[Effects of the newly developed mandibular retraction system in a rat]

Authors have developed a mandibular retraction system in a rat that was constructed by arms having a metal mesh, an incisor metal cap, a pair of closed coil springs and a soft plastic collar. The merit of this system is that the anchor is very stable because it is made on the parietal bones, and the direction and load of the traction are invariable regardless of head position of the rat compared to the previous methods in which the anchor was made on the neck collar of a rat. Seventy of 8-week-old male Wistar rats were divided into five groups that were intact, collar, sham operation, straight-pull and high-pull. The anchor was implanted with a metal mesh into the subperiosteal space of the parietal bones just in front of the lambda suture of a rat. The coil spring attached on the sliding hook on the arm was connected with a hook soldered with an incisor metal cap. Therefore, the mandible was retracted in the TMJ direction (straight-pull) and some were 20 degrees upper than TMJ (high-pull) for 15 days at a tension of 10 g. All operations except for traction by the coil springs were performed on a rat in the sham operation group. Only the plastic collar was set on the neck in the collar group. Mandibular retraction for 15 days showed significant inhibition of the sagittal growth of the mandible in both high- and straight-pull groups. No inhibition of sagittal cranial growth was observed according to morphometrical and microscopical investigations.(ABSTRACT TRUNCATED AT 250 WORDS)