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It is a challenge to attain good stability in patients who have mandibular prognathism with open bite for a long time after surgical orthodontic treatment. In this study, we analyzed the cephalometric changes after sagittal split ramus osteotomy (SSRO) in mandibular progna­ thism patients with open bite in order to investigate the factors influencing the long­term stability. Fourteen patients were enrolled in this study. All the patients were diagnosed as mandibular prognathism with open bite and underwent SSRO at Tokyo Medical and Dental University Dental Hospital, and were followed up for more than 10 years. Overbite (OB) was used as a parameter for the stability of occlusion. OBs were evaluated at two stages, i.e., at the beginning of retention and more than 10 years after surgery. The samples were divided into two groups : Unstable (U) group (8 cases) in which OB decreased by 1 mm or more, and Stable (S) group (6 cases) in which OB decreased by less than 1 mm. Dento­facial changes were analyzed by lateral cephalograms at 3 stages (T1 : first visit, T2 : beginning of retention, T3 : more than 10 years after surgery) and cephalometric measurements were per­ formed to compare the two groups. The following results were obtained : 1. At T3, OB of the U group was significantly less than that of the S group. No significant difference was observed in overjet at all stages. OB of the U group significantly decreased during retention. 2. Significant differences were found in the amounts of setback between the two groups. 3. L1 to MP significantly increased during active treat­ ment but it decreased during the retention period in the U group. Mandibular plane angle (MP) significantly increased during active treatment and retention in the U group. 4. A negative correlation was found between the changes of L1 to MP and OB during active treatment and retention in the U group. From our data, unstable samples that showed an increase of MP and a decrease of L1­MP as a result of SSRO for mandibular prognathism with open bite tend to exhibit a reduction of OB along with labial tipping of the lower incisors during long­term follow­up. It is therefore suggested that excessive lingual tipping of lower incisors should be avoided during active treatment by considering the balance of soft tissues, such as the tongue and lip, for the long­term stability.

Long-term Stability after Bilateral Sagittal Split Ramus Osteotomy for Mandibular Prognathism Patients with Open Bite