Author:

Abstract:

Condylar resorption (CR) is a disorder affecting the temporomandibular joint (TMJ), characterized by the progressive loss of condylar volume. This condition can occur post-orthognathic surgery (PCR), spontaneously (ICR), or as part of autoimmune disorders (ACR). CR is clinically identified by the (re)ocurrence of a malocclusion (class 2 malocclusion and anterior open bite) and facial changes, including retrognathia of the mandible and increased anterior lower facial height. CR can also limit joint function, resulting in pain and restricted movement. This makes CR a particularly dreaded complication as it destroys the results of lengthy treatments of combined orthodontics and orthognathic surgery. Cone beam computed tomography (CBCT) plays a crucial role in diagnosis of CR. Investigations into PCR should utilize voxel-based registration using a portion of the mandibular ramus, along with automated or artificial intelligence (AI)-driven segmentation techniques and three-dimensional (3D) volumetric analysis, which have shown excellent accuracy and consistency. The use of AI-driven segmentation also improves time efficiency. Automated 3D dense phenotyping for shape analysis allows for the comparison of preoperative mandibular shapes with and without condylar resorption. PCR occurs in 9.5% of patients having orthognathic surgery of the mandible. On average, patients with CR experience a 17% reduction in condylar volume, a 3.9mm decrease in ramal height, and a 3.1mm posterior displacement of the mandible. Several risk factors were identified on a patient level: younger age, having combined bimaxillary and genioplasty surgery, greater mandibular advancements, upward movements of the distal segment, a pronounced counterclockwise pitch rotation of the distal segment, smaller preoperative condylar volumes, and a higher ratio of anterior to posterior lower facial height. Additional condylar-level risk factors include compressive movements of the ramus and an increased mandibular plane angle. Utilizing machine learning for multivariable analysis, we determined that the extent of mandibular advancement is the most critical predictor of CR. CR is a complex phenotype, with a minority of patients having monogenic causes The majority of patients have a mutlifactorial model behind the susceptibility. Haploinsufficiency of the BMP2 gene causes taurodontism and a high susceptiblity for CR. Variants in the EFCAB3 and ACAN genes warrant further investigation into a possible link with CR. This work indicates that is seems prudent to screen patients with CR for medical issues or signs indicative of a possible monogenic condition.