• Puntip Dongpaiboon D.D.S.
• Paiboon Techalertpaisarn D.D.S., Ph.D., Diplomate, Thai Board of Orthodontics
• Namchok Promsopa
• Sarik Kananurak

Objective To evaluate the effect of using 3 light curing units with different light intensity on initial
shear bond strength of orthodontic adhesives.

Materials and methods Sixty human upper premolars were divided into 4 groups of 15 each.
Tooth surfaces were treated with pumice and phosphoric acid, then rinsed and blown dry. Brackets
were bonded to tooth surfaces with light cured adhesive under 4 conditions; Group 1 a conventional
halogen unit (Demetron LC^TM) at an intensity of 410 mW/cm² for 20 seconds (control), Group 2 LED
unit (Demetron A.2^TM) at an intensity of 1,140 mW/cm² for 20 seconds, Group 3 LED unit as group
2 for 6 seconds and Group 4 LED unit (Valo) at an intensity of 2,230 mW/cm² for 6 seconds. Shear
bond strength of the specimens were tested after light activation for 4 minutes. The means of bond
strength among groups were compared, using ANOVA. The adhesive remnant index in each group
were measured and tested by the Chi-square at 95% confidence.

Results Means shear bond strength and standard deviation of groups 1, 2, 3 and 4 were 4.76 ± 0.99,
5.35 ± 1.47, 3.98 ± 1.07 and 5.69 ± 1.11 MPa, respectively. Those of group 2 and 4 were more than those
of group 3 significantly. No statistically significant differences were found between the ARI scores
among groups.

Conclusion The shear bond strength of LED light-curing unit with high intensity 2,230 mW/cm²
(Valo) for 6 seconds was not significantly different from that obtained when the bracket were cured
with the conventional halogen-based light-curing unit (Demetron LC^TM) at an intensity of 410 mW/
cm² for 20 seconds and a commercial LED unit (Demetron A.2^TM) at an intensity of 1,140 mW/cm²
for 20 seconds.

(CU Dent J. 2014;37:149-60)