THE EFFECT OF COMPLETE AND PARTIAL CONTOUR ZIRCONIA COPINGS ON THE FRACTURE RESISTANCE OF ALL CERAMIC RESTORATIONS

Abstract

INTRODUCTION Veneer chipping is a common failure of zirconia based restorations, especially in the presence of high occlusal loads. Modifying zirconia design may influence veneer chipping. OBJECTIVES: Purpose of this study was to evaluate fracture resistance of complete and partial contour zirconia crowns. MATERIALS AND METHODS: Twenty standardized epoxy resin dies, prepared to receive zirconia based crowns, were divided into 4 groups, 5 specimens each. Zirconia framework designs were: (a) Full contour zirconia crown (FC), (b) Partial contour zirconia coping with buccal veneering (PC), (c) Anatomically reduced zirconia coping with palatal and proximal collar (ARD) and (d) half mm zirconia coping without collar (CON) (control group). Dual scanning technique was done for the test groups to fabricate zirconia copings with the use of standardized resin patterns, while normal scanning was made for the control group. After milling and sintering of zirconia specimens, veneering was done for all desired surfaces. All crowns were adhesively luted to their corresponding dies, and subjected to thermal cycling and mechanical loading corresponding to one year clinical service. Single load to fracture was applied to all the specimens. Type of failure was recorded for each specimen, investigated visually then by using Stereomicroscope and SEM. RESULTS: Complete and partial contour zirconia restorations showed high resistance to fracture. The presence of collar was insignificant for increasing fracture resistance, but had an influence on the fracture extension toward the proximal surface of the veneered restorations.