Effects of the masticatory demand on the rat mandibular development

The influence of masticatory loading stimulus on mandibular development is not fully clear. In this paper, experimental alterations in the daily muscle use, caused by a changed diet consistency, were continuously monitored, while adaptations in bone and cartilage were examined. It is hypothesised that decreased muscular loading will result in a decrease in the growth factor expression and mandible growth. Fourteen 21-day-old Wistar strain male rats were randomly divided into two groups and fed on either a hard or soft diet for 14 weeks. An implanted radio-telemetric device recorded continuously muscle activity of the superficial masseter muscle. Chondroblast proliferation in the condylar cartilage was identified by insulin-like growth factor-1 receptor (IGF-1r) immunostaining. Furthermore, an X-ray was taken for cephalometric analysis. In the soft-diet group, the duty time of the superficial masseter muscle at higher activity levels was significantly lower than that in the hard-diet group. This decrease in muscular loading of the jaw system was accompanied by: a significant reduction in (i) articular cartilage thickness, (ii) expression of IGF-1r immunopositive cells and (iii) mandible ramus height. In conclusion, a decrease in masticatory demand during the growth period leads to insufficient mandibular development.