Effects of cyclic loading on occlusal contact area wear of composite restoratives

To investigate the effects of cyclic loading on occlusal contact area (OCA) wear and the possible presence of fatigue wear mechanisms in four composite resins (Silux, Z100, Ariston and Surefil) using a reciprocal compression-sliding test apparatus.

Six specimens were made for each composite material and the amalgam alloy (Dispersalloy) control. The wear specimens were subjected to wear testing at 20 MPa with artificial saliva as lubricant. Wear depth (microm) was measured using profilometry every 20,000 cycles up to 120,000 cycles. The worn specimens were subjected to SEM to determine the presence of fatigue wear mechanisms. Results were analyzed using ANOVA/Scheffe's test (P<0.05) and Pearson's Correlation (P<0.01).

Dispersalloy had the lowest wear at all cyclic intervals. For all materials, OCA wear increased with increased number of cycles. Although Dispersalloy, Ariston and Surefil experienced no significant increase in wear between each 20,000 cycles increment, a significant increase was observed with Silux. For Z100, a significant difference was observed only from 40,000 cycles onwards. Both Z100 and Dispersalloy exhibited fatigue wear after wear testing for 120,000 cycles. Cyclic loading resulted in deep and wide microcracks in Silux. Fatigue wear was not observed with Silux, Ariston and Surefil.

The effects of cyclic loading on wear is material dependent. While some restorative materials exhibit fatigue wear, others exhibit deep microcrack formation with extended cyclic loading. The latter may precipitate catastrophic failure despite the low wear observed. Care should, therefore, be exercised when selecting materials for posterior stress-bearing areas.