Comparison of Four Universal Adhesive Protocols for the Internal Adaptation of Composite Restorations in Primary Teeth: An In Vitro Micro-CT Study

Achieving an acceptable adhesive interface is necessary for the long-term success of composite restorations in primary teeth. This study compared the three-dimensional internal adaptation of composite restorations in primary second molars among four prespecified universal adhesive product–application protocol combinations using micro-computed tomography (micro-CT). Seventy-six extracted primary second molars were randomly allocated to four experimental groups (n = 19): G2-BOND Universal/self-etch, G2-BOND Universal/selective enamel etching, G-Premio Bond/self-etch, and G-Premio Bond/selective enamel etching. Following restoration and thermocycling (5000 cycles), whole-cavity interfacial gap volume percentages were quantified using micro-CT. Data were analyzed using the Kruskal–Wallis test followed by Dunn–Bonferroni-adjusted pairwise comparisons. An overall difference was detected among the four experimental groups (p = 0.016). Following adjustment for multiple comparisons, the G2-BOND Universal self-etch group showed a lower whole-cavity interfacial gap volume percentage than the corresponding selective enamel-etching group (adjusted p = 0.013). No other adjusted pairwise comparison reached statistical significance. Within the limitations of this laboratory study, these findings are restricted to the tested product–application protocol combinations and do not demonstrate an interaction between adhesive system and application mode.