Estrogenicity of orthodontic adhesive resins

OBJECTIVES: The purpose of this study was to assess the estrogenic action of a chemically-cured, no-mix (Rely-a-bond, Reliance, IL, USA) and a light-cured (Reliance) orthodontic adhesive resin. MATERIALS AND METHODS: The adhesives were bonded to 40 maxillary incisor stainless steel brackets divided in two groups of 20 brackets each, employing a method which simulated the clinical handling of materials. A standardized volume of adhesive was applied to the bracket base and the bracket was pressed firmly on a surface covered by a cellulose film to facilitate detachment of the bracket-adhesive complex with a recovery of the set material; any excess resin was removed before polymerization. Irradiation in light-cured adhesive specimens was performed from the incisal and cervical bracket edges for 10 seconds at each side. In total, three series of specimens were prepared for each adhesive-bracket group. All specimens were immersed in normal saline. Samples of eluent were removed from each group at 1 day and 1 week following incubation and tested for estrogenicity by measuring their effect on the proliferation of the estrogen-responsive MCF-7 breast cancer cells, whilst an estrogen-insensitive cell line MDA-MB-231 (human breast adenocarcinoma) was used as a negative control control; positive (estradiol and bisphenol-A) and negative (normal saline) controls were also used to differentiate potential synergistic or antagonistic action of other adhesive constituents. The results were analyzed with a three-way ANOVA (adhesive, concentration of eluent and immersion period). RESULTS: The ANOVA indicated that no parameter was singificant in inducing proliferation; interactions were also insignificant (p>0.05), whereas bisphenol-A increased proliferation to estrogen-responsive cell-line to 160% (p<0.05). CONCLUSIONS: The concern associated with the use of resins with a double benzoic ring seems not to be validated in the case of orthodontic adhesives.