Orthodontic implications of protein undernutrition in mandibular growth. A cephalometric study in growing rats.

The present experimental work analyzes the development of different mandibular units and its likely impact on the direction of mandibular displacement during facial development, and the relation between the mesiodistal dimension of the first, second, and third molars and the length of the mandibular corpus in a model of protein undernutrition with muscular atrophy in growing rats. Sixteen Wistar rats weaned at the age of 21 days were assigned to one of the following groups: control (fed a regular hard diet ad libitum) and experimental (fed a diet lacking in protein, corn flour, ad libitum). All the animals were euthanized five weeks after the onset of the experiment. Following resection of the mandibles, the mandibles were hemisected at the symphysis and fixed in 10% formalin. Remaining soft tissue was removed. Metallic landmarks were placed in the mental and mandibular foramens of one hemimandible of each rat. The hemimandibles were radiographed. The cephalometric study was performed on paper tracings of the projected image of the radiographs. Both groups exhibited a slight increase in body weight (b.w) throughout the first ten days of the experiment. After this point, the undernourished group showed no further increase in b.w., and exhibited significantly lower b.w. than controls at the end of the experiment. The cephalometric study showed that the length of the mandible as a whole, and of the condylar and angular processes was significantly lower in the undernourished group. In addition, significant differences in the vertical relation between the angular process to the mandibular corpus, the convexity of the angular process, and the ratio between total molar width (from the first to the third molar) and the length of the mandibular corpus were observed.