| Fixed orthodontic treatment is an effective way to cure malocclusion. However, demineralization of the enamel bonded with brackets duing fixed orthodontic treatment occurs rapidly because of the high and continuous challenge of plaque when associated with orthodontic appliances,etching,toothbrushing careless. Patients'teeth esthetics and health are effected by white lesions or caries resulted from demineralization. Therefore, all orthodontists must think about how to inhibit the demineralization of the enamel bonded with brackets during fixed orthodontic treatment.In this study, we try to inhibit the demineralization by surface sealing with flowable composite resin. The efficiency and feasibility were investigated by premolars in vitro. The study composed of three experiments as following:Experiment 1 is to investigate the effect of surface sealing on the shear bond strength of the brackets. Twenty extracted premolars were chosen for the study. They were modeled into required shape, embedded by poly(methyl methyacrylase) (PMMA) and etched by TransbondTM Plus self-etching primer. Then they were divided into two groups of 10 teeth pieces each randomly.①experimental group, the buccal surface of the enamel was sealed with Filtek Flow 1400A3 flowable composite resin before bracket bonding;②control group, the bracket was bonded to the buccal surface of the enamel directly. The test for the shear bond strength (SBS) was done after thermostat water bathing and thermocycling. Then the resin remnant index (RRI) on the tooth surface after debonding was investigated. Results: The SBS in the experimental group and the control group was 8.08±1.38MPa,8.34±1.37MPa respectively, whereas the RRI was 2.80±1.03,3.20±1.03 respectively. The SBS and RRI between experimental group and control group revealed no statistically significant differences. Conclusion: Surface sealing dosen't decrease the SBS of brackets bonded to enamel. It is suggested that SBS is enough for orthodontic treatment. The debonding of bracket is not effected by the surface sealing.Experiment 2 is to study the wear resistance of surface sealing. Nineteen extracted premolars were chosen for the study. They were divided into four groups randomly: undemineralizing group , self-etching group, direct demineralizing group, demineralizing after surface sealing group. The teeth in the later two groups were demineralized by 0.1M lactic acid gelatin (LAG) for 48h after thermostat water bathing and thermocycling. It is to imitate the demineralization of enamel bonded with brackets by dental plaque and debris. The microstructure of the buccal surface of enamel and the change of the sealing layer were observed through scanning electron microscope (SEM) after the toothbrush wear testing 31,000 times. Results: After wearing, the"pit-shape" structure of the enamel prisms hexagon was fuzzy, the brush mark couldn't be seen in the undemineralizing group. The dispersed"honeycomb-shape"pore was seen, pore diameter was about 0.11.3μm, brush mark was deeper, enamel prisms hexagon and sheath was clear in the self-etching group. The"pebble-shape"structure of the enamel prisms hexagon was clear, brush mark of the buccal surface of the teeth was deeper and the widest enamel prisms gap was 2.17μm in the direct demineralizing group. In the demineralizing after surface sealing group, filler was more prominent and brush mark was shallow on the surface of the flowable composite resin, some bigger filler fell off and the"arc-pit-shape"structure was easily seen. But the layer of surface sealing with flowable composite resin was still on the buccal surface of the sealed teeth. The thickness of the layer of the flowable composite resin was 171.70±7.90μm,137.00±2.16μm between before and after wear. The average wear quantity was 34.70±5.74μm. After the paired samples T test, the thickness of the layer of the flowable composite resin between before and after wear revealed statistically significant differences. Conclusion: Demineralization decreases the wear resistance of the enamel bonded with brackets. Some flowable composite resin was removed after wear, but the layer of surface sealing with flowable composite resin was still on the buccal surface of the sealed teeth to improve the wear resistance of the enamel bonded with brackets.Experiment 3 is to study the inhibiting demineralization of enamel by surface sealing. Nine extracted premolars were chosen for the study. They were divided into three groups of 3 teeth each randomly: undemineralizing group, direct demineralizing group, demineralizing after surface sealing group. In the later two groups, the teeth were demineralized by 0.1M LAG for 48h after thermostat water bathing and thermocycling. Then, the teeth in the three groups were cut into teeth pieces about 4.0mm×3.0mm×2.5mm and 3.0mm×2.0mm×3.0mm to make the surface and the section plane observation respectively by SEM. Results: Surface observation:The surface of enamel was smooth in the undemineralizing group. There were much regular pore as"fries circle"on the surface of the enamel, diameter of pore about 0.21.4μm in the direct demineralizing group. The layer of surface sealing with flowable composite resin was still on the buccal surface of the enamel in the demineralizing after surface sealing group. The section plane observation:No pore could be seen in the undemineralizing group. There was little pore in the demineralizing after surface sealing group. However, there was much bigger regular pore in the direct demineralizing group, average width about 4.05.0μm,average depth about 14.016.0μm. Conclusion: Surface sealing can isolate the enamel bonded with bracket from acid environment and inhibit it demineralization.As above statement, the surface sealing with flowable composite resin doesn't effect the SBS of the brackets. It can improve the wear resistance of the surface of the enamel bonded with brackets. It can resist wear and inhibit demineralization of the enamel bonded with brackets during fixed orthodontic treatment about two years. |
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