| Desired orthodontic forces were ranged from 0. 49 Newton (50g) to 1. 96 Newton ( 200g ) . The adhesion between dental enamel surfaces and orthodontic brackets was a basic requirement for any fixed orthodontic treatment. Owing to the adhesion, it is possible to get the desired tooth movements in the three dimensions by orthodontic force. This adhesion system was composed of the dental enamel, bonding agent and the mesh of the bracket. Any change in these three parts will result in a different bonding strength which is an important part of adhesive property. Usually the composite resin was used as bonding agent because of the available bonding strength of it between brackets and dental enamel. It is discovered, however, recently that the composite resin have a tendency of degradation in the oral environment which is an important reason for bonding strength decrease. Enamel adhesive surface morphology reflects the biological degrade directly. Therefore, there was an increasing concern on the enamel surfaces changes and bonding strength changes during orthodontic treatment.Objective: The purpose of this study is to observe different in-vivo enamel adhesive interface morphology during orthodontic treatment and its relationship to the in-vivo shear bonding strength which is an important part of the biological degradability of bonding agent.Methods: A total of 296 first premolars (74 patients) designing to be extracted were chosen, which came from orthodontic department of the stomatological school of Wu Han university. Including criteria: teeth planed to be extracted for the orthodontic treatment, which can be extracted at the different time during treatment. Excluding criteria: teeth with buccal enamel defect, teeth with buccal caries, teeth which can not be extracted at the planed time with any reason. The patients were between 11 and 14 years old, and the average age is 12. 36 years old. The same clinician bonded all the teeth following the manufactures' instructions. The enamel surface of the teeth were pumiced with pumice and rinsed with copious amounts of water. They were dried with compressed air, and acid-etched with 37% phosphoric acid liquid for 60 seconds and then washed and dried. A coat of 3M Unitek primer-adhesive was applied to the enamel surface. Then 3M Unitek MBT Versatile brackets, precoated with Concise chemical cure composite resin, were placed on the buccal surfaces of the teeth. Appropriate pressure was used to completely seat the bracket on the tooth, expelling excess resin from around the bracket base. The teeth were extracted by the same clinician after keeping in the oral circumstance for certain times. 276 teeth were acquired, including 20 teeth of no- disposal group (A) , 20 teeth of pumice group (B) , 20 teeth of etching after pumice group (C) , 20 teeth of etching without pumice group(D), 20 teeth of primer group(EK 42 teeth of adhesion 1 month group(F), 40 teeth of adhesion 3 month group(G), 39 teeth of adhesion 6 month group (H), 38 teeth of adhesion 9 month group (I), 17 teeth of debonding bracket group (J). After preparation, the teeth werescanned by the SEM. And the brackets of the F, G, H, I groups were debonded with an ceramic Test machine. Then the enamel surfaces was examined by the stereomicroscope.Results: Under SEM , we found that there were many cocci and molecules on the teeth surfaces of A group, regular hexagon heaves on the teeth surfaces of the B group, regular honeycomb-like image on the teeth surfaces of the C group, irregular honeycomb-like image on the teeth surfaces of the D group. And between F, G, H, I groups, the longer the brackets kept in the oral environment, the less adhesive residua retained on the teeth surfaces after debonding brackets and composite resin . The difference between each group was significant at a=0. 05 And the teeth surfaces of the I group were almost smooth after pumiced. We also found the shear bond strength of the F, G, H, I groups declined with the time prolong. The consequent LSD test showed the difference between E group and F... |
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