Influence of preheating resin composites: a nano-CT assessment on voids and internal adaptation

Gap percentage at the restoration-tooth interface and internal voids remain significant limitations in resin-based composite restorations, contributing to marginal leakage, secondary caries, and restoration failure. Preheating composite resins has been proposed as a strategy to enhance adaptation and reduce polymerization-induced stress. To evaluate the influence of preheating resin composites and varying light-curing durations on gap percentage at the restoration-tooth interface, internal adaptation, and void formation in Class II restorations using high-resolution Nano-CT imaging. Fifteen human maxillary premolars were prepared with standardized Class II cavities and allocated into three groups (n = 5). Group 1 received room-temperature composite cured for 20 s. Groups 2 and 3 received composite preheated to 68 °C using the Compex HD warmer, cured for 20 and 5 s, respectively. All restorations were bulk-filled. Internal adaptation (gap percentage) and voids were assessed using a Bruker Skyscan 2214 Nano-CT, followed by quantitative analysis with ImageJ and CTAnalyser software. Statistical comparisons were performed using one-way ANOVA with Tukey's post hoc test. Preheated composites (Groups 2 and 3) demonstrated significantly reduced gap percentages compared to room-temperature controls (p < 0.0001). Group 3 exhibited the lowest gap percentages and void volume, even with a 5 s curing protocol. No significant differences were observed in void frequency between groups. Preheating resin composites enhances internal adaptation and reduces interfacial gap percentage and void volume, even with reduced curing time. This technique offers a promising, efficient approach for improving posterior composite restoration outcomes.