Influence of contact stress on OCA wear of composite restoratives

Occlusal contact area (OCA) wear has been shown to exceed contact-free area wear by three-to-five times in clinical studies. A reciprocal compression sliding wear device was used to investigate the influence of contact stress on OCA wear of four resin composite restoratives (Silux, Z100, Ariston and Surefil). A dental amalgam (Dispersalloy) was used for comparison. The pat tern and mechanisms of wear, and the relationship between wear and composit e surface hardness were also studied. Thirty wear specimens and six hardnes s specimens were made for each material. Wear specimens were tested at 20 t o 60 MPa contact stresses against SS304 counter-bodies with artificial sali va as lubricant up to 20,000 cycles. Wear depth (mum; n=6) was measured usi ng profilometry. Hardness testing (KHN) was done with a digital microhardne ss tester (load=500 gf, dwell time=15 seconds). Results were analyzed using ANOVA/Scheffe's test (p<0.05). At ail contact stresses Dispersalloy had si gnificantly better OCA wear resistance than the composites. The wear of Z10 0 was significantly greater than Silux, Ariston and Surefil. The influence of stress on wear and counter-body loss was material dependent. Correlation between contact stress and wear was significant for all materials with cor relation coefficient (r) ranging from 0.96 for Z100 to 0.88 for Ariston. Th e wear mechanisms for the different composites varied depending on their mi crostructure and the contact stress. There was no significant correlation b etween material hardness and wear/counter-body loss.