Comparative dental development and microstructure of ... - UCL

190 A. D. BEYNON ET AL.
Figure 13. The combined totals of cuspal enamel formation times estimated from the histological part of
the study and lateral enamel formation times estimated from perikymata counts from replicas (see in
Appendix 2). The inner vertical lines denote the cuspal enamel formation times. In this chart all
perikymata counts for each tooth type (both upper and lower) have been combined and the error bars
(1 S.D.) indicate the overall variation for lateral enamel formation only for each tooth type of P. heseloni.
surface. The total number of perikymata
on any tooth surface appears in the last but
one column. In general the perikymata
counts for P. nyanzae are slightly higher
than those for similar tooth types in P.
heseloni. The total perikymata counts for
anterior teeth presented here give a clearer
idea of the completed lateral enamel formation
times in a large number of Proconsul
teeth and so complement the striae counts
made from the histological sections on the
buccal aspect. Table 2 contains data for
total striae counts on all aspects of all the
tooth sections prepared in the histological
part of the study. When data for upper and
lower teeth of the same tooth type are
combined the likely true extent of the contribution
of the cuspal and lateral enamel
formation times to total crown formation
times of P. heseloni can be appreciated
(Figure 13).
Cuspal enamel formation times deduced
from the histological sections were used to
calculate crown formation times in three
ways (i) by summing cuspal and lateral
enamel formation times in the teeth where
complete crowns are represented in the
histological sections (Table 2) and (ii) by
summing cuspal formation times with data
for buccal or mesiobuccal perikymata
counts. The average crown formation times,
derived for this purpose from the perikymata
data for each tooth type, appear in the last
column of Appendix 2. A five day cross
striation repeat interval between perikymata
and striae of Retzius in lateral enamel has
been assumed for all P. heseloni specimens
and a six day interval for all the larger P.
nyanzae, and P. major specimens represented
in this study. (iii) In five of the
juvenile and four of the adult specimens of
P. heseloni and in both molar teeth attributed
to P. nyanzae, it was possible to estimate
crown formation times using dentine. All
these estimates for crown formation times
appear in Table 4.
Root extension rates and the timing of root
formation
In four sections, the dm 2 of the infant,
the M 1 , the P 4 and the M 2 of the adult
specimen, it was possible to make each of