Purpose: The purpose of this in vitro study was to evaluate the marginal adaptation and the fracture resistance of endodontically treated molars restored with zirconia reinforced glass ceramic endocrown restoration with or without incorporating a fiber-reinforced composite (FRC) layer into the pulp chamber.
Materials and methods: Mandibular first molars (n= 30) were prepared by computerized numerical control (CNC) in a standardized way to receive standardized CAD/CAM fabricated zirconia reinforced glass ceramic endocrowns after root canal treatments. The selected teeth were divided into two groups (n=15) according to the presence of fiber reinforced composite (FRC) in the pulp chamber. Group NF (Non filled) represented teeth with the pulp chamber without filling and Group F (Filled)represented teeth with the pulp chamber filled with FRCs. Marginal gaps (µm) were measured using stereomicroscope (32x) before cementation and after cementation. Thermal aging (3000 cycles) was performed then marginal gaps measurements were repeated. Then, fracture resistance test was performed. ANOVA test was used to study the interactions while Independent t-test was used to study the effect of using FRCs in the pulp on marginal adaptation in each stage and on the fracture resistance (N).
Results: The results of independent t test showed that there was no statistically significant effect of incorporating FRCs into the pulp chamber on the marginal adaptation during all stages before (p= 0.844) or after cementation (p=0.884) or after thermocyclying (p=0.875). Regarding the fracture resistance, the test showed that Group NF had higher mean fracture load value than Group F and the difference was statistically significant (p=0.004)
Conclusions: Within the limitation of this study, the incorporation of FRCs into the pulp chamber of endodontically treated teeth restored with zirconia reinforced glass ceramic endocrowns had no influential effect on the marginal adaptation of the restoration before or after cementation or after thermocycling. However, the presence of the FRCs unexpectedly decreased the mean values of the fracture resistance of the restorations. Further investigations are needed to confirm these findings before clinical application.