Context: Conventional treatment of XLH was reported to prevent dental complications, but whether the preventive effect was different among different types of teeth, including anterior teeth and molar teeth, is uncertain. Evidence of the preventive effect of conventional treatment on ectopic ossifications is also limited.

Objective: To compare dental complications and ectopic ossifications among XLH adults with early (< 5 years old) or late (≥5 years old) conventional treatment.

Methods: This retrospective observational study included a total of 30 adults with XLH using orthopantomograms, spinal computed tomography scans and X-rays of hip/knee joints. Dental complications, including decayed, missing filled (DMF) index and devitalized tooth, apical periodontitis, and periodontitis, were evaluated. The index of ossification of the anterior/posterior longitudinal ligament and yellow ligament (OA/OP/OY index) and the sum of the OA/OP/OY index (OS index) were utilized to evaluate the severity of spinal ligament ossification. The severity of the hip/knee osteophytes was evaluated by the Kellgren-Lawrence (KL) classification.

Results: The number of sound teeth was significantly lower, and the DMF index was significantly higher in patients with late treatment. The severity of dental complications in the anterior tooth and molar tooth, OA/OP/OY/OS index, and KL grade were not significantly different among patients with early treatment and those with late treatment.

Conclusion: Early treatment could prevent dental complications but did not prevent ectopic ossification in adult patients with XLH. The difference in the preventive effect was not observed among different types of teeth.