Removable orthodontic appliance

Definition Removable orthodontics appliances refers to those devices that can be inserted into and removed from the oral cavity by the patient will .

History

• First fixed appliance prototype, 1728. Historically, the development of the fixed appliances preceded that of removable appliances. Pierre Fauchard, father of modem dentistry, in his 2-volume opus entitled, ‘The Surgeon Dentist’ published in 1728 described the bandeau, an expansion arch consisting of a horseshoe-shaped strip of precious metal to which the teeth were ligated. This fixed appliance tied to the teeth became the basis for Angle’s E-arch.

• Removable appliance, 1836. A German dentist “Friedrich Christoph Kneisel (1797-1847) was first to use plaster models to record malocclusion in 1836 and use chin strap for his prognathic patients which perhaps was the first removable orthodontic appliance. He also used a removable plate quite similar to the one used nowadays . Further evolution of the removable appliances was linked to the development of the process of rubber vulcanization.

Advantages of removable orthodontic appliance

• Removable nature of appliance make it possible for the patient to maintain good oral hygiene during treatment

• take less chair side time for orthodontics , as they are fibricated in labrotary

• Damaged appliances can be removed by patients .• Apparently simple to fabricate, use and adjust. Hence require

minimal chair time• Less orthodontic scars compared to fixed appliances such as

decalcification, caries under molar bands and white spots around bonded brackets and gingivitis.

• Cost-effective • Efficient to use for certain type of tooth movements • Removable appliances are the appliances of choice in

the first stage of the correction of a posterior crossbite • They are used commonly during mixed dentition for

treatment of a variety of interceptive procedures. If one considers the factors of risk and the relationship between work volume and effect, removable appliances deserve preference.

Disadvantages

• Not effective with uncooperative patient• Only treat the minor cases of malocclusion• Only capable of tipping tooth movement• Limited control over tooth movement• Only certain types of malocclusion can be corrected.• Tooth movement in three dimensions is not possible.• May hinder with speech and eating• Appliances may be lost or broken• Residual monomer of acrylic resin may cause allergy and/or

irritation.

Components of removable appliances

Retentive component They are the component that help in keeping the appliance in

place and resist displacement . Adequate retention of a removable appliance is achieved by incorporating certain wire component that engage undercuts on the teeth . These wire components that aid in retention of a removable appliance are called clasp .

Mode of action of clasp clasps act by engaging certain constricted areas of the teeth

that are called undercuts. When clasps are fibricated the wire is made to engage these undercuts so that there displacement is prevented .

Requirement of ideal clasp 1. It should offer adequate retention . 2. It should permit usage in both fully erupted as well as partially

erupted teeth . 3. They should not themselves apply any active force that would bring

about undesired tooth movement of the anchorage teeth . 4. It should be easy to fabricate . 5. It should not impinge on the soft tissues .

6. It should not interfere with normal occlusion .

Guidelines of appliance activation 1) The path of tooth movement should be free of any obstructions 2) The retraction/tipping of maxillary incisors should not be initiated till

sufficient bite opening has been achieved . Early retraction of maxillary anterior tooth will further cause extrusion and relapse

3) Activated labial bow appliance without sufficient relief of acrylic base plate for incisor retraction is a common mistake . The palatal acrylic is so trimmed that it would allow greater movement of incisors at the cingulum , thereby minimising tipping at incisal edge

4) The conventional labial bow should uniformly touches labial surface of all the teeth being retracted . To retract the single malpositioned incisor , labial bow activation should be minimal and gentle . heavy force can produce pain , pulpitis and non-vital tooth .

5) For distal canine retraction , enough acrylic should be removed in the alvelous are to accommodate large buccolingual dimension of the distally moving maxillary canine .6)To minimize tipping and rotation during canine retraction , the point of contact of activated spring arm should be as gingival as possible without damaging the gingiva .7) The free end of retraction spring should gently touch the mesial surface of the canine at its neck on its entire labiolingual thickness . It is slightly extended to passively turn around on labial surface for palatal canine retractor and palatal surface for labial canine retraction8) The premolar should be prevented from mesial tipping and anchorage loss with the ‘c’ clasp on its mesial proximal surface . It may require to be gently activated in a distal direction if the anchorage loss is anticipated.

Circumferential clasp It is also known as three-quarter clasp or `C’ clasp . They are simple

clasp that are designed to engage the bucco-cervical undercut This clasp cannot be used in partially erupted teeth where the

cervical undercut is not avilable for clasp fabrication .

• Adaptation A wire is engaged from one proximal undercut along the cervical

margin then carried over the occlusal embrasure to end as a single retentive arm on the lingual aspect that gets embedded in the acrylic

base plate .

Advantages :-Simple design and fabrication

Disadvantage :-It cannot be used in partially erupted teeth wherein cervical undercut is

not avilable fo clasp fabrication

Jackson’s clasp• It is also called full clasp or ‘U’ clasp . The clasp engage the bucco-

cervical undercut and also the mesial as well as distal proximal undrecuts.

• Adaptation Wire is adapted along the buccocervical margin and both the

proximal undercuts ,and carried over both the occlusal embrasures to end as retentive arms on both side of the molar

• Advantages : simple to construct and offers adequate retention .

• Disadvantage : it offers inadequate retention in partially erupted tooth.

Adams clasp• Adams clasp was first descried by professor phillip Adams . it is also known as liverpool clasp ,universal clasp and modified

arrowhead clasp . The clasp is constructed using 0.7mm hard round stainles steel wire . Adams clasp is made up of three parts (a) two arrowheads (b)bridge (c)two retentive arms Two arrow heads engage the mesial and the distal proximal

undercuts . The arrow heads are connected to each other by a bridge that is at 45 degree to the long axis of the root

• • :-:

• fig :- adams clasp

Advantages of adams clasp• It is rigid and offers excellent retention • It can be fibricated on decidious as well as permanent teeth.• They can be used in partially or fully erupted teeth.• It can e used on molars ,premolars and on incisors .• No special instrument is needed .• It is small and occupies minimum space .

• The clasp can be modified in a number of ways .

Steps in fabrication of adams clasp

Modifications in adams clasp a) Adams with single arrowhead : This type are indicated in partially

erupted tooth ,which usually is last erupted molar . The single arrow head is made to engage the mesio-proximal undercut of the last erupted molar . The bridge is modified to encircle the tooth distally and ends on the palatal aspect as a retentive arms .

b)Adams with J hook : J hook can be soldered on the bridge of the adams clasp . These hooks are useful in engaging elastics .

c) Adams with incorporated helix : A helix can be incorporated into a bridge of the adams clasp . It also help in engaging elastics .

d) Adams with additional arrow head : Adams with additional arrow head can e constructed to engage the proximal undercuts of the adjacent tooth and is soldered on the bridge of the adams

e) Adams with soldered buccal tube :For extra oral anchorage using face bow and headgears , a buccal tube can be soldered on the bridge of adams clasp.

f)Adams with distal extension : The adams can be modified so that he distal arrow head has a small extension incorporated distally .They can be used in engaging elastic .

f) Adams on incisor and premolars : Adams clasp can be fabricated on the incisor and premolar areas when the retention in these area is required .

Southend clasp Southend clasp is used when retention in the anterior region is

required .The wire is adapted along the cervical margin of both the central incisors . The distal ends are carried over the occlusal embrasures to end as retentive arms on the palatal side .

Traingular clasp They are small traingular shaped clasp that are used between

two adjacent posterior teeth . Thus they engage the proximal undercuts of two adjacent teeth . These clasp are indicated when additional retention is required .

Schwarz clasp Schwarz clasp or arowhead clasp can be said to be the predecessor

of the adam clasp . The clasp is designed in such a way that a number of arrowhead engage the interproximal undercuts between the molar and between the premolars and molars . This clasp is not used routenly due to numbers of drawbacks .

Crozat clasp This clasp resemble a full clasp but has but has an additional piece

of wire soldered which engages into the mesial and distal proximal undercuts .thus it offers better retention than the full clasp .

Active component of removable orthodontic appliances

• They are components of the appliances that exert forces to bring about the necessary tooth movements .

The active component includes : (a) bows (b)springs (c)screws (d)elastics

• Bows Bows are active components that are mostly used for incisor

retraction .

Types of the bows : (a) Short labial bows : They are constructed using 0.7mm hard round stainless steel

wire . It consist of bow that make contact with the most prominent labial teeth and two U loops that ends as retentive arms distal to the canine . The short labial bow is activated by compressing the U loop .

Indication : Minor overjet reduction and anterior space closure .

(b) Long labial bows This labial bow is similar to the short labial bow except that it extends

from one first premolar to opposite first premolar . The distal arms of the U loops are adapted over the occlusal embrasure between the two premolars to get embedded in the acrylic plate .

Indications :• minor anterior space closure• minor overjet reduction • closure of space distal to canine • guidance of canine during canine retraction using palatal retractor• as a retaining device at the end of fixed orthodontic treatment

(c) Split labial bow This is a labial bow that is split in the middle . This result in two

seprate buccal arms having a U loop each . This type of labial bow show the increase flexiblity as compared to the conventional short labial bows .

This type of labial bow is used for anterior retraction . The split bow is activated by compressing the U loop 1-2mm at a

time .

(d) Reverse labial bow This is also called reverse loop labial bows . Here the U loop is

placed distal to the canine and the free end of the U loop are adapted occlusally between the first premolar and canine .indication are similar to that of short labial bow . Activation is done in two step . First the U-loop is opened resulting in lowering of the labial bow in incisor region . The compensatory bend is then made at the base of U loop to maintain proper level of the bow .

(e) High labial bow with apron springs It consist of heavy wire bow of 0.9 mm thickness that extends into the buccal vestibule . Apron spring made of 0.4mm wire is attached to high labial bow . The apron spring can be designed for retraction of one or more teeth . This type of labial bow is highly flexible and is thus used in cases of large overjet . The apron spring is the active component that is activated by bending it towards the teeth , activation of upto 3mm can be done .

(e) Robert’s retractor This is a labial bow made of thin guage stainless steel wire having a

coil of 3mm internal diameter mesial to the canine . As very thin wire is used for its fabrication ,the bow is highly flexible and lacks adequate stability in the vertical plane . Thus the distal part of the retractor is supported in a stainless steel tubing of 0.5 mm internal diameter .

Indications :- Patient having severe anterior proclination with over jet of over

4mm .

(f) Mills retractor This is a labial bow having extensive looping of the wire so

as to increase the flexibility and range of action . Mills retractor are indicated in patient with a large overjet .

Disadvantage :-• difficult in construction • poor patient acceptance

• Springs Springs are the active component of removable

orthodontic appliance that are used to effect various tooth movements .

Classification of springs – (1) Based on the presence or absence of helix they can be classified as simple –without helix compound –with helix (2) Based on the presence of loop or helix they can be classified as helical springs – have a helix looped springs – have a loop(3) Based on the nature of stability of the springs they can be classified as : self –supported spring = made of thicker gauge wire ,can support themselves supported springs = made of thinner gauge wire and thus lack adequate

stability , springs are encased in metallic tube to give adequate support .

Ideal requisites of a spring :- a) the spring should be simple to fabricate . b) it should be easily adjustable . c) It should fit into the avilable space with out discomfort to the

patient . d) It should be easy to clean . e) It should apply force of required magnitude and direction . f) It should not slip or dislodge when placed over a sloping tooth

surface . g) It should be roust . h) It should remain active over a long period of time .

• Factor to be considered in designing a spring .a) Diameter of wire :- flexibility of the spring to a large extent depends upon diameter of wire F = D4/l3 where F= force applied by spring D=diameter of wire L= length of wire

b) Length of wire :- force can be decreased by increasing the length of wire . Thus springs that are longer are more flexible and remains active for long duration of time . By doubling the length of wire force can be reduced by eight times .

c) Patient comfort :- spring should be comfortable to patient in design , shape , size or force

generation . The patient should be able to insert the appliance with spring in proper position.

d) Direction of tooth movement :- the direction of tooth movement is determined by the point of contact between the spring and the tooth . Palatally placed spring are used for labial and mesio – distal tooth movement .buccally placed spring are used when the tooth is to be moved palatally and in a mesio-distal direction .

Finger spring Finger spring is also called single cantilever spring as one end is fixed

in acrylic and the other end is free . It is constructed using 0.6mm wire . It consist of active arm of 12-15mm length ,a helix of 3mm internal diameter and retentive arm of 4-5 mm length . It is used for mesio distal tooth movement when teeth are located correctly in bucco lingual direction .it is activated by moving active arm toward the teeth intended to be moved .

• Cranked single cantilever spring It is constructed with 0.5mm wire . The spring consist of coil , close to

its emergence from base plate . The spring is cranked to keep it clear of the other teeth .it is used to move teeth labially .

Z spring The ‘z’ spring is also called double cantilever spring . It is made up of

0.5mm wire . The spring consist of two coil of very small internal diameter .it should be placed perpendicular to palatal surface of tooth . The spring can be made for movement of single incisor or two incisor . It is activated by opening helices by about 2-3 mm at a time .

• T spring It is made of 0.5 mm wire . The spring consist of t shaped arm whose

arm are embedded in acrylic. It is used for buccal movement of premolar and some canine . It is activated by pulling the free end of the t toward the intended direction of tooth movement.

Coffin spring It is made of 1.2mm wire . It consist of a u or omega shaped wire

placed in the midpalatal region with retentive arm incorporated in base plates .it is retended by adams clasp in molar .it is used in slow dentoalveolar arch expansion in patient with upper arch constriction or in unilateral crossbite.

Canine retractors Canine retractors are springs that are used to move canine in a distal

direction . classification of canine retractorsa) Based on their location buccal canine retractor palatal canine retractorb) Based on the presence of helix or loop canine retractor with helix canine retractor with loopc) Based on their mode of action push type pull type

• U loop canine retractor It is made up of 0.6 or 0.7 mm wire . It consist of u loop , an active arm

and a retentive arm that is distal . It is used when minimum retraction of 1-2mm is required . It is activated by closing loop by 1-2mm or cutting the free end of active arm by 2mm and readapting.

• Helical canine retractor It is also called reverse loop canine retractor and is made of 0.6 mm

wire . It consist of a coil of 3mm diameter , an active arm and a retentive arm . It is activated by opening helix by 1mm or by cutting 1mm of free end and readapting it around the canine .

Buccal canine retractor It is indicated in bucally placed canine and canines placed high in the vestibule . They are used to move canine in distal as well as palatal direction . It consist of a coil of 3mm diameter , an active arm and a retentive arm .Buccal canine retractor are of two types supported self supportedSelf supported are made of thicker gauge wire(0.7mm) so that the spring can support itself and supported are made of thinner gauge wire (0.5mm) thus they are more flexible and mechanically efficient

• Palatal canine retractoin It is made up of 0.6mm wire . It consist of coil of 3mm diameter , an

active arm and a guide arm . It is indicated in canine that are palatally placed . Activation is done by opening the helix 2mm at a time .

• Screws Screw are active component that can be incorporated in a

removable appliance . Screw can be activated by the patient at regular intervals using a key .

Removable appliances having a screw usually consist of split acrylic plate and adams clasps on the posterior teeth. The screw is placed connecting the split acrylic plate .

screw key

Screw can bring about three types of movement :-

(a) expansion of arch . (b) movement of one or a group of teeth in a buccal or labial

direction . (c) movement of one or more teeth in a distal or mesial

direction

• Elastics Elastics as active components are seldom used along with

removable appliances . They are mostly used in conjunction with fixed appliances .

Base plate The bulk of removable appliance is made of the acrylic base

plate . The prime function of the base plate is to incorporate all the components together into the single function unit .

Uses of base plates in removable appliances : (a) The base plate unites all the components of the appliance into one

unit . (b) Helps in anchoring the appliance in place . (c) It provides support for the wire components . (d) Helps in distrubting the forces over a larger area . (e) Bite planes can be incorporated into the plate to treat specific

orthodontic problems . (f) Baseplate of 1.5 to 2mm thickness offers adequate strength.

• Avoidable complications of Removable appliance1. Pain in teeth due to over activation o f the wire components. The

activation should be gentle and should not produce force of more than 20-40 gm/ tooth.

2. Appliance activated, but tooth has no freedom to move. This might result in severe pain, non-vitality and tooth extrusion.

3. Ulcers in the palate. Check for acrylic pimples on tissue surfaces of the appliance. Acrylic pimples can be avoided by filling up air bubbles on the working dental cast prior to acrylization.

4. Ulcers in oral cavity due to sharp ends o f wires. Check prior to delivery outside the mouth. Check on delivery in patient’s mouth.

5. Gagging is usually due to over extended base plate, or a thick rough appliance. Base plate should not compromise volume of the oral cavity.

Summary

Removable appliances need a careful use and thoughtful design by the clinician with regards to anchorage and type of tooth movement required and therefore clear instructions to the laboratory technician are a must. The spring designs should be preferably drawn on the laboratory requisition form with specified size of the wire to be used for each of the components and modifications from conventional design if any desired for individual patients need.

Removable appliances do have a significant role in an orthodontic armamentarium, particularly during interceptive orthodontics, in conjunction with fixed appliance therapy and during the retention phase.