Effects of light direction and exposure times of plasma arc light on shear bond strength of metal brackets

Roh, Sang Jeong; Lee, Hyun Jung; Jeon, Young Mi; Kim, Jong Ghee

Abstract

The purpose of this study was to compare the effects of different light direction, exposure times and setting times when using plasma arc light on shear bond strength of metal brackets. 240 extracted human premolars were randomly assigned to one of 16 groups. Standardized brackets were bonded to enamel using different light curing units (Plasma arc light and Halogen light), exposure times (Plasma arc light 2, 4, 6 seconds and Halogen light 20 seconds), and light directions (Vertical direction [V] and Oblique direction [O]). 8 groups were tested after 5 minutes and the remaining 8 groups after 24 hours. The metal brackets were bonded with Transbond XT. Shear bond strength was measured by a universal testing machine. The results were as follows: There were no differences between the shear bond strengths of the Vertical groups (V) and Oblique groups (O), regardless of exposure times and types of light curing units (p > 0.05). The shear bond strength of the group with 2 seconds of plasma light were significantly lower than other exposure time groups (p < 0.05). The shear bond strength tested after 5 minutes was lower than after 24 hours (p < 0.05). The Adhesive Remment Index (ARI) score showed no statistically significant difference among the different groups. The results of this study suggested that the light direction of plasma arc light had no influence on the shear bond strength of metal brackets to enamel, and exposure times more than 4 seconds produced shear bond strengths similar to those produced with a conventional halogen curing light.