CONVERGENCE ANGLES OF ALL-CERAMIC FULL CROWN PREPARATIONS

Palkov T. A.

DENTISTRY

Scentific article

The creation of the excessive taper in prepared teeth is a common sign of inadequate preparation that is one of the typical reasons for the retention loss of ceramic crowns and bridges. Based upon the experiments, the optimal convergence angle of axial walls of prepared tooth was believed to be 6°-7°. Unfortunately, in clinical practice the prevention of excessive taper creation proved to be difficult. Various studies, both classic and contemporary, demonstrated that convergence angle of clinically prepared teeth ranged from 1° to 50°. In cases with sufficient height of created core the convergence angle can exceed the 10°-20° range and more rounded transition lines between the walls can be formed that reduces a tension of the framework and improves the fit. The purpose of the study: to investigate retentive properties of the teeth preparated for ceramic crowns and bridges. Object and methods. During the experiment, three- and two-dimensional 3D images of scanned die stone casts casts (class IV gypsum) for different patients with dental defects were studied from the MM-Lab dental laboratory database (Lviv). These casts were scanned by the Wieland Dental Zeno non-contact CAD \ CAM Zeno CAD \ CAM scanner to produce a virtual model followed by computer simulation and computer-aided polishing of the Zirconia skeleton. 120 teeth, 39 incisors, 17 canines, 24 premolars and 40 molars were examined. All the teeth examined were repaired under full crowns for the production of the whole ceramic construction. Research results. The research showed that the predominant majority of the examined teeth 85,83% were characterized as being of unsatisfactory qualities to provide adequate retentive properties of preparated teeth. The best paramateres of the сonvergence angle characterized premolars. Аt the same time third molars characterized the most unfavorable paramateres of the сonvergence angle. Mesiodistal convergence angle of lateral teeth in mesio-distal projection (22,64±0,45) exceeded the similar indexes of preparation of teeth in the frontal area (20,10±0,60). Mesiodistal convergence angle of the preparation (23,90±0,44) slightly exceeded the buccolingual convergence angle (22,64±0,45).

сonvergence angle, ceramic, fixed prosthodontics.

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«Bulletin of problems biology and medicine» Issue 1 (155), 2020 year, 378-380 pages, index UDK 616.314-089.818.1: 616.314-089.29-24

10.29254/2077-4214-2020-1-155-378-380