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In vivo and in vitro study of the shear bond strength of brackets bonded to enamel using halogen or LED light.

AIM
To evaluate the shear bond strength in vivo and in vitro of metallic brackets bonded to human teeth with light-curing bonding material, using two types of light-curing units.


METHODS
Sixty human premolars were divided into six groups. In the GI and GII groups, the brackets were directly bonded to volunteers' maxillary and mandibular second premolars on the right and left sides, respectively, of their mouths. In the other groups, the brackets were bonded to extracted first premolars. The polymerization was performed in GI, GIII, and GV with an LED (light-emitting diode) device, while in GII, GIV, and GVI, a halogen light was used. In GI and GII, shear strength tests were conducted using a portable digital dynamometer placed directly in the patients' mouths. The teeth from GIII, GIV, GV, and GVI were stored in distilled water at 37 degrees C for 24 hours. Afterward, they were thermocycled between 5 degrees and 55 degrees C. Then, in GIII and GIV, a Universal Testing Machine was used; in GV and GVI, mechanical tests were performed with a digital dynamometer. The bracket/adhesive failure modes were evaluated with the Adhesive Remnant Index (ARI).


RESULTS
The average values of the shear strengths in MPa were: GI = 3.65; GII = 4.39; GIII = 6.45; GIV = 7.11; GV = 4.67; and GVI = 4.21.


CONCLUSIONS
The type of light-curing unit did not interfere with the results of the mechanical tests in vivo or in vitro. The tests performed with a portable digital device obtained average values that were significantly lower than those performed with the Universal Testing Machine.