A custom mandibular distraction device for the rat

In the last several years, the rat model has been used as a reliable means of studying distraction osteogenesis (DO). This model has several benefits, including lower cost, the availability of molecular reagents for the rat, and the ability to perform a large number of operations in a short time. We have recently developed an external device that is custom-made for the rat mandible and secured at the mandibular ramus. The device consists of a Leone (Florence, Italy) jackscrew distraction assembly (0.2 mm per one-quarter turn), 2 Luhr L-shaped 0.8-mm five-hole microplates, and four 0.8-mm x 3-mm microscrews (Stryker-Leibinger Corp., Kalamazoo, MI) for fixation. Additionally, there is a methylmethacrylate block that is placed on the lingual surface of the angle of the mandible to support the posterior screws. Sterile surgical technique was used, and the same two surgeons performed all operations. To date, we have operated on 153 Sprague-Dawley rats. The procedure has been well tolerated by the animals. We had 17 postoperative deaths (11% mortality), largely as a result of anesthetic complications. There were no wound infections or dehiscence. A mandible fracture was noted in 6 rats (4%), which occurred at the time of device placement. There were no device dislodgments. Postmortem examination showed the device to be well positioned in all rats, with good callous formation at the distraction site. The rats surpassed their preoperative weight after an average of 9.2 days. These results compare favorably with those of other models currently in use. We have developed a device that is currently being used in the study of DO in the rat mandible. Our device is small in size, does not require wide undermining for its placement, and has had a low incidence of device dislodgment or infection. This model has shown great reproducibility and thus should be effective in its application for the histologic and biochemical investigation of DO in the rat.