Effect of pulse vs continuous micro-xenon irradiation on the shear bond strength of a light-cured orthodontic composite resin

The aim of the study was to evaluate the effect of pulse vs. continuous irradiation on the shear bond strength of a conventional orthodontic composite resin cured with a microxenon light (Aurys, Degre` K, Schiltigheim, France). Ninety freshly extracted bovine permanent mandibular incisors were randomly assigned to one of six groups; each group consisting of 15 specimens. Three groups were exposed to continuous irradiation of micro-xenon light for 10, 5, and 2 s, respectively, and used as controls. The remaining three groups were exposed to pulse irradiation of the same light source for 10, 5, and 2 s, respectively. After 24 h, all samples were tested in a shear mode on an Instron Machine (Instron Corp., Canton, MA, USA). Analysis was made by ANOVA with Scheffe´ ’s test for comparisons. The chi-square test was used to determine significant differences in the Adhesive Remnant Index scores. The mean shear bond strength of the brackets continuously cured for 10 s was not statistically different from that of the brackets pulse-activated for the same curing time. Also, no statistically significant differences were found between both groups cured for 5 s. The group pulse-activated for 5 s, however, had a significantly lower mean shear bond strength than the control group cured for 10 s. Finally, the group pulse-activated for 2 s showed significantly lower bond strength values than all the other groups tested. Compared with continuous light curing, the micro-xenon pulse activation provides similar shear bond strength values, except when used for only 2 s; but despite lower performance characteristics, the shear bond strength may be clinically acceptable.