Case Presentation: 
The patient felt that the upper front teeth were positioned lingual to the lower front teeth, constituting a severe anterior crossbite. The anterior teeth felt abnormal during mastication, with impaired incising function of food. Additionally, the temporomandibular joint was persistently uncomfortable, becoming more severe after overtime work and late nights.
 

Treatment Plan:

During the initial clinical examination, a temporomandibular joint (TMJ) assessment was performed, which revealed that the patient's centric occlusion (CO) and centric relation (CR) positions were not coincident, and that the mandible had a retruded/backward seating space. After measuring the edge-to-edge (end-to-end) position of the mandible, the clinician determined that the lower anterior teeth could be retracted following extraction. Although the crossbite appeared severe due to a deep overbite, this did not represent a true discrepancy of the maxillomandibular relationship. By retracting the lower anterior teeth, the upper anterior teeth could be brought into proper overjet over the lower teeth, while positioning the joint in a healthy state. Given the patient's aesthetic concerns, clear aligner therapy was selected. Utilizing the occlusal splint (bite-block) effect of the aligners, this approach reduced joint loading while facilitating the correction of the lower anterior crossbite.
 

Treatment Outcome: 
After two years of orthodontic treatment, the facial profile has become more aesthetically pleasing; the previous underbite ("reverse bite") appearance has been corrected to normal. Functionally, the patient reports noticeably improved masticatory efficiency, and symptoms of masseter muscle fatigue and joint clicking have been significantly alleviated.