2419 - Comparative Effects of Standard and Hypofractionated Radiotherapy on the Mechanical, Structural, and Morphological Integrity of Dental Enamel

Purpose/Objective(s): Head and neck cancer is commonly treated with concurrent chemoradiation. Radiation-associated caries is a major oral toxicity characterized by rapid progression and functional impairment. Experimental evidence suggests a multifactorial pathogenesis involving salivary alterations and direct radiation-induced damage to mineralized dental tissues. However, data evaluating contemporary therapeutic dose and fractionation regimens remain limited. This study assessed the effects of different radiotherapy fractionation schemes on the mechanical, structural, and morphological properties of dental enamel.

Materials/Methods: Forty healthy bovine incisors were randomly distributed into five groups (n = 8 per group): four irradiated groups simulating therapeutic fractionation schemes — 17 Gy in 1 fraction (G17), 35 Gy in 5 fractions (G35), 55 Gy in 20 fractions (G55), and 70 Gy in 35 fractions (G70) — and one non-irradiated control group (G0). Irradiation was applied using a 6 MV linear accelerator. Mechanical properties of the enamel were evaluated by Knoop microhardness (KHN). Morphological and topographical characteristics were evaluated using three-dimensional surface roughness analysis and confocal laser scanning microscopy. Structural and compositional changes were analyzed by scanning electron microscopy coupled with energy dispersive spectroscopy. Biologically effective dose and equivalent dose in 2 Gy fractions were calculated using the linear-quadratic model, assuming an a/ß ratio of 10 Gy, used as comparative parameters between fractionation schemes. Statistical analysis included the Shapiro-Wilk test for normality, one-way ANOVA followed by Tukey's post hoc test, and Pearson's correlation coefficient (a = 0.05).

Results: All irradiated groups demonstrated a statistically significant reduction in enamel microhardness compared with controls (G0: 429.8 ± 96.2 KHN vs irradiated groups: 303.8–309.8 KHN; p<0.05), corresponding to an approximate 30% decrease. No significant differences were observed among fractionation schemes (17–70 Gy). Dose–response analysis revealed an early reduction in mechanical properties after initial radiation exposure, followed by stabilization without progressive decline at higher cumulative doses. Morphologic evaluation showed only discrete superficial changes, and quantitative elemental analysis demonstrated preserved global structural composition. No linear correlation was identified between KHN and elemental parameters.

Conclusion: RT induces early mechanical impairment of dental enamel, characterized by a significant reduction in microhardness at low doses followed by stabilization independent of fractionation scheme. Despite this mechanical degradation, global morphological and structural properties remain preserved.