Impact of topical fluoride agents on radiation-induced dentin hardness alterations: a laboratory study

Radiation therapy for head and neck cancers often leads to radiation-induced caries and microstructural dentin alterations. This laboratory study evaluated the impact of radiation on dentin microhardness and the effectiveness of various topical fluoride treatments in mitigating these effects. One hundred dentin specimens from extracted human teeth were irradiated with a cumulative dose of 60 Gy, simulating therapeutic conditions. Post-irradiation, specimens received weekly applications of silver diamine fluoride (SDF), SDF with potassium iodide, or sodium fluoride varnishes with and without additional compounds. Dentin microhardness was measured using the Knoop hardness test at three key phases: baseline, immediately after reaching a cumulative irradiation dose of 60 Gy, and weekly for five weeks following repeated fluoride applications. At baseline, the average Knoop Hardness Number (KHN) was 57.6 ± 3.9. After irradiation, the average KHN decreased significantly to 41.2 ± 8.1, reflecting an approximate 30% reduction in dentin hardness across all groups (p < 0.0001). Five weeks of weekly fluoride treatments led to partial recovery of microhardness, with average KHN values ranging from 42.4 to 54.3, but none of the groups returned to baseline hardness levels. Notably, no significant differences were found among the fluoride treatments in their ability to enhance microhardness. These findings underscore the detrimental effects of radiation therapy on dentin integrity and emphasize the need for targeted dental management strategies. While fluoride applications provide some protective benefit, their limitations highlight the necessity of comprehensive approaches to prevent radiation-related dental deterioration in head and neck cancer patients.