Polymerization with the argon laser: Curing time and shear bond strength

The objective of this study was to determine the efficiency of an argon las er in polymerizing a tight-cured orthodontic adhesive. Metal brackets were bonded to 185 premolars, divided into 5 different protocol groups of 37 eac h as follows: light 40-second buccal, light 10-second lingual, laser 5-seco nd lingual, laser 10-second lingual, and laser 15-second lingual. All bonde d specimens were placed in distilled water for 30 days at 37 degrees C foll owed by thermal cycling for 24 hours. Brackets were detached using a shear- peel load delivered by an Instron machine. The site of bond failure was exa mined under 10X magnification. The difference in the shear-peel bond streng th between the light -10-second buccal (13.31 MPa) and the light 40-second lingual (11.95 MPa) groups was not statistically significant. The mean shea r-peel bond strengths for the laser cured groups were quite similar for the 5-, 10- and 15-second laser groups (10.86, 11.32, and 10.80 MPa). The diff erence in mean lingual bond strength between the light 40-second and laser 5-second groups was not statistically significant (t = 1.26; P =,212). The adhesive remnant index analysis revealed principally cohesive bond failures . An increased frequency of enamel fractures at debond was noted in the lin gual light-cured and 10-second laser-cured groups, at 35.1% (13/37) and 21. 6% (8/ 37), respectively. All other groups displayed enamel fractures of 16 .2% (6/37), A 5-second cure using an argon laser produced bond failure load s comparable to those obtained after 40 seconds of conventional light cure, with less than half the frequency of enamel fracture at debond.