Bisphenol A release from orthodontic adhesives and its correlation with the degree of conversion

Abstract

Our objective was to quantitatively assess and compare the bisphenol A (BPA) released from an orthodontic adhesive using a light-emitting diode device (LED) or a halogen light-curing unit (HLC) at 3 tip-to-bracket distances (0, 5, and 10 mm) and varying curing times using high-performance liquid chromatography. BPA release with self-etching and moisture-insensitive primers with light-cured and chemically cured composites was also evaluated. BPA release was correlated to the corresponding degree of conversion. Our sample consisted of 598 stainless steel first premolar brackets. Of these, 520 were used for assessing BPA release and divided into 13 groups of 40 each. In groups I, II, and III, the composite was cured with the LED for 20 seconds at distances of 0, 5, and 10 mm, respectively. Groups IV, V, and VI were cured with the HLC for 40 seconds at the same 3 distances. Groups VII and VIII were cured for 5 and 10 seconds with the LED, and groups IX and X were cured for 10 and 20 seconds with the HLC at 0-mm distance. Groups XI, XII, and XIII consisted of brackets bonded with a self-etching primer and Transbond (3M Unitek, Monrovia, Calif), with a moisture-insensitive primer and Transbond, and with a chemically cured composite. The remaining 78 brackets were also divided into 13 groups and used for assessing the degree of conversion. The LED devices demonstrated significantly less BPA release and greater degrees of conversion (P <0.05). For both units, BPA release increased and the degree of conversion decreased as the tip distance increased and curing time decreased. The chemically cured group showed significantly less BPA release (P <0.05). Among the light-cured composites, those cured according to the manufacturers' recommendations (40 seconds and 0-mm distance for the HLC unit) released less BPA than did the self-etching primer and the moisture-insensitive primer. The degree of conversion was greatest for the chemically cured composite, whereas it was similar for the conventional, self-etching primer, and moisture-insensitive primer groups. However, correlations ranged from strongly negative to weakly positive between BPA release and degree of conversion. Clinicians should consider using LEDs in clinical practice and should keep the light-cure tip as close to the bracket as clinically possible. Curing time should be according to the manufacturer's recommendations. These steps will ensure less BPA release and a greater degree of conversion. Since chemically cured composites had less BPA release and a greater degree of conversion, they can be considered superior to light-cured composites in this aspect.