Effect of curing mode and composite pre-heating on bonding performance of flowable resin composite to enamel.

OBJECTIVES

This study aimed to investigate the influence of application methods combining different curing modes (pre-curing or co-curing) and flowable composite temperature (room temperature or pre-heating to 68 °C) on the shear bond strength (SBS) and microleakage of flowable composite to enamel.

MATERIALS AND

METHODS

Bovine enamel specimens (5 × 5 mm) were prepared (n = 10/group) and embedded in acrylic resin. A universal adhesive (Single Bond Universal Adhesive, 3M ESPE) and flowable resin composite (Filtek Z350 XT Flowable Restorative, 3M ESPE) were applied under four protocols: (1) Pre-curing adhesive combined with room-temperature composite (pre-curing + room-temperature); (2) Pre-curing adhesive combined with pre-heated composite (pre-curing + pre-heating); (3) Co-curing adhesive combined with room-temperature composite (co-curing + room-temperature); (4) Co-curing adhesive combined with pre-heated composite (co-curing + pre-heating). The immediate and aged (after 10,000 thermocycles) SBS were measured. Microleakage was assessed using the methylene blue dye penetration method (n = 10/group). The ultrastructure of adhesive-enamel interfaces was characterized by scanning electron microscopy (SEM). Data were analyzed using two-way ANOVA and Kruskal-Wallis tests (p < 0.05).

RESULTS

SBS was not significantly influenced by the application methods (p > 0.05), indicating no significant difference in SBS was found among the groups, either immediately or after aging. Aging significantly reduced SBS (p < 0.05). Microleakage scores showed no significant difference among four protocols (p > 0.05), though aging increased marginal microleakage in most groups (p < 0.05) except co-curing with room-temperature composite. SEM revealed typical composite-adhesive-enamel interfaces with clear adhesive layers, while the adhesive layer in co-curing groups showed a slightly less uniform thickness.

CONCLUSIONS

Neither curing mode nor pre-heating of the flowable composite resin significantly influenced the bonding performance to enamel, either immediately or after thermocycling aging. In the scenario of simple enamel restoration, the co-curing technique offers the advantages of simplifying the clinical procedure with comparable bonding performance to the conventional pre-curing method.

CLINICAL RELEVANCE: The co-curing protocol provides a simplified application method without compromising bonding performance when bonding to enamel.