Functional Units Analysis of Mandibular Morphology in Patients With Parry-Romberg Syndrome.

Objective: To characterize mandibular morphology in patients with Parry-Romberg syndrome (PRS).

Design: Retrospective study.

Setting: A craniofacial center.

Patients: Thirty-three patients with PRS affecting mandible.

Interventions: Preoperative computed tomography data were analyzed using Mimics 26.0 (Materialise Inc.). Distances between landmarks-condyle process (Con), coronoid process (Cor), mandibular foramen (IAF), gonion (Go), and mental foramen-were measured to represent the sizes of skeletal units. Positional asymmetry was reflected by angles between lines connecting bilateral landmarks and the occlusal plane.

Main outcome measure(s): Bilateral differences in unit sizes were compared. Absolute difference (Δ) > 5 mm and relative size (RS) < 80% were set to evaluate the severity of hypoplasia. Angular measurements were compared to 0° using one-sample t tests. Pearson correlation analysis was conducted to examine the relationship between onset ages and both RS and angular measurements.

Results: The affected side's skeletal units were smaller. Severe hypoplasia was more common in the angular unit. Angles between Con-Con', Cor-Cor', IAF-IAF', and the occlusal plane were less than 0°, whereas the angle with Go-Go' was greater than 0°. Age of onset was positively correlated with the condylar unit size and the Con-Con' to occlusal plane angle.

Conclusions: Patients with PRS affecting mandible exhibit smaller skeletal units on the affected side, particularly in the angular unit. Most landmarks on affected side tend to cluster toward the occlusal plane. Earlier onset of PRS correlates with more pronounced condylar asymmetry. Evaluating the severity of functional units involvement and implementing appropriate treatment should be considered.