Growth layer patterns in <i>Arctocephalus australis</i> canine teeth: evaluation of techniques for age determination

Abstract

A total of 75 canine teeth from 27 A. australis (13 males and 14 females) were examined. The animals were found dead from 1977 to 1997 on the coast of Rio Grande do Sul, Brazil. Growth Layer Groups (GLGs) in each canine were compared and examined for age determination using four techniques. These four techniques were evaluated according to the visible number of GLGs in dentine and cementum (techniques 2, 3 and 4) or external rings (technique 1). Technique 4 (decalcified and stained thin section) was the best technique for age determination in A. australis, as it showed the highest conspicuousness of the growth layers (GLGs and accessory layers) in dentine and cementum (especially in old exemplars with pulp cavity closed). Technique 3 (half-tooth etched in 5% formic acid and rubbed with graphite powder) was selected as second best, and recommended for use in dentine counts up to 10 GLGs in males and 6 GLGs in females. Technique 1 (external rings on canine root) offered easy readings until approximately the seventh ring, beyond which misreadings in age determination occurred. Technique 2 (thick unstained and undecalcified sections) presented limitations for obtaining sections of the same thickness compromising a good reading of the GLGs. This in turn could influence the resolution of the growth layers, as the GLGs reading in dentine and cementum were more difficult in this technique than in technique 4.