Developing a universal and reliable temporomandibular joint reference system for quantifying morphological and positional changes

Objectives This study aimed to provide a universal and reliable reference system quantifying temporomandibular joint (TMJ) morphological and positional changes.Methods Large field-of-view (FOV) cone-beam computed tomography (CBCT) images (20 TMJs) from 10 preorthognathic surgery patients and limited FOV CBCT images (40 TMJs) from 20 splint therapy-treated patients with temporomandibular disorders were collected. TMJ-specific reference system including a TMJ horizontal reference plane (TMJHP) and a local coordinate system (TMJCS) was constructed with landmarks on cranial base. Its application for TMJ measurements and its spatial relationship to common Frankfort horizontal plane (FHP) and maxillofacial coordinate system (MFCS) were evaluated.Results Five relevant landmarks were selected to optimally construct TMJ-specific reference system. General parallelism between TMJHP and FHP was demonstrated by minimal angular and constant distance deviation (1.714 +/- 0.811o; 2.925 +/- 0.817 mm). Additionally, tiny axial orientational deviations (0.181 +/- 6.805o) suggested TMJCS rivaled MFCS. Moreover, small deviations in orientations and distances (1.232 +/- 0.609o; 0.310 +/- 0.202 mm) indicated considerable reliability for TMJCS construction, with intraclass correlation coefficients (ICCs) ranging from 0.999 to 1.000. Lastly, slight discrepancies in translations and rotations revealed high reliability for condylar positional and morphological measurements (ICC, 0.918-0.999).Limitations TMJ-specific reference system was merely tested in two representative FOVs.Conclusions This study provides a universal and reliable reference system for TMJ assessment that is applicable to both limited and large FOV CBCT. It would improve comparability among diverse studies and enable comprehensive evaluations of TMJ positional and morphological changes during TMJ-related treatment follow-up such as splint therapy and disease progression.