Fracture resistance of CAD CAM endocrowns bonded to teeth with different number of remaining walls :An In-Vitro Study.

Abstract

Objective: Currently, there is no recommendation for the minimum number of remaining walls for Zirconia endocrown. Materials and methods: Fifty resin specimens were divided into 5 main groups according to the remaining wall number; group W0 no remaining walls, group W1 1 remaining wall, group W2 2 remaining walls, group W3 3 remaining walls, group W4 no missing walls. Ten resin dies for each group were fabricated using epoxy resin and assigned to each group. Resin dies from all groups were individually scanned using an extraoral scanner. Second generation zirconia monolithic (three mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) endocrowns were milled. All endocrowns were sintered according to the manufacturer’s recommendations. After trial fitting, all endocrowns were cemented to their corresponding resin dies using resin cement. After 1000 thermal cycles alternating between hot and cold baths with 20-second immersions at 55±1º C and 5±1ºC, respectively, and a 10-second delay between each immersion, each specimen was fixed to the lower fixed part of a universal testing machine with a load cell of 5 kN at a crosshead speed of 0.5 mm/min. All specimens were loaded to failure, and recorded in Newton using computer software. Data were collected, tabulated and statistically analyzed. Results: Group W1 showed higher mean values (2933±733.61) followed by W0 group (2453.5±492.48), then W4 group (2187±576) and group W2 (2108.17±451.28) and finally W3 group (1992±205.63). At a 95% of confidence level, One-Way ANOVA revealed significant differences between tested groups (P= 0.033). Conclusions: There was a significant difference in fracture resistance between groups with different numbers of remaining walls. The mean fracture resistance values were not consistent with the number of remaining walls. The number of remaining walls is not directly proportional to the fracture resistance values.