Abstract: Objective: To investigate the wear resistance of four low-shrinkage commercial composite resins and two traditional composite resins in vitro and discuss the relative influencing factors, and to illustrate the inner relationship of the wear resistance of resins and material composition. Methods: Four low-shrinkage commercial composite resins including CLEARFIL MAJESTY Posterior(CMP), Filtek LS(LS), Admira(AD), Kalore(KA) and two traditional composite resins including Filtek Z350XT (Z350), Solitaire2(S2) were chosen. The bar-shaped specimens were fabricated and mounted in a UMT-2 wear testing machine and abraded with the two-body media (distilled water) with a Si3N4 ball as antagonist.The maximum wear depth was determined after 14 400 cycles. The friction coefficient was determined during the test. The worn surfaces were examined with SEM. Results: CMP showed the lowest maximum wear depth and KA presented the highest maximum wear depth. The maximum wear depth ranked as follows:CMP< S2≈LS< Z350≈AD< KA(P<0.05). The wearing surfaces of Z350, S2, AD and KA were flatter and smoother, showing attrition wear and adhesive wear, whereas the wearing surfaces of CMP and LS were rougher, showing fatigue wear. Conclusion: The wear resistance of composite resins correlated to their type of filler, filler content and filler-resin matrix bonding.

Key words: wear resistance, low-shrinkage composite resin, friction coefficient, maximum wear depth