A load-to-fracture and strain analysis of monolithic zirconia cantilevered frameworks.

STATEMENT OF PROBLEM: The dimensions of implant-supported fixed cantilevered prostheses are important to prevent mechanical and biological complications. Information on the optimum thickness and cantilever length for improving the strength of zirconia cantilevered frameworks is limited in the literature. PURPOSE: The purpose of this in vitro study was to investigate the effect of cantilever length and occlusocervical thickness on the load-to-fracture and strain distribution of zirconia frameworks. MATERIAL AND METHODS: Twenty-seven rectangular prism-shaped specimens (6 mm thick buccolingually) were fabricated using a computer-aided design and computer-aided manufacturing (CAD-CAM) milling technique. The specimens were prepared in 9 groups (n=3) according to their vertical dimensions (6×6 mm, 8×6 mm, and 10×6 mm) and cantilever loading distance (7 mm, 10 mm, and 17 mm). All specimens were heat treated in a porcelain furnace and thermocycled for 20000 cycles before the tests. Each framework was secured using a clamp attached to the first 20 mm of the framework. A 3-dimensional image correlation technique was used for a full-field measurement of strain during testing. A load-to-fracture test was used until the specimens fractured. Maximum force and principal strain data were analyzed by 2-way analysis of variance using the maximum likelihood estimation method (α=.05). RESULTS: No statistically significant effects (P>.05) were found for occlusocervical thickness and cantilever length or between them on the strain distribution. The results showed that the effect of occlusocervical thickness and cantilever length was significant on the load to fracture (P<.001). No statistically significant interaction was observed between the 2 factors (P>.05). CONCLUSIONS: Increased occlusocervical thickness and decreased cantilever length allowed the cantilever to withstand higher loads. The occlusocervical thicknesses and cantilever lengths of zirconia frameworks tested withstood the maximum reported occlusal force. The properties of components in the implant-abutment framework assembly should be considered in the interpretation of these results.