Relationship Between the Number of Rat Littermates per Dam and Mandibular Incisor Growth

Abstract

The relationship between the number of littermates per dam and tooth growth of the mandibular incisor taken out of occlusion by experimental shortening was investigated. The variation in eruptive growth was statistically significant.Tooth eruption may be accelerated or retarded by systemic factors such as nutrition and body growth.YA Ness5,6 studied the secondary effect of body size on the tooth eruption rate of mammals of different sizes and species, and interprets this correlation with caution.Variations in the eruption rate of the incisor have been observed in rats fed different kinds of diets.7'8 Conversely, protein restriction, disturbances in the amount of calcium, phosphorus, and vitamin D,9 and restriction of food intake'0 have not been found to influence eruption rate.Although the eruptive mechanism of continuously growing teeth has been studied extensively,59 no information was available that related rats from litters of different sizes with incisor eruption rate. We previously observed" an association between somatic growth and third molar emergence time of rats from small and large litters and found that larger animals experienced an earlier emergence. In the present study we investigated the possible effects of natural nutritional variations on incisor eruption rate and body weight of suckling and weaned rats from litters of various sizes. Materials and MethodsThe study was made on 164 male and female albino Wistar rats born within an eight-hour period.At one day after birth, 27 litters were sepReceived for publication February 16, 1973. 634 arated into three groups: group A, 10 litters of 2 littermates each (20 rats); group B, 10 litters of 6 littermates each (60 rats); and group C, 7 litters of 12 littermates each (84 rats) . Laboratory chow and water were available ad libitum to the dams and litters. However, before weaning (at 30 days of age) and according to the number of young per cage, competition existed for the main food, milk. At 25 and 46 days of age the animals were weighed.To determine the rate of incisor eruption, measurements were made immediately after cutting (25 and 44 days) and also 48 hours after each cutting. Thus, the eruption rate was calculated during lactation (25 to 27 days of age) and after weaning (44 to 46 days of age). The difference between the two measurements represented the amount of unimpeded eruption for that measurement period. A combination of the measurement methods of Bryer9 and Schour and van Dyke'2 was used.