Page 985 - My FlipBook
P. 985
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ABRASION. 995
In a considerable number of cases I have noted an habitual disposi-
tion to rub the teeth together—to gritting, as it is called, of the teeth
and this seemed to be connected Avith abnormal abrasion. It will read-
ily be seen that a habit of this kind, once formed, may be maintained
for years, and by the abnormal wear which it occasions may tend to
remove the cusps of the teeth quite rapidly, and as these are removed
the lateral and back-and-forward movements take a wider range, until
the cusps disappear. Then the abrasion will proceed as if the antag-
onism had been faulty from the beginning. In this class of cases it is
not unusual to see the upper incisors worn from their palatine surfaces
until they become very thin, and finally only the enamel of the labial
surface is left, this breaking away, leaving a jagged edge. As the jagged
portions are gradually removed a wider range is given to the forward
motions of the lower jaw, and the wear proceeds more rapidly than
before. It thus appears that as the abrasion progresses it becomes
more rapid, and it is not infrequent to find the teeth worn down to the
gum within a very few years after they become distinctly flat, so as to
permit of rotary movement upon a given plane.
In these cases, if a few teeth have been lost in one jaw, the teeth in
the opposite jaw, having no antagonists, are not worn down ; and if the
loss has occurred early, they will be found to have retained their cusps,
serving to show the original form of the denture. In addition to this,
they will have risen in their sockets also ; so that their crowns will pro-
ject much beyond the plane of the other teeth. Occasionally irregular-
ities formed in this way become very prominent.
When flat surfaces have been formed and wear has proceeded so far
as to expose the dentine, this, being softer than the enamel, is hollowed
out in the form of a cup by the trituration of food. These cup-shaped
cavities are often of considerable depth, especially in case the enamel is
very thick and strong. They are apt to be deepest when the teeth are
about one-third or one-half worn, for the reason that on this part of the
crown the enamel is thicker than it is farther toward the neck of the
tooth. Where this cupping out is considerable, the enamel is liable to
be broken away as the wear approaches those portions about the neck
of the tooth, where it is thinner. In these cases it is very liable at such
points to split away from the dentine up to its junction with the cemen-
tum. Then the dentine wears in such a way that food slides away from
between the teeth during the process of trituration, a deep groove being
abraded ; or if the loss of enamel has extended over the greater part of
one side, while it remains intact on the other, the tooth may be worn to
a wedge-shape. By such mechanism as this teeth occasionally become
very much worn and misshapen.
It is therefore characteristic of simple abrasion of the teeth that a
flat surface is formed as the leading abnormality. Tliis results from
the rubbing away of the cusps by lateral and back-and-forward move-
ments of the jaws, either from a habit acquired or from an original
imperfection in the antagonism. As yet no way of checking this, when
it has once made sufficient progress to be noticeable, has been put into
practice. It seems prol table that the judicious building of cusps at suit-
able points, so that they would interlock in such a way as to prevent the
ABRASION. 995
In a considerable number of cases I have noted an habitual disposi-
tion to rub the teeth together—to gritting, as it is called, of the teeth
and this seemed to be connected Avith abnormal abrasion. It will read-
ily be seen that a habit of this kind, once formed, may be maintained
for years, and by the abnormal wear which it occasions may tend to
remove the cusps of the teeth quite rapidly, and as these are removed
the lateral and back-and-forward movements take a wider range, until
the cusps disappear. Then the abrasion will proceed as if the antag-
onism had been faulty from the beginning. In this class of cases it is
not unusual to see the upper incisors worn from their palatine surfaces
until they become very thin, and finally only the enamel of the labial
surface is left, this breaking away, leaving a jagged edge. As the jagged
portions are gradually removed a wider range is given to the forward
motions of the lower jaw, and the wear proceeds more rapidly than
before. It thus appears that as the abrasion progresses it becomes
more rapid, and it is not infrequent to find the teeth worn down to the
gum within a very few years after they become distinctly flat, so as to
permit of rotary movement upon a given plane.
In these cases, if a few teeth have been lost in one jaw, the teeth in
the opposite jaw, having no antagonists, are not worn down ; and if the
loss has occurred early, they will be found to have retained their cusps,
serving to show the original form of the denture. In addition to this,
they will have risen in their sockets also ; so that their crowns will pro-
ject much beyond the plane of the other teeth. Occasionally irregular-
ities formed in this way become very prominent.
When flat surfaces have been formed and wear has proceeded so far
as to expose the dentine, this, being softer than the enamel, is hollowed
out in the form of a cup by the trituration of food. These cup-shaped
cavities are often of considerable depth, especially in case the enamel is
very thick and strong. They are apt to be deepest when the teeth are
about one-third or one-half worn, for the reason that on this part of the
crown the enamel is thicker than it is farther toward the neck of the
tooth. Where this cupping out is considerable, the enamel is liable to
be broken away as the wear approaches those portions about the neck
of the tooth, where it is thinner. In these cases it is very liable at such
points to split away from the dentine up to its junction with the cemen-
tum. Then the dentine wears in such a way that food slides away from
between the teeth during the process of trituration, a deep groove being
abraded ; or if the loss of enamel has extended over the greater part of
one side, while it remains intact on the other, the tooth may be worn to
a wedge-shape. By such mechanism as this teeth occasionally become
very much worn and misshapen.
It is therefore characteristic of simple abrasion of the teeth that a
flat surface is formed as the leading abnormality. Tliis results from
the rubbing away of the cusps by lateral and back-and-forward move-
ments of the jaws, either from a habit acquired or from an original
imperfection in the antagonism. As yet no way of checking this, when
it has once made sufficient progress to be noticeable, has been put into
practice. It seems prol table that the judicious building of cusps at suit-
able points, so that they would interlock in such a way as to prevent the
