Purpose: This study investigated the effect of diamond bur grit size on the repair bond strength of fresh and
aged resin composites.
Materials and Methods: Blocks of microhybrid composite (Opallis, FGM) were stored in distilled water at 37ēC
for 24 h (fresh composite) or subjected to 5000 thermal cycles (aged composite). The surfaces were roughened
using diamond-coated, flame-shaped carbide burs with medium grit (#3168), fine grit (#3168F), or extra-fine grit
(#3168FF). The control group underwent no surface treatment. Surface roughness, water contact angle, and
surface topography by scanning electron microscopy (SEM) were evaluated (n = 3). Samples were restored with
resin composite and sectioned into beam-shaped specimens, which were subjected to microtensile bond testing.
Failure modes were classified using a stereomicroscope. Data were statistically analyzed using the Student-
Newman-Keuls test and two-way ANOVA, with significance set at p < 0.05.
Results: Higher surface roughness was observed for groups treated with the medium- and fine-grit burs; aged
composites were rougher than fresh composites. The water contact angle formed on the aged composite was
lower than that on the fresh composite. The highest repair bond strength was observed for the fine-grit bur
group, and the lowest was recorded for control. Interfacial failures were more predominant. SEM images showed
that the surfaces treated with fine- and extra-fine-grit burs had a more irregular topography.
Conclusion: Surface roughening of fresh or aged resin composites with diamond burs improved retention of the
repair material. Fine-grit burs generally performed better than medium- and extra-fine-grit burs.