Evaluation of a multifunctional orthodontic adhesive incorporating zinc oxide quantum dots

The objective of this study was to further evaluate the long-term antibiofilm and fluorescence properties as well as enamel demineralization prevention ability, removal efficiency, and biocompatibility of an orthodontic adhesive modified with zinc oxide quantum dots (ZnQDs).

ZnQDs were synthesized and characterized by transmission electron microscope and fluorescence observation. Minimal inhibitory concentration and minimum bactericidal concentration of ZnQDs against Streptococcus mutans were evaluated. ZnQDs (20% by weight) were incorporated into Transbond XT adhesive paste to form the multifunctional orthodontic adhesive (quantum dots adhesive 20 [QDA20]). Long-term antibiofilm capability and fluorescence properties were evaluated after saliva storage aging. A biofilm demineralization model was constructed, and the enamel demineralization degree was evaluated by color analysis, Raman analysis and microcomputed tomography. Bracket bonding and debonding procedures were performed on a head simulator, and the effectiveness of adhesive removal was assessed. Subcutaneous tissue, blood, and organ compatibility assays were performed on a rat subcutaneous tissue implant model.

ZnQDs had a diameter of approximately 5 nm, and the minimal inhibitory concentration and minimum bactericidal concentration against S mutans were 0.32 and 1.25 mg/mL. ZnQDs showed long-lasting antibiofilm and fluorescent properties and could reduce the color change and mineral loss of enamel during the biofilm demineralization process. On the head simulator, QDA20 could help the operator remove adhesive more thoroughly without damaging enamel. Histologic analysis of subcutaneous tissue and organs, and blood analysis proved that QDA20 was well-biocompatible.

ZnQDs showed excellent antibiofilm and fluorescent properties and thus could be a multifunctional adhesive to overcome the 2 major challenges of enamel demineralization and difficulty in recognizing adhesives during fixed orthodontic treatment.