For unobstructed covering of the tooth with an artificial crown, it is necessary to perform tooth preparation, i.e. removal (sanding) of hard tooth weavers (enamel, dentin).

The specifics of preparing teeth for crowns depend on the type of crown and the material from which it is made.

During the preparation of the tooth , the doctor faces the following tasks:

 to create a tooth shape that would meet all the requirements for the selected design of artificial crowns, taking into account the removal of a minimum amount of hard tissue;

■ perform grinding without injuring adjacent teeth, marginal periodontal, without irritating or injuring the pulp of the tooth;

* dissect in such a way that the patient experiences as few unpleasant sensations as possible.

Before starting the preparation, the doctor should check:

- working condition of dental equipment (installations, chairs, handpieces);

- the presence on the instrument table of the necessary sterile dental (dental mirror, dental tweezers, angle probe) and cutting tools;

- availability of means and devices for anesthesia and disposable disposable protective equipment for the patient's clothing, the doctor, his assistant.

The preparation of teeth is facilitated with a comfortable position of the patient in a chair. The hand holding the tip of the drill with an abrasive tool must be stable. This is achieved by the fact that the tip is held in the right hand with three fingers, like a writing pen, and the fourth and fifth fingers rest on the teeth or chin. At the same time, the left hand holding the oral mirror pushes away the soft tissues of the cheeks, lips, tongue or tissues of the bottom of the oral cavity, protecting them from possible damage.

Preparation of teeth is the process of removing (grinding) the hard tissues of teeth (enamel, dentin) for unobstructed covering with an artificial crown.

Dissection is a therapeutic procedure that is crucial for the preservation of living pulp, protection of preserved hard tissues of the tooth, ensuring static and dynamic occlusion, high long-term aesthetic and functional results of treatment.

Basics of preparation;

- in order to avoid injury to the pulp during preparation, it is recommended to keep a distance of 1 mm to the pulp (at least 0.7 mm), therefore it is necessary to use data on the thickness of the walls of the tooth at different ages and safety zones;

- thermal irritation of the tooth pulp during preparation can be avoided if sufficient water cooling is used (50 ml/min, the water cooling temperature should not exceed 35 ° C);

- preparation should be carried out intermittently, without pressure and vibration.

Preparation of teeth with live pulp is performed after anesthesia, depulpated teeth are reinforced with pin structures.

The pulp of the tooth in response to the preparation of enamel and dentin responds with a certain reaction. To clarify her character, special experiments were conducted on animals. Microscopic studies of histological preparations of teeth have shown that within an hour after the start of preparation, acute vascular disorders occur in the pulp in the form of dilation of blood vessels, hyperemia and hemorrhages.

  Hemorrhages in the form of hematomas and hemorrhagic infiltrates were determined mainly in the crown part of the pulp and its peripheral and pododontoblastic layers and were localized against the place where the removed layer had a large thickness.

The pulp preparations of the 10-15-day experiment showed signs of mild aseptic inflammation. After I year and 30 days, vascular disorders are eliminated, but in the crown pulp of some teeth there are residual phenomena in the form of mesh dystrophy and false intrapulpar cysts. In addition to the vascular reaction, a late deposition of replacement dentin was found in the pulp of most teeth. This phenomenon should be regarded as a protective reaction of the pulp.

Destructive phenomena of nerve conductors were also noted in the pulp of teeth. To a greater extent, they were observed in the crown pulp, gradually spreading to the root part (by the time they began to show up well in the root part, the neural structures in the crown acquired a normal appearance). It is also noted that the mildew-free fibers undergo less changes

Vascular and other changes in the pulp during the preparation of hard tissues of teeth undergo reverse development, but residual phenomena remain in the pulp, which makes it less resistant to subsequent influences.

With a severe injury, hemorrhages can be extensive, causing destruction of the pulp, and sometimes its inflammation with subsequent necrosis. Inflammation and death of the pulp are possible when infection penetrates into the tooth cavity through open dentine tubules.

  Pain is the main manifestation of the body's reaction to the preparation of the tooth. The severity of pain depends on many factors: the type of nervous system, the general condition of the body, the nature of the pathology of hard tissues, the quality, type, speed of rotation and rules of use of abrasive tools, the mode of preparation, the use of painkillers, etc.

Pain reaction during tooth preparation occurs due to:

- overheating of the tooth;

- microtraumas due to vibration of abrasive materials;

- uneconomical grinding of hard tooth tissues.

The following factors are involved in overheating of the tooth: the speed of rotation, diameter and pressure force of the abrasive tool on the tooth, the time of its contact with the fabric.

       The appearance of pain and overheating of the tooth is influenced by the size, location and direction of crystals on the surface of the abrasive tool, shape, size, quality of the abrasive material.Strict centrality of the instrument is necessary, eliminating vibration and injury to the tissues of the marginal periodontal.