Effect of various methods of Enamel Re-preparation on shear bond strength of orthodontic brackets after debonding

Abstract

Achieving desirable bond strength in orthodontics is a fundamental subject; because bracket replacement is time-consuming and costly, but bond failures happen anyway. Bond or rebond strength determinants are factors such as : enamel preperation or re-preparation methods, utilizing new or debonded brackets and the type of the adhesive used. Aim: The aim of this study was to evaluate the effect of various methods of enamel re-preparation on the shear bond strength of orthodontic brackets after debonding. Methods and Material: Fifty four sound bovine lower incisors were embedded in an acrylic resin on a mounting jig, where the toothEs facial surface was oriented in a way that it was perpendicular to the floor of the jig. The samples were then divided into 4 groups. Then the brackets were bonded by conventional acid etch method. Subsequently, Universal Testing Machine was applied for debonding and measuring of shear bond strength. Bracket rebonding repeatedly was done after enamel re-preparation by means of E?tungsten carbide bur (TCB) + acid etch , E?sandblast (san.) + acid etching , E?Er,Cr:YSGG laser alone and E?Er, Cr:YSGG laser + acid etching methods in the first, second, third and forth groups, respectively for a total of four times. Incubation and shear bond testing repeated each time. Also, there was an evaluation of Adhesive Remnant Index (ARI) under a stereomicroscope for each specimen at each debonding. 6 extra samples from different groups were deemed to undergo SEM studies. GLM Repeated measure tests were used for within group and nonparametric Kruskal Wallis test for between group comparisons. Results: Analytic statistical tests showed significant differences only between the laser only group and other groups at the second, third and forth bonding sequences (P<0.001). They also depicted significant linear increase in shear bond strength from the first to the forth bonding sequences in the E?TCB + acid etching , E?san. + acid etching and E?Er,Cr:YSGG laser + acid etching groups (P=0.026, P=0.034 and P=0.015, respectively). Significant bond strength value decrease in E?Er,Cr:YSGG laser alone group was also documented (P<0.001). maximum percentage 0 score of ARI was recorded for the third group from the second to the last sequence of debonding. SEM illustration showed the finest and coarsest surface pattern for the TCB + acid etching and laser + acid etching groups, respectively. Conclusions: All study groups showed significantly greater amounts of shear rebond strength values in multiple repeated bonding sequences with the exception of the laser only group which showed a very significant decrease. There were no dereferences between groups from the shear rebond strength point of view, again except for the laser only group which showed significantly smaller rebond strength values as compared to all other groups.