| Fixed orthodontic treatment has become the most effective and widely used method in the treatment of malocclusion. However, oral environment has been changed, and the difficulty of brushing teeth was increasing after bonding the fixed appliance. Meanwhile,the reasons that the acid act on the tooth surface during the treatment, and patients pay less attention to oral hygiene leading to the high incidence of the enamel demineralization during the bonding process in orthodontic treatment. Demineralization leading to white spot lesions or cavities, which have a great influence on the patient's dental health, appearance and their satisfaction. Therefore, how to prevent enamel demineralization during bonding process in orthodontic treatment becomes a great issue for orthodontist.FQ light-cured fluoride varnishes for preventing dental caries is a kind of homemade light-cured methacrylate resin by School of Stomatology, Fourth Military Medical University which possesses the advantages, such as good fluidity before curing, availability of thin coating, colorless after curing and having no significant effect on the appearance of tooth surface. In this study, we sealed the isolated teeth surface bonding to brackets in vitro by FQ light-cured fluoride varnishes for preventing dental caries. Dental aesthetics, anti-demineralization performance, and the adhesive strength of orthodontic brackets and the coating thickness and abrasion resistance and many other indicators were measured. It is assumed that the applicable and feasible way to prevent surface demineralization by FQ light-cured fluoride varnishes for preventing dental caries.Experiment 1: The observation of in vitro teeth with FQ light-cured fluoride varnishes for preventing dental caries and thickness measurement. After cleaning the in vitro teeth, surface morphology were observed before and after coating was observed under natural light, and comparative analysis on surface appearance and morphology were made after applying FQ light-cured fluoride varnishes for preventing dental caries. The thickness measurement of layer was taken after the scanning of in vitro teeth and analysis by software. Conclusion: colorless and transparent coating layer into the hidden layer on the surface of the teeth had no effect on morphological appearance, and thin layer can evenly distributed in the tooth surface.Experiment 2: Study on FQ sealing method to prevent enamel demineralization. The six premolars in vitro were randomly divided into control and experimental group. Experimental group was placed in 0.1M / L lactic acid gel demineralization before sealing by FQ for 48 hours under hot and cold cycles of constant temperature, and slices were scanned by electron microscopy. Results: The surface sealed layer which protect the dentin remains exist after applying FQ in lactic acid demineralization procedure.On contrary, control group without applying FQ has phenomenon of enamel demineralization.Experiment 3: Study on shear bond strength of enamel surface by applying FQ. To 20 in vitro premolars which were randomly divided into 2 groups (each group 10) were made into slices, and then embedded by self-curing resin. Control group was bonding with conventional clinical means; the experimental group was bonding before sealing by FQ, and shear bond strength of slices were utilized under hot and cold cycles of constant temperature. Results: The experimental group and control group have no significant differences in shear bond strength.Experiment 4: Study on wear resistance of enamel by applying FQ. Twenty premolars were randomly divided into 2 groups after regular cleaning. The experimental group was applied by FQ. The groups were placed in brush wear testing machine for 31000 times, and then scanned by electron microscope. Results: The anti-abrasion characteristic of FQ can meet the clinical requirements.Experiment 5: The evaluation of biological safety of FQ. Materials were made into light-cured round pieces by the requirements, in accordance with the GB/T16886.5-2003 "Biological Evaluation of Medical Devices": The in vitro cytotoxicity test was performed. Results: FQ paint curing dental has no cytotoxicity.In summary, FQ is a new aesthetic dental sealing material, and it possesses the advantage such as convenience for clinical work and no need for cooperation of patient. It can fully meet the clinical need of orthodontic work.
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