Damage mechanics and load failure of fiber-reinforced composite fixed partial dentures

Objectives Damage mechanics has been defined as the study of the initiation (initial failure) and accumulation of damage to and including rupture (final failure). This study was designed to evaluate the effect of increasing fiber-reinforced composite (FRC) substructure within a standardized fixed partial denture (FPD) model on the failure performance, in terms of damage mechanics. Methods The two FRC restorative systems, Targis/Vectris (TV) (Ivoclar Vivadent) and EverStick (ES) (Stick Tech with Gradia, GC Corp.), were used to restore the molar FPD model (1.5 mm axial and 2.0 mm occlusal reduction). Templates were used to standardize substructure designs with 0, 18, 43, and 66% cross-sectional FRC volume fraction (VFRC) of fiber substructure. Specimens (n=5) were homogenized at 29 points and stored for 1 week at 37 °C in distilled water. Specimens were luted with calcium hydroxide, then statically loaded until failure. Initial failure (IF), final failure (FF) and the mode of failure were recorded. Results The lowest mean load to initial failure was 530 N (TV 18%) and the highest was 1208 N (ES 66%). Linear regression analysis calculated the Pearsonʹs correlation coefficient (r) for the interactions between VFRC and IF (ES: r=0.7879, TV: r=0.6184), VFRC and FF (ES: r=0.912, TV: r=0.8152), and between IF and FF (ES: r=0.892, TV: r=0.7237). Unreinforced specimens universally fractured instantaneously. Significance The highest loads to initial and final failure were yielded by specimens with the highest cross-sectional VFRC.