This study was conducted to determine the degree of difficulty of sagittal splitting of the mandibular ramus and utilize the results to aid in training those who plan to perform the procedure.
Two surgeons, both skilled in sagittal splitting of the ramus, conducted the procedure on 23 sides of deformed jaws. The relationships among the anatomical features of the mandibular ramus obtained by 3-D imaging, the extent of mouth opening during the surgical procedure, and the time required for the 7 separate surgical stages were studied and the following factors that are responsible for prolonging the surgical time at each stage were confirmed.
(1) The length of the vertical diameter of the anterior border of the mandibular ramus is positively related to the time spent between the start of incision and placement of Ramushaken on the coronoid process.
(2) The lateral curvature of the mandibular ramus when the mandibular angle is viewed upward is positively related to the time from the start of desquamation of external ramus periosteum to the placement of the Progenie-haken on the external side.
(3) The time from the start of desquamation of internal ramus periosteum to the internal placement of the Progenie-haken is prolonged when the lateral surface of the mandibular ramus is large, the mandibular angle is small, the projection of the lateral section of the anterior border of the mandibular ramus is exaggerated, and the degree of mouth opening is limited.
(4) Significant morphological differences were not related to the time required for the completion of internal osteotomy of the mandibular ramus.
(5) The extent of lateral curvature of the mandibular ramus when the mandibular angle is viewed upward is positively related to the time required to complete external osteotomy of the mandibular ramus by using the Lindemann bur.
(6) The position showing a significant morphological difference had no effect on the time required from the start to the completion of anterior osteotomy of the mandibular ramus.
(7) The time required to complete splitting of the mandibular ramus is positively related to the lateral surface area of the mandibular ramus and its lateral curvature when the mandibular angle is viewed upward.

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The purpose of this study was to investigate the prevalence of TMJ internal derangement, the pathologic status, and the relation of craniofacial morphology.
Seventy-one patients (14 males and 57 females, mean age: 22y 0m) with jaw deformities were selected as subjects. MRI and tomogram were taken of each subject to identify the intraarticular pathologic status with reference to Wilkes/Schellhas criteria. Craniofacial morphology was analyzed by using posteroanterior and lateral cephalograms. Association between intraarticular pathologic status and craniofacial morphology was examined by means of Spearman rank correlation analysis.
Internal derangement was found in 37 (52.1%) patients. In patients with unilateral TMJ internal derangement, a significantly positive correlation was found between lateral shift of the mandible and the TMJ pathologic stages. Ramus height (r=0.300, p<0.05) and maxillomandibular relation (r=0.594, P<0.01) significantly correlated with the pathologic stage of TMJ internal derangement.
The results also showed a significantly positive correlation (r=0.926, p<0.05) between clockwise rotation of the mandible and the stage of TMJ internal derangement in subjects with bilateral TMJ internal derangement.
These findings revealed a significant relation of mandibular or craniofacial morphology and the degree of TMJ internal derangement.

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