Soft-start polymerization and marginal gap formation in vitro

Purpose : To determine the effect of soft-start polymerization of resin-based composites on the marginal gap formation in dentin cavities. Materials and Methods: Cylindrical cavities were prepared in dentin in extracted human molars. The cavities were distributed into 8 groups. The teeth in groups 1-4 were treated with Scotchbond Multi-Purpose and restored with Z100, and the teeth in groups 5-8 were treated with OptiBond FL and restored with Herculite XRV. The restorations were light-cured for 40 s by four different curing modes. The marginal gap formation was measured in a light microscope after a 20 min water-storage, and the wall-to-wall contraction was calculated as the widest gap in percent of the cavity diameter. Results: Soft-start light curing did not influence wall-to-wall contraction in dentin cavities. OptiBond FL and Herculite XRV showed less wall-to-wall contraction than did Scotchbond Multi-Purpose and Z100.