The purpose of this study was to clarify the positional relationship between the hyoid bone and the mandible in patients with mandibular protrusion. Pretreatment records, including both CT images and postero-anterior cephalograms, of 15 females were used to generate 11 angular measurements, to study the relationship between the mandible, the hyoid bone and the cervical vertebrae. Using a submental CT view, from CT scan, an imaginary reference line was created perpendicular to the midpoint of a line tangent to the anterior borders of the right and left foramen ovale.
The results were as follows:
1) There was a strong positive correlation between the deviation of ANS-Me in the anteroposterior view and the hyoid bone axis and a strong positive correlation between the hyoid bone axis and the line connecting the most posterior point of both condyles. In addition, there was also a strong positive correlation between the hyoid bone axis and the long axis of the third and fourth cervical vertebrae.
2) There was also a strong positive correlation between the line connecting the most posterior points of both condyles and the long axis of the third and fourth cervical vertebrae.
As a conclusion, the results suggested that the positional relationship of the mandible, the hyoid bone, and cervical vertebrae tended to deviate to the same direction in patients with mandibular protrusion.

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The purpose of this study was to clarify molar dental compensation and its longitudinal changes following orthognathic surgery in facial asymmetry patients.
Eleven adult patients with facial asymmetry, who underwent surgical orthodontic treatment, formed the basis of this study. Serial sets of gnathostatic model, frontal and lateral cephalogram were used for analysis. Materials were taken at the stages of first examination, the end of active treatment, and during retention (more than two years after the end of active treatment). Buccolingual tooth inclinations of the upper and lower first molars at each stage were measured on the three-dimensional graphics of the dental model generated by a noncontact threedimensional measuring unit. First, craniofacial deformity of the subjects at the first examination was evaluated, using lateral and frontal cephalometric analysis. Second, a characteristic molar dental compensation, and its correlation to the skeletal deformity, were examined. Third, longitudinal changes of molar dental compensation following orthognathic surgery were analyzed.
The results were as follows:
1. Skeletal deformity of the subjects was characterized by remarkable protrusion and asymmetry of the mandible, coupled with a small amount of asymmetry of the midface.
2. Distinguishing transverse dental compensations were found in the upper and lower molars. The upper molar on the shifted mandibular side showed significantly greater buccal inclination than that of the nonshifted mandibular side (p<0.05), while the lower molar on the shifted mandibular side showed greater lingual inclination than that on the non-shifted mandibular side (p<0.05). There was a significantly high correlation between the tooth inclination of the upper molar on the non-shifted mandibular side and the amount of mandibular deviation (r=0.75, p<0.05).
3. At the end of active treatment, molar dental decompensation was achieved. There were no significant differences in the amount of tooth inclination change between the upper and lower molar on both the shifted and the non-shifted mandibular sides. In retention, however, the amount of tooth inclination change in the upper molar was small, while that in the lower molar was great. The lower molar on the shifted mandibular side showed a significantly greater amount of tooth inclination change than that of the upper molar on both the shifted and the non-shifted mandibular sides (p<0.05). A tendency of lingual tooth inclination following mandibular relapse was found in the lower molar on the shifted mandibular side.

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There have been many studies on orthognathic surgery of class III patients with mandibular excess. In such patients, it is necessary to achieve the proper transverse relationship between the upper and lower jaws, as well as incisors, in the upright position, and alignment of both arches before surgery. However, it is difficult to diagnose discrepancies in transverse widths related to the inclinations of the upper and lower molars. The purpose of this study was to determine the proper transverse relationship by evaluating basal arch width discrepancies.
Ten patients were diagnosed as skeletal class III characterized by mandibular excess. They underwent presurgical orthodontic treatment, with extraction of bilateral upper first premolars, to reduce the labial inclination of the upper incisors, and to obtain an adequate basal arch width relationship between the mandible and maxilla. Then they were treated by bilateral sagittal split ramus osteotomy and postsurgical orthodontic correction. Lateral cephalometric radiographs before and after orthognathic surgery (T1 and T2, respectively) were used for Wits appraisal. Dental models were also taken before and after orthognathic surgery. Measurements in dental models included 1) bucco-lingual inclinations of the upper and lower first molars to the occlusal plane, and 2) transverse widths of the upper and lower basal bones (basal arch width).
Improved transverse relationships between the mandible and maxilla were achieved in all cases after treatment, although three of the ten cases showed crossbite on the first molars after orthognathic surgery. Inclinations of the upper or lower molars are correlated with discrepancy in the basal arch widths between upper and lower jaws. Discrepancy in the basal arch widths less than -0.5mm (minus means the lower jaw is wider than the upper jaw) has limited the position of the first molars in the proper bucco-lingual relationship.

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The biodegradable poly-L-lactic acid (PLLA) screw is a newly developed surgical material for use in fixing bone segments in sagittal split ramus osteotomy (SSRO) of the mandible for jaw deformity patients. The purpose of this study was to examine the stability of dento-facial morphology of mandibular prognathism patients after SSRO using PLLA screws. Six patients who underwent SSRO with PLLA screws (3 males and 3 females; the PLLA group), and six patients who underwent SSRO with conventional titanium screws (2 males and 4 females; the titanium group), were compared using frontal and lateral cephalograms taken before, as well as at 0, 6, and 12 months after, the surgery. The cephalometric changes, which were evaluated using standard scores, revealed no significant difference between the two groups at any postsurgical stages. No complications, such as allergy, inflammation, and pain, were reported in either the PLLA or the titanium group. These results suggested that the PLLA screw might be a useful surgical material that can be chosen for bone fixation in SSRO of jaw deformity patients.

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Past studies have shown that malposition of the tongue is recognized as a major cause of anterior open bite, and many studies have investigated the relationship between open bite and the tongue. However, no studies have measured changes of the tongue position for a long period after orthognathic surgery. A new wireless telemeter system was developed to measure the tongue position and head posture in skeletal mandibular prognathism with anterior open bite before and after orthognathic surgery.
The purpose of this study was to investigate the mechanism of adaptation of the peri-oral soft tissue to the new jaw relationship that had been reconstructed by orthognathic surgery. Data were obtained presurgically and after a debonding period for three cases whose occlusions were stable, and they were compared with the corresponding data of 23 normal occlusions.
The results were as follows:
1) Change in the tongue-contacting area
The tongue-contacting area was larger in two cases before orthognathic surgery than that of the normal occlusions. In another case, at the area of the mandible, similar results were obtained, but at the maxilla, the presurgical tongue-contacting area was smaller than that of the normal occlusions.
In all cases, the tongue-contacting area before orthognathic surgery became similar to that of normal occlusions by correction of the jaw-relationship and occlusion.
2) Change of head posture
In all cases, the head posture was not significantly different from that in normal occlusions. However, the head posture showed a slight backward inclination after orthognathic surgery.
The results suggest that head posture and the peri-oral soft tissues, including the tongue, might have adapted to the jaw-relationship and occlusion that is newly reconstructed by orthognathic surgery.

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A case of mandibular prognathism with acromegaly treated by orthognatic surgery is presented. The patient was a 26-year-old female who complained of malocclusion. She was diagnosed as having acromegaly from the results of clinical findings and endocrine examinations, and underwent surgery to remove a pituitary tumor, by neurological surgeons. As the value of Growth Hormone (GH) in the blood became normal after the operation, orthognathic surgery by SSRO was performed in our clinic. The postoperative course has been uneventful, and no sign of skeletal relapse has been found. Malocclusion and facial esthetics have been improved. However, long-term follow-up, considering the value of GH and facial form, including occlusion, is necessary.

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The skeletal open bite of a 52-year-old female which condition was accompanied by temporomandibular joint disorder, was treated by orthognathic surgery that distracted the lower border of the mandibular body using an extra-oral device, to change the angle of the mandibular body with the ramus. A wedgeshaped osteotomy was performed at the third molar area, and multi-guide distraction devices were applied bilaterally. Mandibular bone was distracted with three-dimensionally controlled displacement of the distal fragment. After a waiting period of 8 days, the device was advanced 0.1mm, or 3°, per day, for 16 days. As a result of this treatment, the open bite was improved, and the occlusal relationship was stabilized. Although a cutaneous scar and difficulty in device-setting were problems, control of osteodistraction was very easy.

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Severe facial asymmetry with a large occlusal transverse cant is difficult to treat by usual orthognathic surgery. Postoperative relapse is associated with severity of the facial asymmetry. Relapse has been correlated to the amount of surgical movement. This is thought to be related to the sudden repositioning and stretching of the masticatory muscles and perimandibular soft tissues. Overcoming soft tissue adaptation capability can be avoided by means of gradual traction.
Distraction osteogenesis of the mandible for treatment of hemifacial microsomia in children is a wellestablished surgical procedure. However, in adults, mandibular distraction osteogenesis presents the disadvantage of post-surgical malocclusion that complicates the postsurgical orthodontic treatment. To avoid this problem and improve facial symmetry, simultaneous distraction of the maxilla and mandible has been proposed by other authors.
We report a case of a 24-year-old female with severe facial asymmetry that was treated by simultaneous mandibular and maxillary lengthening using distraction osteogenesis. A High Le Fort I osteotomy was performed simultaneously with a unilateral ascending mandibular ramus osteotomy. Distraction was carried out after a seven-day latency period, at a rate of 1.0mm/day. The patient was on intermaxillary fixation during the latency and distraction phases. The hardware was removed after three months of consolidation. After two years of follow-up, no relapse has been observed. This technique proved adequate and stable for the treatment of severe facial asymmetries.

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