The effect of retention grooves on gingival marginal leakage in class II posterior composite resin restorations

In this laboratory study, the effect of retention grooves in the proximal portion of class II cavities on the marginal microleakage using light-cured composite resin was examined. The retention grooves were placed at the axio-facial and axio-lingual line angles and in the gingival floor of the cavities. The teeth were restored with Herculite composite resin with etching and dentine bonding and polymerized in two different ways: (i) a single mass of restorative material was polymerized all at once; and (ii) incrementally placed amounts of restorative material were each polymerized separately until the cavity was completely filled. Marginal microleakage was evaluated by the degree of dye penetration at the gingival margin of the restorations after suitable thermocycling procedures. It was concluded that marginal microleakage was significantly reduced when the composite resin was placed and polymerized incrementally, and that no advantage was gained from retention grooves with this incremental technique. However, when polymerizing in one single mass of material, retention grooves were found to be necessary in order to reduce marginal microleakage at the gingival wall.