Comparison of Medial Aspect of Ramus for Sagittal Split Ramus Osteotomy in Patients With Different Skeletal Pattern

The sagittal split ramus osteotomy(SSRO) is the most common surgical technique for the correction of cases of mandibular deformity. Advantage of SSRO is that the surgical access to the mandible is intraorally, which does not produce scars on the face and lowers risk of the injury to the facial nerve. SSRO starts with a horizontal cut on the medial aspect of the mandible just above the lingula, deepening half-way through the thickness of the ramus. "Rai triangle," a new anatomic landmark on the medial surface of the ramus of the mandible, which when identified and taken into consideration, may have a definite advantage. Our hypothesis is the mandibular ramus of patients with prognathic mandible are thinner than the retrognathic mandible. The aim of this retrospective clinical study is to evaluate and compare the RAI triangle area of the mandibular ramus with skeletal class I, II and III patients who undergo orthognathic surgery.

The mandibular rami of 35 patients were evaluated by high-resolution computed tomography (CT) scans and 3D-Doctor software. Those patients were divided into three groups. Group 1: skeletal class II (n:11); group 2: skeletal class III (n:11) and group 3: skeletal class I (n:13) patients. Group 3 patients served as control group for comparing the results of groups 1 and 2. Group 1 and 2 patients' had orthognatic surgery (Le Fort I osteotomy and SSRO) in Ankara University Faculty of Dentistry Oral and Maxillofacial Surgery Department. The medial cuts were made 1 mm above the level of the mandibular lingula. All the images were high-resolution scans, that were carried out in the radiology department of our hospital by the same doctor. Group 1 and 2 include 17 female and 18 male patients.

All patients in study groups had mandiblar osteotomies and some patients had bimaxillary osteotomies. The mediolateral width of the RAI triangle area and the distance between the fusion point of the external and internal cortical plates above and posterior to the mandibular lingual were measured in all patients. Each mandibular ramus was measured separately. The measures were analyzed by two way anova test.

In cephalometric analysis, the mean ANB angle values of group 1, 2, 3 were 5.17 º, -2.57º, 1.03 º respectively. The mean thicknesses of RAI triangle area in group 1,2,3 were 114,7795 mm,² 109,3350 mm,²  123,3558mm,² respectively. The mean volumes of RAI triangle were 16,3015, 15,7595 and 13,8486 mm³  in groups 1,2,3. There is not a statistically significant difference in the thickness and volumes of the ramus between the 3 groups.Our clinical observations showed that the lindemann cut area is smaller and thinner in class III patients than in class II patients. However the radiological examination showed that there is no statically significant diference in RAI triangle area and volume of the patients with different skeletal realtionship.

 

References:

 1. Kirthi Kumar RAI, Gururaj Araker, et al: A bony landmark "RAI Triangle" to prevent "Misplaced" and "Misdirected" medial cut in SSRO. J Oral Maxillofac Surg 10(1):90-92, 2011.

 2. Muto T, Shigeo K, et al : Computed tomography morphology of the mandibular ramus in prognatism: Effect on the medial osteotomy of the sagittal split ramus osteotomy. J Oral Maxillofac Surg 61:89, 2003.

3. Kim HJ, Lee HY, Chung IH, et al: Mandibular anathomy related to sagittal split ramus osteotomy in Koreans. Yonsei Med J 38:19, 1997.