Effect of altered loading on condylar growth in the rat.

The aim of this investigation was to ascertain whether lessening of function by feeding rats a soft diet and cutting their incisors can change the growth of the condyle. Sixty Wistar rats were divided into two groups; a control group fed whole pellets and a soft-diet group fed ground pellets. At the age of 21 days the upper and lower incisors of the soft-diet group were shortened by cutting with a wire cutter twice a week. Ten control rats and 10 soft-diet rats were injected with alizarin red (200 mg/kg) intraperitoneally at the age of 22, 30, or 40 days and killed at the age of 30, 40, or 50 days, respectively. The heads were freed of soft tissues, and the growth of the condylar process and the mandible was measured. The height growth of the condylar process was significantly greater in the soft-diet group by 30 and 40 days, and its length growth was greater in the soft-diet group by 50 days. It is concluded that the change in the amount of chewing force and the place of articulation of the condyle alters the growth of the condylar process. Lessening of the load increases condylar growth until a new balance is achieved.