White spot lesions are common complications around orthodontic brackets, caused by Streptococcus mutans . The main aim of this study was to evaluate the antimicrobial properties of orthodontic light-cured resin-modified glass ionomer cement (RMGIC) containing silibinin against S.   mutans biofilm. Secondary objectives included assessing the physicomechanical properties (such as shear bond strength and fluoride release) and the cytotoxicity of the modified RMGIC.

The liquid component of the RMGIC was combined with varying concentrations of silibinin (0%, 1%, 2%, and 5%). The antimicrobial effect was assessed using the biofilm inhibition test, measuring colony-forming units (CFU)/mL. Shear bond strength (SBS) was determined using a universal testing machine, while adhesive remnant index (ARI) scores were evaluated under a stereomicroscope. Fluoride release was measured at 1, 7, 15, and 30 days using the pH/ion meter. Cytotoxicity was assessed using an indirect MTT assay on human gingival fibroblast (HGF) cells.

The lowest bacterial colony count was observed in the chlorhexidine group (2.50 ± 1.60 × 10 ⁵  CFU/mL; CI:95%), followed by the RMGIC containing 5% silibinin (2.87 ± 5.11 × 10 ⁶  CFU/mL; CI:95%). Although the addition of silibinin at different concentrations reduced the SBS in a dose-dependent manner, there were no significant differences between the SBS of composite resin – the gold standard adhesive for bracket bonding – and that of RMGIC containing silibinin at any concentration ( P = 0.70). The most common ARI scores in all groups were 1 and 2, and cohesive failure was the predominant mode of failure. The incorporation of silibinin into RMGIC did not alter the fluoride release pattern, and none of the silibinin concentrations exhibited cytotoxic effects on HGF cells.

RMGIC containing 5% silibinin effectively reduced S.   mutans biofilm around orthodontic brackets without adversely affecting its physical-mechanical properties and showed no toxicity to HGF cells.