Removable Orthodontic Appliances K Vijayalakshmi
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Introduction1

 
DEFINITION
Lischer defined an orthodontic appliance as a mechanism for the application of force to the teeth and their supporting tissues, to produce changes in their relations and to control the growth and development of this structure.
Graber defined as a device through which an optimal orthodontic force is delivered to a tooth or a group of teeth in a predetermined direction.
 
Mechanical Appliances
It may be defined as device through which an optimal orthodontic force is delivered to the alveolar bone via teeth in a predetermined direction by means of screws, elastics and springs.
 
Attributes
Appliance should possess the following qualities. They are divided into four categories.
  1. Biologic
  2. Mechanical
  3. Aesthetics
  4. Hygienic
 
Biologic
  1. It must not impede normal development of teeth.
  2. It must be free from inherent qualities which may be harmful to oral tissues and should not be damaged by oral secretions.2
  3. It should interfere as little as possible with movements of lips, cheeks and tongue.
  4. It must not produce movement of teeth already correctly aligned. It must not cause damage to tooth, bone or soft tissue structures.
 
Mechanical
  1. Less bulky, comfortable to wear.
  2. Adequate retention for fixation in proper position.
  3. It should be capable of exerting the correct sufficient force in correct direction and offer sufficient anchorage resistance to induce the necessary bone changes for orthodontic tooth movement.
  4. Pressure exerted must be positive and under proper control and operate for as long as possible between adjustments. It should be stable in the mouth so less interference with the functions of oral cavity.
  5. It should be easy to construct and repair.
  6. It should be easy to remove and wear.
  7. It should be light and inconspicuous but sufficiently strong to withstand the stresses of mastication and general wear and tear.
 
Aesthetic
  1. Base plate used for appliance should have color matching with individual's mucosa.
  2. For functional appliances, since they are bulky with many wire parts, transparent resin is used and aesthetically look good.
  3. It should be well trimmed, finished and polished.
 
Hygienic
  1. It is easy to clean daily.
  2. Avoid depositions of food and calculus.
  3. Discoloration due to some habit is possible so get it changed.
 
CLASSIFICATION OF APPLIANCE
It is classified into
  • Mechanical appliance3
    • Removable
    • Fixed
    • Combination of removable and fixed
  • Functional appliance.
    (In this text, I concentrate only on removable mechanical appliance.)
 
Advantages and Disadvantages of Removable Appliances
 
Advantages
Removable orthodontic appliances have many advantages like:
  1. Majority of cases will require only simple tipping of teeth.
  2. It can incorporate bite platforms to eliminate occlusal interferences and displacement.
  3. Simple to fabricate and easy to maintain
  4. Adjustments are possible by an educated patient.
  5. Inexpensive and any dentist can deal with appliance.
  6. Less visible and easy repair.
These advantages for both the patient and the dentist have ensured a continuing interest in removable appliances. There are also obvious disadvantages.
 
Disadvantages
  • The response to treatment is heavily depended on patient compliance.
  • Bodily movement and multiple rotations are not possible to correct.
  • In extraction cases, uprighting of roots of canine and 2nd premolar is not possible.
  • It is not indicated in certain skeletal cases.
  • The amount of activation is minimal which in turn affect the tooth movement
Because of these limitations, removable appliances are most useful for the first of two phases of treatment and contemporary comprehensive treatment is dominated by fixed but not by the removable appliances.4
 
Development of Removable Appliance
In the United States, Victor Hugo Jackson was the Chief proponent of removable appliances among the pioneer orthodontists of the early twentieth century. At that time, neither the modern plastics for base plate materials nor stainless steel wires for clasps and springs were available and the appliances were rather clumsy combinations of vulcanite bases and previous metal or nickel-silver wires.
In the early 1900s, George Crozat developed a removable appliance fabricated entirely of precious metal that is still used occasionally. The appliance consisted of an effective clasp for first molar teeth modified from Jackson's designs, heavy gold wires as a framework, and lighter gold finger springs to produce the desired tooth movement. At that time the Crozat appliance was developed, a typical fixed appliance consisted of bands only on first molars, with wire ligatures tied to a heavy labial or lingual arch wire to align malposed teeth by expanding the dental arch. The Crozat appliance was a removable but more flexible version of the same device. Its metal framework and improved clasps made it greatly superior to alternative removable of that time. The clasping was good enough to allow the use of light interarch elastics, and Class II elastics were employed with Crozat appliances to treat Class II malocclusions.
The Crozat appliance attracted a small but devoted following, primarily in the area around New Orleans. It is still used by some practitioners, but had little impact on the main stream by American orthodontic thought and practice. From the beginning, the emphasis in American Orthodontics has been on fixed appliances and the steady progression of fixed appliance techniques in the US was described.
For a variety of reasons, development of removable appliances continued in Europe despite their neglect in the US. There were three major reasons for this trend:
  1. Angle's dogmatic approach to occlusion, with its emphasis on precise positioning of each tooth, had less impact in Europe than in the US
  2. Social welfare systems developed much more rapidly in Europe, which meant that the emphasis tended to be on limited 5orthodontic treatment for large numbers of people, often delivered by general practitioners rather than orthodontic specialist;
  3. Precious metal for fixed appliances was less available in Europe, both as a consequence of the social systems and because the use of precious metal in dentistry was banned in Nazi Germany, forcing German orthodontists to emphasize removable appliances that could be made with available materials (Precision steel attachments were not available until long after World War II; fixed appliances required precious metal).
The interesting result was that in the 1925 to 1965 era, American orthodontics was based almost exclusively on the use of fixed appliances, while fixed appliances were essentially unknown in Europe and all the treatment was done with removable, not only for growth guidance but also for tooth movement of all types.
A major part of European removable orthodontic appliance was functional appliances for guidance of growth.
Within the past 20 years, the dichotomy between European and American orthodontics has largely disappeared. European style removable appliances, particularly for growth modifications during first stage mixed dentition treatment have become widely used in the United States while fixed appliances have largely replaced by removable for comprehensive treatment in Europe and elsewhere throughout the World. At present, removable appliances are indicated primarily for three major uses:
  1. Growth modification during mixed dentition.
  2. Limited tooth movements, especially for arch expansion or correction of individual tooth position.
  3. Retention after comprehensive.
The design, fabrication and clinical use of removable mechanical appliance alone in mixed dentition treatment and retention appliance are covered in this text.
The use of a removable appliance is to retract flared incisors. The labial bow with loops for greater flexibility and adjustment is normally used. The classic labial bow with loops in the canine regions bilaterally was designed by Charles Hawley in the 1920s and a removable appliance incorporating it is still often called a Hawley appliance or since it is frequently used as a retainer after comprehensive 6treatment, a Hawley retainer. A wire labial bow is usually included in removable appliances even if there is no desire to reposition the anterior teeth, because it provides some anterior stabilization for the appliance and helps control the position of incisor teeth that are not meant to be moved.
 
Components of Removable Appliance
It consists of:
  1. Active components – Bows/springs/elastics/screws
  2. Retentive components – Clasps
  3. Base plates – It provides framework to hold clasps and springs in position and also anchorage.