Incisor Inclination after Presurgical Orthodontic Treatment in Patients with Mandibular Prognathism

Abstract

To obtain information on the actual condition of dental decompensation by incisor inclination with presurgical orthodontic treatment (PSO) and to prove the effectiveness of PSO in patients with mandibular prognathism, upper and lower incisor inclinations after PSO and the change of incisor inclination with PSO were examined.
Fifty-three patients with mandibular prognathism who had been treated with orthognathic surgery in the University of Tokyo Hospital (UTH) were included in this study. Upper and lower premolar extraction was carried out in 32 and 6 patients, respectively. Mandibular setback surgery (sagittal split ramus osteotomy or intraoral vertical ramus osteotomy) was performed in 39 patients and bimaxillary osteotomy (Le Fort I osteotomy and mandibular setback surgery) in 14 patients. Orthodontic treatment had been performed at UTH for 20 patients and at other private clinics for 33 patients. Lateral cephalograms taken before (T0) and after (T1) PSO were used and SNA, SNB, ANB, Wits value, overjet, overbite, upper and lower incisor inclinations (U1-FH, L1-MP) were measured. Amount of jaw movement was estimated using dental models at T1.
PSO was effective in decompensating the incisor inclination but many patients still had labial inclination of the upper incisors and lingual inclination of the lower incisors after PSO. Labial inclination of the upper incisors was improved in cases with upper premolar extraction, but it became worse in cases without extraction. The mandibular dentition was aligned without premolar extraction in most patients. Lingual inclination of the lower incisors had improved but it was not adequate in many patients. Comparing patients who were treated by bimaxillary osteotomy and by mandibular setback surgery, the bimaxillary patients had more severe skeletal disharmony but the difference between these patient groups in the incisor inclinations after PSO was not significant. There were no differences between the surgical procedures and between clinics in which PSO was performed.
PSO was effective for the decompensation of incisor inclination but the dental compensation remained after PSO in many cases. Premolar extraction was useful for improvement of the incisor inclination in maxilla. Further studies on the crowding before treatment, on the use of anchorage for tooth movement and on the acceptable goal of presurgical-orthodontic treatment are required.