In vitro evaluation of the marginal degradation of dental composites under simulated occlusal loading

Objectives: Our objective was to use an in vitro oral wear simulator to compare the susceptibility to marginal breakdown of different classes of dental composites. Methods: Two microfill composites (Silux Plus, 3M and Heliomolar, Vivadent), two minifills (Z100, 3M and Herculite, Kerr) and two midifills (Fulfil, Caulk and Clearfil, Kuraray) were placed in two increments (40 s cure) into class I cavities (5 × 3.5 × 2 mm³ deep) cut into the facial enamel surfaces of bovine incisors treated with an adhesive (Scotchbond MP, 3M). The restored teeth were aged 1 day in water, mounted in the OHSU oral wear simulator, covered with a slurry of poppy seeds/PMMA beads and subjected to 50 K cycles of wear against an enamel stylus [J.R. Condon, J.L. Ferracane, Evaluation of composite wear with a new multi-mode oral wear simulator, Dent. Mater. 12 (1996) 218-226). The specimens (n = 10) were positioned to produce abrasive wear (load = 20 N] across one margin and attrition wear (load = 70 N) across the second margin. Volume loss of material (mm³ × 1000) was estimated from 10 profilometric tracings perpendicular to the attrition margin, and then differentiated into composite and enamel degradation. Fracture toughness of the composites was measured in bending with the single-edge notch technique. Results were compared with ANOVA and Tukey's test at p < 0.05. Results: Signficant wear of the composite was produced at the attrition margin. Enamel degradation at the margin paralleled the composite results. The microfills, and to a lesser extent the minifills, showed more marginal breakdown than the midifill composites. Marginal breakdown shows an excellent inverse correlation with fracture toughness for these composites. Significance: These results are in general agreement with clinical studies showing greater marginal degradation for microfill composites and suggest that the OHSU oral wear simulator may be a useful adjunct for the study of the marginal degradation of dental composites.