Deformities of the mandibular condyle, including hypoplasia and resorption, are often associated with severe open bite and mandibular retrusion. These conditions can lead to various functional and esthetic problems, such as masticatory dysfunction, speech impairment, facial esthetic concerns, sleep-disordered breathing, and temporomandibular joint dysfunction, all of which are closely linked to a reduced quality of life. In such cases, orthognathic surgery may be required to improve occlusion and facial appearance. However, treating skeletal Class Ⅱ open bite with condylar deformities presents significant challenges in achieving long-term stability. Condylar abnormalities can lead to instability of mandibular positioning during or after treatment, increasing the risk of open bite relapse and mandibular retrusion. Additionally, progressive condylar resorption following orthognathic surgery has been reported to further exacerbate open bite and mandibular retrusion. Therefore, when planning treatment for skeletal Class Ⅱ open bite with condylar deformities, a thorough evaluation of the temporomandibular joint （TMJ） and a strategic approach to ensure long-term stability are essential.
In typical cases of skeletal Class Ⅱ open bite, favorable occlusion and facial balance can be achieved through mandibular advancement and rotational adjustments of the maxilla and mandible. However, in cases with condylar abnormalities, the instability of mandibular positioning and the increased risk of postoperative condylar resorption necessitate special considerations for TMJ health during treatment planning. Increasing the amount of mandibular advancement to achieve an ideal facial profile places greater stress on the TMJ, elevating the risk of condylar resorption and relapse. Conversely, prioritizing postoperative stability requires a surgical approach that minimizes TMJ stress, which may result in suboptimal facial esthetics and reduced patient satisfaction. This creates a fundamental dilemma between “occlusal stability” and “facial esthetics,” posing a major challenge in treatment planning.
The present case involved a 16-year-old female patient with bilateral condylar hypoplasia without temporomandibular disc displacement, resulting in mandibular retrusion and hypoplasia, skeletal Class Ⅱ with a high-angle pattern, and anterior open bite with a two-plane formation in the maxillary anterior region. Soft tissue findings included marked lip incompetence, and a convex profile associated with severe chin retrusion. We applied a stabilization splint preoperatively to achieve a stable mandibular position, followed by surgical orthodontic treatment consisting of a two-piece Le Fort I osteotomy in the anteroposterior direction, bilateral sagittal split osteotomy （BSSO）, and genioplasty. As a result, a favorable soft tissue profile and occlusion were achieved. In this report, we describe the treatment approach, outcome, and key considerations for managing this case.

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Spinocerebellar ataxias （SCAs） are progressive neurodegenerative disorders marked by cerebellar degeneration. Symptoms of these diseases are motor uncoordination, particularly of gait. Additionally, SCAs show clinical signs relating to oral functions including speech and swallowing. The incidence of these diseases is extremely rare, occurring in approximately 18.5/100,000 in Japan. This report describes a case of surgical orthodontic treatment for mandibular prognathism with SCAs.
The male patient developed walking disturbance at 12 years of age; occasionally, speech disturbance has occurred. At the age of 19, he was referred to our clinic for surgical orthodontic treatment with a chief complaint of mandibular prognathism. The Department of Neurology of our hospital revealed SCAs and genetic testing showed autosomal recessive spastic ataxia of Charlevoix-Saguenay （ARSACS）.
Preoperative orthodontic treatment started at the age of 30. SCAs are progressive ataxia diseases, which can affect orthognathic surgery under general anesthesia, so it is necessary to shorten the preoperative period. For this reason, we selected non-extraction of both jaws. Bimaxillary orthognathic surgery at the age of 31 corrected the mandibular prognathism, and a good profile and occlusion were obtained. Five years have passed since the orthodontic treatment, and his occlusal condition is stable.
There is only one report of surgical orthodontic treatment for these diseases. SCAs can cause impairment of motor coordination including the stomatognathic system, which can be a factor of relapse. In this report, we discuss the treatment results and stability after treatment from the viewpoint of these disorders progressively affecting motor function including the orofacial region.

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