Effect of different irradiation times on microhardness and depth of cure of a nanocomposite resin

ABSTRACT

To determine the microhardness and depth of cure of nanocomposite using different irradiation times on both upper and lower surfaces of composite material. In-vitro experimental study design. Dr. Ishrat-ul-Ebad Khan Institute of Oral Health Sciences, Dow University of Health Sciences and NED University of Engineering and Technology, Karachi, from March to May 2010. Total 120 cylinder shaped specimens; 60 specimens for depth of cure test and 60 specimens for micro hardness test were fabricated using A3 shade of nanocomposite [Filtek Z350 XT, 3M ESPE]. For each irradiation time four groups were made [Group 1 = 20s] [Group 2 = 30s], [Group 3 = 40s] and [Group 4 = 60s]. For each group fifteen specimens were used. The resin was placed and polymerized into a cylindrical plastic mold. Depth of cure was measured by using micrometer. Micro Vickers hardness was measured on both top and bottom surfaces. SPSS-16.0 was used for statistical analysis. There was statistically significant difference in the depth of cure between all groups showing the highest value in group 4 [p < 0.001]. For hardness on top surface, there was a statistically significant difference in between groups 1 and 2 [p=0.001], groups 1 and 3 [p < 0.001], groups 1 and 4 [p < 0.001] There was no statistically significant difference between groups 2 and 3, groups 2 and 4 and in between groups 3 and 4. For hardness on bottom surface, there was statistically significant difference in between all groups showing the highest value in group 4 [p < 0.001]. Depth of cure and hardness was increased by increasing irradiation time. Hardness on the top surface was higher than bottom surface values