Page 244 - My FlipBook

This chart properly represents the time of the eruption
of the permanent teeth that replace the decidnous teeth ; the
succedaneous' teeth, they are sometimes called—the incisors,
cuspids and bicuspids, the bicuspids taking the place of the
child's molars. The roots of the teeth are not complete when
the crowns first present through the gum ; they are only par-

tially grown. That is a general rule to which there are some
exceptions. The exceptions are almost wholly with teeth
that have been delayed in erupting from the causes of which
I have spokeni. Generially the root of the, tooth will be com-
pleted somewhere near its normal time, even though the
eruption of the tooth may be dela3^ed. There are exceptions,
however, to that rule. Sometimes a permanent tooth is de-
layed in its formation, so that the delay is actually caused by
the later development of the tooth. This is a condition that
is difficult to diagnose, but occasionally we are surprised to
find the root of a tooth not fully developed at a much later
time than the normal.
The first molar is the slowest tooth in its development

with which we have to deal. The calcification of this tooth
has usually ibegun at ibirth. I have made examinations in, I
am afraid to say how nuany, cases of still birth, and in but
one or two out of the many have I found a failure of the be-
ginning of calcification of this tooth at birth. Yet the tooth
does not erupt until the child is six years old, or during the
sixth year; the child is generally nearer six and a half years
old; occasionally we will see them presenting a little while
before the sixth year, but the average is somewhat later than
the six-year-old point. Now, the roots of these teeth are rarely
completed before the tenth year, giving four years after the
eruption of the crown for the development of the root, and in
many instances the length of the root is not complete until
five years after eruption. Before the eleventh or twelfth year
if we extract these teeth we will generally find that the apical
foramen has not been clo'sed down to a small opening. And
remember that the important point now for us is the rela-
tion of this closure of the apical foramen to the destruction
and removal of the pulp and the filling of the roots. This
chart represents the contemporaneous calcification lines of
the teeth, a line drawn for each year. It is an old chart,
made about twenty years ago, to show the time that an

232