Relationship of mandibular condylar length and anterior disk displacement of the temporomandibular joint to facial asymmetry in orthodontic Class II patients

One of the most predominant causes of mandibular retraction is mandibular condylar head deformities, such as osteoarthritis （OA） and idiopathic/progressive condylar head resorption （ICR/PCR）. Although temporomandibular joint （TMJ） disk dynamics have been strongly linked to OA and ICR/PCR, and disk displacement can cause facial asymmetry, early detection and prevention of TMJ disk displacement are difficult. Therefore, this study sought to compare the connection between facial asymmetry, mandibular condylar length, and TMJ disk displacement in skeletal Class II patients without condylar head deformity. The study included 33 orthodontic Class II patients without condylar head deformity but did have TMJ symptoms. Those with mandibular deviation were assigned to Group A （Group A-L for long condylar heads and Group A-S for short condylar heads）, while those without were assigned to Group B （Group B-L for long condylar heads and Group B-S for short condylar heads）. Both Groups A and B had a laterality in the length of the condylar head, with the A-S group having a significantly shorter condylar head than the other groups. Severe disk displacement was noticed in 25％ of patients in the A-L group, 40.0％ in the A-S group, 15.4％ in the B-L group, and 15.3％ in the B-S group. Conclusively, even in cases without condylar head deformity or facial asymmetry, 15.3％ of patients had a severe anterior displacement of the TMJ disk, indicating that the degree of disk displacement does not always correlate with the presence or absence of condylar head deformity.