Objectives: Flexure at the tooth cervix has been suggested to dislodge cervical restorations more rapidly. The objective of this randomized controlled clinical trial was to test the hypothesis that a higher composite flexibility better withstands tooth flexure stress.
Methods: One hundred and forty-two non-carious cervical lesions were restored with composites with contrasting stiffness. Seventy-one patients randomly received two cervical restorations placed following two out of the three experimental groups: (1) the three-step etch-and-rinse adhesive Permaquick applied with the stiff micro-hybrid composite Amelogen Hybrid (PMQ/A-Hy, Ultradent), (2) Permaquick applied with the more flexible micro-filled composite Amelogen Microfill (PMQ/A-Mi, Ultradent), or (3) the 'golden standard' three-step etch-and-rinse adhesive Optibond FL applied with the micro-hybrid composite Prodigy (O-FL/Pro, Kerr).
Results: The recall rate at 7 years was 80%. No statistically significant difference was found for any of the parameters evaluated neither between both adhesives, nor between both composites (McNemar, p>0.05). Eleven percent of the O-FL/Pro restorations were clinically unacceptable due to loss of retention (5.5%) and severe marginal discoloration (5.5%). In the PMQ-group, 22% of the PMQ/A-Mi restorations (8% loss of retention, 5% severe enamel margin defects, 3% severe dentin margin defects, 6% severe marginal discoloration, 3% extreme sensitivity) and 19% of the PMQ/A-Hy restorations (13% loss of retention, 3% severe enamel margin defects, 3% severe marginal discoloration) needed repair or replacement.
Significance: The clinical performance of the three adhesive/composite combinations was good and reliable during the 7-year clinical trial. It was concluded that the composite stiffness does not affect the clinical longevity of cervical composite restorations.