural shape of the tooth is not ideal and has convex shapes. When turning, the excess parts of the enamel are ground off and the tooth is given the correct geometric shape. A crown can easily be put on such a prepared tooth.
• In addition, the dental structure has a certain thickness, which must also be taken into account so that it does not cause discomfort and does not interfere in the mouth.
• In the process of grinding the tooth, the tissues affected by caries are removed. This is very important so that secondary caries does not develop under the crown and further tooth decay does not occur.

How is turning

Anesthesia is given before the preparation.

If a vital tooth is being ground, then there is no need for anesthesia, except in the case when the gum is retracted with a special thread.

When preparing, the anatomical features of the teeth and the reaction of soft tissues are taken into account without fail.

Before the procedure, an x-ray examination is performed, on the basis of which the dentist gets an idea of ​​the structure of the patient's teeth and possible places for opening the tooth cavity.

Methods

At present, several methods are used for turning a tooth under a crown.

Ultrasonic preparation

The advantages of this technique:

• Minimum pressure of working tips on dental tissues.
• A small amount of heat does not cause overheating of dentin and enamel.
• No pain during the procedure.
• Chips and cracks on the walls of the pin are not formed.
• Does not adversely affect the pulp.

Laser turning

Pulsed lasers can be used for tooth preparation.

Advantages of the laser technique:

• Noiseless operation of the equipment.
• manipulation safety.
• Absence of strong tissue heating.
• Speed ​​of preparation.
• Complete absence of pain.
• There are no cracks and chips of pin structures.
• No possibility of infection.

Tunnel preparation of a tooth for a crown

• Turbine dental units, which are widely used by dentists, allow you to adjust the speed of work and use diamond and metal tips.
• The quality of the equipment has an impact on the final result.
• The use of worn instruments is fraught with significant tissue overheating, which increases the risk of further tooth decay.

The main advantage of the method is the ability to control the volume of the removed layer and clearly predict the results.

Handling Disadvantages:

• There is a possibility of overheating of the tooth tissues, and if the amount of anesthetic was insufficient, pain may occur.
• If the technique of the procedure is not followed, injury to the surrounding gums is possible.
• If low-quality instruments are used, then there is a high probability of cracks and micro-chips in the tooth tissue.

Air abrasive turning

For preparation, an air mixture containing an abrasive powder is used. The mixture, falling under high pressure on the surface of the tooth, causes a fine destruction of hard tissues, and the removal of tooth dust.

Advantages of the technique:

• High speed, as well as simplicity of the procedure for turning the tooth.
• Absence of pain and overheating of tissues.
• There is no negative effect on the pulp, as there is no vibration.
• Ability to preserve the maximum amount of hard tissue.

Chemical preparation

Chemicals (usually acids) are used to remove hard tissues. They soften the tissues with their subsequent removal.

The disadvantage of the procedure is the duration, which can be up to half an hour.

This method has found wide application in prosthetics with crowns of milk teeth in pediatric practice.

Advantages:

• There is no thermal damage to the tooth.
• Anesthesia is not required as the procedure is painless.
• Microcracks and chips do not form on the enamel.
• Due to the fact that there is no sound of a working drill, the patient feels comfortable.

Video: "Incisor preparation part 1"

Types of ledges

Turning the tooth with a ledge is a prerequisite for fixing the crown.

Unledged preparation is a violation of prosthetic standards because the crown will not fit snugly against the tooth surface, which can cause serious complications as a result.

Depending on the type of crown, the ledge can be:

• Knife-edge ledge is the most commonly used type, the width of which is 0.3-0.4 mm. It is used when preparing teeth for solid crowns and when turning inclined teeth.
• For ceramic-metal prosthetics, a rounded grooved (Chamfer) ledge will be more relevant. Its thickness is 0.8-1.2 mm.
• The most uneconomical type of ledge, which requires mandatory depulpation, is the shoulder (Shoulder). The width of this ledge is 2 mm. However, this method contributes to a stronger fixation of the crown and has high aesthetic performance.

Features of preparation for crowns

Does it hurt to grind your teeth

The preparation procedure is painless under adequate anesthesia.

But, in some cases, after the termination of the anesthesia, pain may occur, both in the tooth and in the gum.

Causes of pain can be as follows:

• If too much hard tissue is removed from the vital tooth. As a result, there is very little hard tissue above the pulp and the tooth reacts not only to cold or sour food, but also to touch. In this case, it may be necessary to cement the thinned area or install a temporary crown on the tooth stump.
• In order for the doctor to have a sufficient overview of the working area, when turning a tooth with a ledge, the gum edge is pushed back with a special thread. The presence of a thread between the tooth and the gum leads to squeezing of the soft tissues, causing them soreness and swelling. Within a day or two, these sensations pass on their own.
• The occurrence of pain in the tooth some time after turning may indicate the development of inflammation of the pulp or periodontium.

Video: "Incisor preparation part 2"

“Preparation of teeth for a one-piece cast combined crown”

I. Material support:

• 
  dental unit;
• 
  dental handpieces (mechanical straight, turbine);
• 
  a set of dental instruments (mirror, probe, tweezers, spatula)
• 
  single-sided separating discs with diamond coating (push, push)
• 
  abrasive shaped heads and burs are cylindrical, cone-shaped with a diamond coating);
• 
  torus and diamond heads, burs for forming a ledge;
• 
  retraction rings and threads;
• 
  carbon paper, wax plate;
• 
  rubber gloves, mask, goggles.

P. Basic level of knowledge required to perform the skills:

• 
  know the anatomy of teeth and dentition;
• 
  know the safety zones within which it is possible to prepare hard tissues of the tooth with confidence;
• 
  know the classification of artificial crowns;
• 
  know the comparative characteristics of artificial crowns;
• 
  know the requirements for artificial crowns;
• 
  know the clinical and laboratory stages of manufacturing artificial crowns;
• 
  know the principles and stages of teeth preparation for artificial crowns;
• 
  know abrasive and cutting instruments for odontopreparation;
• 
  know the indications for the use of high-speed handpieces in the preparation of teeth;
• 
  know the effect of tooth preparation on the structure and function of the tooth;
• 
  know the possible complications of preparation and ways to prevent them;
• 
  know provisional crowns, indications for their use;
• 
  know the technique of subgingival preparation;
• 
  know the methods of gum retraction;
• 
  know the location of the edge of the crowns, depending on the type of artificial crown;
• 
  know the factors that affect the quality of fixation of crowns.

Sh. Indications for dental procedures:

Defects in the hard tissues of the teeth that cannot be restored by therapeutic methods of treatment;

• 
  with anomalies in the shape of the tooth - a change in the color of the tooth;
• 
  when prosthetics with bridges (supporting teeth are covered with fixing crowns);
• 
  for fixing various medical devices that are used for the duration of treatment;
• 
  fixation of the maxillofacial apparatus;
• 
  for fixing a removable prosthesis with clasps, if the supporting tooth has an unsatisfactory shape;
• 
  with pathological abrasion;
• 
  if necessary, significant grinding of the crown of the tooth, which has advanced or bent towards the defect of the dentition.

Contraindications for dental procedures:

• 
  the presence of severe systemic diseases in a patient (cardiovascular system, blood diseases, etc.);
• 
  local diseases;
• 
  psycho-emotional state.

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IV. Algorithm for performing practical skills