The effect of selective carious lesion removal on gap formation and bond strength of bioactive restorations

Selective carious lesion removal aims to preserve affected dentin and minimize unnecessary removal of tooth structure. However, the influence of residual demineralized dentin on the interfacial performance of different restorative materials remains unclear. This study evaluated the effect of selective carious lesion removal on gap formation (GF), microtensile bond strength (μTBS), and mineral-related characteristics of teeth restored with different restorative materials. Seventy-eight molars with Class I cavities were divided into six groups according to restorative material (conventional/nanohybrid; bioactive/alkasite, giomer) and carious lesion removal method [selective (incomplete) or non-selective (complete)]: selective + nanohybrid (Estelite Posterior); non-selective + nanohybrid; selective + alkasite (Cention Forte); non-selective + alkasite; selective + giomer (Beautifil II); and non-selective + giomer. Artificial demineralization of the pulpal floor was performed using acetic acid (pH 4.8) for 35 days. In the non-selective groups, demineralized dentin was removed with an excavator, whereas it was left untreated in the selective groups. DIAGNOdent Pen, micro-computed tomography (micro-CT), and microhardness measurements were used to characterize mineral changes. Restored teeth were stored in artificial saliva for 30 days. GF at the cavity floor ( n = 8) was evaluated using micro-CT. µTBS was measured using a universal testing machine at a crosshead speed of 0.5 mm/min ( n = 20). Dentin–restoration interfaces were examined by scanning electron microscopy (SEM), and elemental composition was analyzed using energy-dispersive X-ray spectroscopy (EDS) ( n = 5). Data were analyzed using two-way analysis of variance (ANOVA) with Bonferroni and Spearman’s correlations, Kruskal–Wallis, and Dunn tests ( p < 0.05). Non-selective groups showed significantly higher μTBS than selective groups. For giomer and nanohybrid materials, selective groups showed significantly higher GF than non-selective groups ( p <0.05). For alkasite, no significant differences in GF were found. In addition, no significant differences in μTBS and GF were observed among restorative materials. No significant correlation was observed for μTBS-GF ( p >0.05). In non-selective groups, SEM images showed an intact interface. In particular, a higher post-storage Ca/P ratio was detected in alkasite than in nanohybrid. Non-selective carious lesion removal did not significantly influence gap formation in alkasites. However, it was more beneficial for giomer, in which selective carious lesion removal was associated with increased gap formation. Additionally, this approach enhanced the adhesion of bioactive restorations. Bioactive restorations demonstrated comparable interfacial performance regarding all tested parameters.