Functional stabilization and neuromuscular adaptation in active condylar hyperplasia: a comparative cohort study

Active unilateral condylar hyperplasia (UCH) is a progressive mandibular growth disorder characterized by facial asymmetry, occlusal alteration, and mandibular deviation. Although single-photon emission computed tomography/computed tomography (SPECT/CT) is widely used to assess condylar hyperactivity, little is known about the clinical and neuromuscular adaptations occurring during the observation period before definitive treatment. This study evaluated whether conservative functional stabilization is associated with adaptive clinical and neuromuscular changes during this period.

This prospective comparative observational cohort study included 49 patients with active unilateral condylar hyperplasia confirmed by SPECT/CT. Thirty-seven patients received full-time orthopedic stabilization with a rigid mandibular intraoral orthosis, whereas 12 were managed by observation alone. Clinical outcomes included pain intensity, maximum mouth opening, and mandibular midline deviation. Surface electromyography (sEMG) was performed at baseline and after approximately 3 months. SPECT/CT examinations were obtained at baseline and follow-up (mean, approximately 14 months). Within-group and between-group comparisons, effect sizes, percentage changes, and 95% confidence intervals were calculated.

Orthopedic stabilization significantly improved mandibular midline deviation, maximum mouth opening, and neuromuscular function. Composite resting sEMG activity decreased, whereas functional muscle recruitment increased in the treated cohort. In contrast, the observation cohort demonstrated increased resting muscle activity with minimal functional changes. Significant between-group differences were observed for resting and functional sEMG outcomes. SPECT/CT metabolic changes were also detected, but were less consistent and clinically informative than the documented clinical and neuromuscular adaptations.

Full-time orthopedic stabilization was associated with measurable clinical and neuromuscular adaptation during the observation period preceding definitive treatment. These findings support functional stabilization as a conservative approach that may promote a more favorable neuromuscular and biomechanical environment while treatment decisions are being made. SPECT/CT findings should be interpreted as complementary semiquantitative observations rather than definitive indicators of growth modification.