Effects of acid etching times on enamel surface morphology and shear bond strength of orthodontic attachment to enamel

Nahm, Dong Seok; Suhr, Cheong Hoon; Yang, Won Sik; Chang, Young II

Abstract

The porpuse of this in vito study was to evaluate the effects of different acid etching times on the enamel srface morphology, shear bond strength and debinding failure mode of orthodontic attachment. Ninety six extracted human mandibular premolars were divided into eight groups of twelve teeth. The buccal surfaces were etched with 37% phosphoric acid 5, 10, 15, 30, 45, 60, 90 and 120 seconds, respectively. Two teeth from each group were used for scanning electron mocroscope examination. On the etched buccal aurfaces of remaining teeth, orthodontic attachments(lingual buttons) were bonded with light cured orthodontic adhesive. Twenty four hours after bonding, a Instron universal testing machine was used to determine shear bond strength of orhtodontic attachment to enamel. After debonding, bases of orthodontic attachments and enamel surfaces were examined under stereoscopic microscope to determine failure mode. Statistical analysis of the data was carried out with one way ANOVA and Duncan';s multiple range test. The results were as follows : 1. There was no statistically significant difference in shear bond strengths between the various etching times(p<0.05). 2. The failure modes of orthodontic attachments had some differences. In 5, 10 and 15 seconds etching groups, the percentage of adhesive/ enamel interface failure was higher than that of adhesive/attachment interface failure. On the contrary, 30, 45, 60, 90 and 120 seconds etching groups, the recults were reersed. 3. The etching parerns of enmel surfaces had a great variation. So, we could not find any correlation between etching pattern and bond strength. 4. The findings in this study indicate that in vito reduction of the etching time to 5 seconds maintains clinically acceptable bond strength. However, further study is required to determine the cause of failure mode in 5, 10 and 15 seconds groups.