OBJECTIVE: To evaluate the dentofacial effects of mandibular symphyseal distraction osteogenesis produced by using a Hyrax-type tooth-borne distractor.

SUBJECTS AND METHODS: Seven patients, 4 girls and 3 boys between 16 to 19 years of age, underwent mandibular symphyseal distraction osteogenesis. Distraction was accomplished with a tooth-borne appliance which was consisted of a Hyrax-type distractor placed between the right and left first mandibular premolar and molar teeth at the lingual side of the lower jaw. After the placement of distractor, posteroanterior and submental vertex radiographs were taken in a standardized way just before the application of any distraction force. All distractions were carried out as a rate of 1 mm per 24 hours. The amount of distraction was 7 mm for each patient. The posteroanterior and submental vertex radiographs exposed again at the completion of symphyseal distraction. Anatomical landmarks were traced on these radiographs and the first and second tracings were superimposed. The distances and angular measurements between these two records were measured and compared by using Student's t-test for paired samples at the 95 % confidence level.

RESULTS: Statistically significant differences were found between the values measured before and after symphyseal distraction for inter condylar distance (the distance between the right and left condyle) (p = .006) and angle (p = .03), inter molar distance (p = .001) and angle (p = .005), and inter gonial distance (p = .001).

CONCLUSION: The distance between the right and left sides of mandibula was significantly increased by the tooth-borne mandibular symphyseal distraction. However, this increase was more pronounced at the inter condylar and symphyseal regions than that of the inter gonial region. Long term skeletal effects of tooth-borne mandibular distraction should also be evaluated.

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