Effects of Irradiation Period on Toothbrush Wear of Restorative Materials

Objectives: This study evaluated the effect of irradiation period on wear behavior of various materials after toothbrushing. Methods: A cavity (2.5 x 4.0 mm, 2.0mm in depth) was prepared in a porcelain denture tooth. The cavities were air-abraded, primed with a mixture of bonding agent (Clearfil New Bond, Kuraray) and silane coupler (Clearfil Porcelain Bond Activator, Kuraray), and filled with restorative materials including an indirect composite (Solidex, Shofu), a direct composite (Solare, GC), and a polyacid-modified glass ionomer (Dyract Extra, Dentsply DeTrey). Each material was packed with two increments, and each increment was polymerized according to the manufacturers' instructions. Solidex was polymerized in a photo-polymerizing unit (α-Light II, Morita) for 90seconds, Solare and Dyract were photo-polymerized using a light-curing unit (G-Light, GC) for 20 seconds and 10 seconds, respectively. Specimens polymerized under doubled irradiation period were also fabricated for each composite (n=5). Specimens were stored in 37˚C water for 24 hours, and then polished with a 600-grit Si-C paper and 1-µm alumina suspension. Specimens were subjected to 25 minutes of toothbrushing with a 1.47 N load using a powered toothbrush (Oral-B AdvancePower, Braun) with an oscillating-rotating brush head (Oral-B FlexiSoft, Braun). The mean surface roughness (Ra) was measured using a profilometer (Surfcom 130A, Tokyo Seimitsu). The data were statistically analyzed by 3-way ANOVA and Bonferroni's test (α=0.05). Results: There were no significant differences between Ra values of normal and doubled irradiation period for all the composites before toothbrushing. Ra of normal irradiation period after toothbrushing (Solidex: 0.965±0.109 µm, Solare: 0.648±0.122 µm, Dyract: 0.739±0.134 µm) were significantly decreased to those of doubled irradiation period (Solidex: 0.494±0.149 µm, Solare: 0.407±0.068 µm, Dyract: 0.542±0.062 µm). Conclusion: Doubled irradiation period significantly decreased the surface roughness after toothbrushing for all the materials tested.