Degree of Conversion of Three Light-Cured Orthodontic Adhesives

Abstract

Introduction: The aim of this in-vitro study was to analyze the polymerization ability of 3 light-cured orthodontic adhesives by determining the degree of conversion (DC). Materials and Methods: Fourier transform infrared spectroscopy (FTIR) was used to evaluate the DC after polymerization immediately, 1 day, 7 days, and 30 days. The adhesives investigated were Transbond XT (3M Unitek, USA), Grengloo (Ormco Corp., USA), and Green Glue (Hangzhou Biomaterials, China). Twelve stainless steel brackets (n=4) were used and the adhesives were cured with Bluephase G2 (Ivoclar Vivadent, Liechtenstein). The data were analyzed by Kruskal-Wallis test for comparing materials and Friedman test for comparing the time periods. Results: The DC values were significantly different among the materials and among the time periods. The highest DC in each period was obtained for Grengloo and the lowest DC was observed for Transbond XT. Thus, there were significant differences between the DC values of Grengloo and Transbond XT in each period. Among the time periods, DC% at T1 (Immediately) and T3 of the material were significantly different. The DC values of all adhesives increased extremely from immediately following curing to 1 day and then slightly increased from 1 day to 7 days. Conclusions: Grengloo showed the highest levels of DC at all tested periods. The percentage values of DC largely increased from immediately following curing to 1 day. This concluded that monomers in orthodontic adhesives kept converting even after completion of photoactivation.