Evaluation of fracture resistance and failure risks of posterior partial coverage restorations.

STATEMENT OF PROBLEM: Interest in posterior partial coverage restorations has increased because these restorations provide a more conservative treatment option than traditional cohesively based restorations; however, material selection has been a controversial topic in the current literature. PURPOSE: To evaluate the fracture resistance of posterior partial coverage restorations restored with different materials, examine their stress distribution, and calculate failure risks using three-dimensional (3D) finite element analysis. METHODS: Sixty extracted third molar teeth received 2-mm occlusal reduction maintaining cusp steepness of 45 degrees relative to occlusal surface. Teeth were allocated into four groups (N = 15) and restored with different materials: feldspathic ceramic, leucite-reinforced ceramic, lithium disilicate-reinforced ceramic (EMX), or indirect resin-based composite (COM). Restorations were luted with resin cement and submitted to compressive loads (Instron Corp, Norwood, MA, USA). The data were analyzed with one-way analysis of variance, followed by Tukey's HSD tests. A 3D finite element model of posterior partial coverage restorations was developed and validated. The model was used to approximate the maximum principal stress in each of the materials under a 100-N static vertical compression at the occlusal surface of the tooth. The risk of restoration failure was quantified and compared among the four different materials. RESULTS: Group EMX had fracture resistance significantly higher than other testing groups. Group COM presented the most extensive fractures involving tooth and root structures. When compared with the other materials, group EMX exhibited higher stress concentration; however, the failure risk of the restoration was lower. CONCLUSIONS: Fracture resistance and failure risks of posterior partial coverage restorations are significantly influenced by material selection. CLINICAL SIGNIFICANCE: Many restorative materials have been advocated for partial coverage restorations. It is essential to ensure that restorative materials have sufficient strength to support occlusal forces and, in case of fracture, the remaining tooth structure is not compromised or placed at risk. This study revealed that all-ceramic materials had high incidences of fractures involving the materials themselves, whereas the predominant failure of resin-based composite involved the tooth structure in a catastrophic manner.