MICROSTRUCTURAL EFFECTS OF SINGLE-FRACTION PHOTON IRRADIATION ON HUMAN DENTAL HARD TISSUES: A HIGH-RESOLUTION MICRO-CT STUDY

Objective: This study aimed to investigate microstructural changes in human dental hard tissues following single-fraction irradiation using high-resolution micro-computed tomography (micro-CT), with particular emphasis on potential differences between flattening filter (FF) and flattening filter-free (FFF) photon beam modalities. Methods: Sixteen extracted, non-carious human third molar teeth were included. All samples underwent baseline micro-CT imaging prior to irradiation. Teeth were then irradiated with 20 Gy in a single fraction using either 6 MV FF (600 cGy/MU) or 6 MV FFF (1400 cGy/MU) photon beams. Micro-CT images following irradiation were obtained with identical imaging conditions. Changes in bone volume (BV), total volume (TV), bone volume fraction (BV/TV), bone surface (BS), specific bone surface (BS/BV), bone mineral density (BMD), trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp) were measured before and after irradiation. Results: Irradiation resulted in a substantial decrease in BV/TV and increases in BS and BS/BV (p < 0.05), suggesting micro-architectural remodeling and enhanced surface irregularity. No significant changes were detected in BV, TV, BMD, Tb.Th, or Tb.Sp. Comparison between FF and FFF beam modalities revealed no statistically significant differences in any micro-CT-derived parameter. Conclusion: Single-fraction 20 Gy irradiation induces early microstructural alterations in dental hard tissues characterized by changes in surface-related parameters rather than bulk mineral loss. Dose-rate differences between FF and FFF photon beams did not result in detectable micro-CT differences, supporting the clinical use of FFF beams at equivalent doses.