• Cannot produce bodily movement of teeth
• Space closure is difficult
• Rotation correction is difficult
• Compliance is poor with lower arch appliances
• Treatment success rate depends on patient compliance
• Can cause soft tissue trauma
• Can cause speech difficulties
• Good OH required
• Compliance is poor with lower arch appliances

• Tipping movement
• Moving blocks of teeth
• Influencing the eruption of opposing teeth (by using an anterior bite plane or buccal capping)

Extractions are usually deferred until the removable appliance is fitted due to the following rationale:

1. If teeth are extracted first, posterior drift of teeth adjacent to the extraction site may cause the removable appliance to fit poorly or not fit at all.

2. Sometimes patient decide to no longer carry on with treatment following the fitting of an appliance.

If a displaced tooth interferes with the design of an appliance then it may require extraction prior to the fitting of the appliance. However, impressions for the appliance should be taken prior to the extraction and

The Acronym ARAB may be used when designing a removable appliance:

COMPONENT	EXAMPLE OF COMPONENT
Active component- Often applies force onto tooth to cause movement	Z-Springs, T-spring, Screws, Elastics, buccal canine retractor
Retention- Prevents displacement of appliance by active component. Retentive component should be positioned as close as possible to active component	Adam’s clasp, South end clasp, Ball end clasp, Plint clasp, Labial bow
Anchorage- Resists force generated by the active component	Can be somewhat provided by the baseplate. Extra oral head gear, temporary anchorage device, temporary bone screw, mini-plate.
Baseplate- All the parts are connected together by the baseplate which can be passive/active component of an appliance. Also provides indirect retention and protects the active components from distortion.	Self-cure or heat-cure acrylic, anterior bite plane, buccal capping

Active Component

• Most active component wires are 0.5mm hard stainless steel, however if the wire size is increased to 0.6mm then the force applied for a given deflection will be doubled

• Springs are most commonly used as an active component as they are versatile and cheap. Force exerted in the spring can be calculated F=dr4/l3.

• Double cantilever Z-spring can treat anterior crossbites by moving single anterior teeth through the bite
  • Often constructed with 0.5mm hard stainless steel

Double cantilever Z-spring

• T- spring can correct posterior localised crossbites
  • Constructed in 0.5mm hard stainless steel for premolars
  • Constructed in 0.6mm hard stainless steel for molars

T-spring

• Activation should not be greater than 3mm at a time

Retention

• Primary retention is often found opposing/close to the active component

• Secondary retention is the retentive component holding the main body of the appliance in place (usually placed on the 6’s)

• Adams clasp:
  • Arrow heads (B) engage in the mesiobuccal and mesiodistal undercuts of teeth.
  • 0.7mm SS wire used; 0.6mm used for premolars and primary molars.
  • Easily modified to incorporate more than one tooth.
  • Adjustments of adams clasps are made in pairs, first at point A, then B then C.

A= Bridge
B= Arrow head
C= Shoulder
D= Tag

• Southend clasp: 0.7mm SS wire used; the U-loop engages the undercut between the incisors. May need adjustment by pushing loop towards baseplate.

Southend clasp

Anchorage

• Greater demand is placed on anchorage when several teeth, rather than a single tooth are being moved or when the intended final tooth position is of relatively large distance.

• If anchorage demands are high, they are best treated by a specialist, as they could require anchorage reinforcement by way of intra-maxillary reinforcement or extra-oral, such as head gear, or even temporary anchorage devices (TAD’s) in the form of temporary bone screws and miniplates.

Baseplate

• All the parts are connected together by the baseplate which can be passive/active component of an appliance. Also provides indirect retention and protects the active components from distortion.

Anterior Bite Plane:

• Increasing the thickness of acrylic behind the upper incisors forms a bite plane onto which the lower incisors occlude.
• For overbite reduction– by allowing increased eruption of the molars
• Also used for elimination of possible occlusal interference that is needed to allow tooth movement to occur.

Buccal Capping:

• When occlusal interferences need to be eliminated to allow tooth movement to be completed
• Reduction of the overbite is undesirable.
• Thin acrylic goes over the occlusal surface of the buccal segment and this props the incisors apart – allowing increased eruption of the incisors.

Posterior bite plane

Before Insertion:

• Check correct appliance for patient in the chair, and prescription of appliance is the same and what you asked for in the design.
• Check fitting surface for roughness/sharp edges of acrylic or metal. Ensure wires don’t impinge on soft tissue/muscle attachments on the model. Ensure active component moves freely under the baseplate.
• Show the patient and explain to them how it works

On Insertion:

• Show patient how to put appliance in and out and let them practice.
• Ask if it feels comfortable – check stability and retention and adjust if necessary.

Review:

• Ask if they have had any difficulties wearing the appliance or if they are used to it
• Look for evidence of wear
• Activate at this appointment as patient is now used to having an appliance in their mouth
• Assess stability and retention
• Bite plane/buccal capping adjusted so it is not bulky for the patient

Information For Patient:

• Wear at all times during meals and night
• Removed for cleaning/vigorous sports. Clean after meals with toothbrush
• Usual to experience some discomfort and speech initially – will get used to it
• Avoid hard sticky foods and chewing gum
• Book another appointment if problems with appliance (broken, loose etc)

Monitoring Progress:

• Ideally patients should be seen every month to see if they have been wearing the appliance and to reactivate it
• Can check if the patient is wearing the appliance if:
  • Patient no longer lisps while wearing the appliance
  • Demarcation intra orally on palate and gingival margins palatally
  • It can be taken out and put in mouth easily
  • Should see signs of tooth movement
  • Retentive components slightly loose
• Active component should now be inactive
• Ideal rate of tooth movement: 1-2mm per month

Repairs:

If an appliance is broken consider:

• How the appliance broke – if due to the patient failing to follow instructions, confirm these instructions with the patient before carrying out repairs
• If it would be more cost-effective to make a new appliance
• If possible, adapt what remains of the spring/ other component to continue the desired movement.
• If the study model is available, or is an up to date impression required in order to repair the appliance
• How will tooth movements be retained while the appliance is being repaired – repair as quickly as possible

Low rate of tooth movement may be caused by:

• Patient may not be wearing it full time. Motivate them but if this fails, consider abandoning treatment.
• The active component may not be in the correct position /incorrectly activated
• If the active component is a screw – is the patient adjusting it correctly and often enough?
• Tooth movement may be obstructed by the acrylic or the wires of the appliance
• Tooth movement may be being prevented by occlusion with the opposing arch

Frequent breakage may be caused by:

• The appliance is not being worn full time
• The patient has a habit of clicking the appliance in and out
• The patient is eating inappropriate foods whilst wearing the appliance – ie hard, sticky foods

Patient may experience:

• Poor oral hygiene, due to removable appliance acting as a plaque trap
• If the area of inflammation matches coverage of the appliance, it could be chronic erythematous candidosis.

1. Littlewood, S.J. and Mitchell, L., 2019. An introduction to orthodontics. Oxford university press.
2. Martz, M.G. and Brining, R.D., MB Orthodontics Inc, 1992. Removable orthodontic appliance. U.S. Patent 5,145,364.