Sequence and principles of preparation of hard tissues of teeth.

Importance of tooth preparation

To create a prosthetic space and the possibility of imposing artificial crowns.

Changes that occur in the hard tissues of the teeth during preparation.

The preparation of enamel and dentin, being an acute surgical injury, causes general and local reactions of the human body. Tooth tissues are affected by many factors: vibration, temperature increase, mechanical pressure. Tooth preparation, even if the processing rules are followed, causes irritation of the pulp in the form of vasodilation, slight edema and leukocytes exiting the capillaries into the surrounding connective tissue.

Fundamentals of gentle preparation.

● Use of effective anesthesia

● Compliance with the speed mode of preparation

● Use of sharp abrasive tools

● Vibration warning

● Knowledge of tooth anatomy

● The preparation should be carried out under full air-water cooling. Water cooling temperature should not exceed 35 degrees. As water cooling, it is desirable to use solutions with a weak antiseptic, feeding into the surgical field through the tip, which prevents microbial invasion during preparation.

● For cervical preparations, gingival retraction should be performed to avoid injury to the gingival margin

Safety zones of hard tissues of intact teeth.

Safety zones – areas in the crowns of the teeth, within which hard tissues can be excised with confidence, without fear of opening the tooth cavity.

The safety zones at the upper and lower incisors are located as follows:

a) at the cutting edge

b) from the oral and vestibular sides at the level of the equator

c) at the level of the neck.

At the fangs of the security zone are:

a) at the cutting edge

b) at the level of the equator from the vestibular, oral and contact sides

c) at the level of the neck from the vestibular, oral surfaces, and for the upper canines and from the distal surface.

In the upper premolars , the safety zones are located on the masticatory surface of the tips of the tubercles and along the mesio-distal fissure. On the oral, vestibular and both contact surfaces, they are at the level of the equator, and at the level of the neck – from the oral and vestibular surfaces.

In lower premolars , the safety zone at the level of the neck extends to the distal contact surface.

Sequence and principles of preparation of hard tissues of teeth.

1) The needle burr is installed at the point of transition of the vestibular surface to the contact one and, guided by the diameter of the tooth neck, moves in the oral direction so as to be constantly in the thickness of the hard tissues of the prepared tooth until the separation is completed

2) Quality check by probe

3) Separation on the other side

4) Quality check by probe

5) After separation, the preparation of the vestibular and oral sides of the tooth is started, for which the bur is placed in contact with its greatest convexity; as the hard tissues are ground off, the contact of the bur with them gradually increases, until full contact with the tooth surface

6) the processing of the oral surface of the incisors and canines should also be started with the largest convexity of the equator, which will more strictly observe parallelism with the vestibular surface of the tooth. For these purposes, a torpedo-shaped bur is first used, needle-shaped, and then flame-shaped.

7) Then proceed to the preparation of the occlusal surface of the tooth using a rhomboid bur with a diamond coating.

8) After preparation, the tooth should have a cylindrical shape, in which the diameter of the stump throughout the entire length should not exceed the diameter of the neck of the tooth. (If it is impossible to obtain a cylindrical shape with parallel surfaces, the tooth is given the shape of a truncated cone with a base at the neck of the tooth)

9) Quality check by probe

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