Bond strength performance of a self-curing bulk-fill restorative system and light-cured restorative systems after aging: an in vitro study

The microtensile bond strength (µTBS) and failure patterns of a self-curing bulk-fill restorative system (STELA, SDI) were investigated and compared with those of a light-cured bulk-fill and a conventional light-cured restorative system following short- and long-term aging in artificial saliva. Forty-eight human teeth were randomly assigned to three groups (n = 16): G1, self-curing bulk-fill restorative system; G2, light-cured bulk-fill restorative system; and G3, conventional light-cured restorative system applied incrementally. Intact restored teeth were stored in artificial saliva for either 24 h or 18 months (n = 8 per condition) and were sectioned only after completion of the respective aging period to obtain five beam-shaped specimens (≈ 0.9 mm²). The tooth was considered the experimental unit. Specimens were stored for either 24 h or 18 months (n = 8 per condition). µTBS was assessed at a crosshead speed of 1 mm/min, and failure modes were determined using stereomicroscopy, with representative samples analyzed by scanning electron microscopy. Data were subjected to two-way ANOVA and Tukey's post hoc test (α = 0.05). Bond strength was significantly influenced by both restorative system and aging time (p < 0.001). A significant interaction between restorative system and aging condition was also detected (p < 0.001). G2 exhibited the lowest µTBS values and a higher prevalence of adhesive failures. In contrast, G1 showed bond strength comparable to G3 and significantly higher than G2. Cohesive failures predominated in G1 and G3, whereas adhesive failures were more frequent in G2. Within the limitations of this in vitro study, the self-curing bulk-fill restorative system demonstrated adhesive performance similar to the conventional restorative system and preserved its relative behavior after aging, under the respective adhesive strategies recommended by the manufacturers.