Palatal Expansion in Child and Adult

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The correction of transverse maxillary deficiency can be an important component of an orthodontic treatment plan. Numerous factors can result in transverse maxillary deficiency including genetic, environmental, traumatic and functional, which includes abnormal habits such as mouth breathing.   

Various expansion appliances have been introduced with different force levels and duration of treatment, and the factors that influence the selection of these appliances to quantify the amount of skeletal or dental expansion depend on age, growth, amount of force and even gender of the patient. Expansion may also be gradual or slow (3–14 months). The difference in expansion rates reflects differences in the frequencies of activation, the magnitude of applied force, the duration of treatment and the proportion of dentoalveolar to skeletal effects.

History

The history of expansion dates back to 1860 where Emerson C. Angell reported his first case of successfully splitting the maxilla using a jackscrew appliance, thus he was considered to be the father of rapid maxillary expansion. 

Later Farrar and Clark Godard (1893) stressed the effectiveness of transverse expansion of the palate with opening up of the mid-palatal suture. Lathamin (1971) believed that growth at the mid-palatal suture ceases at the age of 3 years which was contradicted in the year 1974 by Bjork and Skieller who did a study with implants which proved that growth at mid-palatal suture can continue up to13 years of age.

Classification of expansion (McNamara)

1.Orthodontic or dental expansion

• This is produced by conventional fixed appliances and different types of removable

1. 1.appliances.

• Expansion is dentoalveolar in nature i.e. there is lateral movement of the buccal segments resulting in buccal tipping of the crowns and lingual tipping of the roots.
• Aberrant soft tissue pressure from cheeks can cause relapse of the achieved expansion.

2. Orthodpedic or skeletal expansion

• Changes are produced mainly in the skeletal structures.
• Less amount of dentoalveolar expansion.
• Rapid maxillary expansion (RME) appliances are classical examples of true orthopaedic expansion.
• RME causes separation of mid-palatal suture resulting in effects on circumzygomatic and circummaxillary sutures.
• After expansion, new bone is deposited in the mid-palatal suture.

3. Passive expansion

• Intrinsic forces from the tongue play a major role.
• With the use of buccal shields (e.g. Frankel), the forces from the labial and buccal musculature are prevented from acting on the dentition, which results in the widening of the arches, because the forces from tongue exert expansible forces on the arches. 
• Passive expansion is not achieved by mechanical appliances but by the vestibular or lip shields.

Broadly classified into:

Diagnosis

The patient is evaluated for maxillary expansion using the following diagnostic records:

1. Orthodontic study model

2. A thorough clinical history

3. Radiographs

• Orthopantomogram OPG 
• Lateral and PA view cephalogram
• Occlusal radiographs.

Sutures – Mid Palatine Suture plays a key role in Maxillary expansion

Infancy – Y-shape, Juvenile – T-shape, Adolescence – Jigsaw puzzle 

Normal palatal growth is completed by age of 6. Increasing interdigitation of the suture makes  separation difficult to achieve after puberty.

Rapid Maxillary Expansion Appliances

I. Indications for RME 

• RME appliances are ideally indicated in growing individuals with severely constricted maxillary arches, involving airway impairment or mouth breathing tendencies.
• Posterior cross bites with real or relative maxillary deficiency
• Cleft patients
• Along with face mask therapy, RME is used to loosen the maxillary sutural attachment in order to facilitate protraction of deficient maxilla.
• Class III cases with minor maxillary deficiency
• In interceptive orthodontic treatment mechanics.

The medical indications include:

• Allergic rhinitis
• Septal deformity
• Recurrent ear, nasal or sinus infections
• Poor nasal airway
• As a preliminary measure to septoplasty
• Cleft palate patients with collapsed maxillary arch.

II. Contraindications of RME Appliances

• Patients with poor compliance
• Steep mandibular plane angle and convex profile.
• Cases of single tooth crossbite and anterior open bite
• Subjects with skeletal asymmetry of maxilla and mandible
• Patients with severe anteroposterior and vertical skeletal discrepancies.

III.Principle of RME 

Classification

1. Removable RME – Removable appliances are not effective for RME because they are not rigid enough to produce skeletal expansion.

2. Fixed RME Types –

• Bonded or Banded type 
• Tooth-borne or Tooth and Tissue-Borne Type

Removable RME Appliances

The appliance basically consists of a screw in the midline with retentive claps on the posterior teeth. The acrylic plate is split in the middle and activations of the screw forces the two halves to move apart, resulting in the desired expansion.

This appliance is more effective when used in the early mixed dentition phase. Its efficiency in the late mixed dentition and older patients is suspect because of the ossification of the mid-palatal suture and the resulting delay in splitting causes the retention of the appliance to get compromised. Patient compliance is paramount to all removable appliances. Efficiency is less compared to fixed.

Fixed RME Appliances

Fixed rapid maxillary expansion appliances are fixed expanders which cannot be removed by the patient. The fixed RME appliances can be either tooth-borne or tooth and tissue-borne.

Tooth-borne appliances:  Isaacson type or the Hyrax type of appliance

Tooth and tissue-borne appliances: Derichsweiler or the Hass type of appliances

Further classified as:

Banded RME	Bonded RME
Haas	Acrylic splints
Isaacson	2.   Cast metal splints
Hyrax
Derichsweiller

Banded RME appliance

Fabrication

First premolars (deciduous molars) and first permanent molars are banded. They are joined labially and palatally by soldering with heavier gauge wire. The basic RME appliance is the screw which is placed in the midline. The difference in appliance design is based on the various types of screws and mode of attachment. The different types of banded RMEs are as follows:

Derichsweiler type: This expansion appliance consists of molar bands on right and left permanent first molars and first premolars with wire tags soldered into the palatal surface. The jack expansion screw is connected to the bands by means of tags that are welded and soldered to the palatal aspect of the band on one side and embedded in acrylic on the palatal aspects of all non-banded teeth except the incisors. Acrylic adapts to the palate and is in two halves to permit activation of the screw in the midline.

Haas type: This appliance is a rigid appliance which not only transmits forces on to the teeth but also on to the palatal shelves directly. Heavy stainless steel wire (0.045 inch/1.15 mm) is welded and soldered along the palatal aspects of the band. The free ends are turned back to be embedded in acrylic plate which contains an expansion screw in the midline. Both Derichsweiller and Haas types use similar kinds of screws.

Isaacson type: This type uses the Minne-Expander, which is a special spring-loaded screw. It is adapted and soldered directly to the molar and premolar bands with a closing nut which tends to compress the spring, and activates the expander. Acrylic plates are not used in this. The drawback of the basic expansion screw is the build-up of pressure, which is hazardous to tissue. To overcome this, and to make the force application smooth and constant, Issacson type was introduced.]

Biedermann type: It was introduced by Willian Biedermann in 1968. This tooth-borne appliance uses a HYRAX (hygienic rapid expansion) screw, named after the ability to keep it clean. The screw has heavy wire extensions, which can be adapted to follow the contour of the palate and are soldered to either metal bands or cast cap splints or a wire framework that has acrylic splints or is embedded in acrylic splints. 

The expansion screw is turned with a key either once or twice daily (0.2 mm expansion/turn) for the entire expansion phase of treatment which usually lasts from 2-4 weeks. It is capable of providing sutural expansion of 11mm within a very short period of wear and a maximum of 13mm can also be achieved. RPE utilizes large forces to produce maximal orthopaedic repositioning with a minimum of orthodontic movement.

Bonded RME appliance

The bonded RME was first described by Cohen and Silverman in 1973. In bonded RME, instead of bands, metallic cap splints or acrylic covering is used.

Cast metal cap splints: Cast cap splint to all the teeth is prepared to which the screw is soldered. The entire assembly is cemented/bonded.

Acrylic splints: Thick gauge stainless steel wire is closely adapted around the posterior teeth from premolars to molars both buccally and palatally. The screw is soldered to the wire. Acrylic is covered over the occlusal, buccal and palatal occlusal third of all the posterior teeth. The assembly is cemented/bonded.

Advantages of bonded RME;

• Bonded appliances are useful in high-angle cases.
• The occlusal acrylic covering prevents the increase in mandibular angle by acting as a splint.
• Reduced posterior teeth tipping and extrusion.
• Provides bite block effect to facilitate the correction of anterior crossbite.

V. RME Appliance management 

The basic principle of the appliance involves the generation of forces that are capable of splitting the mid-palatine suture for expansion but some dentoalveolar expansion effects are also produced. Hence, the forces should be definitely more than the usually used orthodontic forces. The forces generated are close to 10 to 20 pounds. 

An expansion of 0.2 to 0.5mm should be achieved per day. The screw when turned 90 degrees, the mid-palatal suture will open by 0.2 mm and narrows the periodontal membrane by 0.1 mm on each side. The screw is activated at between 0.5 to 1mm per day and about 1 cm of expansion can be expected in 2 to 3 weeks. The activation schedules tend to vary depending upon the age of the patient and form of the appliance. According to Proffit, most screws open 1mm per complete revolution, so that a single quarter turn produces 0.25mm of tooth movement.

 The suture expansion is around 20 to 50% of the total screw expansion (Bazargani et al., 2013). RME also leads to an increased dimension of the nasal cavity (Ballanti et al., 2010) and moderate evidence exists that RME in growing children improves the conditions for nasal breathing from a short-term perspective (Baratieri et al., 2011). 

In Haas and Hyrax, the screw is activated once or twice a day, normally 0.2 mm per activation, and both appliances have been shown to be effective in correcting transverse maxillary deficiency (Weissheimer et al., 2011). Every turn of the screw opens the appliance by 0.25 mm. Each turn involves 90° activation.

Timms has suggested an activation of 90° morning and evening for patients up to the age of 15 years. In patients above this age, he suggests an activation of 45° four times per day. 

Zimring and lsaacson recommended two turns per day for initial  4 to 5 days followed by one turn per day in growing individuals. 

For adults, the recommended two turns each for the first two days followed by one turn per day for the next 5 to 7 days and then only one turn every alternate day until the desired expansion is achieved. Surgery can be used as an adjunct to RME therapy in adult patients, especially in the third decade of life or later.

VI. Clinical Implications OF RME

• Mid-palatal suture does not open evenly but opens in a ‘V’ fashion.
• The broad end of V is in anterior region and apex of V is at the posterior region.
• Appearance of median diastema.
• Occlusal and PA cephalometric radiograph will reveal the suture opening.
• Usual treatment period is 2 weeks.
• Relapse is higher after RME; hence overcorrection is advised.

RME can also be successfully achieved for unilateral or bilateral posterior crossbite without engaging the permanent teeth (Cozzani et al.,2007). A modified Haas-type RME appliance is used, and the appliance is anchored to the maxillary primary molars and canines.

Temporary anchorage devices (TADs) can be used as skeletal anchorage in combination with the expansion appliance. Thus, miniscrews can be inserted on each side of the median palatal suture to replace teeth as anchorage units (Ludwig et al., 2013).

Also called MICROIMPLANT-assisted R.M.E technique (MARPE).

 Miniscrews are employed onto the maxillary expanders that recruits palatal and nasal cortices. This provides anchorage that facilitates opening of mid-palatal suture and helps to overcome resistance from circum-maxillary sutures. 

Paramedian area 3mm lateral to the suture in 1st premolar region is considered the most appropriate site for placement of miniscrews, anterior screws are placed in rugae.

Skeletal anchorage should permit orthopaedic change without adverse dental changes by applying force directly to the maxillary bone.

Indications – The skeletal anchorage could be reserved for

• moderate to severe skeletal discrepancies, 
• skeletally mature individuals, 
• periodontally involved cases, 
• patients with missing teeth.

Skeletal-anchored RPE produced less molar tipping than the tooth-tissue-borne RPE. Comparing the bone-anchored to the bonded tooth-tissue-borne expander treatment, expansion efficacy demonstrated in both has significant skeletal changes. However, the bone-anchored devices achieved (25%) significantly more skeletal change without dental compensation than did the bonded tooth-tissue-borne device. 

The advantage of correcting a transverse skeletal discrepancy is

(1) to prevent periodontal problems 

(2) to achieve greater dental and skeletal stability 

(3) to improve dentofacial aesthetics by eliminating or improving lateral negative space. 

With a jackscrew attached to skeletal anchors, rapid disruption of the suture would be a disadvantage, so slow (<2 mm per week) rather than rapid expansion is indicated.

In severe maxillary transverse constriction or after growth has ceased, orthodontic treatment alone is not sufficient for successful expansion. These cases require a combination of surgery and orthodontic treatment, i.e. Surgically Assisted Rapid Maxillary Expansion (SARME). 

SARME

Surgically assisted palatal expansion (SARPE) that cuts the bone for reducing the resistance without completely releasing the maxillary segments succeeded by jackscrew rapid expansion is another possible treatment approach in adults with narrow maxilla.

Before surgery, fixed appliances can be used to move apart the roots of the central incisors to prevent the damage of roots by a midline maxillary surgical cut. Expansion is typically carried out at a rate of 0.5 mm a day. Due to the inelasticity of the palatal mucoperiosteum there will be more chances of relapse after surgical correction, so overcorrection is required to compensate the relapse.

Technique for SARME– Hyrax expander is cemented onto the maxillary first molars and premolars before the surgical treatment, which includes bilateral osteotomies performed from the piriform rims to the pterygomaxillary junction. A screw expansion of approximately 2 mm is performed directly after surgery, and the screw is then activated once or twice a day until the desired expansion has been achieved.

Indications

SARPE is indicated for the treatment of the adults with narrow palatal arch for the following:

• To expand the arch for correcting posterior crossbite when no other surgical jaw movements are considered
• To widen the collapsed maxillary arch in cleft palate.
• For pre-surgical arch expansion even in planned orthognathic surgery to prevent increased risks and inaccuracies with segmented total maxillary osteotomies.
• It is also done when the expansion required exceeds that which can be performed by segmental expansion (i.e. greater than 8 mm).
• To expand the arch for creating space without premolar extractions if the space required could be gained reasonably due to maxillary expansion and if other factors, like maxillary incisor protrusion on the underlying bone, have been considered.

Complications

• Palatal tissue irritation is a frequent complication of SARPE.
• Irritation occurs due to impingement of appliance or rapid rate of expansion.
• Other complications include haemorrhage, gingival recession, root resorption, sinus infection, extrusion of teeth, relapse and unilateral expansion.

VII. Effects of the RME

On the Maxillary Teeth and Alveolar Bone

• The posterior teeth are used as handles to transmit forces to the maxilla which tends to tip buccally due to the compression of the periodontal ligament on the pressure side. 
• Bending of the adjacent alveolar process along with limited tipping and/or extrusive orthodontic movement of the teeth.
• Distinct appearance of a midline diastema, which appears within days of initiating RME therapy. The diastema is generally half the distance of the distance by which the screw is activated. The diastema is reported to close simultaneously within 6 months due to the trans-septal fiber traction.

Maxillary Skeletal Effects

• The palatine processes separate in a triangular or wedge-shaped manner when viewed occlusally. A similar triangular opening is also seen in the supero-inferior direction, maximum towards the oral cavity and progressively less towards the nasal aspect.
• Maxilla moves laterally due to expansion and also rotates with the fulcrum at frontonasal suture.
• Increase in nasal airway, reduction in airway resistance.
• Downward and backward rotation of mandible.
• Increase in mandibular angle.

On the Mandible

• The mandible rotates downward and backwards due to the downward movement of the maxillary posterior teeth in a buccal direction. 
• The palatal cusps of the maxillary posterior teeth, which should ideally occlude in the occlusal grove of the mandibular posterior teeth, tend to occlude with the lingual slopes of the buccal cusps of these teeth, thereby giving the effect of opening the bite.

On the Nasal Cavity and Adjacent Cranial Bones

• The RME tends to increase the intranasal space as the outer walls of the nasal cavity move apart and the palatal shelves flatten out, making the nasal floor broader. 
• Improvement in t nasal breathing is almost universally accepted.
• The parietal as well as the zygomatic bones show signs of some form of realignment at the sutures, especially in younger individuals.

VIII. Retention following RME Therapy

• The objective of retention is to hold the expansion while the forces generated have decayed.
• The same fixed RME appliance is used as retainer for first 3 months. The hole of the screw is filled with self-cure acrylic to prevent accidental unwinding of the screw. 

• At the end of active expansion treatment, 80% skeletal and 20% dental expansion is achieved. Therefore when relapse occurs after active treatment, there is more skeletal relapse and dental correction is retained.
• Relapse is highest during the first 6 weeks after expansion.
• Removable retainers are given from the 4^th month and are worn full time for about 9 months after expansion. After 9 months, half time wear is advised.
• Alternatively, the expansion can be maintained using a trans-palatal arch (TPA) or any of the other appliances, The TPA has the advantage that the fixed appliance treatment can proceed unhindered.
• Selection of the appliance for the transverse correction required and skeletal age also plays an important role in retention.

Slow Maxillary Expansion Devices

Slow expansion was developed by the brainchild of the father of modern dentistry, Pierre Fauchard. Slow expansion involves the use of relatively lesser forces (2 to 4 pounds) over longer periods (2 to 6 months) to achieve the desired results. 

These appliances are designed primarily to produce dentoalveolar expansion or changes. In young children, slow expansion appliances might produce skeletal expansion with opening of mid-palatal suture. The effect of skeletal versus dental changes purely depends on the age of the patient and the magnitude of force applied. However, it was not until 1978 when Hicks with his cephalometric study used a fitted split acrylic plate to expand the maxillary arch and proved the effectiveness of slow palatal expansion.

i. Indications of slow expansion

• Correction of unilateral cross bites- Posterior dental crossbite
• Correction of ‘V’ shaped arches as in “thumb suckers”
• Cleft palate cases with collapsed maxilla and preparation for bone grafts in cleft cases
• Minimal crowding in the upper arch (1-2 mm), i.e. < 4 mm in minimal space discrepancy cases
• Elimination of a displacement 
• Constricted maxillary arch

ii. Advantages

• Slow expansion delivers a constant physiologic force until the required expansion is obtained
• Less damage to the teeth
• Produces skeletal effect in young children
• Requires minimal adjustment throughout its use, and allows easy adjustment when necessary 
• Maintenance of sutural integrity and the reduced stress loads within the tissues
• Least strain is exerted on anchored teeth
• The appliance is light and comfortable to the patient
• It can be used for sufficient retention after the expansion 
• Relapse tendencies are less 
• Time required for retention is less 
• Less pain and discomfort due to light forces

iii. Disadvantages

• Slow expansion produces predominantly tipping rather than bodily expansion of teeth
• Longer treatment duration compared to RME

iv. Classification

The slow expansion appliances can be broadly classified as:

Removable and Fixed appliances:

V. Removable Appliances for Slow Expansion

Screw Appliances: These screws have a smaller pitch and are activated less frequently compared to screws used for RME appliances.

a) Expansion plate with screw

The concept of active plate was introduced by Pierre robin in 1902

Appliance framework – The appliance consists of a split acrylic palatal plate which is thoroughly adapted to the contours of the palate with a central expansion screw (jackscrew), retained by stainless steel clasps on the first primary and permanent molars. 

Activation  To expand the plate, the screw is activated one or two notches per week (0.2–0.4 mm). For each activation, a quarter turn is given. One quarter turn will produce 0.25 mm activation. Tooth movement is about 1 mm/month created by exerting pressure on the teeth in contact with the plate, thus mostly dentoalveolar expansion is created. The appliance is intended to be worn day and night, except for meals and tooth brushing. 

Disadvantages

• Expansion plates are patient-dependent for both wearing and activation
• Excessive activation causes dislodgement of the appliance
• Requires readjustment, even if the appliance is not worn for one day
• Appliances are bulky

Modifications of expansion plate

Apart from the horizontal placement for transverse expansion, screws can be placed in the following ways:

1. Screws are placed in the anterior aspect of the palate parallel to the mid-palatal suture for anterior expansion. E.g., cases of anterior crossbite.
2. 2. A ‘Y’-shaped plate will produce simultaneous lateral expansion of posterior teeth and anterior expansion. 
3. Distalisation of buccal segments can be achieved using expansion screws.
4. Expansion plates can be modified for asymmetric expansion.

Schwarz applianceis the first removable appliance with jackscrew. It is a horseshoe-shaped removable appliance that fits along the lingual border of the mandibular dentition, with a midline expansion screw. 

• It is indicated in patients with mild crowding in the lower anterior region or when there is significant lingual tipping of the posterior dentition. 

• The appliance is activated once per week. It produces on an average 3–4 mm arch length interiorly.

b) Coffin Spring

The coffin spring was introduced by Sir Walter Coffin in the year 1875.

This appliance is capable of producing slow expansion, even though it has been shown to split the palate especially when used in patients in the early mixed dentition

Appliance Framework  Wire used: 1.25-mm heavy stainless steel wire. The appliance consists of an omega shaped wire, with the base of the omega placed posteriorly in the midline. The distal ends of the U loop are limited to the distal of the first permanent molar. Anteriorly, the loop gets constricted and recurved into the baseplate. Two separate acrylic wings are made around the wire framework on the slopes of the palate, these also contain the retentive clasps. 

Activation Simply pulling the wings apart activates the appliance. This should be done first in the premolar region and then in the molar region. It can also be activated using three-prong pliers at the base of the omega, but are rarely used as they tend to distort the spring. Care must be taken to maintain the sides of the appliance in the same plane during adjustment.

Ideally, marking holes should be drilled on the two wings and a divider should be used to measure the amount of activation given. An expansion of 2–3 mm is made during activation.

Indications

• Expansion of constricted maxillary arch
• Correction of crossbite (unilateral cross bites)
• Conditions requiring differential expansion

Advantages

• Cheaper when compared to expansion screws
• Differential expansion of arch in the premolar or molar region is possible
• Less bulky

Disadvantage

Coffin spring tends to be unstable if it is not made precisely.

c) Removable quad helix appliances

Removable quad helix is inserted into the lingual attachment (lingual sheath) which is welded or soldered to the molar band. This permits adjustment of the appliance outside the mouth.

VI. Fixed Appliance for Slow Expansion

d) W-arch appliance

The W-arch appliance was introduced by Ricketts 1975.

Appliance framework  Constructed with 0.036-inch stainless steel wire. Wire is adapted to the form of ‘W’ which extends from the first permanent molar to the canine in the anterior palate. Free ends of the ‘W’ are adapted closely to the palatal surfaces of premolars/deciduous molars. Appliances should be away from the palatal mucosa to prevent tissue irritation. Lingual arch is soldered to bands on molars. The finished appliance is cemented to the first permanent molars.

Activation

• For anterior expansion – opening of apices of ‘W’ (position 2)
• For posterior expansion – opening near anterior region (position 1)

The appliance delivers proper force levels if opened 4–5 mm wider than the passive width and should be adjusted to this dimension before being inserted. The appliance is activated at the rate of 2mm per month until the cross bite is mildly overcorrected.

Quad/ Tri/Bi Helix appliance

Quad helix was introduced by Robert M Ricketts.

The appliance is a precursor to the tri- and the bi-helix appliances. They are all named after the number of helices incorporated in the appliance. 

Appliance framework  ̶ The quad helix consists of four helices made of 0.038″ diameter wire (elgiloy or stainless steel wire), soldered to the molar bands. The length of wire increases the range of action and flexibility, and decreases the force levels. The tri- and the bi-helix appliances incorporate only three and two helices respectively. 

It is a fixed appliance comprising stainless steel bands cemented onto the maxillary first molars and a standard stainless steel arch attached to the palatal surfaces of the teeth. 

Parts of quad helix: (A) posterior helix, (B) palatal bridge, (C) anterior helix, (D) anterior bridge and (E) outer arm.

The quad-helix consists of two anterior and two posterior helices. The portion of wire in between the two anterior helices is called the anterior bridge and that connecting the anterior helices and the posterior helices is called the palatal bridge. The free ends that are usually adapted close to the premolar teeth are called the outer arms. The outer arms are soldered to the molar bands. The posterior helix should not extend more than 2 mm distal to the first permanent molar.

Activation – The appliance is capable of producing differential expansion i.e. it can be activated to produce expansion levels in the premolar and molar regions. 

It can be activated prior to cementation of the bands by stretching the molar bands apart or in the mouth with the use of three-prong pliers. 

• In the anterior bridge: Results in expansion in the molar region
• In the palatal bridge: Derotation and expansion of molar on the same side and distalization of molar on the opposite side
• Outer arms are activated to expand canines and premolars
• Opening of posterior helix expands the buccal arm

An initial expansion of 8 mm will produce 14 oz of force. Average force is 200–400 g depending upon the amount of expansion or activation. The expansion of the steel arch (normally 10 mm before insertion) exerts a lateral force on the teeth, resulting in a predominant transverse dentoalveolar expansion of the maxillary arch. If necessary, the appliance can be reactivated after 6 weeks. Once inserted, the appliance is not dependent on patient compliance.

Indications of quad helix appliance

• Narrow upper arch that needs expansion, e.g. in crossbites
• Crowded, mixed or permanent dentition in which long range growth can be predicted and requires mild expansion as there is lack of space for the upper laterals
• Class II malocclusions where the upper arch needs effective widening and upper molars need distal rotation
• Class III malocclusions where the upper arch needs effective widening and advances with class III elastics
• Thumb sucking and tongue thrusting cases with their modifications
• Unilateral or bilateral cleft palate

Advantages

• It provides excellent expansion in cleft palate patients
• Expansion is smooth and controlled
• In young children, skeletal expansion can be achieved
• Anterior bridge with helices acts as reminder for habit breaking

For correction of unilateral posterior crossbite in mixed dentition, it has been proved that the Quad Helix appliance is superior to the expansion plate in terms of effectiveness and cost minimisation and is therefore the preferred method of treatment (Petrén et al., 2013). 

Disadvantages

• One major disadvantage of this appliance is buccal tipping of molars during excessive activation. This can be prevented by torquing the roots buccally.

(F) Ni-Ti Expanders

Wendell V Arndt, in 1993, developed a tandem-loop NiTi, a temperature-activated palatal expander. This has the capability to produce continuous, light force on mid-palatal suture and uprights, rotates and distalizes maxillary first molars simultaneously.

Appliance Framework – This fixed appliance has stainless steel extensions that could be adjusted and inserted into standard horizontal lingual sheaths which are welded to the molar bands. An indent on the lingual attachment locks the expander to the molar band ensuring patient protection. For increased protection, an elastomer may also be placed.

The appliance has got a central component and a lateral component. The central component is made of thermally-activated NiTi alloy.the lateral arm, which is bracing the palatal aspect of the maxillary posterior teeth, is made of stainless steel. 

Activation – At room temperature, the expander is too stiff to be compressed and inserted into the maxillary arch. The transition temperature of the NiTi alloy used in the expander is 94°F,which is close to intraoral temperature. For the appliance to be inserted into the mouth, it is chilled so that the central part softens and can be easily inserted.Once the appliance is fitted, the expander warms to the body temperature, becomes stiff and returns back to its original position. The expander delivers constant force as it deactivates.

The expander is available in various sizes from 26 to 44 mm in eight different intermolar widths generating 180–300 g of force. The 26–32 mm sizes have softer wires to produce low level force in children. Clinically, the correct size is estimated by measuring the amount of expansion needed and then by adding 3 mm as overcorrection.

Arch Expansion Using Fixed Orthodontic Appliances

Mild degree of arch expansion can be brought about by using expanded arch wires with fixed mechanotherapy. Appliances such as quad helix or transpalatal arch can be used with fixed mechanotherapy.

Spring-Loaded Expander

The spring-loaded expander (SLE) was introduced by Leone in 2003. The

SLE is a new expansion device that produces slow palatal expansion with light, continuous forces. The appliance is indicated in patients whose growth is completed. They produce accurate force levels due to the control on the spring. 

 Appliance framework – The appliance consists of bands surrounding the molar with a screw attached to the centre. The spring provides a continuous force, sufficient to promote a dentoalveolar remodelling that is biologically ideal and biomechanically controlled. The screw has a self-stop mechanism at the end of expansion to prevent it from disassembling in case of excessive activation. 

Activation – Depending on the need of expansion SLE can produce either 500g or 800g of force.  The device is activated on average 4-8 activations (0, 4, 8 mm) every 6 weeks. A different number of activations will not alter the intensity of the force delivered to the dental structures, as this stays constant (500 or 800 g).

There is no risk of over-expansion as the screw, upon reaching the pre-determined expansion, will become passive. However, by changing the activation pattern, rapid maxillary expansion can also be achieved using SLE.

Comparison of effects of slow and rapid palatal expansion

• When the effects of both slow and rapid maxillary expansions are compared, there is no net difference in the skeletal and dental changes produced by rapid and slow maxillary expansions.
• According to various studies, after RME 10 mm of expansion is achieved of which skeletal expansion is 8 mm and dental expansion is 2 mm. 
• After 4 months, 10 mm of the dental expansion is still present and only 5 mm of skeletal expansion is present. Hence, there is 5 mm of skeletal expansion and the remaining 5 mm account for dental movement.
• With slow maxillary expansion, after a 10-week period of expansion, the same amount of 5 mm of skeletal and dental expansion is produced.
• In rapid expansion, there is more skeletal relapse due to delay in the bone fill in the mid-palatal region after rapid expansion during which the relapse of the skeletal expansion occurs, whereas in slow maxillary expansion, the rate of expansion is close to the maximum rate of bone fill (physiological expansion). 

Conclusion 

        The severity of the transverse discrepancy, age, and the appliance are the most important factors in determining appropriate treatment and prognosis. To achieve optimal skeletal correction, the Haas, bonded occlusal, or bone pin expanders that use palatal contour for anchorage and produce orthopaedic response, minimizing adverse dental tipping, are recommended. 

       As the patient matures, the skeletal expansion obtained can be less than one-third of the expansion produced at the level of the jackscrew. A post-expansion PA cephalogram or CBCT view is useful to evaluate the amount of skeletal correction achieved.

Summary

Palatal Expansion in the Primary and Early Mixed Dentition

Three methods can be used for palatal expansion in children: (1) a split, removable plate with a jackscrew or heavy midline spring, (2) a lingual arch, often of the W-arch or quad-helix design, or (3) a fixed palatal expander with a jackscrew, which can be either attached to bands or incorporated into a bonded appliance.

Palatal Expansion in Preadolescents (Late Mixed Dentition) 

By the late mixed dentition period, sutural expansion often necessitates placement of a relatively heavy force directed across the suture, which micro-fractures the interdigitated bone spicules so that the halves of the maxilla can be moved apart. A fixed jackscrew appliance (either banded or bonded) is necessary.

Palatal Expansion in Adolescents (Early Permanent Dentition) / Adults

In mid-adolescence, there is a near-100% probability of opening the mid-palatal suture with a banded or bonded expansion device, but as the adolescent growth spurt ends, interdigitation of the suture reaches the point that opening it may no longer be possible. For patients of this type, tooth-supported expansion should not be attempted.

Instead, micro-implant assisted palatal expansion (MARPE) should be used, with one activation of the screw (0.25 mm) per day, rather than using heavy force against the teeth. This approach along with surgically assisted palatal expansion (SARPE) and segmental osteotomy of the maxilla are the possibilities for the more mature patients in whom tooth-supported expanders will not work.

Guideline

The general guideline is that after any type of maxillary expansion, the fixed expansion device should remain in place until the new bone formed in the midline suture has had time to calcify and at least partially mature, and that a tooth-supported retainer is needed for another 6 to 12 months after that. With RPE, a tooth-supported expansion appliance should remain in place for 3 to 4 months, and then can be replaced with a removable retainer or other retention device. 

After slow expansion, the expansion device is not replaced with a tooth-supported retainer for another 12 weeks after expansion is completed. With implant-supported expansion, the guideline is about the same as with tooth-supported expansion. 

References

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