Degree of Conversion of Experimental Light-Cured Orthodontic Adhesives

Abstract

The objectives of this study were to compare the polymerization of three experimental light-cured orthodontic adhesives by determining their degree of conversion (DOC) and to compare the results with a control (Transbond XT; 3M Unitek, USA). Three formulas of an in-house orthodontic adhesive were divided according to monomer ratio (BisGMA:TEGDMA) into group 1 (8:2), 2 (7:3), and 3 (6:4), respectively, with 60-70 weight % of filler amount and 0.5 % of photoinitiator (TPO). All specimen (n=5 per group) were cured with a LED curing unit. The DOC was estimated using Fourier transform infrared (FTIR) spectrometer (Nicolet 6700, Madison, Michigan, USA) immediately following polymerization and on Day 1, Day 7, and Day 30. For statistical analysis, Kruskal-Wallis and Friedman tests were used to compare the materials and the periods, respectively, with p=0.05. The result showed that the DOC was significantly different among the groups and time periods. The highest and lowest DOC at each of the periods were obtained from group 3 and group 1, respectively. Among the time periods, the DOC values of all groups increased considerably on Day 1 following curing as compared to when it was measured immediately, and the DOC gradually increased until Day 30. In conclusion, the experimental orthodontic adhesive in group 3 with a monomer ratio of 6:4 provided the highest DOC among all the adhesives and was superior to Transbond XT at all periods of examination.