The most common pathology of the dental system is defects in the crowns of teeth. These include loss of enamel and dentin, anomalies of size and shape, discoloration of the tooth.

Long-term defects of tooth crowns can cause: 

1) deformation of the dentition, and as a consequence, a change in the function of the masticatory muscles and the temporomandibular joint; 

2) unilateral chewing and related changes in the function of the masticatory muscles and asymmetry of the facial skeleton; 

3) damage to the oral mucosa by the sharp edges of the teeth; 

4) aesthetic disorders.

The tasks of orthopedic treatment of dental crown defects are determined by the causes that caused them and the morphofunctional changes that accompany them. In case of defects of dental crowns of carious origin, anomalies of the tooth shape, treatment aims to restore the shape, aesthetics and function of the tooth. With hypoplasia of enamel and dentin, changing the color of the tooth, only aesthetic problems are solved.

With defects in the crowns of teeth complicated by deformation of the dentition and changes in the masticatory apparatus, normalization of the shape of the dentition, occlusion, function of the masticatory muscles and TMJ are put forward in the first place, and then the restoration of the shape and function of the tooth follows.

In all patients, the preventive task is also solved. It consists in preventing the most serious destruction of the tooth crown.

The choice of orthopedic construction in the presence of defects in the hard tissues of the teeth should be based on an objective assessment of the clinical situation. For this purpose , the following parameters are taken into account:

1. Etiology, pathogenesis of the defect and the likelihood of progression of loss of hard tooth tissues;

2. Localization of the defect of the hard tissues of the tooth (according to Black's classification);

3. Index of destruction of the occlusal surface during localization of defects on molars and premolars;

4. The depth of the lesion of the hard tissues of the tooth.

The index of destruction of the occlusal surface of the tooth (IROPZ).

In order to determine the degree of destruction of the occlusal surface of chewing teeth in class I-II defects and the choice of the prosthesis design, the index of destruction of the occlusal surface of chewing teeth - IROPZ, proposed by V.Yu. Milikevich (1984), is used. The index is the ratio of the size of the area of the cavity to the chewing surface of the tooth. The entire area of the occlusal surface of the tooth is taken as one. The destruction index (the surface area of the cavity) is calculated relative to the unit (the entire occlusal surface:

The author determined that with an IROPZ equal to 0.55 - 0.6, i.e. with the destruction of the surface by about 50%, the use of a tab is shown in order to prevent further destruction. With an index of 0.6-0.8, sealing and the use of artificial crowns are shown, and in cases where the index is greater than 0.8, the manufacture of pin structures is shown.

Incorrect determination of IROPZ, and, consequently, the choice of design, leads to splinters and splits of the crowns of the teeth after cementing the tabs or filling treatment.