Abstract: Objective To study the fatigue failure characteristics of direct and indirect resin composite restorations in-vitro by using a simulator to mimic chewing.Methods Thirty extracted human molars (prepared with standardized class Ⅱcavities, not bevelled) were randomly divided into three groups (n=10): two indirect resin composite restorations groups (cemented with PermaCem-Dual and ParaCore-Dual respectively) and a direct resin composite restorations group. All the specimens were fixed on a thermocycling and mechanical loading (TCML) chewing simulator. After thermocycling and dynamic mechanical loading ( 1 000, 5 ℃/55 ℃, 1.2×10⁶, 50 N, 1.7 Hz), the specimens were immersed in a 1% Gentian violet solution for 24 h, rinsed, and then incised in a mesial-distal direction. Section surfaces were observed with an optical microscope.Results Compared with the direct composite group, both indirect composite groups showed a significant reduction in the incidence of micro-leakage of gingival margin (P<0.05), but there was no significant difference between the two indirect groups (P>0.05).Conclusion Within the limitations of this in-vitro study, indirect resin composite restoration can tolerate more fatigue failure than the direct-placement light-cured-only composite. The resin composite inlay technique is a promising method introduced to reduce the problem of shrinkage.

Key words: resin composite, inlay, fatigue failure