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Minimally invasive proximal cavities restored with a hybrid, flowable and low-shrinking composite: effect of marginal ridge preservation on failure pattern

Objectives: The present study assessed the restorative potential of silorane, flowable or hybrid-based composite resin for the ultraconservative occlusal fossa technique. Materials and methods: Thirty-two intact human molars received in the proximal ridge a 1x2x4 mm size occlusal cavity leaving the enamel ridge intact. The bur was then tilted at 30° alongside enamel ridge to simulate a typical carious cavity. After enamel etching and application of adhesive system, cavities were filled with three composites and then, a 0.8 mm diameter hole was prepared beneath the proximal contact area to simulate an incipient enamel carious lesion. Restored molars were submitted to mechanical loading. The adhesive interfaces before and after loading were evaluated with SEM. The fracture test was performed on fatigued molars and maximum breaking loads were recorded. Results: The hybrid and silorane composites showed, after the fatigue test, higher percentages of continuous margins (81±12 and 75±17, respectively) in comparison to flowable material (53±24). Similar fracture resistance was recorded by the three composite types, but significantly lower than the fracture resistance of the non-restored group. Nevertheless, a trend to a ductile behaviour, i.e. better capacity for elastic deformation, was observed in the group restored with the hybrid composite. Conclusions: Minimally invasive occlusal restorations with marginal ridge preservation and simulated proximal decay can be efficiently restored with hybrid and low shrinking composites. The flowable composite might not be indicated in this cavity type, in view of the marginal degradation observed after the fatigue test.