Factors and Inheritance of Dental Caries in the Rat

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Abstract
The several statistically independent factors that might be involved in dental caries of the rat were studied by means of the principal component analysis. Classified according to their response to diet 1506, the stocks used in the experiment were the caries susceptible Osborne-Mendel (O-M) strain, the comparatively resistant National Institute of Health black rat (BR) and their F1''s, blackcrosses and F2''s. The number of carious teeth, number of morsal carious lesions, and the total carious enamel areas on bucco-lingual, sulcal and proximal surfaces were determined. The 1st principal component which accounted for 64% of the variation in the sample may represent the general response of all tooth surfaces to the cariogenic challenge of the experiment. The 2nd component which explains an additional 15% of the variation classifies caries into smooth (bucco-lingual and proximal) and occlusal surface (morsal and sulcal) lesions. The possible effects of genetic and nongenetic factors on these 2 factors were studied. After allowing for the effects of "nongenetic" transmissible factors represented by the O-M mother and the O-M maternal grandmother by covariance analysis, it was found that the additive genetic effect of the O-M strain was significant on the 1st compound variable. There is no significant degree of dominance deviation, indicating that the degree of caries activity is proportional to the amount of the "blood" of the O-M strain in these matings. The variable can be represented roughly by a sum of carious areas of the 4 surfaces studied. None of the variables studied had a significant association with the 2nd compound variable.