Effect of photon radiotherapy on microleakage and microhardness of nanohybrid resin composite restoration: an in vitro study

Abstract Background Photon radiotherapy (RT) is widely used in the management of head and neck cancer (HNC) and may affect dental restorative materials. However, limited evidence is available regarding its effects on nanohybrid resin composite (RC) restorations. This research aimed to assess the impact of photon radiation treatment on microleakage (ML) and microhardness (MH) of nanohybrid RC restorations. Methods A total of 54 samples were randomly divided into three groups (18 sample each): a control group (non-irradiated) and two RT groups exposed to 50 Gy (Gy) and 70 Gy of photon radiation. The radiation doses were delivered as a single dose, and post-irradiation assessments were performed immediately after irradiation. For ML, 30 extracted bovine incisors ( n = 10 per group) were standardized, prepared with Class V cavities, and restored using a nanohybrid RC (Grandio, VOCO GmbH, Germany). Microleakage was assessed by dye penetration at the restoration interface using a stereomicroscope. For MH, 24 disc shaped composite samples ( n = 8 per group) were evaluated using the Vickers MH test. Results The median ML scores were 1.0, 1.0, and 2.0 for groups I, II, III, respectively ( p = 0.029), while the median ML percentages were 17.93%, 24.75%, and 46.71%, respectively ( p = 0.003). Before irradiation, mean MH values were 52.39 ± 2.41, 52.53 ± 1.51, and 52.23 ± 2.03, respectively ( p = 0.959). Immediately after irradiation, these values increased to 53.60 ± 1.09, 62.90 ± 3.09, and 72.20 ± 5.53, respectively ( p < 0.001). Conclusions Under the conditions of this in vitro study, photon RT was associated with increased ML at 70 Gy of nanohybrid RC, whereas MH significantly increased following irradiation at both 50 and 70 Gy.