Additional Retention in Large Resin Composite Class II Restorations

Objectives: This in vitro study compared marginal leakage and gap formation in resin composite class II cavities with gingival margin in cementum, using 3 different additional retention in proximal box. Methods: Standardized large MOD cavities, with gingival margins in cementum, were prepared in fourty recently extracted molars and divided into 4 groups according to the retention in proximal box: (G1) no retention; (G2) vertical grooves in buccal and lingual walls; (G3) pins in gingival wall; and (G4) horizontal grooves in gingival wall. All groups were restored with the incremental technique, using hybrid resin composite (QuiXfil – Dentsply) and bonding agent (Prime Bond NT – Dentsply). After polishing, all restored teeth were immersed in dye with simultaneous mechanical loading (alternated loading between 1kg and 17kg). Impressions of gingival margins were made before and after mechanical loading and epoxic resin replicas were evaluated in scanning electron microscope for gap formation. After the impressions, all teeth were seccioned for microleakage evaluation. All SEM photomicrographs and seccioned teeth images were analysed with Image Tools (UTHSCSA) software for a quantitative analysis of both parameters. Microleakage data were evaluated by ANOVA and Tukey's test. Gap extension before and after mechanical loading were evaluated by Student's t test. A correlation analysis was made between gap extension and microleakage (Pearson's correlation test). Results: All groups with additional retention (G2=0.565, G3=0.346 e G4=0.078) showed fewer gap formation than control group (G1=2.076) (p<0.01). Similar results were found for microleakage tests. All groups presented an increase in gap extension after loading, with exception to group with gingival retention groves (G4). This group (G4) showed the best results in both parameters (p<0.01). There was a low correlation between gap extension and microleakage. Conclusion: additional retention may improve marginal adaptation and minimize leakage in large class II resin composite restorations.