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Effect of in vivo aging on the shear bond strength of an orthodontic adhesive.

AIMS
To assess the effect of intra-oral aging on the shear bond strength of a composite resin orthodontic adhesive (Transbond XT, 3M Unitek, Monrovia, CA, USA) after 6 months in the oral cavity and to compare it with control specimens not subjected to intra-oral aging.


METHODS
The sample consisted of patients aged 13-36 years, in need of premolar extractions for orthodontic purposes. Ten premolars were bonded with Transbond XT. After 6 months in vivo, the teeth were carefully extracted, sectioned at the amelo-cemental junction, mounted in cold cure acrylic resin cylinders and subjected to shear bond strength testing using a universal testing machine. The debonded bracket base surfaces were then studied under light microscope, photographed digitally and analysed with SigmaScan Image Measurement Software (Jandel GmbH, Erkrath, Germany) for the percentage of coverage of the debonded brackets with the orthodontic adhesive. The same procedure was followed for 14 premolars from the same patients bonded in vitro with the same adhesive.


RESULTS
No statistically significant differences were found in the shear bond strength between the two groups of composite resin adhesive systems (with and without clinical aging) or in the adhesive remnant coverage following debonding. No significant correlation was detected between the shear bond strength and the adhesive remnant coverage in the test specimens with and without aging.


CONCLUSIONS
Laboratory studies of shear bond strength appear to be clinically relevant.