Page 13 - REMOVABLE ORTHODONTIC APPLIANCES

Introduction 5
is tipped unfavourably, for instance a distaliy
inclined canine, will not respond satisfactorily
to further distal movement with a removable
appliance.

Mesio-distal tipping
Teeth can be tipped towards a space, usually
one which has been created by extraction to
relieve crowding. Where a tooth is mesially
inclined it can be readily tipped and uprighted.
The commonest example of such tooth move-
ment is provided by the retraction of canines.
Upright or distally inclined canines will become
more distaliy inclined as the result of tipping
with a removable appliance. A decision has to
be made as to how much retraction will be
acceptable. There is some evidence that teeth
which have been tipped with a removable
appliance will undergo limited uprighting in the
post-treatment period (Brenchley, 1966).
Figure 1.5 Tipping of the upper incisors, (a) In a
palatal direction, can correct a mild class II case, (b)
In a labial direction, can correct a mild class III case.
Bucco-lingual tipping
Bucco-lingual movement of incisors can be
carried out readily, but in the lower arch, the successful. This is because it is difficult to main-
labio-lingual position of the incisors is tain a controlled, well-positioned force-couple
normally accepted. Movement should only be on a tooth as it moves. Unwanted effects, such
sufficient to compensate for crowding of the as tilting and elongation, are also prone to
lower incisors and deliberate proclination of occur. Where a bonded fixed attachment is
the lower labial segment is highly likely to used it is possible to correct the rotation of a
relapse. single tooth with a removable appliance.
In the upper arch, tipping of the upper Commonly, however, a rotation may be
incisors can readily be accomplished with a combined with an apical malposition and unless
removable appliance. The essential criterion this can also be controlled the result may still be
must be the position of the apices of the unsatisfactory.
incisors, which will only alter slightly when
tipping takes place. Retraction of the incisors in
a mild class II occlusion or labial movement of Occlusal movement
the crowns in a mild class III occlusion can be To achieve such movement it is necessary to
readily achieved (Figure 1.5). Buccal move- provide a point of attachment for an occlusally
ment of the upper posterior teeth is much more directed force on the crown of the tooth. An
difficult to accomplish, except in crossbite cases attachment bonded to the crown makes it rela-
associated with a displacement activity of the tively simple to do this with a removable appli-
mandible. ance, particularly at the front of the arch
(Figure 1.6).
Rotations and controlled apical Intrusion
movements
Relative intrusion of groups of teeth (particu-
-Such movements require two-point contact on larly of the lower labial segment) can be
the crown of the tooth. Many attempts have achieved by contact with an appliance fitted in
been made to design removable appliances that the opposing arch. This is frequently invaluable
will achieve this, but they are not generally because it means that an increased, complete