Orthodontic Adhesive Incorporating ZnO Quantum-Dots for Prevention of Enamel Demineralization

Objectives: The objectives of this study were to develop a multifunctional orthodontic adhesive with fluorescence and antibacterial properties using ZnO quantum-dots (ZnO_QDs) as filler, investigate its fluorescence property, and evaluate its antibacterial activity against Streptococcus mutans as well as cytotoxicity on gingival fibroblasts.
Methods: ZnO_QDs were synthesized using the sol-gel method. XRD, SAED, HRTEM, DLS and fluorospectrophotometry were used to characterize ZnO_QDs. ZnO_QDs were incorporated into Transbond XT adhesive paste with 20%, 30%, 40% mass fraction, respectively, to form the multifunctional adhesive. Ultraviolet photography was used to confirm the fluorescence property of adhesive. Antibacterial activity was evaluated with CFU, MTT kit and Live/Dead Bacterial Staining Kit. Cytotoxicity assay was performed on gingival fibroblasts using CCK-8 kit and Live/Dead cell double staining kit.
Results: XRD indicated that ZnO_QDs had crystal texture of Wurtzite. SAED showed ZnO_QDs had good crystallinity. HRTEM showed that ZnO_QDs were spherical and the diameter is around 5mm while DLS indicated hydrate particle size around 8mm. Fluorospectrophotometry showed that optimum excitation wavelength and optimum emission wavelength of ZnO_QDs were 360mm and 550mm, respectively. Ultraviolet photography showed that adhesive mixed with ZnO_QDs glowed yellow under ultraviolet light. CFU and MTT analysis indicated that the ZnO_QDs contained adhesives all had significant antibacterial activity compared with Transbond XT adhesive paste (P< 0.05). CLSM 3D reconstruction analysis after Live/Dead staining of S. mutans biofilm suggested that ZnO_QDs contained adhesives could reduce the amount of live bacteria in biofilm. CCK-8 and Live/Dead cell double staining analysis showed that the incorporation of ZnO_QDs did not compromise the biocompatibility of original adhesive.
Conclusions: A novel multifunctional orthodontic adhesive was developed based on ZnO_QDs. A series of tests indicated that it has excellent antibacterial and anti-biofilm activities, and is able to emit yellow fluorescence under ultraviolet light without compromising its biocompatibility.