Influence of cavity preparation design on fracture resistance of posterior Leucite-reinforced ceramic restorations

Statement of problem. Controversy exists concerning the preferred cavity design for posterior ceramic restorations to improve their resistance to fracture under occlusal load. Purpose. The aim of this study was to assess the resistance to fracture of leucite-reinforced ceramic restorations placed on molars with different cavity preparation designs. Material and methods. Ninety noncarious molars were selected, stored in 0.2% thymol solution, and divided into 9 groups (n=10): IT, intact teeth; CsI, conservative inlay; ExI, extensive inlay; CsO/mb, conservative onlay with mesio-buccal cusp coverage; ExO/mb, entensive onlay with mesio-buccal cusp coverage; CsO/b, conservative onlay with buccal cusp coverage; ExO/b, entensive onlay with buccal cusp coverage; CsO/t, conservative onlay with total cusp coverage; ExO/t, extensive onlay with total cusp coverage. Teeth were restored with a Leucite-reinforced ceramic (Cergogold). The fracture resistance (N) was assessed under compressive load in a universal testing machine. The data were analyzed with 1-way and 2-way analyses of variance, followed by the Tukey HSD test (alpha=.05). Fracture modes were recorded, based on the degree of tooth structure and restoration damage. Results. One-way analysis showed that intact teeth had the highest fracture resistance values. Two-way analyses showed no significant differences for the isthmus extention factor, but showed a significant difference for the preparation design type of fracture (P=.03), and also for the interaction between both factors (P=.013). The fracture mode observed in all groups tended to involve only restorations. Conclusion. Within the limitations of this study, it was observed that cuspal coverage does not increase fracture resistance of the posterior tooth-restoration complex restored with leucite-reinforced ceramics.