THE EFFECT OF PORCELAIN THICKNESS IN RELATION TO PREPARATION DEPTH ON FRACTURE STRENGTH OF TRANSLUCENT ZIRCONIA CROWNS

Abstract

Objective. The purpose of the study was to evaluate the fracture strength of veneered high translucent Y-TZP crowns with the same outer dimensions, but with different porcelain layer thicknesses, with different inner dimensions (preparation depths). Material and methods. Seventy standardized crowns divided into seven groups (n = 10) were fabricated. The crowns in the first six groups were divided according to different thicknesses of the porcelain layer on Y-TZP copings: 0.3 mm, 0.5 mm, 0.8 mm, 1.0 mm, 2.0 mm, and 2.5 mm. The crowns in the seventh group had the same porcelain thickness as group 1 but with preparation depth as group 6. All crowns underwent thermocycling, storing in moist environment and cyclic pre-loading. After fatigue, the crowns underwent to single-load-to-failure test. Results. The crowns with 1.0, 0.8 and 0.5 mm of porcelain layer thicknesses showed no significant differences in fracture strength (1540 N, 1313 N, and 1286 N). Groups 2.5 mm and 2.0 mm showed significantly lower fracture strength (851 N and 910 N) compared to all other groups. There was no statistical difference in fracture strength of crowns with same thickness but with different preparation depths (1136 N and 1202 N). Conclusions. The reduction in porcelain thickness to 0.5 mm does not impair the fracture strength of crowns significantly. Fracture strength of crowns with micro-coating layer of porcelain (0.3 mm) might be lower, but still in range of what is considered to be clinically sufficient. Preparation depth (die size) do not affect the fracture strength.