Accelerated Aging Effects on Surface Hardness and Roughness of Lingual Retainer Adhesives

Objective: To test the null hypothesis that accelerated aging has no effect on the surface microhardness and roughness of two light-cured lingual retainer adhesives. Materials and Methods: Ten samples of light-cured materials, Transbond Lingual Retainer (3M Unitek) and Light Cure Retainer (Reliance) were cured with a halogen light for 40 seconds. Vickers hardness and surface roughness were measured before and after accelerated aging of 300 hours in a weathering tester. Differences between mean values were analyzed for statistical significance using a t-test. The level of statistical significance was set at P < .05. Results: The mean Vickers hardness of Transbond Lingual Retainer was 62.8 ± 3.5 and 79.6 ± 4.9 before and after aging, respectively. The mean Vickers hardness of Light Cure Retainer was 40.3 ± 2.6 and 58.3 ± 4.3 before and after aging, respectively. Differences in both groups were statistically significant (P < .001). Following aging, mean surface roughness was changed from 0.039 μm to 0.121 μm and from 0.021 μm to 0.031 μm for Transbond Lingual Retainer and Light Cure Retainer, respectively. The roughening of Transbond Lingual Retainer with aging was statistically significant (P < .05), while the change in the surface roughness of Light Cure Retainer was not (P > .05). Conclusions: Accelerated aging significantly increased the surface microhardness of both light-cured retainer adhesives tested. It also significantly increased the surface roughness of the Transbond Lingual Retainer.