Method: 32 human endodontically treated molars were cut 3 mm over the CEJ and divided in four groups (n=8). The pulp chamber was filled with: group A (control), hybrid composite resin (G-aenial Posterior, GC, Tokyo, Japan); B, as group A but covered by 3 meshes of E-glass fibers (StickNET, Stick Tech lcd, Turku, Finland); C, a FRC resin (Ever-X Posterior, GC, Tokyo, Japan); D, as group C but covered by 3 meshes of E-glass fibers. The crowns of all teeth were then restored with CAD-CAM composite restorations. All specimens were then loaded to fracture in a universal testing machine. Maximum fracture loads were recorded in Newtons and data were analyzed using ANOVA and Weibull analysis. Fracture patterns were determined and fragments analysed using SEM.
Result: The mean static loads (N) registered were: A- 2817(873); B- 2128(952); C- 2429(1091); D- 2577(833). No significant differences were found between the groups (p<0.05). All specimens fractured in a catastrophic way, under the CEJ. The fractographic analysis showed that while in groups A and C the origin of the fracture was always at the occlusal surface with a corono-apical direction, in groups B and D the fiber layer originated multiple fractures with apico-coronal direction and in some cases the crack propagation was partially deviated.
Conclusion: The glass fiber reinforcement used in this study did not improve the load-bearing capacity of CAD/CAM composite endocrowns. The SEM analysis showed a certain behavior of the fiber nets in deviating the fracture but this effect was not sufficient to stop the crack propagation and to lead to more favorable fracture patterns.