Comparison of shear bond strength of orthodontic brackets bonded with light emitting diode (LED)

Light-emitting diode (LED) light curing units (LCU) have recently been used to polymerize resin-based orthodontic adhesives and preliminary studies indicate their use has been successful. The objectives of this study were to evaluate the shear bond strength (SBS) oforthodontic brackets bonded to enamel with a LED LCU (LEDMAX 4, Hilux, Kulzer comp.) at 10, 20 and 40 seconds and comparing them with that of 40 seconds light exposure from a conventional halogen-based LCU (Hilux unit, Heraeus Kulzer comp.). Also to assess the amount of adhesive remaining on the tooth after debonding using Adhesive Remnant Index (ARI). 120 extracted human premolars were divided into 4 groups of 30 each. After photo polymerization, all the samples were stored in distilled water at 37 degrees C for 24 hours and then subjected to a shear force with universal testing machine until bracket failure. All the recordings were evaluated statistically ANOVA and Turkey tests revealed that, no statistically significant differences were found among the shear bond strengths of 40 sec halogen (10.15 +/- 1.55), 20 sec LED (9.58 +/- 1.71) and 40 sec LED (10.34 +/- 1.83) cured groups; but the bond strength of 10 sec cure LED group (7.56 +/- 1.47) showed significantly lower than the other groups. Chi-square comparisons indicated that there were no significant differences in the ARI scores between the 4 groups tested. The results of this study are promising for orthodontic application of LED curing units in clinics, but further in vivo trials should be performed before validation.