The Role of Lead Shielding in Preventing Gamma Radiation-Induced Microleakage in Nanohybrid Composite Restorations: An In Vitro Study.

INTRODUCTION: Marginal microleakage is a significant factor that contributes to the failure of cavity restorations, ultimately leading to recurrent caries. These failures are primarily attributed to the properties of the restorative materials, which are often influenced by various environmental factors. Gamma radiation has been shown to have deleterious effects not only on dental hard tissues but also on composite restorative materials, potentially increasing microleakage. A viable approach to mitigate these effects is the implementation of protective shielding for vulnerable structures during radiotherapy. This study aimed to evaluate the impact of gamma radiation on the marginal microleakage of nanohybrid composite restorations, specifically comparing the extent of microleakage in restorations subjected to radiation with and without lead shielding.

MATERIALS AND METHODS: An in vitro study was conducted using 45 freshly extracted premolars divided into three groups: group 1 (control), group 2 (radiated without lead shielding), and group 3 (radiated with lead shielding). Class V cavities were prepared and restored using nanohybrid composite resin. Gamma radiation was administered using a cobalt-60 machine at a total dose of 70 Gy for seven weeks. A lead shielding of 11-mm was placed in the collimator for group 3. Microleakage was evaluated using a dye penetration technique, and data were analyzed using the Kruskal-Wallis test followed by post-hoc Dunn's test for pairwise comparisons.

RESULTS: Significant differences were observed in microleakage between the groups using the Kruskal-Wallis test (p = 0.001); however, post-hoc analysis revealed no statistically significant difference between groups 2 and 3 (p > 0.05). This showed that lead shielding did not significantly reduce microleakage compared with no shielding. Group 1 exhibited the least microleakage, with a mean dye score of 0.87 ± 0.83. Group 3 showed moderate microleakage (mean score = 2.06 ± 0.50), while group 2 exhibited the most severe microleakage (mean score = 2.47 ± 0.51).

CONCLUSION: Gamma radiation adversely affected the marginal integrity of nanohybrid composite restorations, with the control group showing the best performance in terms of minimal microleakage. While lead shielding showed some reduction in microleakage, it was not statistically significant compared with the group without shielding. This highlights the need to optimize radiation shielding strategies to protect dental tissues in patients undergoing head and neck cancer treatment. Further in vivo studies are recommended to evaluate the long-term effects and refine clinical practices for radiation protection.