A Comparison of Three Debonding Techniques Employing Two Methods of Tooth Preparation

Abstract

Traditionally, orthodontic adhesive systems consisted of three separate agents: an enamel conditioner, a primer solution, and an adhesive resin. Newer systems have combined the conditioning and priming agents into a single acidic primer solution. The purpose of this investigation is to evaluate the three debonding techniques (shear-peel, tension, torsion) using stainless steel brackets and two different methods of tooth preparation (37% phosphoric acid+ primer vs. self-etching primer). The null hypotheses of this investigation are (1) the method of tooth preparation will not have a significant effect on the bond strengths and (2) the relative shear-peel, tensile and torsional bond strengths will show consistent results. One hundred and fifty bovine incisors were randomly assigned to 6 groups of 25 specimens per group. Teeth were prepared for bonding by employing either (1) acid-etching with 37% phosphoric acid+ primer or (2) self-etching primer. The brackets were bonded with a resin composite adhesive under controlled temperature and humidity conditions at 74°F ± 2 and 54% ± 5 RH. In addition, specimens were bonded utilizing a bonding jig that held the thickness of the adhesive constant at 0.152 mm. All groups were tested to failure using the MTS Bionix machine. Results from this study showed that the prime-etching method of tooth preparation had significantly greater mean shear-peel bond strength than did the self-etch method and that the prime-etching method had significantly less mean tensile bond strength than did the self-etch method; however there were no significant differences in torque strengths between the two methods of tooth preparation. In addition, results for the true ratio of mean forces showed shear-peel bond strengths lies clearly above the confidence intervals for the other debonding measures, thus the three measures of debonding are dissimilar in the comparison of the two tooth preparation methods. Thus, both null hypotheses were rejected.