Bioactive Orthodontic Adhesive for Clear-Aligner Attachments: Antibacterial Activity, Ion Release, and Bonding Performance.
OBJECTIVE To formulate a novel dual-functional adhesive integrating dimethylaminododecyl methacrylate (DMADDM) for antibacterial activity and nano-amorphous calcium phosphate (NACP) for calcium/phosphate ion release, without compromising enamel bond strength. METHODS A low-shrinkage-stress resin of urethane dimethacrylate/triethylene glycol divinylbenzyl ether (UDMA/TEGDVBE, denoted UV) was used as the base resin. 10-methacryloyloxydecyl dihydrogen phosphate (MDP) was incorporated at 6% by weight to promote chemical bonding to enamel and stabilize the adhesive interface. DMADDM (0%, 3%, 6% by weight) and NACP (0%, 10%, 20% by weight) were incorporated. A commercial adhesive (Assure Plus) served as a control. Degree of conversion (DC), paste flowability, and enamel shear bond strength (SBS) were measured. Streptococcus mutans biofilms were analyzed for colony-forming units (CFU), lactic-acid production, and metabolic activity (MTT). Calcium and phosphate ion release were measured. Data were analyzed using ANOVA/Tukey (α = 0.05). RESULTS Experimental adhesives showed SBS (n = 12) of 15.2 MPa to 18.5 MPa, statistically similar to the control (p > 0.05). DC for the experimental formulations ranged from 48.8% to 65.2% versus 72.5% for the commercial control. Flow (n = 3) decreased with increasing NACP (p < 0.05). Adhesives containing 6% DMADDM reduced S. mutans biofilm CFU by approximately 2-log compared to the control and substantially reduced lactic acid production and metabolic activity of biofilms (p < 0.05). NACP formulations released Ca and PO₄ ions up to (1.55 ± 0.06) mmol/L and (1.0 ± 0.04) mmol/L, respectively, at 35 days and pH 4. CONCLUSION NACP formulations released Ca and PO₄ ions, demonstrating sustained ion release under acidic conditions. These in vitro findings support further investigation of bioactive adhesives for reducing biofilm-related risks around clear-aligner attachments. Direct enamel demineralization and remineralization testing is needed to evaluate their effect on white-spot lesion formation. CLINICAL SIGNIFICANCE This in vitro study developed a bioactive orthodontic adhesive for clear-aligner attachments with antibacterial activity, calcium and phosphate ion release, and bonding performance comparable to a commercial adhesive. These findings support further investigation of bioactive adhesives for reducing biofilm-related risks around clear-aligner attachments.