Cytotoxicity and Degree of Conversion of Orthodontic Adhesives.

Objectives: To test the hypothesis that there is no difference in the cytotoxicity related to the modes of polymerization of five commercially available orthodontic bonding resins, with and without an oxygen-inhibited layer (OIL), and to evaluate the degree of conversion (DC) of these resins and correlate this to cytotoxicity. Materials and Methods: Five commercially available orthodontic bonding resins were tested for cytotoxicity and DC. Thirty-six disks of standardized dimensions, for each resin, were used for cytotoxicity assessment. Half of them were washed with 99% acetone to remove the OIL (washed resins), and the remaining disks were left intact (intact resins). Glass disks were used as a control. Vero cells were exposed to intact and washed resins on day 1. Cell viability was determined by tetrazolium bromide reduction assay 1, 3, and 6 days after exposure. The DC of the adhesive specimens of each resin, prepared with a procedure identical to the clinical bonding process, was assessed by Fourier transform infrared spectroscopy. Results: Single-cured systems were comparatively less cytotoxic than dual-cured systems. With removal of the OIL, increased cell viability was noted only with two resins on all three days. Resins tested showed differences in DC. A positive correlation was demonstrated by two resins. Conclusion: The hypothesis is rejected. Single-cured systems are superior to dual-cured systems in exhibiting comparatively less toxicity and higher DC. A significant positive correlation was not established between cytotoxicity and DC. [ABSTRACT FROM AUTHOR]