Variations in the Morphology of Mandibular first Molars of Albino Rats

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Abstract
A cross sectional study of mandibular first molars from 108 male and 108 female albino rats, highly inbred and provided with opportunity for comparable nutrition during and after tooth development, shows that the maximal mesiodistal crown dimension is larger in the male. No sex differences are expressed in the internal mesial, central and distal crown heights or in the mesiodistal crown size at the cervical level of the tooth. The buccolingual and maximal mesiodistal crown dimensions are highly correlated. Tooth wear between the ages of 21-41, 41-61, and 61-91 days results in widening of the mesial occlusal groove, narrowing of the distal occlusal groove opening, and shortening of the external crown height. Clinical and microscopic examination did not reveal any caries lesions. It is concluded that sex differences are expressed much earlier in the dentition than in the skeleton, and it is suggested that the wide range of normal variation in the size and shape of rat molars, as well as changes caused by tooth wear must be considered when attempting to associate dental caries with tooth morphology.