EXPANSION IN ORTHODONTICS

INTRODUCTIONArch expansion is a method of gaining space. An apparently complex yet relatively simple

procedure in orthodontics is palatal expansion. The correction of transverse maxillary

deficiency can be an important component of an orthodontic treatment plan.

Expansion of palate was first achieved by Emerson C.Angell in 1860.Ever since numerous expansion appliance have been described with varying force levels & duration of treatment.

CLASSFICATIONExpansion of the dental arches can be

classified as:1. Dento-alveolar expansion2. Skeletal expansion

They can also be classified broadly as:3. Slow expansion4. Rapid expansion

Armamentarium1. Screws2. Loops3. Springs4. Flexible wire,e,g NiTi

Slow ExpansionSlow expansion has traditionally been termed as

dento-alveolar expansion ,although some skeletal changes can be observed.

The slower expansion have also been associated with a more physiologic adjustment to the maxillary expansion,producing greater stability & less relapse potential than in rapid expansion procedures

The force generated by such procedures are 2-4 pounds.

Expanded slowly at a rate of 0.5-1mm per week.

Pure dento-alveolar expansion should always be slow

Normal width of PDL is approx 0.25 mm.For orthodontic tooth movement to take place an expansion device should not be activated >0.25mm at a time.

Pitch of a jackscrew is 1mm,i.e. a 360⁰ rotation separates two halves of expansion appliance by 1mm.

Rule for slow expansion :Two ¼th turn per week,that means 8 turns a month

Indication & contraindication of slow expansionINDICATIONS :1. PMBAW (premolar basal arch width)>PMD

(premolar diameter)- Ashley Howe’s Analysis2. Any age3. PMBAW × 100 ≥ 44% = PMBAW% -Ashley

Howe’s Analysis TTMCONTRAINDICATIONS :4. Buccal or labial inclination of teeth5. Bone loss on buccal aspect of teeth6. Mandibular inter-canine width

Appliance used for slow expansionFixed W arch Quad helix Ni-Ti arch wires

Removable Coffin spring Expansion screws Functional appliances Active Passive

W arch0.9mm stainless steel wire soldered to

molar bandsPatient cooperation not requiredPreferred in deciduous and mixed dentition

where mild to moderate expansion is required

Activation : outside mouth,3mm wider than passive width

Quad helixFour helices:more flexibilityHelices in the anterior component impart

bulkiness which can be useful in preventing digit sucking

Activaton :either inside or outside mouth,4mm wider than passive width

Retained for 3-4 months,after overcome is achieved

Ni-Ti expanders It has capacity to rotate,upright,distalize & expand

the anterior & posterior arch with gentle biocompatible force.

It is capable of a uniform,slow,continuous force Depends on shape memory and super elasticity of NiTi Transition temperature is 84°F Continuous force levels between 230gms to 300 gms. Available in 8 intermolar widths; ranging from 26-47

mm Freeze gel packs can be used to make appliance

flexible for insertion

Coffin springIt is a removable appliance capable of

slow dento-alveolar expansionThe appliance consists of an omega

shaped wire of 1.25 mm thickness,placed in mid-palatal region

Activation : the spring is activated by pulling the two sides apart manually.It can also be activated by using three prong pliers

Expansion screwsThe expansion screw is a very small

metallic appliance which may be designed to move a single tooth or a group of teeth or the skeletal bases as required. This screw as a source of force together with the acrylic segment of the plate effect the teeth and the alveolar process.

Different type of screws may be used advantageously for certain procedure during treatment with removable appliance .

Functional appliancesThis expansion is not produced through

the application of extrinsic bio-mechanical but rather than by intrinsic forces in the dental arch such as those produced by the tongue.(passive expansion)

When the forces of the buccal and labial musculature are

shielded from the occlusion, a widening of the dental arches often occurs.

Rapid expansionRapid maxillary expansion is also known by

the terms rapid palatal expansion or split palate.It is skeletal type of expansion that involves the separation of mid-palatal suture & movement of the maxillary shelves away from each other.

Indications of rapid maxillary expansion1. Posterior crossbite2. Class II malocclusion 3. Cleft palate patients4. Face mask therapy5. Medical indications : nasal stenosis,septal

deformities,recurrent ear & nasal infection,allergic rhinitis

Contraindications of R.M.E1. Single tooth crossbites2. Un-cooperative patients3. After ossification of mid-palatal suture

unless it is accompanied by adjunctive surgical procedures

4. Skeletal asymmetry of maxilla & mandible & adult cases with severe antero-posterior skeletal discrepancies

Diagnostic aidsThe routine diagnostic aids such as :Case historyClinical examination & study modelsMaxillary occlusal view radiograph – to see

mid-palatal sutureP.A cephalogram – to estimate the amount of

expansion that has taken place

Occliusal radiograph

Rapid maxillary expansion appliancesNumerous appliances have been used for rapid

maxillary expansion.Broadly they can be classified as :

a. Tooth borneb. Tooth & tissue borne These are fixed appliance & appliance that

are fixed onto the teeth are more reliable & found to produce consistent skeletal effects.

Examples of tooth borne appliances include:i. Isaacson typeii. Hyrax typeTwo of commonly used tooth & tissue borne

appliances are :iii. Derichsweiler typeiv. Hass type

Isaacson type This appliance has a special spring loaded

screw called a MINNE expander,consists of a coil spring having a nut that can compress the spring

It is soldered directly to the bands No acrylic is used Easy to fabricate Expander is activated by closing the nut so that

the spring gets compressed.

Hyrax typeThis type of appliance makes use of a

special type of screw called HYRAX (Hygiene Rapid Expander)

The screws have heavy gauge wire extensions that are adapted to follow the palatal contour & are soldered to bands on premolars & molars.

Derichsweiler typeThe first premolars & first molars are

bandedWire tags are soldered onto the palatal

aspect of the bandsThese wire tags get inserted into a split

palatal acrylic plate incorporating a screw at its centre.

Hass typeThe first premolar & molar of either side

are bandedA thick stainless steel wire of 1.2mm diameter

is soldered on the buccal & lingual aspects connecting the premolar & molar bands

Lingual wire is kept longer so as to extend past the bands both anteriorly & posteriorly

Free ends turned back and embedded in acrylic.

A screw is incorporated.

BONDED R.M.EMost of the RME appliances described earlier are

banded appliances .They incorporate bands on the first premolars & molars.

An alternative design of the appliance would be to have a splint covering variable number of teeth on either side to which the jackscrew is attached.

Raymond Howe in 1982 developed this appliance Clears the palate from acrylic No banding needed- can be used on malposed teeth

where parallel path of insertion is not possible Less error prone as bands don’t have to be placed in

impression Easy to make on deciduous teeth.

Wire framework Completed applianceOn model

Acrylic-lined bondableRME appliance

Instruction on how to expand (activation schedule)Schedule by Timms :Upto age of 15 years : the turn 180⁰ is given as 90⁰ in

the morning & 90⁰ in the evening.

Zimring & Isaacson in 1965 : Young growing patients : two turns each day for the

first 4-5 days & later one turn each day for remainder of RME treatment.

Non growing adult patients : two turns each day for the first two days & one turn each day for the next 5-7 days & one turn every alternate day till desired expansion is achieved.

Effects of RMEEffect on maxilla Opening of the mid-palatal suture Downwards & forward maxillary movement

Effect on maxillary teeth Midline spacing between the two maxillary central incisors Maxillary posterior teeth show buccal tipping & extrusion

Effect on mandible Downward & backward rotation of the mandible Increase in face height Reduction in overbite

Effect on nasal cavity Reduced resistance to nasal air flow Increase in intra-nasal space

Hazards of RMEOral hygieneLength of fixationDislodgement & breakageTissue damageInfectionPain or discomfort,dizziness,pressure at the

bridge of nose etc

Comparison between slow & rapid expansion

Slow expansion Rapid expansion1. Type of expansion – both

skeletal & dental changes seen from beginning

2. Rate of expansion - slow3. Type of tissue retraction -

more physiologic4. Force used –milder force

(2-4 lbs)5. Frequency of activation-

less frequent (0.5-1mm/week)

6. Duration of treatment-long

7. Type of appliance-either fixed or removable

8. Age-any age

9. Retention-lesser chance of relapse

1. Predominantly skeletal changes initially,later dental changes take place with skeletal relapse

2. Rapid3. More traumatic

4. Greater force (10-20 lbs )

5. More frequent (0.5-1mm/day)

6. Short7. Mostly fixed appliance8. Before fusion of mid-

palatal suture9. More chance of relapse

EXPANSION OF CLEFT PALATE CASESExcessive anterior collapse coupled to little

or no posterior collapseMore fan wise expansion needed to restrict

posterior expansion.Screws of longer thread of upto 18mm expansion

More difficult to retain due to clinical crowns not developed properly

Unilateral expansion both cap splints & bands can be used

Formation of fistula could be a complication

Expansion of mandibular archStable expansion is difficult to attain in the

lower archPresent studies state that expanding the

upper arch allows for spontaneous expansion of the lower arch to some extent.

Other methods of expansionSurgically assisted RME Transpalatal archMagnetsUltra rapid expansion Though these methods are not

used frequently.

conclusion Expansion of the arches has seen its ups &

downs in the past.More & more documentation of the effects & stability of this procedure has thrown a new light on its clinical application.

Whether it is slow or rapid expansion,proper

diagnosis & case assessment is very essential to ensure consistent results.As more & more cases are being treated without extractions due to profile considerations,Expansion of the arches forms a valuable adjunct to treat a wide variety of clinical presentations.

Reference 1. Contemporary Orthodontics,5th edition by

William R.Proffit,Henry W.Fields,David M.Sarver

2. Graber Orthodontics text book,5th edition3. Kharbanda Orthodontics text book,5th

edition4. Orthodontics text book by S.I. Bhalaji,6th

edition

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