| Objective:Enamel demineralization characterized as white spots exists generally among people who receive fixed orthodontics and it will be aggravated and even develop into early enamel caries with the course of treatment prolong. It was reported that the incidence of white spots is about 50-70%. Thus the prevention of enamel demineralization during orthodontic treatment has been a chief problem for orthodontists to consider. The benefits of fluoride in the inhibition of carious lesion development and enhancement of lesion remineralization are well-documented. The aim of this in vitro study was to evaluate the effect of three fluoride-releasing adhesive systems on the bond strength of orthodontic brackets and the acid resistance of enamel, thus to provide better methods to guide the clinical practices.Method:By 10 times magnifier, we chose 96 premolars extracted because of orthodontic treatment (aged 12-16 years old, on average 14 years). The teeth surface were perfect without cracks, caries and any chemical processing, tetracycline pigmentation teeth and dental fluorosis were refused. The 96 premolars were randomly divided into 4 groups of 24 specimens. Group 1: spreading 37% phosphoric acid evenly on the central area of tooth surface for 30 seconds, rising and drying, then bonding brackets with JINGJIN composite resin according to instructions; Group 2: spreading 1.23%APF on enamel for 4 minutes, rising and drying, then spreading 37% phosphoric acid for 30 seconds, rising and drying, bonding brackets with JINGJIN composite resin; Group 3: spreading 37% phosphoric acid for 30 seconds, rising and drying, then spreading fluoride protector on enamel for 1 minutes, bonding brackets with JINGJIN composite resin; Group4: cleaning and drying teeth surface, then spreading SEP on enamel for 15 seconds, lightly drying, illuminating for 10 seconds, bonding brackets with resin-modified glass ionomer cements. RMGIC were mixed on demand powder liquid ratio according to the operating instructions, illuminated for 40 seconds. After bonding, each specimen was immersed individually in a test tube that has 5ml acid artificial saliva for thermo-cycling test: 5℃30 seconds,55℃30 seconds, for 1000 times. Then all specimens were bathed with 37℃water. After 1 week,2 weeks,3 weeks, 4 weeks, every time,6 specimens were randomly selected to determine the shear bond strength, the ARI score,and the consistence of Ca2+. Choose four perfect premolars (with standard experimental), conditioned according to the four different treatments above, then coated with gold in an ion coating device, and the specimens'configuration were examined microscopically with the scanning electron microscope.Results:1 There were not significant differences among the group2,3,4 in shear bond strength. Although significantly lower than traditional acid-etching and bonding technique(P<0.05), they can provide adequate shear bond strengths for bracket bonding, which already meet the clinical need. And there were not significant differences during 4 weeks in shear bond strength in each group(P>0.05).2 When bonding with three fluoride-releasing adhesive systems, the bonding failure sites occur in the surface between adhesive and enamel, only a small amount of adhesive left on enamel. This is advantageous to prevent enamel breaking during the course of debonding.3 There were statistically significant differences among the three fluoride-releasing adhesive systems in the consistence of Ca2+(P<0.05). Group 3 and group 4 can effectively prevent demineralization and increase the acid resistance of enamel.4 In the scanning electron microscope, the enamel treated by 37% phosphoric on group 1 was homogeneous, dense, detailed. On group 2, 1.23%APF created nearly no etched pattern, while fluoride protector created moderate etched pattern and some depositions on the surface of enamel on group 3. On group 4, the enamel surface was uneven, rarefaction.Conclusion:The use of fluoride protector after etching and SEP in combination with RMGIC are two effective adhesive systems, which can not only provide adequate shear bond strengths for bracket bonding, but also increase the acid resistance of enamel. For confused oral physiological property, they still need long laboratory and clinical studies.
|
PDF Full Text Request