BACKGROUND: The use of resin-based composites is increasing in clinical practice. The success and longevity of composite-resin restorations highly depends on adequate polymerization and small polymerization shrinkage, which are closely related with light-curing modes.
OBJECTIVE: To investigate the effects of two different light-curing methods on marginal adaptation and microhardness of packable posterior composite restorations.
METHODS: Specimens were made from these moulds with 3 types of packable resin-based composites: Ecusphere-Carat, 3M Filtek P60 and Tetric Ceram HB, and 2 curing modes: standard and soft-start curing mode with halogen light. The marginal adaptation was evaluated by measuring the width of margin gap between the mold and specimens with scanning electron microscope. Vickers microhardness was tested on the top and bottom surfaces of the specimens.
RESULTS AND CONCLUSION: For Filtek P60 and Tetric Ceram HB, soft-start curing mode showed lower values of the widths of marginal gap than that of standard mode (t=5.78, P < 0.05; t=5.64, P < 0.05), but there was no significant difference with Ecusphere-Carat (t=1.62, P > 0.05). The top surface demonstrated higher microhardness values than the bottom surface in all experimental conditions (P < 0.05). The soft-start curing mode showed lower values of top surface hardness for the three resins than that of standard mode (P < 0.05). But no significant differences were found on the bottom surface hardness of the three resins between these two curing modes (P > 0.05). Compared with routine light-cured mode, the soft-start curing mode can reduce the polymerization shrinkage and surface hardness of packable resin-based composites.