A STUDY OF BOND STRENGTH BETWEEN LIGHT-CURED AND SELF-CURED ORTHODONTIC RESIN

Light-cured orthodontic composite resin has been widely advertised recently for use in bonding. However, the curability of light-cured resin when light waves are diff used through metal, ceramic, or resin brackets is doubtful and questionable. This study evaluated the effectiveness of a visible light source in curing the resin under a solid metal bracket, compared the tensile bond strength at different exposures, and analyzed the broken interface distribution between light-cured resin with various light exposure times and self-cured resin. The bond strength results revealed that the difference between light-cured resin (Transbond) with 60, 40, and 20 seconds of light exposure, respectively, and self-cured resin (Concise) was 1.05, 0.92, 0.61, and 0.71 kg/mm2 , respectively. The bond strength of Transbond with 60 and 40 seconds of light exposure was greater than both the bond strength of Transbond with 20 seconds of light exposure and the strength of the self-cured resin of Concise, with statistical significance (p < 0.01). There were also no statistical differences between Transbond with 60 and 40 seconds of light exposure or Transbond with 20 seconds of light exposure and Concise. The bond failure interfaces were located between the bracket and the resin, within the resin itself, or between the resin and the enamel. Tooth fragmentation was rarely found. There were no statistical differences (p > 0.05) among broken interfaces. This indicates that visible light is powerful in curing the visible light-activated composite resin under solid metal brackets. The bond strength of light-cured resin of Transbond, except in cases of light exposure of 20 seconds, is stronger than that of the self-cured resin of Concise. Transbond cured with 40 seconds of light exposure is therefore recommended for clinical bonding application.