Fracture Resistance of Different Cavity Designs and Restorative Materials

Objectives: Cuspal failure of restored teeth is a frequent clinical observation. The purpose of this study was to evaluate the fracture resistance of human teeth restored with either a condensable composite or ceramic inlay. Methods: Ninety freshly extracted intact, noncarious, unrestored maxillary first premolars were cleaned and randomly assigned to 9 groups of 10 teeth each. Mean bucco-lingual widths for each group were measured and ranged within 0.03mm. All samples were mounted in acrylic resin. MOD cavity preparations varying in isthmus width (W=2.0 or 3.0mm) and depth (D=2.0 or 3.0mm) were performed on 8 groups. A 4.0mm proximal extension with a proximal box (1.5mm in width and 2mm in depth) applied to all preparations. Cavity preparations were restored with either a condensable resin composite (Surefil^TM, Dentsply) or a ceramic inlay (Cerec^TM, CEREC 3D, Sirona). An unprepared group of intact teeth was used as a control. All specimens were loaded at the facial and lingual slopes of the cusps with a rounded stylus in a universal testing machine until fracture. Results: Mean and standard deviation of fracture load in newtons for each group are as follows: Intact = 686±255; Resin (W=2;D=2; 417±181), (W=2;D=3; 431±162), (W=3;D=2; 569±266), (W=3;D=3; 589±251). Ceramic (W=2;D=2 694±245), (W=2;D=3; 770±251), (W=3;D=2 643±278), (W=3;D=3 747±299). Data were analyzed using two-way ANOVA with Tukey post-hoc testing (α=.05). Teeth restored with both materials were statistically similar to intact teeth with respect to fracture resistance. However teeth restored with ceramic inlay demonstrated higher mean cuspal fracture resistance than composite in all cavity designs. This difference was statistically significant in cavity preparations of 2.0mm in width (p=.0003). Pulpal floor depth was not a statistically significant factor. Conclusion:Within the limits of this study, fracture resistance of MOD cavity preparations was influenced by restorative material and preparation width.