| Background:Fixed orthodontic appliances are routinely used in clinic.The risk of caries prevalence is increased by the placement of bracket.Caries initiated from demineralization and is a side effect of treatment with fixed orthodontic appliances,the rate of risk of caries prevalence is 50%abroad and 59.4%in China.This process developed in the form of white spot lesions.Therefore,the prevention of demineralization associated with intervention should be emphasized.Previous researches showed that fluoride is effective in the prevention of enamel demineralization.Objective:To improve fluoride release and preserve the properties of resin-modified glass ionomer cements(RMGICs),fluorapatite(FA) and fluorohydroxyapatite(FHA) was addded into RMGICs respectively.Methods:1.Fluorion release detection:1.1 Specimens preparation:FA and FHA were prepared by SOL-GEL method.The shape of FA and FHA was observed with Scanning electron microscope(SEM).The FA and FHA separately incorporated with RMGICs(GC Fuji ORTHO LC,Japan)at 5 %,10%,15%,20%,25%,30%proportion by weight(wt%).The pure RMGICs was the blank as control.The compounds were fabricated as cuboid(5×5×7mm) and soaked in distilled water.1.2 Ultraviolet spectrophotometry:The fluoride levels of 25wt%FA/RMGICs, 25wt%FHA/RMGICs and pure RMGICs specimens soak were analysed at 1,2,3,4, 7,14,21,28 day.The fluoride levels of other specimens soak were analysed at 1,2, 3,7 day.1.3 X-ray diffraction(XRD):The chemical compositions of 25wt%0 FA/RMGICs, 25wt%FHA/RMGICs and pure RMGICs specimens were analysed with X-ray diffractometer(X'Pert PRO,holland).2.Tensile strength detection:2.1 Specimens preparation:Forty-eight extracted caries-free human premolars were collected and the enamel of buccal/lingual surfaces was polished by sand paper (600#).Z100 resin was fabricated as cuboid(5×5×7mm).2.2 Grouping:The adhesive systems were divided into three groups:RMGICs was GC group,RMGICs+25wt%FA was GFA group,RMGICs+25wt%FHA was GFHA group.The enamel bonded to composite with experiment adhesive.Then each group was randomly divided into 2 subgroups according to the storage time(3 and 30 days). Thermal cycling(3000 cycles) was done in 30 days group.2.3 Specimens cutting:The bonding specimens were cut as oblong(1×1mm cross section) by low speed diamond saw(Buehler.USA).The cutting direction was vertical according to the bonding surface.2.4 Tensile strength test:The tensile strength of the specimens was tested by tensile strength tester(BIS-CO.USA).The results were analysed using variance analysis and T-test.2.5 SEM observations:The longitudinal section of specimens and the the fractured enamel surfaces after the bond-strength test were investigated by SEM.Results:1.Fluorion release:All of the specimens exhibited a high fluoride ion elution in the early days,decreased quickly,and then decrease became slowly.25wt%FA-added and FHA-added RMGICs had higher quantity of fluoride release than other compounds. 25wt%FA-added RMGICs also showed higher fluoride release than RMGICs and 25wt%FHA-added RMGICs.2.X-ray diffraction.The XRD results showed that FA/RMGICs and FHA/RMGICs compounds had FA and FHA chemical compositions.3.Tensile strength test:Tensile strength test at 3d GFA and GFHA showed higher bond strength compared with control(p＜0.05).At 30d GFHA showed higher bond strength compared with GFA and control(p＜0.05).To the RMGICs there was no significant difference between 3d and 30d.4.SEM observation:It is showed that the diameter of FA granules is about 10～100μm and FHA granules is about 10～50μm,smaller than RMGICs.The thickness of adhesive is about 400μm.SEM demonstrated the cohesive type of fracture in the interface of the specimens.Conclusion:In this study,the suitable level of FA and FHA was 25wt%proportion.The experimental fluoride release adhesives of FA and FHA showed comparable higher bond strength to conventional adhesive to a certain extent.The fluoride ion elution of FA-added adhesives increased.It will be potential new enamel adhesive. |
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