Permanent tooth calcification in chimpanzees (Pan troglodytes): patterns and polymorphisms.

Tooth calcification is an important developmental marker for use in constructing models for early hominid life history, particularly for its application to the fossil record. As chimpanzees are commonly utilized in interspecific comparisons in such research, this study aims to improve available baseline data for tooth calcification patterns in chimpanzees (Pan troglodytes), and to quantify basic patterns and polymorphisms. We present an analysis of developmental patterns for the left mandibular dentition (I1-M3) based on intraoral radiographs obtained from a cross-sectional sample of chimpanzees (58 males, 60 females) housed at LEMSIP (NYU Medical Center) and Yerkes (Emory University). No significant differences with previous descriptions of the basic sequences of tooth calcification in chimpanzees were found, but variation in such patterns was documented for the first time. In the overall sequence, polymorphisms between the canine and the group (M2 P4 P3) reached significant levels. This is due to the relative delay in canine crown formation compared to other teeth. Differences in the basic sequence between males and females were recorded, but are due to minor shifts in the percentages of occurrence for polymorphic sequences which are common to both genders. Perhaps our most important findings are that a) different polymorphic sequences occur in tooth calcification and tooth emergence in chimpanzees, and b) developmental relationships among teeth fluctuate throughout tooth calcification. Thus, characterizations of dental developmental patterns based on particular stages of development cannot necessarily be extrapolated to other stages without supporting data.