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.

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 …