Consistency of diet and its effects on mandibular morphogenesis in the young rat.

The purpose of this study was to evaluate the relationship between mandibular morphogenesis and masticatory function in 30 male Sprague-Dawley rats, 28 days of age. Animals were randomly divided into three groups and they received diets of different consistency: liquid, normal (as control group) and elastic diet. The experiment lasted 28 days, at the end of which lateral radiographs of the cranium and photographs of the hemimandibles were made. These images were magnified fourfold and analysed in two dimensions (V = vertical dimension; S = sagittal dimension). Condylar morphology was also assessed. The photographic analysis of the hemimandible showed a significantly higher growth of the mandibular ramus stimulated by the elastic diet: V2 2.4 mm, V3 2.4 mm, V4 1.9 mm, V5 4.1 mm (p < 0.05). In contrast, a statistically significant (p < 0.05) lengthening of the mandibular corpus occurred in the rats subjected to liquid diet (S1 4.5 mm, S2 2.7 mm, S3 1.6 mm, S4 2.6 mm). Measurements were taken on both the radiographic and the photographic records. The variation coefficient showed that photographic analysis was more accurate than the radiographic analysis. From these data it appears that an increase in the tonus of the protrusive muscles could be beneficial in mandibular hypoplasia and the increased tonus of the masticatory muscles in skeletal open bite.