Effect of 3D-Adaptation on Fracture Resistance of CAD/CAM All-Ceramic Crowns

Objective: To assess the effect of 3D-adaptation on the fracture resistance of alumina all-ceramic crowns made by Procera and Cerec systems at 2 different computer pre-set cement thickness ( 50&100 µ).

Methods: 54 Maxillary premolars were copy milled using a Celay machine from a standardised preparation to receive full all-ceramic crowns. Three groups (18/group) of high purity Alumina crowns were fabricated with 0.4mm coping thickness and universal occlusal thickness of 2mm. The crowns fabricated were: Procera all-Ceram crowns (Procera) with the 50µ default computer cement relief, Alumina Cerec crowns with 50µ computer cement relief (Cerec50) and alumina Cerec crowns with 100 µ (Cerec100). Crowns were cemented using either Ketac Cem (K) or Panavia21 (P) to yield the following 6 groups (9/group): Procera/K, Procera/P, Cerec50/K, Cerec50/P, Cerec100/K, and Cerec100/P. The 3D-adaptation was assessed using a Micro-CT machine and the attached CT-analyser software. Crowns were then loaded to fracture in a universal testing machine and loads recorded.

Results: Cerec100 with the two cements (K&P) showed wider overall gaps (171.8 µ &155.5 µ) compared to Procera (120.3 µ & 123.1µ) and Cerec50 (134.9 µ &114.7 µ) respectively. Median of fracture loads were: Procera/K (1317.35N), Procera/P (1412.16N), Cerec50/K (1473.07N), Cerec50/P (1749.66N), Cerec100/K (2032.40N), and Cerec100/P (1447.07N). A Kruskal Wallis test showed no statistically significant differences between all groups (P>0.05).

Conclusion: 3D cement space widths of 120µ -180µ provided fracture loads well above the mean maximum occlusal loads. Increased cement thickness was not associated with reduced fracture resistance