Page 72 - REMOVABLE ORTHODONTIC APPLIANCES

64 Removable Orthodontic Appliances
Soft tissues
Patients with competent, or potentially compe-
tent, lips and with a lower lip-line that is high
relative to the upper incisors, may be well
suited to removable appliance treatment,
provided other factors are favourable. Reduc-
tion of the overjet should reposition the upper
incisors so that the lower lip comes to rest labial
to them and assists stability. If the patient has
difficulty in achieving a lip-seal before treat-
ment a stable result is less likely (Figure 8.2).
Occasional cases may exhibit a marked
tongue thrust with an atypical swallowing
behaviour - often associated with an incom-
plete overbite and sometimes an anterior
sigmatism. The prospect for reducing the over-
jet in these cases is poor with any form of appli-
ance treatment so they are best avoided.
Digit sucking habits can exaggerate a class II
division 1 malocclusion. Removable appliances
may be very suitable for reducing the overjet in
such cases (provided the underlying skeletal
pattern is not too severe) because the very pres-
ence of the appliance will frequently help the
patient to overcome the habit. Parents should
be warned, however, that the result might only
be stable if the habit is discontinued
completely.
Figure 8.2 (a) Favourable soft tissue pattern for
overjet reduction in a class II division 1 case, (b)
Unfavourable soft tissue pattern at the end of
treatment, the lower lip does not cover the upper
Dental factors incisor tips.
Overjet

The overjet should only be modestly increased proclination. Reduction of the overjet in these
(up to about 8 mm) and should be due more to cases will usually demand Ungual movement of
proclination of the upper incisors than to the the lower incisor crowns, which will entail fixed
patient's skeletal pattern. Upright incisors can appliances. Conversely, the lower incisors are,
only be retracted a very short distance before on occasion, excessively retroclined and these
giving an unacceptable appearance and often cases also require fixed appliances to achieve a
an unstable result. satisfactory inter-incisor angulation.

Lower incisors Overbite
One of the aims of treatment for a class II divi- In a growing patient, a moderate increase of
sion 1 case is that the average labio-lingual overbite can be reduced by the use of a remov-
position of the lower incisors should be able appliance incorporating an anterior bite
accepted. (The relief of crowding will allow plate. An overbite that is excessive and perhaps
some spontaneous alignment of individual labi- causing trauma to the palatal gingivae may be
ally or lingually crowded incisors.) In a small less amenable to removable appliance treat-
number of cases the lower incisors are also ment, particularly if it is associated with a low
proclined, producing a consequent bi-maxillary Frankfort mandibular planes angle. If the over-