A comparison of shear bond strengths of orthodontic brackets using various light sources, light guides, and cure times

Abstract

The objective of this study was to evaluate the effects of different cure times, light sources, and light guides on shear bond strength of orthodontic brackets bonded with Transbond XT (3M Unitek, Monrovia, Calif) to bovine enamel. Specifically, the Power Slot (Reliance Orthodontic Products, Itasca, Ill) light guide was placed on 4 visible light sources to compare shear bond strengths and recommended cure times with the light guides provided with each light source. We randomly divided 240 bovine mandibular incisors into 16 groups; each group consisted of 15 teeth mounted in an acrylic block. Each group of teeth was polymerized with a specific light and light guide combination. Eight groups were sheared after 5 minutes and the remaining 8 groups after 24 hours. After bonding, all brackets were subjected to a shear force with a testing machine. Overall, there was a significant increase in bond strengths of the 24-hour groups compared with the 5-minute shearing groups. However, there were no statistical differences (P = .05) within the 24-hour test groups or the 5-minute test groups. The results of this study indicate that, compared with standard light guides, the Power Slot and the Turbo Tip (Ormco Sybron Dental Specialties, Orange, Calif) light guides can significantly reduce the curing times (10 seconds per bracket; 5 seconds each from mesial and distal) without affecting their shear bond strengths. Therefore, the Power Slot and the Turbo Tip light guides with their collimation of visible light to increase its intensity can be recommended as advantageous alternatives for curing composite resins for orthodontic bonding procedures. (Am J Orthod Dentofacial Orthop 2002;121:510-5)