Failure analysis of adhesive restorations with SEM and OCT: from marginal gaps to restoration loss

Objective: The objective of this study was to analyse the failure mode of adhesive interfaces by comparing OCT and scanning electron microscope (SEM) analysis of class V restoration margins located on enamel and dentin. Materials and methods: Three groups were tested that differed in the application of a 3-step etch-and-rinse adhesive system (OptiBond FL) prior to cavity filling with restorative composite resin (Clearfil AP-X). After tooth restoration and polishing, the samples were loaded in a fatigue machine, and adhesive interfaces were evaluated with OCT and SEM. Results: Important and complementary information could be obtained with OCT analysis in respect to how marginal defects can propagate inside the cavity, compromising the restoration's long-term performance. A self-etching effect was observed with OptiBond FL due to the presence of an acidic primer (GPDM) within its composition. Our results could show that areas of bonding and gaps coexisted within the same restoration. Conclusions: When marginal imperfections, or non-continuous margins, were detected by SEM, also imperfections beneath the surface could be observed at the tooth-restoration interface with OCT. Restoration loss occurred above the borderline of 50% of marginal gaps on enamel and dentin. Clinical relevance: Marginal discrepancies of adhesive restorations can propagate inside the cavity and lead to restoration loss