Methods: : Three groups of onlay restorations were fabricated (n = 8/group); Group A: made from conventional particulate filler composite resin (Z250, 3M-ESPE, USA, control), Group B: made from short fiber-reinforced composite (Xenius Base, StickTeck Ltd, Turku, Finland) as substructure with 1 mm surface layer of PFC, Group C: made from FC composite resin. The specimens were incrementally polymerized with a hand-light curing unit for 80 s before they were statically loaded with two different sizes (3 & 6 mm) of steel ball until fracture. Failure modes were visually examined. Data were analyzed using ANOVA ( p = 0.05).
Results:
ANOVA revealed that onlay restorations made from FC (gr C) composite resin had statistically significantly higher load-bearing capacity (1733 N) ( p < 0.05) than the control PFC (gr A) composite resin (1081 N). Onlays made of FC composite resin with a surface layer of PFC (gr B) gave force values of 1405 N which was statistically higher than control group ( p < 0.05). No statistically significant difference was found in the load-bearing capacity between groups loaded by different ball sizes.
Conclusions: Onlay restorations combining base of short fiber reinforced composite resin as substructure and surface layer of conventional composite resin displayed promising performance in high load bearing areas.