Environmental damage and occlusal contact area wear of composite restoratives

The chemical environment is one aspect of the oral environment, which could have an appreciable influence on the in-vivo degradation of composite resins. The resin matrix can be softened and fillers constituents can be leached out when composites are exposed to certain chemicals/food-simulating liquids (FSLs). A reciprocal compression sliding wear device was used to study the effects of the chemical environment on occlusal contact area (OCA) wear of four composite restoratives (Silux Plus, Z100, Ariston pHc and Surefil). The effects of FSL on hardness was also investigated and correlated to wear. Thirty-six hardness/wear specimens of each material were made and stored in artificial saliva at 37 degrees C for 24 h. The specimens were then divided into six groups of six specimens and stored in the following FSL for 1 week at 37 degrees C: distilled water (W), 0.02 N citric acid (C), 0.02 N lactic acid (L), heptane (H) and 75-25% ethanol-water solution (E). Conditioning in artificial saliva (S) was used as control. After conditioning, the specimens were wear tested at 20 MPa contact stress against SS304 counter-bodies in the respective FSL/artificial saliva up to 20 000 cycles. Wear depth (lm, n=6) was measured using profilometry. Change in hardness (DeltaKHN, Knoop hardness number) was determined by microhardness testing pre- and post-conditioning. Results of statistical analyses (ANOVA/Scheffe's at significance level 0.05) of wear data were as follows: Silux - S, W > L, H, E and C, L > H; Z100 - S, W > all other mediums and E > H; Ariston - all other mediums > H; Surefil - W, C > S, L, H, E (> indicates significantly more wear). With the exception of Surefil, the greatest wear was observed with conditioning and wear testing in water. This ranged from 93.18 +/- 21.96 lm for Z100 to 31.43 +/- 2.80 lm for Surefil. For all materials, conditioning in heptane resulted in the least wear. This ranged from 8.9 +/- 2.2 microm for Ariston to 16.5 +/- 5.9 lm for Silux. The effects of the different FSL on OCA wear were material dependent. No correlation was observed between DeltaKHN and wear.