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

Objective: To determine the microhardness and depth of cure of nanocomposite using different irradiation times on both upper and lower surfaces of composite material. Study Design: In-vitro experimental study design. Place and Duration of Study: 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. Methodology: 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. Results: 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). Conclusion: Depth of cure and hardness was increased by increasing irradiation time. Hardness on the top surface was higher than bottom surface values. (author)