An anatomical study of the mandibular ramus in Korean patients with dentofacial deformity

ABSTRACT

Orthognathic surgery of the mandibular prognathism and the retrognathism is tend to be performed on the mandibular ramus to prevent inferor alveolar nerve injuries. The purpose of this study is to find a safe and accurate reference point on mandibular ramus for orthognathic surgery by comparative anatomical study of dentofacial deformity patients. We use 38 Korean Cadavers with normal occlusion(Group 1), 3-dimensional simulation of computerized tomogram of 23 patients with retrognathism (Group 2), 27 patients with mandibular prognathism (Group 3). Following results are obtained 1. The maximum thickness of the mandibular ramus is 8.78+/-1.15mm for Group 2, 7.61+/-1.26mm for Group 1, 6.95+/-0.82mm for Group3 respectively (P=0001). The minimum thickness is 5.51+/-1.08mm for Group 1 , 5.06+/-0.40mm for Group 2, 4.56+/-0.78mm for Group3, respectively (p=0.0001). But, the thickness at the level of 5mm above the lingular is 0.78+/-0.65mm for Group 2, 5.63 +/-1.28mm for Group 1, 5.32+/-0.91mm for Group 3, respectively. There is no significant difference between these groups(P=0.0510). 2. The horizontal location from the midwaist point to lingular is 0.18+/-1.57mm for Group 1, 0.69+/-1.33mm for Group 2, 0.66+/-1.66mm for Group 3, and there is no significant difference between these groups(p=0.0835). But the vertical location from the midwaist point to lingular is 1.45+/-2.64mm for Group 1, 0.63+/-1.44mm for Group 2, 0.34+/-1.81mm for Group 3, and there is significant difference between these groups(p=0.0030). 3. The horizontal location from the midwaist point to mandibular foramen is 0.29+/-1.75mm for Group 1, 0.63+/-1.44mm for Group 2, 0.34+/-1.81mm for Group 3, and there is no significant difference between these groups(p=0.5403). But the vertical location from the midwaist point to mandibular foramen is -3.33+/-4.43mm for Group1, -4.79+/-2.26mm for Group 2, -6.06+/-2.99mm for Group 3, and there is significant difference between these groups(P=0.0001). 4. The horizontal length from the disto-buccal cusp tip of mandibular second molar to lingula is 30.97+/-4.17mm for Group 3, 28.29+/-2.65mm for Group 1, 25.48+/-0.77mm for Group 2 (p=0.0000), and also vertical length is 7.72+/-3.22mm for Group 3, 6.38+/-1.83mm for Group 1, 5.89+/-2.30mm for Group 2 (P=0.0014). 5. The location of lingular is 0.50 from anterior border of mandibular ramus in all groups, if it assumed the length from anterior border to posterior border is 1. And it is almost 0.33 from the sigmoid notch, if it assumed the length from sigmoid notch to antegonial notch is 1. 6. In Group 1, Antilingular prominence is located on (1.12+/-1.43mm, 4.01+/-2.36mm) from the midwaist point, and there is no correlation between antilingular prominence and lingular, mandibular foramen.