Page 73 - REMOVABLE ORTHODONTIC APPLIANCES

Class II malocclusions 65
bite is incomplete, due to* adaptive tongue and overjet, the relief of crowding, an improve-
behaviour or to a habit, then a satisfactory ment in appearance and the achievement of a
correction is usually achieved following reduc- stable result.
tion of the overjet. Where an anterior open bite Overjet reduction must be carried out solely
exists, associated with skeletal factors or with by alteration of the angulation of the upper
unfavourable tongue behaviour, it may not be incisors, the labio-lingual position of the lower
possible to achieve a satisfactory incisal rela- incisors has to be accepted because it cannot be
tionship. reliably altered by removable appliances. The
stability of the result will depend upon the
upper incisors being retracted to a position
where they are under the control of the lower
Crowding
lip. If this cannot be achieved then the lower lip
The degree of crowding should be such that may cause the upper incisors to relapse.
alignment can be achieved by simple move- In adult patients, treatment may be under-
ments. Gross displacement of individual teeth, taken with the understanding that retention
marked rotations, apical malpositions or distal must be on a permanent basis because a stable
inclination of the canines are contraindications result cannot be achieved. This is not an option
to removable appliance treatment. to be undertaken lightly and the patient must
Most removable appliance treatments only understand, before treatment commences, that
involve active tooth movement in the upper permanent retention will be necessary.
arch. The lower arch must therefore either be
acceptable or else be one in which alignment
will occur naturally as the result of relief of Extraction choice
crowding produced by the extraction of lower
first premolars. Such movements occur best in Removable appliances offer two main avenues
a growing child and once the pubertal growth for the management of a class II division 1
spurt is past there is a marked reduction in the malocclusion. The more common approach
amount of natural alignment that will take involves the extraction of upper first premolars
place. This is especially relevant for female (and sometimes also the lower first premolars)
patients in whom growth ceases earlier to relieve crowding while providing space for
(Stephens, 1983). canine retraction and overjet reduction. A
much smaller group of patients can (provided
they are still growing) be treated without
Missing teeth and those of doubtful premolar extractions, using headgear to move
prognosis the upper buccal segments distally prior to
reduction of the overjet.
Where teeth are congenitally absent it is often The decision concerning extraction depends
impossible to establish a satisfactory contact upon a careful assessment of the malocclusion
point by the use of removable appliances alone. and will be decided by the severity of the
Missing lower second premolars, for example, malocclusion (as demonstrated by the molar
will almost invariably require fixed appliances relationship and the overjet) as well as on the
to achieve satisfactory contact points. Similarly, degree of crowding. Some suggested guidelines
where teeth are of a doubtful prognosis, espe- are given below.
cially first molars, satisfactory results are diffi-
cult to achieve with removable appliances
alone. Occasionally, sensibly planned extrac- Molar relationship class I or less than
tions, carried out at an early stage, may allow half unit class II
satisfactory contacts to develop.
In all cases, the degree of crowding in the lower
arch provides a guide to lower arch extraction.
Aims of treatment With less than half a unit class II molar rela-
tionship and an uncrowded lower arch, lower
The aims of treatment for a class II division 1 premolar extractions are contraindicated and
malocclusion are the reduction of the overbite the upper arch can usually be treated by distal