The Study Of Rebonded Orthodontic Breackets On Shear Bond Strength

Prior to the introduction of the acid-etach, bands were the only means of attaching a bracket to a tooth, which was uncomfortable and inconvenient. With the development of modern bonding techniques, directly bonded attachments became popular. More recently, more and more advanced orthodontic adhesives have increased the bond strength. However, the brackets will be dislodged regardless of modern adhesives, patients'caution and doctors'operation. The orthodontic result can be affected by the dislodged bracket, so the bracket must be rebounded. Then, compared to the first bonding sequence, does the bond strength of the rebounded bracket decrease? And is the bond strength of the rebounded bracket clinically acceptable? At the third bonding sequence, whether the bond strength between the bracket and the tooth is strong enough? And then, what kind of treatment methods to remove residual adhesives from the base mesh is better for increasing the bond strength and protecting enamel surface? At present, there were few reports about the bond strength of the rebounded bracket. Objective:Our study used the method of the completely randomized controlled studying in the environment of artificial mouth to compare the shear bond strength(SBS) of bonded and rebonded orthodontic brackets and the influence of rebonded orthodontic brackets using different treatment methods on SBS, to report the adhesive remnant indexes(ARI) and to observe the ultrastructure of the bonding interface.Methods:60 extracted premolars for orthodontic reason were randomly divided into three groups of 20 teeth, the brackets were debonded with conventional techniques after the removal of residual adhesives from the base mesh using three different treatments. In groupⅠ, residual adhesives removed from turhe base mesh with fire at the second and third debonding sequence of the bracket. In groupⅡ, residual adhesive remnant polished at the second and third debonding sequence, In groupⅢ, rebonded a new bracket at the second and third debonding sequence, the SBS of three group were tested and their ARI were measured and compared were reported . The ultrastructure of the bonding interface was observed by scanning electron microscope(SEM). The data were dealt with by statistical methods. The results were discussed .ResultIn the aspect of shear bond strength,the SBS of three groups at the first bonding sequence were 10.00±2.95Mpa, 9.57±2.45Mpa and 9.09±2.58Mpa respectively(P>0.05). In groupⅠ, the SBS at the second, third debonding sequence were 7.30±2.15MPa and 7.14±1.93Mpa, and compared at the first bonding sequence dropped by 27% and 28.6% respectively(P<0.05). But the SBS at the second, third debonding sequence is clinically acceptable. In groupⅡ, the SBS at the second, third debonding sequence were 12.13±2.93MPa and 12.86±3.08Mpa, and were higher than the SBS at the first bonding sequence by 26.7% and 34.3% respectively(P<0.05). In groupⅢ, the SBS at the second, third debonding sequence were 9.55±2.84MPa and 10.32±2.59Mpa. Compared to the SBS at the first bonding sequence, the results showed no significant differences(P>0.05). In three groups, there was no significant difference in the SBS between the second and the third debonding sequence(P>0.05).In the aspect of ARI,In groupⅠ, the ARI scores at the first, second and third debonding sequence were 12 , 20 and 20 respectively. The ARI scores at the second, third debonding sequence were significantly higher than that at the first bonding sequence(P<0.05). In groupⅡ, the ARI scores at the first, second and third debonding sequence were 13, 19 and 18 respectively. The ARI scores at the second, third debonding sequence were significantly higher than that at the first bonding sequence(P<0.05). In groupⅢ, the ARI scores at the first, second and third debonding sequence were 15 , 16 and 17 respectively. Statistically significant differences among three debonding sequence were not observed(P>0.05).In the aspect of the ultrastructure of the bonding interface,In groupⅠ,Ⅲand at the first bonding sequence, the bracket-adhesive interface showed a high degree of consistency. In groupⅡ, the pictures of SEM showed that the ultrastructure of the base mesh of the brackets was granular, and the adhesives at the second debonding sequence were tightly integrated into those at the first bonding sequence. In three groups, the adhesives were tightly integrated into the enamel surface. At the first bonding sequence, the enamel-adhesive interface was smooth, and the convexity structure was similar, about less than 40 microns. While the enamal-adhesive interface was granular and rough at the second debonding sequence, and the convex structure was obvious, about 120 microns.ConclusionThe dislodged orthodontic brackets can be rebonded repeatedly. In groupⅠ, the SBS at the second, third debonding sequence decreased, which is clinically acceptable. While the SBS at the second, third debonding sequence increased. Therefore, the optimal procedure for rebonding dislodged orthodontic brackets is to polish residual adhesives from the base mesh rather than remove residual adhesives with fire.