Absence of the Periodontal Space in Impacted Third Molars: A Cross-Sectional Study Using Cone Beam Computed Tomography

Background: This study aimed to determine the frequency of tomographic signs indicating the absence of the periodontal space (APS) in impacted third molars using cone-beam computed tomography (CBCT) and to assess its association with demographic and anatomical variables, as well as the presence of replacement resorption (RR). Material and Methods: A cross-sectional and retrospective observational study was conducted using 258 randomly selected tomographic volumes from a radiological center in Lima, Peru, in 2025. The study evaluated 457 impacted upper and lower third molars. Two trained and calibrated evaluators analyzed the impaction of the third molars using multiplanar CBCT reconstructions with a voxel size of 0.2 mm. The variables assessed included age, sex, dental arch, third molar position, affected root zone, angulation of the third molar (APS), and root resorption (RR). Chi-square tests and logistic regression analyses were performed, with p < 0.05 considered statistically significant. Results: 221 cases (48.35%) exhibited an absence of periodontal ligament spaces. The absence of the periodontal space was significantly associated with third molar position, being more frequent in horizontal (27.1%) and distoangular (23.1%) positions (p = 0.003). The apical third was the most commonly affected root zone (43.0%) (p < 0.001). Replacement resorption (RR) was observed exclusively in molars without a detectable periodontal space (3.6%) (p = 0.003). Age was identified as the only significant predictor; with each additional year, the risk of APS increased by a factor of 1.07 (p < 0.001). Conclusions: The absence of the periodontal ligament space in third molars is highly prevalent, especially in older patients, particularly those with horizontal or distoangular positions and when the apical region is involved.