COUNTS OF GROWTH LAYER GROUPS IN CEMENTUM AND DENTIN IN RINGED SEALS (PHOCA-HISPIDA)

We compared counts of growth layer groups (GLGs) in the dentine of und ecalcified, unstained cross-sections and in the cementum of decalcifie d, stained longitudinal sections of canine teeth from 144 ringed seals (Phora hispida). Although there was a statistically significant corre lation until approximately 10 GLGs, about 75% of paired readings at le ss than or equal to 10 cementum GLGs disagreed. After 10 GLGs, the num ber of GLGs in the cementum usually was greater. The maximum GLG count in cementum was 33, compared to a maximum in dentine of only 19. Inte robserver differences in median counts were not statistically signific ant using cementum or dentine counts. Regression analysis revealed tha t for cementum in female seals, readers differed at higher counts (P < 0.05), and for dentine, there was a constant difference of about 0.6 G LGs (P <0.05) for male seals and 1.1 GLGs (P <0.05) for female seals. Counting GLGs in the cementum of decalcified and stained longitudinal sections provided higher counts and more agreement between readers, an d it was the better of the methods examined for ageing ringed seals.