Comparative dental development and microstructure of ... - UCL

200 A. D. BEYNON ET AL.
Figure 19. Composite summary chart of dental development in P. heseloni based on the maximum values
of crown formation times presented in Table 6, the calculated rates of root extension summarized in Table
5, and the information about the sequence of dental development summarized in Figure 17. Solid lines are
crown formation times and dashed lines are root formation times. The following additional key points
were used in constructing this chart: (i) the neonatal line in M 1 indicates formation began 30 days before
birth, (ii) the neonatal line in dm 2 indicates formation began 60 days before birth, (iii) root extension rates
suggest the dm 2 root took 200 days to form, (iv) dentine formation times indicate I 2 formation began 12
days after I 1 , (v) the absence of a neonatal line in dm 1 enamel suggests crown completion occurred before
birth in this tooth, (vi) root extension rates suggest premolars and molars take between 2·3 years and 3
years to complete root formation, (vii) root lengths in Proconsul suggest M 1 roots take longer to form than
M 2 roots and that M 3 roots take the longest time to form, (viii) in this study we estimate 2·3 years for M 1 ,
2·7 years for M 2 and 3·0 years for M 3 root formation for P. heseloni. The overlap of M 3 with M 2 crown
formation is an estimate.
cervix (see Figure 1). This implies that there
was actually some root formation, although
there is no occlusal wear to suggest this
tooth was in functional occlusion. No direct
estimates of crown formation time were
possible for this tooth but based on this
evidence and other crown formation time
estimates for the first permanent molar,
combined crown and root formation times
might have been greater than one year.
This M 1 crown is also a little different in
morphology to the other M 1 crown of the
adult individual (see Figure 4). It is tall
and narrow and not so broad and squat.
The angles of the striae to the EDJ are
higher than for other Proconsul molar teeth
sectioned here, especially in the cervical
region, and judged from the long-period
striae in the cuspal dentine it had dentine
formation rates that exceed those observed
in other posterior teeth (but which are
compatible with the taller cusps).
The period of dental development in Proconsul
Figure 19 is a composite reconstruction of
dental development in P. heseloni and
summarizes the developmental sequences,
the crown formation periods and the root
formation periods estimated histologically
and from perikymata counts. In this chart
we have used the greatest of the mean values
calculated as they appear in Table 6.
(Additional key points used to construct this
chart are given in the legend to Figure 19.)
It seems reasonable on this basis to assume
that dental development in P. heseloni took
between six and seven years. It is important
to stress that this estimate is to the end of
M3 root completion and that this differs
from estimates for the period of dental