Page 409 - My FlipBook

THE CHILDHOOD PERIOD OF THE PERMANENT TEETH. 259
The incisors, cuspids and bicuspids are often called the suc-
cedaneous teeth, because they take the place of the deciduous
incisors, cuspids and molars. The roots of the teeth are not
complete when the crowns first present through the gum; they
are only partially 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 which
have been mentioned. Generally the root of the tooth will be
completed somewhere near its normal time, even though the
eruption of the tooth may be delayed. There are exceptions,
however, to this rule. Sometimes a permanent tooth is delayed
in its formation, so that the delay is actually caused by the later
development of the tooth. This seems to occur to the lateral
incisors oftener than to other teeth. It is not very uncommon
to find these one or two years late. Occasionally, but much less
frequently, a bicuspid, or some other tooth, is late in its devel-
opment. Excellent and very reliable studies of this may be made
when one has learned to read the signs correctly, in cases of
atrophy. The atrophy marks in the enamel occur on the partic-
ular part of each tooth that was being developed at the same
time. The irregularities in the position of these lines show
clearly what teeth, if any, have been late in the development of
their crowns. Occasionally a bicuspid is found to have begun
the formation of its crown abnormally early and receives the
atrophy mark with the incisors, which is contrary to the rule.
It is not very uncommon to find the marks on the lateral incisors,
showing that they have been late in their calcification. Occa-
sionally, also, when we find an atrophy mark near the incisal
edge of incisors and look to the first molars, we find the atrophy
mark at half length of the crown, showing that these teeth had
begun their calcification at an earlier date than normal, etc.
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 begun at birth. I have made examinations in many
cases of still-birth at term, and in but few have I found a failure
of the beginning of calcification of this tooth. 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 before
the sixth year, but the average is somewhat later than the six-