Tooth Geometry-dependent Sensitivity Variations in L-band Electron Paramagnetic Resonance Tooth Dosimetry: A Parametric Approach Based on Quasi-tooth Models Mimicking Human Maxillary Central Incisors

L-band in vivo electron paramagnetic resonance (EPR) tooth dosimetry is a rapid, non-invasive method for determining the ionizing radiation dose of individuals. Tooth positioning and geometry are the dominant factors influencing EPR intensity. However, the delineation of the geometric parameters and their influence on EPR intensity is still unclear. This induces limitations in the availability of dosimetry for triage and leads to the imperfect consideration of geometric variations affecting EPR intensity. This study aimed to analyze the dosimetric sensitivity variations for each geometric parameter separately. Using finite element analysis, model-based parametric analyses were performed on five geometric parameters: labial enamel thickness (τlab), enamel area (Aen), aspect ratio (RA), horizontal curvature (CH), and vertical curvature (CV). The distributions of these parameters were investigated using micro-CT images from 12 human maxillary central incisors. A quasi-tooth model was proposed to mimic the tooth geometry based on the geometric parameters. The quasi-tooth model well simulated the sensitivity variations observed in the micro-CT derived tooth model. The sensitivity showed a strong linear correlation with the three geometric parameters (τlab, CH, and CV), whereas Aen exhibited a plateau around its average value (75 mm2), and no clear trend was observed for RA. After normalization, τlab, CH, and CV were identified as the dominant contributors to sensitivity variations, whereas Aen and RA had less influence. Considering the correlation between τlab and Aen (r = 0.67, p = 0.017), previous geometric correction methods using Aen may have accounted not only for the direct influence of Aen but also for the indirect correction of τlab. These results demonstrate the principles and limitations of previous geometric correction methods and imply the need for an enhanced method that incorporates multiple parameters for L-band in vivo EPR tooth dosimetry.