Evaluation of an orthodontic adhesive containing 2 wt% nano-hydroxyapatite synthesized from a biogenic calcium precursor: antibacterial activity, calcium ion concentration, and enamel demineralization

Abstract

Objective: Enamel demineralization and white spot lesions remain common adverse effects during fixed orthodontic treatment, primarily due to plaque accumulation around brackets and the limited functionality of conventional orthodontic adhesives. This study aimed to evaluate the effect of incorporating 2 wt% nano-hydroxyapatite (nHAp), synthesized using a biogenic calcium precursor derived from Asian moon scallop (Amusium pleuronectes) shells, on antibacterial activity, calcium ion concentration, and enamel demineralization. Materials and Methods: nHAp powder was synthesized from scallop shell-derived calcium carbonate via calcination and precipitation methods and incorporated into a commercial orthodontic adhesive under controlled conditions. Antibacterial activity against Streptococcus mutans was assessed using a disc diffusion assay. Calcium ion concentration in the immersion medium was measured using UV-Vis spectrophotometry (λ = 515 nm) with a murexide indicator. Enamel demineralization adjacent to bracket interfaces was evaluated using a standardized scoring system. Statistical analysis was performed using appropriate parametric and non-parametric tests with significance set at p < 0.05. Results: The nHAp-modified adhesive showed significantly greater antibacterial activity compared with the control group (p < 0.05). The experimental group demonstrated higher calcium ion concentration in the immersion medium than the control group. Enamel demineralization scores were significantly lower in the experimental group. Conclusion: Within the limitations of this in vitro study, incorporation of 2 wt% nano-hydroxyapatite synthesized using a biogenic calcium precursor was associated with increased antibacterial activity, higher calcium ion concentration in the surrounding medium, and reduced enamel demineralization. Further studies are required to evaluate mechanical properties and clinical applicability

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