Condylar position-dependent cerebellar connectivity changes in painful temporomandibular disorder: a brief report

The cerebellum contributes to sensory, cognitive, emotional, and pain-modulatory processes beyond motor coordination. In temporomandibular disorders (TMD), alterations in spontaneous cerebellar neural activity and strengthened functional connectivity with limbic structures have been reported, suggesting involvement of central neuroplastic mechanisms. Mandibular displacement and occlusal imbalance may further modulate brain networks related to motor regulation, sensory integration, and pain-related emotional processing.In this study, magnetic resonance imaging(MRI) and diffusion tensor imaging(DTI) was used to examine cerebellar connectivity across different mandibular positions in a patient with painful TMD. Functional MRI and diffusion tensor imaging were acquired in three conditions: centric occlusion, centric relation, and stabilization splint. Cerebellar regions of interest were defined using SUIT parcellation, and position-dependent structural-functional connectivity was assessed using diffusion-based tractography and Δ-metrics computed as the difference between the two tractography-derived matrices (Δ = MNI_NORM - COUNT_NORM); scale-invariant similarity metrics were used for between-condition comparisons.Under centric occlusion (CO), the Δ-derived connectivity pattern was sparse and included ROIs with zero-variance profiles, yielding mathematically undefined correlation entries; these were treated as missing values. In contrast, centric relation and stabilization splint conditions demonstrated heterogeneous Δ patterns and structured ROI-wise correlation profiles.In contrast, both centric relation and stabilization splint conditions showed moderate effect sizes in summary metrics. Pairwise comparison of vectorized Δ matrices (upper triangle; N = 378 ROI pairs) demonstrated a moderate association between CR and splint (Pearson r = 0.452, 95% CI 0.368-0.527; p = 2.0 × 10⁻²⁰; cosine similarity = 0.428). The Euclidean distance between Δ vectors was 1554.5, corresponding to a normalized per-element RMS difference of 81.1, and the mean absolute difference was 42.2.These single-subject findings suggest that mandibular position may be associated with measurable differences in Cerebellum-SUIT connectivity profiles in painful TMD. The results should be interpreted as exploratory and hypothesis-generating, and they require confirmation in larger prospective studies before clinical or therapeutic implications can be inferred.