下颌前突患者下颌支部下颌管的定位和走行

The position and course of mandibular canal through mandibular ramus in patients with prognathism

目的:应用CT观测下颌前突患者下颌管的定位和走行,以给临床医师提供有意义的信息,减少对下牙槽神经的损伤。方法:38例实施下颌支矢状劈开术的骨性Ⅲ类下颌前突患者,术前进行颌骨CT扫描。以下颌管最先形成的平面作为0平面,向下每5mm作为一个测量平面,测量下颌管内径、下颌骨的厚度、颊舌侧骨皮质的厚度和下颌管外侧壁到颊舌侧骨皮质之间的距离。测量结果采用SPSS13.0软件包进行统计学分析。结果:从下颌小舌到下颌骨下缘,下颌骨厚度增加,颊舌侧骨皮质也逐渐增厚,下颌管内径变化不大。舌侧骨髓腔的宽度是从无到有的逐渐递增趋势,而在每一层测量值中,颊侧骨髓腔的宽度均大于舌侧。根据下颌管在下颌骨内的位置分类,绝大多数为分开类型(n=391),占总测量平面456的85.75%,接触和融合型分别占12.71%和1.54%。各测量值左右两侧无显著性差异,下颌管内径(ID)值和下颌管外侧壁到颊骨皮质的距离(BP)值的性别差异有显著性(P<0.01;P<0.001)。结论:下颌管形成后,渐渐远离舌侧而向颊侧靠近,然后又渐远离,但其总体走行还是靠近舌侧。对颊侧骨髓腔缺失的病例,尤其是融合型患者,建议选用其他术式,以免造成下牙槽神经损伤。

PUEPOSE： To investigate the position and course of mandibular canal through mandibular ramus in patients with prognathism using computed tomography, and to relate the findings to sagittal split ramus osteotomy, and also to describe the anatomical variability of mandibular canal in order to reduce injuries to the inferior alveolar nerve. METHODS： The mandibles of 45 patients with skeletal Class Ⅲ prognathism undergoing sagittal split ramus osteotomy were examined by spiral computed tomography. The region from a plane containing the lowest point of mandibular foramen （base plane 0） to 25 mm below it was measured with 5mm distance every plane. The following parameters were measured： total thickness of mandible through the center of mandibular canal, thickness of buccal and lingular cortical plate, and narrowest portion of bone marrow space between the outer mandibular canal and both the buccal and lingular cortex. All measurements were analyzed with SPSS 13.0 software package. RESULTS： The thickness of mandible increased from the mandibular formen to mandibular body, there was no statistical difference among the sites with regards to the inner diameter of mandibular canal （F=1.044,P=0.391）. The width of bone marrow space at the buccal side was significantly different between 3,4 plane and 0 plane,and the measured widths on the lingual side were significantly increased. The width of the buccal side bone marrow space at each site could be classified into three types, the separate type was most prevalent in this study（n=391 of 456,85.5%）, contact and fusion type were 12.71% and 1.54% respectively. There was no significant difference between the left and right side. CONCLUSION： On average, the mandibular canal is situated more lingually at all sites, and the width of bone marrow space at the buccal side is more narrow at 15-20mm below the mandibular foramen. When the width of marrow space at buccal side is absent, especially the fusion type, it is suggested to select an other procedure rather than sagittal split ramus osteotomy.