Apparently complex yet relatively simple

Apparently complex yet relatively simple procedure in orthodontics is palatal expansion. Its versatility is unique for despite the many controversies surrounding it, desirable results are achieved when used in the appropriate situation by a skilled clinician.
Expansion of the palate was first achieved by Emerson C. Angell in 1860. Palatal expansion can be carried out in different ways which are broadly classified as rapid & slow.

RAPID MAXILLARY EXPANSION (R.M.E.)
Rapid maxillary expansion is also known by the terms rapid palatal expansion or split palate. It is a skeletal type of expansion that involves the separation of the mid - palatal suture and movement of the maxillary shelves away from each other.
Emerson C. Angell is considered the father of rapid maxillary expansion. Angell, for the first time in 1860, used a jack screw type of device between the maxillary premolars in a 14 year old girl and achieved an increase in arch width by 1/4 inch in 14 days (fig 1).

Walter Coffin in 1877 introduced a spring called Coffin spring for the purpose of expanding the arch. These efforts however were not accepted by the orthodontic community at that time.
It was the oral surgeons and E.N.T. surgeons who popularized this technique during the early part of this century. E.N.T. surgeons used this technique in treatment of nasal insufficiency and constricted naso-maxillary complex with great success.
Korhkaus and Andrew Hass during the 1950's reintroduced rapid maxillary expansion to the orthodontic community. They popularized the concept with excellent research publications on animals and humans using a variety of techniques and methods.

APPLIED ANATOMY
The maxilla together with the palatine bone forms the hard palate, floor and greater part of the lateral walls of the nasal cavity. The maxilla is a paired bone that articulates with its opposite member and various other bones including frontal, ethmoid, nasal, lacrimal, vomer, zygomatic and the palatine bones. Most of the sutural attachments of the maxilla to the adjoining bones are at its posterior and superior aspects leaving the anterior and inferior aspects free, which makes it vulnerable for lateral displacement.
The inter-maxillary and the inter-palatine sutures are collectively called the mid-palatal suture. Rapid maxillary expansion should be initiated prior to the ossification of the mid - palatal suture. Various studies have been done to ascertain the age at which the mid - palatal suture ossifies. Melsen reports that the transverse growth of the mid - palatal suture continued up to 16 years in girls and 18 years in boys. Most studies report a broad range of association timetable i.e. between 15 - 27 years. The clinician should hence ascertain that. The suture is not ossified by using appropriate diagnostic aids to be described later in this chApter.
The sphenoid and the zygomatic bones have a buttressing effect resisting mid - palatal suture opening.







INDICATION FOR R.M.E.
Rapid maxillary expansion has been carried out for dental as well as medical purposes. The following are some of the indications for rapid maxillary expansion:
(1) Posterior crossbite (fig 2)

associated with real or relative maxillary deficiencies. A real maxillary deficiency is associated with an undersized / narrow maxilla. Relative maxillary deficiency is characterized by normal maxilla but oversized mandible.
(2) Class III malocclusion of dental or skeletal cause. Improvement is seen in both anterior as well as posterior crossbites.
(3) Cleft palate patients with collapsed maxillary
arch.
(4) In cases requiring face mask therapy, R.M.E. is used along with face mask to loosen the maxillary sutural attachments so as to facilitate protraction.
(5) The medical indications for rapid maxillary expansion include nasal stenosis, poor nasal airway, septal deformities, recurrent ear and nasal infection, allergic rhinitis, D.N.S., e.t.c.,.

DIAGNOSTIC AIDS
The routine diagnostic aids such as case history, clinical examination and study models are useful in diagnosis. The mid - palatal suture can be visualized in a maxillary occlusal view radiograph. These radiographs are also useful during treatment to check for mid - palatal split and also to estimate the amount of maxillary expansion achieved. P.A. cephalogram is another valuable diagnostic aid in rapid maxillary expansion procedures to estimate the amount of expansion that has taken place.

THE EFFECTS OF R.M.E.
Though R.M.E. is essentially a dento-facial orthopaedic appliance used by orthodontists, it finds application in other fields such as oral surgery, E.N.T. and plastic surgery.
Maxillary skeletal effect: The maxillary posterior teeth are used as handles to apply a transverse reciprocal force so as to open the mid - palatal suture. Since the force employed for the procedure is very high, not much of orthodontic changes can be observed. The appliance on activation compresses the periodontal ligament and bends the alveolar process bucally and slowly opens the mid - palatal suture. The opening of the mid - palatal suture is fan-shaped or tzriangular with maximum opening at the incisor region and gradually diminishing towards the posterior part of palate (fig 3 a).

This can be appreciated in a post R.M.E. occlusal radiograph. Similar fan shaped or non-parallel opening is also seen in the superio-inferior direction. The maximum opening is towards the oral cavity with progressively less opening towards the nasal aspect (fig 3 b).

According to Krebs, the two halves of the maxilla rotate in the sagittal and coronal planes. In the coronal plane the two halves of the maxilla rotate away from each other. The point at which the rotation takes place is around the frontomaxillary suture. In the sagittal plane, the maxilla is found to rotate in a downward and forward direction.
Amount of expansion achieved: An increase in maxillary width of upto 1 Omm can be achieved by rapid maxillary expansion. The rate of expansion is about 0.2 to 0.5mm per day.
Effect on alveolar bone: The alveolar bone in the area adjacent to the anchor teeth bends slightly. This is due to the resilient nature of the alveolar bone.
Effect on maxillary anterior teeth: The appearance of a midline spacing between the two maxillary central incisors is the most reliable clinical evidence of the maxillary separation. The incisor separation is about half of the distance the screw is opened. By three to five months, the midline diastema closes as a result of the transseptal fiber traction.
Effect on maxillary posterior teeth: The maxillary posterior teeth are used as anchors during rapid maxillary expansion. These teeth show buccal tipping (fig 4)

and are also believed to extrude to a limited extent.
Effect on mandible: Most authors have observed a downward and backward rotation of the mandible following rapid expansion. This is accompanied by a slight increase in the mandibular plane angle. The reason attributed for the mandibular rotation is the extrusion and buccal tipping of the maxillary molars.
EFFECT ON ADJACENT CRANIAL BONES AND SUTURES:
Rapid maxillary expansion not only results in opening of the mid - palatal suture but also has far reaching effects on adjacent cranial
Fig 4 (A) Normal axial inclination of the anchor molars (B) Buccally tipped anchor molars
Structures. In addition to the effects on those bones directly articulating with the maxilla, bones of the cranium such as parietal and occipital were also found to be displaced.
Effects of R.M.E. on nasal cavity: Following rapid maxillary expansion an increase in intranasal space occurs due to the outer walls of nasal cavity moving apart. This increase in nasal cavity width is maximum in the inferior region of the nasal cavity and gradually decreases towards the superior aspect. Similar gradient is also found in an anterio-posterior direction with the greatest increase being in the anterior region.
Air flow resistance is believed to reduce by 45 - 60 %, thereby improving nasal breathing.
Numerous appliances have been used for rapid maxillary expansion. Broadly they can be classified as:
1. Removable appliances
2. Fixed Appliances
a. Tooth borne
b. Tooth and tissue borne





REMOVABLE APPLIANCES
The reliability of these appliances in producing skeletal expansion is highly questionable. Although it is possible to split the sutures using removable plates, it nevertheless is unpredictable. Treatment during the deciduous or early mixed dentition is considered more favorable in producing appreciable skeletal effects.

A removable type of rapid maxillary expansion device consists of a split acrylic plate with a midline screw. The appliance is retained using clasps on the posterior teeth. The disadvantages of a removable rapid expansion appliance is the need for patient co-operation
and the difficulty in retaining the plate inside the mouth.

FIXED APPLIANCES
Appliances that are fixed onto the teeth are more reliable and found to produce consistent skeletal effects. These fixed rapid expanders can be classified into tooth and tissue borne appliances and tooth borne appliances. Two of the commonly used tooth and tissue borne appliances are :
1. Derichsweiler type
2. Hass type
I Examples of tooth borne appliances
Include:
1. Isaacson type 2. Hyrax type



Derlchsweller type
The first premolars and the first molars are banded. Wire tags are soldered onto the palatal aspect of the bands. These wire tags get inserted into a split palatal acrylic plate incorporating a screw at its center (fig 6.a).


HASS TYPE
The first premolar and molar of either side are banded. A thick stainless steel wire of 1.2 mm diameter is soldered on the buccal and lingual aspects connecting the premolar and molar bands. The lingual wire is kept longer so as to extend past the bands both anteriorly and posteriorly. These extensions are bent palatally to get embedded in the palatal acrylic. The split palatal acrylic has a midline screw. The plate does not extend over the rugae area (fig 6.b).

ISAACSON TYPE
This is a tooth borne appliance without any acrylic palatal covering. This design makes use of a spring loaded screw called a MINNE expander (developed at the University of Minnesota, Dental School) .
The first premolars and molars are banded. Metal flanges are soldered onto the bands on the buccal and lingual sides. The expander consists of a coil spring having a nut which can compress the spring. This coil spring is made to extend between the lingual metal flanges that have been soldered. The expander is activated by closing the nut so that the spring gets compressed (fig 6.c).

HYRAX TYPE
This type of appliance makes use of a special type of screw called HYRAX (Hygienic Rapid Expander). The screws have heavy gauge wire ex. tensions that are adapted to follow the palatal contour and are soldered to bands on premolar; and molars (fig 6.d).




BONDED R.M.E
Most of the rapid maxillary expansion appliances described earlier are banded appliances. They incorporate bands on the first premolars and molars. An alternative design of the appliance would be to have a splint covering variable number of teeth on either side to which the jack screw is attached. Splints can be of two types:
1 . Cast Cap Splints 2. Acrylic Splints
The cast cap splints are made of silvercopper alloy. The acrylic splints are made of polymethyl-methacrylate. A wire framework may be adapted around the teeth to reinforce the acrylic. These splints are bonded to teeth using either glass ionomer or other bonding adhesives, after adequate etching.

DESCRIPTION OF A TYPICAL EXPANSION SCREW
A typical expansion screw consists of an oblong body divided into two halves. Each half has a threaded inner side that receives one end of a double ended screw. The screw has a central bossing with four holes. These holes receive a key which is used to turn the screw (fig 8).

The turning of the screw by 90 degree (i.e. one turn) brings about a linear movement of 0.18 mm. The pattern of threading on either side is of opposite direction. Thus turning the screw withdraws it from both sides simultaneously.

ACTIVATION SCHEDULE
Various authors have advocated different activation schedules to achieve the desired results.
Schedule by Timms
For patients of upto 15 years of age, 90° rotation in the morning and evening. In patients over 15 years, Timms recommends 45° activation 4 times a day.

Schedule by Zimring and Isaacson
In young growing patients, they recommend two turns each day for 4 - 5 days and later one turn per day till the desired expansion is achieved. In case of non growing adult patients, they recommend two turns each day for first two days, one turn per day for the next 5- 7 days and one turn every alternate day till desired expansion is achieved.

TREATMENT EVALUATION DURING R.M.E.
Clinically, the most noticeable feature during rapid maxillary expansion is the appearance of 0 midline diastema. Studies by various authors show that the amount of incisor separation is roughly half the amount of jack screw separation. But the amount of diastema should not be taken as 0 reliable factor in estimating the amount of expansion. Maxillary occlusal radiograph and
P.A. cephalogram are more reliable in estimating the amount of maxillary expansion.





CONTRAINDICATIONS OF R.M.E.
Some cases where R.M.E. is contraindicated
are:
1. Single tooth crossbites.
2. In patients who are un-cooperative, R.M.E. is contraindicated as the appliance requires frequent activation and maintenance of good oral hygiene.
3. Rapid maxillary expansion is not carried out after ossification of the mid - palatal suture unless it is accompanied by adjunctive surgical procedures.
4. Skeletal asymmetry of maxilla and mandible and adult cases with severe antero-posterior skeletal discrepancies.
5. Vertical growers with steep mandibular plane angle are usually a contra-indication.
6. As the posterior teeth are used as anchors to move the bones apart, the procedure is not
indicated in a periodontally weak dentition.

RETENTION FOLLOWING R.M.E.
Failure to retain the expansion results in relapse. Most authors recommend a retention period of not less than 3 - 6 months. Isaacson recommends the use of the R.M.E. appliance itself for the purpose of retention. The screw shou Id be immobilized using cold cure acrylic (fig 9).

Alternatively, either a removable or fixed retainer (e.g. TPA) can be used.


SURGERY AS AN ADJUNCT
Patients who exhibit unusual resistance to separation of the palatine bones may require surgical intervention. This usually occurs in female patients over 16 years of age and male patients over 18 years of age in whom the mid-palatal suture has ossified. Surgical separation may also be required in patients exhibiting increased circum-maxillary rigidity as a result of aging.
Maxillary expansion can be brought about by surgery alone or by surgery along with a rapid expansion appliance. The surgical procedures usually carried out are:
a. Palatal osteotomy
b. Lateral maxillary osteotomy
c. Anterior maxillary osteotomy

CLINICAL TIPS FOR R.M.E.
1. Oral hygiene instructions should be given to the patient and reinforced during the procedure.
2. Orthodontic movement of the anchor teeth should be avoided prior to rapid maxillary expansion, as mobile teeth do not offer adequate anchorage for palatal split. Recently moved teeth tend to tip.
3. The patient should be trained to use the key. The key should be tied to a string and the free end should be secured around the patient's wrist to avoid accidental swallowing.
4. Maxillary occlusal radiographs should be taken at regular intervals to monitor the
expansion.
5. The possible immediate effects of premature appliance removal include dizziness, pressure at the bridge of nose, pressure under eyes, blanching of soft tissues under the eyes, etc.,. These symptoms may occur on removal of the appliance for repair or recementation. The patients should therefore be kept seated and asked not to stand immediately after appliance removal.

SLOW EXPANSION
According to the proponents of slow expansion, the results are more stable when the maxillary arch is expanded slowly at a rate of 0.5- 1 mm per week. The forces generated by such procedures is much lower i.e. 2-4 pounds as against 10-20 pounds generated during rapid maxillary expansion. Unlike in rapid maxillary expansion where the treatment is completed in 1 -2 weeks, slow expansion may take a$ much as 2-5 months.
Slow expansion has traditionally been termed dento-alveolar expansion, although some skeletal changes can be observed. The slower expansion techniques have also been associated with a more physiologic adjustment to the maxillary expansion, producing greater stability and less relapse potential than in rapid expansion procedures.

APPLIANCES USED FOR SLOW EXPANSION
Jack screws
The various jack screws incorporated in the appliances described for rapid expansion can be used for slow expansion (fig 1 0),

but with a more spread out activation schedule. The screws used for slow expansion have a smaller pitch than those used in R.M.E.

Coffin spring
This appliance was designed by Walter Coffin around the beginning of this century (fig 11 ).

It is a removable appliance capable of slow dentoalveolar expansion. The appliance consists of an omega shaped wire of 1.25 mm thickness, placed in the mid-palatal region. The free ends of the omega wire are embedded in acrylic covering the slopes of the palate. The spring is activated by pulling the two sides apart manually. It can also be activated by using three prong pliers. Coffin spring is believed to bring about a

Table 1 comparison between slow and rapid expansion.
Feature Slow expansion Rapid expansion
Type of expansion Mostly dental Skeletal
Rate of expansion Slow Rapid
Type of tissue reaction Force used More physiologic More traumatic
Force Used Milder force Forces Greater
Frequency of activation Less Frequent More frequent
Duration of treatment Long Short
Type of appliance Either fixed or removable Mostly fixed appliance
Age Any Age Before fusion of midpalatal suture
Retention Lesser chance of relapse More chance of relapse

dento-alveolar expansion. However use of this appliance in younger patients is believed to bring about some amount of skeletal expansion.





Quad helix
One of the appliances used to expand a narrow maxilla is the quad helix (fig 12).

It is said to have evolved from the original Coffin loop. The quad helix incorporates four helices that increase the wire length. Therefore the flexibility and range olaction of this appliance is more. The appliance is constructed using 0.038 inch wire and is soldered to bands on the first molars.
The quad helix consists of a pair of anterior helices and a pair of posterior helices. The portion of wire between the two anterior helices is called the anterior bridge. The wire between the anterior and posterior helices is called the palatal bridge. The free wire ends adjacent to the posterior helices are called outer arms. They rest against the lingual surface of the buccal teeth and are soldered on to the lingual aspect of the molar bands.
The quad helix can be used to expand a narrow arch as well as to bring about rotation of molars. It can be pre-activated by stretching the two molar bands apart prior to cementation or by using three prong pliers after cementation (fig 13).



The quad helix brings about a slow dento-alveolar expansion. But when it is used in children during the deciduous and early mixed dentition periods, a skeletal mid-palatal splitting can be achieved.
ARCH EXPANSION USING FIXED APPLIANCES
Arch expansion can be achieved in a patient who is undergoing fixed mechanotherapy. Mild expansion can be brought about by using expanded arch wires. In addition appliances such as the quad helix or the transpalatal arch can be used along with fixed mechotherapy.

























TREATMENT OF TRANSVERSE MAXILLARY CONSTRICTION:-


Skeletal maxillary constriction is distinguished by a narrow palatal vault. It can be corrected by opening the mid palatal suture, which widens the roof of the mouth and the floor of the nose. This transverse expansion corrects the posterior crossbite, sometimes moves the maxilla forward, increases space in the arch, and repositions underlying permanent tooth buds, it can be done at any time prior to the end of the adolescent growth spurt. The major reasons for doing it sooner are to eliminate functional problems and mandibular shifts on closure, and to provide more space for the Erupting maxillary teeth.
Several methods of arch expansion are possible, but to obtain skeletal effects, it is necessary to place force directly across the suture. In preadolescent children. Three methods can be used for palatal expansion:
1. A split removable arch with a jackscrew or heavy midline spring.
2. A lingual arch often of the w arch or quad helix design.
3. A fixed attached to bands or incorporated into a bonded appliance. Removable palates and lingual arches produce slow expansion. The fixed expander can be activated for either rapid (0.5 mm or more per day)( semi-rapiD (0.25mm/day) or methods appropriate questions. Are does it achieve the expansion ? does it have iatrogenic side effects? And is the expansion stable?

PALATAL EXPANSION IN THE PRIMARY AND EARLY MIXED DENTITION:
Because less force is needed to open the suture in you8nger children, it is relatively easy to obtain palatal expansion. In the early mixed dentition, all three types of expansion appliances produce both skeletal and dental changes.
With a removable appliance, the rate of expansion ust be quite slow, and the force employed during the process must be low, because faster expansion produces higher forces that create problem with retention of the appliance, multiple clasps that are well adjusted are mandatory. Because of the instability of the teeth during the expansion process, failure to wear the appliance even for 1 day requires adjustment of the jackscrew, usually bye the practitioner, to cAn resumed. Compliance in activation and wear time are always issue with these appliances. Successful expansion with a removable appliance can take so much time that it is not cost effective.
Ligual arches of the W-arch and helix designs have been demonstrated to open the midpalatal suture in young patients. These appliances generally deliver a few handred grams of force and provide slow expansion they relatively clean and reasonably effective, producing a mix of skeletal and dental change.

Fixed jackscrew appliances attached to bands or bonded splints also can be used in the early treatment of maxillary second molars is relatively simple, but banding primary first molars can be challenging. Using a bonded appliance in the mixed dentition is relatively straightforward. This appliance can deliver a variety of forces and can extinguish habits by virtue of its bulk. In young children, in comparison with a lingual arch, there are two major disadvantages. First , the fixed jackscrew appliance is more bulky than an expansion lingual arch and more difficult to place and remove. The patient inevitably has problems in cleaning it and either the patient or parent must activate the appliance, second a fixed appliance of this type can be activated rapidly which in young children is a disadvantage, not an advantage, rapid expansion should not be done in a young child. There is a risk of distortion of facial structures with rapid expansion movement and high forces produce better or more stable expansion.
Many functional appliances incorporate some components to expand the maxillary arch either intrinsic force generating mechanism like springs and jackscrews or buccal shields to relieve buccal soft tissue pressure. When arch expansion occurs during functional appliance treatment. It is possible that some opening of the midpalatal suture contributes to it. But the precise mix of skeletal and dental change is not well documented.
On balance, therefore, slow expansion with an active lingual arch is the preferred approach to maxillary constriction in young children in the primary and early mixed dentitions. A fixed jackscrew appliance is an acceptable alternative if activated carefully and slowly.

PALATAL EXPANSION IN THE LATE MIXED DENTITION

With increasing age, the midpalatal suture becomes more and more tightly inter digited, but in most individuals, it remains possible to obtain significant increments in maxillary width up to age 15 to 18.expansion in adolescents is discussed.
Even in the late mixed dentition, satural expansion requires placing a relatively heavy force directed across the suture to move the halves of the maxilla apart. A fixed jackscrew appliance (either banded or bonded 0 is required.

as many teeth as possible should be included in the anchorage unit. In the late mixed dentition. Root resorption of primary molars may have reached the point that these teeth offer little resistance, and it may be wise to wait for eruption of the first premolars before beginning expansion.
Although Some Studies Have reported increases in vertical facial height with maxillary expansion. Long term evidence in dictes this change is transitory. A bonded appliance that covers the occlusal surface of he posterior teeth may be a better choice for a child with a long face tendency by producing less mandibular rotation than a banded appliance but this is not totally clear. Perhaps the best summary is that the older the patient when maxillary expansion is done. The less likely it is that vertical changes will be recovered by subsequent growth.
RAPID OR SLOW EXPANSION:
In the late mixed dentition, either rapid or slow expansion is clinically acceptable. It now appear that slower activation of the expansion appliance (i.e.at the rate of about 1 mm/week) provides approximately the same ultimate result over a 10 to 12 week period as rapid expansion with less trauma to the teeth and bones.
Rapid expansion typically is done with two turns daily of the jackscrew (0.5 mm activation ) this creates 10 to 20 pounds of pressure across the suture enough to create microfractures of interdigitating bone spicules. When a screw is the activating device the force is transmitted immediately to the teeth and then to the suture. Sometimes a large coil spring is incorporated along with the screw which modulates the amount of force, depending on the length and stiffness of the spring.


the suture opens wider and faster anteriorly because closure begins in the posterior area of the midpalatal suture and there is a buttressing effect area of the midpalatal suture and there is a buttressing effect of the other maxillary structures in the posterior regions with rapic or semi rapid expansion a diastema usually appears between the central incisors as the bones separate in this area.

expansion usually is continued until the maxillary lingual cusps occlude with the lingual inclines of the buCCal cusps of the mandibular molars. When expansion has been completed a 3 month period of retention with the appliance in place is recommenced. After the 3 month retention period, the fixed appliance can be removed, but a removable retainer that covers the palate is often needed as further insurance against carly relapse

A relatively heavy expanded maxillary archwire provides retention if further treatment is being accomplished immediately.
The theory behind rapid activation was that force on the teeth would be transmitted to the bone, and the two halves of the maxilla would separate before significant tooth movement could occur. In other words rapid activation was conceived as a way to maximize skeletal hange and minimize dental change. It was not realized initially that during the time it takes for bone to fill in the space that was created between the left and right halves of the maxilla, skeletal relapse begins to occur almost immediately, even though the teeth are held in position. The central diastema closes from a combination of skeletal relapse and tooth movement created by stretched gingival fibers. The net treatment effect therefore is approximately equal skeletal and dental expansion.
Slow activation of the expansion appliance at the rate of 1 mm /week which produces about 2 pounds of pressure in a mixed dentition child, opens the suture at a rate that is close to the maximum speed of bone formation. The suture is not obviously pulled apart on radiographs, and no midline diastema appears but both skeletal and dental changes occur. After 10 to 12 weeks approximately the same roughly equal amounts of skeletal and dental expansion are present that were sEen at the same time with rapid expansion. When bonded slow and rapid palatal expanders in early adolescents were compared, the major difference was greater expansion across the canines in the rapid expansion group. This translated into a predicted greeted arch perimeter change but similar opening of the suture posterioly. So by using slow palatal expansion (one turn) every other day in a typical fixed expansion appliance or by using a spring to produce about 2 pounds of force, effective expansion with minimal disruption of the suture can be achieved for a late mixed dentition child.

CLINICLA MANAGEMENT OF PALATAL EXPANSION DEVICES
Most traditional palate expansion devices use bands for retention on first premolars and permanent first molars if possible. During the late mixed dentition years the first premolars often are not fully erupted and are difficult to band. If the primary second molars are firm they can be banded along with the permanent first molars. Alternatively cotacting the other posterior primary and erupting permanent teeth near their gingival margins.
The bands are stabilized in an impression while it is poured, so they are retained in the completed working model. A soldered wire framework and palatal portions, if desired are added during appliance fabrication.
After crossbite correction is completed, band removal can be difficult because the teeth are mobile and sensitive. In those cases, sectioning the bands is appropriate.
An alternative approach is to use a bonded palatal expander during fabrication of the working casts, plastic is generally extended over the occlusal and facial and lingual surfaces of the posterior teeth. When the appliance is returned from the laboratory, because of poor dimensional stability and distortion of the plastic portion, it may be necessary to relieve the acrylic where it seats on the maxillary teeth, reline this area with additional plastic, and refit the appliance in the mouth. By removing the appliance before final polymerization, it can be trimmed and further adjusted without complication. Generally, a composite resin is used to retain the appliance, with only the facial and lingual surfaces is not recommended bonding there is unnecessary for retention and can greatly complicate appliance removal.
Removal of the appliance is accomplished with a band remover engaged under a facial or lingual plastic margin and is facilitated by including loops of wire extending from the facial surfaces the appliance can be sectioned but this is time consuming and usually unnecessary. Complete resin removal can be sectioned but this is time consuming and usually unnecessary. Complete resin removal can be laborious, so using only an adequate amount of resin is crucial. There is a delicate balance. Inadequate resin will lead to excessive leakage onto the no bonded surfaces, which can result in decalcification, or appliance loss. Too much resin, on the other hand, can make tooth and appliance cleaning, as well as appliance removal, difficult. For these reasons, some clinicians use glass ionomer cement for retention. The strength of the material usually is adequate but bonding failure may occur. Fluoride release from these cements may prove advantageous in the short term.










ARCH EXPANSION COMPONENTS:-
Plastic buccal shields and lip pads, both of which are incorporated into the frankel appliance hold the soft tissues away from the teeth.



The effect is to disrupt the tongue ckeck equilibrium, and this in turn leads to disrupt the tongue ckeck equilibrium, and this is in rurn lead to facial movement of the teeth and arch expansion. A buccal shield is more effective in producing buccal expansion than wires to hold the cheeks away from the teeth, lip pads positioned low in the vestibule force the lip musculature to stretch during function.

A combination of lip pads and buccal shields will result in an increase in ardh circumference as well buccal shields and lip pads are an integral part of the frankel appliance, but can be added to any appliance. They add to the potential for soft tissue irritation that can inhibit patient compliance, and must be monitored to prevent this.
Expansion screws and springs can be used to actively increase the transverse dimension of the arches or to modify the anteroposterior dimension of the appliance.




They generate toothmoving forces within the applicance, beyond those generated by the patients soft tissues and function, which almost always is undesirable when the goal is growth modification.

APPLIANCES FOR BILATRAL MAXILLARY CONSTRICTION:
The preferred appliance for modest expansion of the maxillary arch to correct a posterior crossbite in a preadolescent child is an adjustable lingual arch that requires little patient cooperation. Both the W-arch and the quad helix are reliable and easy to use. The w-arch is a fixed appliance constructed of 36 mil steel wire soldered to molar bands. It is activated simply by opening the apices of the W and is easily adjusted to provide more anterior than posterior expansion, or vice versa, if this is desired. The appliance delivers proper force levels when opened 4-5 mm wider than the passive width and should be adjusted to this dimension before being inserted. It is not uncommon for the teeth an maxilla tomove more on one side than the other, so precise bilateral expansion is the exception rather than the rule, but acceptalble correction and tooth position are almost always achieved.

The quad helix is a more flexible version of the W-arch. The helices in the anterior palate are bulky, which can effectively serve as a reminder to aid in stopping a finger habit. The combination of a posterior crossbite and a finger sucking habit is the best indication for this appliance. The extra wire incorporated in this appliance gives it forces are equivalent. Attention to soft tissue irritation is also recommended with this appliance. Both the W-arch and the quad helix leave an imprint on the tongue, about which the parents and child should be warned. This will disappear when the appliance is removed.

With both types of expansion lingual arches, some opening of the midpalatal suture can be expected in a young child so the expansion is not solely dental. This is of no consequence and will require no difference in either treatment or retention. Expansion should continue at the rate of no consequence and will require no difference in either treatment or retention. Expansion should continue at eh rate of 2 mm per month (1 mm tooth movement on each side) until the corssbite is slightly overcorrected. In other words, the lingual cusps of the maxillary teeth should occlude on the lingual inclines of the buccal cusps of the mandibular molars at the adjustment is possible but may lead to unexpected changes. For this reason removal and recementation are recommended at each active treatment visit. Most posterior cross bites require 2 to 3 months of active treatment and 3 months of retention (during which the lingual arch is left passively in place)
Some children do have true unilateral crossbites due to unilateral maxillary constriction of the upper arch.

in these cases the ideal treatment is to move selected teeth on the constricted side. To a limited extent, this goal can be achieved by using different length arms on a W-arch or quad helix.

but some bilateral expansion must be expected, an alternative is to use a mandibular lingual arch to stabilize the lower teeth and attach cross elastics to the maxillary teeth that are at fault. This is more complicated and requires cooperation to be successful, but is more unilateral in its effect. A third alternative is to use a removable appliance similar to the one but secioned asymmettically. This has the effect of pitting more teeth against fewer teeth and results in asymmetric movement. Of course, this appliance has the same restrictions as all removable appliances; its success depends on both the quality of its retentive clasps and the patients cooperation.