OBJECTIVETo introduce the internal tri-focal distractor developed by the authors and evaluate its primary application and feasibility in animal experiment.

METHODSFour hybrid dogs were selected and segmental resection at the mandibular symphysis was performed. Two transfer disks, 10 mm in width, were respectively fixed at the two ends of bone defect and the internal tri-focal distractor was installed. The force was applied one week after the operation, with a tractive speed of 0.5 mm/12 h. After 13 - 16 days, the traction was completed when the two transfer disks were combined. The occlusal films were taken at the 1st day, 4th, 8th and 12th week after traction. The animals were killed at the 12th week, samples of the traction area taken and histological examination performed. Finally, the new bone formation was observed.

RESULTSAll the animals survived in the experiment, abruption and rust-eaten was not found in distractor. In the 12th week after installation, new bones in traction gap were mature and bony union between the two transfer dishes was accomplished.

CONCLUSIONSThe internal tri-focal distractor used in this study may become a potential device in reconstruction of mandibular symphyseal defects.