Page 119 - REMOVABLE ORTHODONTIC APPLIANCES

Appendix 1

Laboratory procedures

Removable appliances can perform only It is best to use a standard design-form
limited tooth movements. They are simple and agreed with the laboratory. (An example of a
it is often assumed that their design and design form is shown on page 112.) Ideally, this
construction demand little thought. This is should allow the prescription to be written and
untrue - and especially so because a removable the design to be drawn. It is sensible to adopt a
appliance has limited adaptability. The mode of routine sequence for design. For example, one
action of a fixed appliance, for example, may be might commence by specifying retentive wire-
totally altered by changing the type or form of work before going on to active springs. Next
the archwire, by adding hooks, power-chains would come additions such as screws or pros-
and auxiliaries, or by introducing intra- or thetic teeth and finally any adaptations or
intermaxillary elastics. A removable appliance, extensions necessary to the baseplate. Wire
by contrast, is designed to carry out a limited dimensions should normally be stated unless
number of specific tasks and is constructed in they are to standards accepted by the clinician
the laboratory to this end. The need to alter its and the laboratory. It goes almost without
mode of action will often require a return to the saying that legibility brings benefits to all those
laboratory - involving expense and the need for involved.
a further appointment, which is inconvenient to The appliance should be designed to carry
the patient. out a limited number of tasks and retention
It is most important that every appliance is should be planned in the light of these tasks.
designed to be as effective and trouble free as An embrasure will usually afford space to
possible and this implies a good working rela- accept a single wire but will rarely accept two
tionship between the laboratory and the clini- wires and appliances are best designed to
cian. avoid this.
The impression for a working model should
be sufficiently extended to show all teeth that
Design may impinge on the appliance, to reveal the full
vault of the palate, to provide good sulcus
The appliance should ideally be designed while depth and to demonstrate any muscle attach-
the patient is still in the chair. This allows teeth ments. An impression that contains sizeable
to be inspected for their suitability for clasping air-blows, has distorted or has come away from
and permits them to be checked in occlusion the tray must be retaken. To avoid the risk of
and the position of muscle attachments to be cross-infection it is recommended that the
located. To design an appliance from the impressions should be rinsed briefly under the
'mirror-image'' presented by an impression tap immediately after being removed from the
carries obvious risks. mouth and then disinfected by immersion for