| Objective:The aim of this study was to evaluate metal brackets after re-bonding before the heat treatment after the bottom bracket of the tensile strength. Modern fixed appliance technology is the direct bonding brackets technology. For a variety of man-made and natural factors led to the failure of the bond Bracket, It is clinicians often encounter problems. Whether The shedding Brackets can be used of once more, what kind of Processing method was required before the brackets were re cycled and whether its bond strength will be affected, it is orthodontic clinic physicians are very concerned about the issue.Materials and Methods:To select 36 human premolarls which extracted for orthodontic reason, All of them was preserved in 1% chloramine solution at 4℃. The brackets were edgewise resin made in China with a cross section 0.022×0.028 inches and with a base area 11.78 mm2, trenches to. Experimental group: isolated teeth were randomly divided into three groups, each 12, respectively for the new bracket group (group A), after heat treatment of ultrasonic cleaning group (group B), heat treatment after ultrasonic cleaning Group (C). A group etch 30 seconds with 37% of the phosphoric acid later, washing, drying tooth surface. The use of enamel adhesive will make brackets in place on the tooth surface, to pressure, to curette redundant adhesive with probe and wait to solidify . Group B, Group C the shedding Brackets after bonding , using liquefied petroleum gas lighters heat treatment, processing temperature of 700-800℃on the bottom of brackets about 20 seconds, after adhesive was burned with completely carbonized, to remove the adhesive carbonized with probe. Group B will be treated the brackets after heat treatment washing, drying after repeated Group A bonding process. Group C after heat treatment on the bracket for ultrasonic cleaning five minutes then dried. and repeated group A bonding process. Bonding after 10 minutes, the tested teeth will be placed in 37℃constant temperature water to preserve for 24 hours. After drying out. Then the brackets will be texted with universal testing machine about tensile bond strength . After heat treatment to remove slot groove binder carbonization brackets, heat treatment after ultrasonic cleaning of the brackets and the new brackets, electron microscopy of Chatuo slot chassis trenches surface of the contrast. This study 1: different approach Bracket floor trenches structure of the surface. Study 2: different ways to deal with shedding Bracket Bracket tensile strength of the impact. By comparing two kinds of treatment tensile strength of the brackets, as well as the impact of new brackets and brackets after heat treatment of the electron microscope observation to guide clinical operations.Results:1 Brackets of the three groups observed by SEM Scanning Electron Microscope floor trenches surface structure, the new brackets floor trenches surface was of the convex and concave,was uneven, very rough. The bracket after heat treatment withoutt ultrasonic cleaning ,its floor trenches surface structure , may see some surface damage and some impurities. the surface there are obviously Scratch ,more rough.The bracket of Heat treatment after ultrasonic cleaning ,its floor trenches surface structure is similar to the bracket after heat treatment without ultrasonic cleaning ,the same obvious scratches, and a rough surface, but no impurities.2 Tensile bond strength of the three brackets there was no significant difference (P> 0.05). The tensile strength of Brackets of new group average 10.5108 MPa, the tensile strength of heat-treated group without ultrasonic cleaning average 9.0575 MPa , the tensile strength of heat treatment after ultrasonic cleaning group average of 9.7950 MPa.the average tensile strength ofGroup of new brackets is maximum among the three. Next followed by heat treatment after ultrasonic cleaning group, after heat treatment without ultrasonic cleaning group.3 ARI score. To observate with a 10 times magnifying glass the remaining adhesive of enamel surface, converted to the ARI score.A score of 1 indicates:no adhesive is left on the tooth, a score of 2 indicates: 0% < amount of residue≤25%; a score of 3 indicates: 25% < amount of residue≤50%; a score of 4 indicates: 50%< amount of residue≤75%; a score of 5 indicates: 75% < amount of residue <100%; a score of 6 indicates:all the adhesive is left on the tooth, that is 100%. the result of observation showed that there was no significant difference (P> 0.05) about ARI scores, mutual comparison have no significant difference also.Conclusion: The tensile strength of shedding metal brackets after heat treatment is more than the minimum tensile bond strength of orthodontic clinical requirements which is the 6 kPa. The bracket of heat treatment have the same adhesive strength that can be achieved clinical requirements. Whether the brackets after ultrasonic cleaning or without ultrasonic cleaning can be able to achieve a satisfactory bonding strength.The result can be used to guide clinical.
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