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Study of Late Sensory Paralysis in the Lower Lip after Sagittal Split Osteotomy
-- Part 2: Investigation of Location of Mandibular Canal by Computed Tomography --
Masataka Kaji, Yasushi Ohashi, Yuuichi Mutoh
Second Department of Oral and Maxillofacial Surgery, Niigata University, School of Dentistry
(Chief: Prof. Yasushi Ohashi)
Abstract
The relationships between late sensory paralysis (LSP) in the lower lip after sagittal split osteotomy and the location of the mandibular canal by computed tomography were evaluated in 103 mandibular ramus cases (59 patients). Location of the mandibular canal was investigated with 6 axial scans at a 4 mm interval below the mandibular foramen, and the cases were classified into 3 types (separated, contact and fused). Separated type was regarded as clearance between the mandibular canal and the buccal cortical bone in the mandible, contact type as the bony plate of the mandibular canal touching the inner surface of the buccal cortical bone, and fused type as the bony plate of the mandibular canal being fused to the buccal cortical bone.
The results were as follows;
1. In the separatedCcontact and fused typesCLSP had incidences of 19% (24 of 71 cases), 64% (9 of 14 casesjand 84% (16 of 19 cases), respectively. In these separated type, there was no clear difference in the incidence of LSP based on the shortest distance between the mandibular canal and inner surface of buccal cortical bone.
2. In the relationship between LSP and the number of scans with no clearance between the mandibular canal and buccal cortical bone in the mandible, in the cases with one scan, two scans, three scans, four scans, five scans and six scans had LSP incidences of 50“, 71“, 80“, 100“, 75“ and 100“, respectively.
3. There was a strong tendency for LSP in the fused type to continue at a severe degree for more than one year postoperatively.
In conclusion, it is important to evaluate the location of the mandibular canal by CT before performing sagittal split osteotomy to prevent LSP.