Page 110 - REMOVABLE ORTHODONTIC APPLIANCES

Chapter 11

Retainers

Orthodontics can only confer benefit to the consider, however, that treatment should be
patient if tooth movements that are achieved based on the principle of the relief of crowding
remain stable after treatment. A period of and that teeth should be placed in a position of
retention is always necessary after active treat- stability before retention is commenced. It is
ment. In a few situations the corrected occlu- physiologically unsound to hold teeth in an
sion will provide its own retention (for example unstable position.
a corrected incisor, formerly in lingual occlu- Removable retainers have an important part
sion, which has good, positive overbite) but to play in all forms of orthodontic treatment
usually a period of retention must be consid- and may be used following removable, fixed or
ered. functional appliance treatment.
The aim of the retention phase is to ensure
that the tooth movements that have been
carried out are held while the periodontal
fibres and the surrounding alveolar bone reor- Types of retainers
ganize. Treatment usually aims to achieve a Converted appliance
stable result, but the work of Little et al. (1988)
has shown that crowding is a progressive condi- The final removable appliance used during
tion which may continue to increase through- treatment can sometimes be converted into a
out life, with no identifiable predisposing retainer by deactivating any springs and adding
factors. This is particularly marked in the lower cold-cured acrylic to make them passive and to
labial segment and, even when the lower inter lock any screws into position. The appliance
canine width has not been increased by treat- can then be worn full time for 2-3 months
ment, lower incisor crowding may continue to before, if necessary, being worn only at night
increase. Patients should be made aware of this for a further 6 months. This type of retention
possibility and alerted to the fact that, even might follow, for example, the correction of a
though orthodontic treatment may align the lingual crossbite in the mixed dentition, which
lower incisors, permanent retention will be is frequently carried out with an upper remov-
necessary if perfect lower incisor alignment is able appliance using springs or screws. If molar
to be guaranteed indefinitely. capping has been used it should be removed
At a time when retention times are tending before the appliance is converted to a retainer.
to increase and more cases are being consid- If the corrected incisor has an overbite of 2 mm
ered for permanent retention it might be asked or more the prognosis for stability is good, but
whether extractions are necessary and whether if the overbite is reduced then the appliance
treatment could not be limited to non-extrac- should be converted to a retainer by the
tion alignment and permanent retention. We method described.