Page 113 - REMOVABLE ORTHODONTIC APPLIANCES

Retainers 105
full time for 6 months, followed by a further 6 for spontaneous space closure is good but a
months of night-time wear, giving a total of 12 conventional retainer may have the disadvan-
months' retention. tage of preventing space closure while it main-
When standard retention is required, it is tains the corrected tooth positions. The need to
rarely appropriate to use the last removable clasp teeth makes it difficult to design a retainer
appliance. An appliance with flexible springs, which will permit continuing space closure and
such as an apron spring or a Roberts' retractor, by the time retention is complete much poten-
is unsuitable for conversion to a retainer because tial for closure may have been lost so that space
the springs cannot readily be made passive and remains. A compromise must be reached
will deform easily. Purpose-made retainers are between these two conflicting requirements
usually better for standard retention. and careful judgement is necessary. In cases
where residual space is expected it may be wise
to allow some spontaneous closure to occur
after the initial extractions before the
Long-term retention
commencement of active treatment. In cases of
Long-term retention will be required following doubt a vacuum-formed retainer which only
the correction of rotations, closure of a median retains the labial segments can be useful to
diastema and also where there is doubt about maintain a reduced overjet while leaving the
the stability of overjet reduction, perhaps due buccal teeth free to move forwards and close
to the upper lip posture or to existing proclina- the residual spaces.
tion of the lower labial segment. Long-term
retention is also required following a combina-
tion of complex treatment using both func- Functional appliances
tional and fixed appliances.
Where long-term retention is required for an Following functional appliance therapy with an
adolescent patient it may be wise to continue Andresen or activator type of appliance the
this until growth is complete, but the deciding retention follows much the same rules as for
factor must still be the clinical response rather single arch removable appliances. Hours of
than the age of the patient. wear can be reduced gradually. It is often
When the teeth are clinically firm and the necessary to trim the acrylic to allow the buccal
patient reports that the retainer does not feel teeth to settle into a comfortable class I inter-
tight, even when first inserted after being left cuspation. Any type of functional appliance
out for a day or two, wear of the retainer can be may produce some proclination of the lower
reduced to three nights a week. Later, if all labial segment so the alignment of the lower
seems well, then wear can be further reduced to labial segment must be carefully watched
one or two nights a week before finally being during the retention phase because the teeth
left out. Even then it is a good idea to check the may be in an unstable position. It is likely that
fit of the retainer from time to time, to confirm this tendency to relapse will remain however
that there has been no tooth movement. A wise long retention is maintained.
orthodontist never tells his patients to throw
away the retainer.
Some adult patients may require permanent Fixed appliance treatment
retention, but such an intention must be made
clear to the patient at the outset of treatment. Removable retainers are routinely used in
upper and lower arches following fixed appli-
ance treatment. Progressive withdrawal of the
appliances following the end of a year of reten-
Treatment methods tion is almost invariably undertaken.
Fixed appliances are associated with the
treatment of difficult malocclusions or of signif-
Removable appliances
icant local problems. Two types of tooth move-
At the end of removable appliance treatment ment are especially prone to relapse: rotations
some residual extraction space may be present. and space closure. Rotated teeth need a long
During a patient's growth phase the potential period of careful retention after alignment.