Variations of rat skull bone robusticity evoked by malnutrition

Weanling Holtzman rats of both sexes were fed a control (25% protein), a 10% protein, and a 2% protein semisynthetic diet. Protein deficit (PD) and protein calorie malnutrition (PCM) were estimated from comparisons between control and 10% protein, and control and 2% protein-fed animals, respectively. Animals were killed when they were 56 days old and their skulls cleaned and disarticulated. Individual bones and incisors were ovendried to constant weight. Total weight (TW), maximal projected length (MPL), and robusticity index (RI) were determined on each bone and incisor. It was found that all the bones and incisors did not behave uniformly. They followed two main patterns: (1) Proportional variation. RI values were not affected by nutritional deficiencies. All basicranial bones and 4 of 10 facial bones followed this pattern. (2) Non-proportional variation. RI values were affected by nutritional deficiencies. This pattern was subdivided into two trends: (2a) PD-diminished RI values. Both upper and lower incisors and 1 of 10 facial bones followed this trend. (2b) PCM, but not PD, decreased RI values. All vault bones and the remaining five facial bones followed this trend. It was concluded that there was a differential robusticity response among cranial base, calvaria, and incisors. This response may be connected with the differences in both histogenetic characteristics of those components and the functional roles they have to perform. The nonvault intramembranous bones showed a nonspecific behavior. This fact precluded the classification of the facial region in some of the previously defined patterns.