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Expansion appliances /certified fixed orthodontic courses by Indian dental academy
INDIAN DENTAL ACADEMY
Leader in continuing dental education
The earliest cited report is that of
E.C .Angell published in the Dental
cosmos in 1860.
Angell’s thesis was discreditied and it was
J.H.Mcquillen who tried to demolish it by
arguments that ranged from the specious to
Four important points were put forth by
1) lateral maxillary expansion by bony
2) use of a jackscrew with contra rotating
Walter Coffin introduced the Coffin
Spring in 1881 and was modified by Ricketts
The design , construction and clinical
management of the standard Quad helix has
been described by Birnie and Mc Namara in
James and Waters in 1989 derived the
behavior of the quad helix theoretically in
terms of the properties of the wire used and
its dimensions and spatial geometry.
Expanding the arch with appliances were not
accepted by the orthodontic community in
E.N.T surgeons popularized the technique
which they used in treatment of nasal
insufficiency and constricted nasomaxillary
According to the rate
According to type of expansion
c) passive e.g Vestibular shield, FR2, Lip
According to direction
According to type of appliance
b) fixed -- banded or bonded
1. Tooth borne e.g. HYRAX ,
2. Tooth and tissue borne e.g Hass
According to the jaw
a) maxillary e.g Transpalatal arch,HYRAX
b) mandibular e.g. Active lingual arch
According to the active element
1) Dental expansion e.g Sectional
2) Skeletal e.g HYRAX
Rapid maxillary expansion or Split
• 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.
♦ These appliances are the best examples of true orthopedic
♦ The maxilla together with the palatine bone forms the hard
palate,floor & greater part of the lateral walls of nasal
cavity. It is paired bone that articulates with its opposite
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 & Inter-palatine sutures are called
mid-palatal suture. RME should be initiated prior to
the ossification of mid-palatal suture.
In infancy, the sutures in vertical coronal section has a
‘Y’ shape and binds the vomer with the palatine
By adolescence, the oro-nasal course of the
suture may become so inter-digitated that
mechanical inter-locking is as in a jig-saw puzzle
and islets of bone are formed.
Melsen reports that transverse growth of midpalatal suture continued upto 16 yrs in girls and
18 yrs in boys. Most studies report a broad
range of ossification between 15-27 yrs.
The suture starts to ossify posteriorly and always
shows a greater degree of obliteration posteriorly
then anteriorly, while ossification comes very
late anterior to Incisive foramen.
In Late Adolescence
While Considering RME for young adults, occlusal
radiographs can be used for analysing the palatal
1. A radiologically visible midpalatal suture
corresponds histologically to a predominantly straight
running oronasal suture, which projects largely into
the saggital X – ray path. Only small areas of
interdigitation, if any are to be expected and the
percentage of suture obliteration is low.
2. Radiological invisible suture corresponds
histologically to a relatively large area of
interdigitation, an oblique running suture course in
relation to X ray path or bone structures projecting
above the suture course. Percentage of suture
obliteration to be expected is also low in this group.
3. A radiologically invisible suture is not
1. Posterior Cross bite (unilateral/bilateral)
2. Elimination of inter arch tranverse dicrepancies prior
to orthopedic intervention in class II malocclusions
3. Activation of the circummaxillary sutural system in
treatmentprotocols or Class III .
Cleft palate patients with collapsed maxillary arch.
In cases requiring face mask therapy.
Increase of supplementary arch perimeter to
accommodate teeth in patients with tooth size – arch
1. Poor Nasal airway
2. Septal Deformity
3. Recurrent ear, nasal (or) sinus infections
6. As a preliminary to septoplasty.
Contra - Indications:
1. Single tooth cross bites.
2. In patients who are unco-operative.
3. Skeletal asymmetry of maxilla & mandible & Adult cases
with severe antero posterior skeletal discrepancies.
4. Vertical growers with steep mandibular plane angle.
5. Anterior open bite.
1. Patent mid-palatal suture.
2. Normal buccal occlusion.
Effects of RME:
1.Maxillary skeletal effect:
The maxillary posterior teeth are used as handles to apply a
The appliance on activation compresses the periodontal
ligament and bends the alveolar process buccally and slowly
opens the mid-palatal suture.
Opening of mid-palatal suture is triangular with maximum
opening at the incisor region and gradually diminishing
towards the posterior part of palate.
In superior-inferior direction the maximum opening is
towards oral cavity with progressively less opening towards
the nasal aspects.
Amount of expansion achieved:
An increase in maxillary width upto 10mm can be achieved
• The rate of expansion is about 0.2 - 0.5 mm per day .
• Every mm of posterior expansion produces 0.7 mm of addotional
• Effect on Alveolar bone:
• The alveolar bone in the area adjacent to the anchor teeth
bends slightly due to the resilient nature of bone.
Effect on Maxillary anterior teeth:
♦ Effect on Maxillary Posterior teeth:
♦ these teeth are used as anchors during RME. Theses teeth show buccal
tipping & are also believed to extrude to a limited extent.
♦ Effect on mandible:
♦ most authors have observed a downward & backward rotation of
mandible following RME accompanied by a slight increase in M.P.
angle. Mandibular rotation is due to extrusion & buccal tipping of
Effect on adjacent cranial bones & sutures:
RME not only results in opening of mid-palatal suture but also has far
reaching effects on adjacent cranial structure. In addition to effects on
those bones directly articulating with the maxilla, bones of the cranium
such as parietal & occipital were also found to be displaced.
Effects of RME on nasal cavity:
The evidence of increased inter-hamular width indicates some widening
of choanae. The maxillary air passages are widened throughout their
entire lengths from piriform aperture to choanae. This would account for
the improved respiratory changes. This increase in nasal cavity width is
maximum in the inferior region & decreased towards the superior aspect.
Similar gradient is found in A.P direction with the greatest increase in
Effect on Face
♦ The measurements of upper lip length, lower lip-chin
length, upper face width, lower face width, upper lip vermilion, and lower lip vermilion demonstrated changes
during treatment but showed no significant change from
initial values after 1 year of retention.
♦ Overall face height, intercanthal distance, average eye
width, and nose length did not change over time.
♦ Soft tissue nasal width increased 2.0 mm during treat-ment.
Effect on pulp
♦ Fibrotic changes occur long after the forces have faded.
♦ Reliability of these appliances in producing skeletal
expansion is highly questionable.
♦ If used during the deciduous (or) early mixed dentition
phase produces some effects.
♦ Consists of a split acrylic plate with a midline screw
retained using clamps on posterior teeth.
♦ Disadvantages:1. Need for patient co-operation
2. Difficulty in retaining the plate inside the mouth unless
The bonded expander produces changes in transverse
as well as vertical and A-P
The acrylic occlusal coverage opens the bite
posteriorly facilitating correction of anterior cross
A slight superior movement of the posterior aspect of
the palatal plane occurs with these appliances
Two impressons are made,one for wire framework,one
for application of acrylic
Mandibular impression is taken for fabrication of an
invisible retainer to prevent the occlusal wear caused
by these appliances
These incorporate a Hyrax type screw into a wire
framework made of .040 type of ss.
Wire framework extends around the buccal and
lingual surfaces of the dentition with the wire
crossing the occlusion between the upper
deciduous canines and the deciduous first molars
The wire also curves around the distal aspect of the
Screws positioned in the palate with the midline of
the screw aligned with the palatal midline and
about 2mm away from the surface of the palate
The wire extensions of the screw are adjusted to
contact the lingual surfaces of the first deciduous
molars and the distolingual cusps of first
The appliance is bonded with chemical or light
Patient is appointed at two week intervals until
expansion is terminated
Average amount of expansion with these appliances
is 6 to 8 mm which translates to about 28 to 40
expansions that is 4-6 weeks of active expansion
The patient is reviewed every 6 weeks for an
additional 5 months to allow for reossification
and reorganisation of mid palatal suture to occur
Retention with a simple palatal plate is given, if
deciduous teeth are lost,transpalatal can be used .
These are fixed on to the teeth & more
reliable & found to produce consistent
These usually involve the banding of first
molars and first pre-molars, when preformed
bands are used it is advisable to select bands
that are one size larger then the normal as it
is difficult to seat 4 tightly fitting bands
Hass type and Hyrax type of band fall into
Wires may be soldered to the buccal aspects of the bands to
increase rigidity (or) brackets may be welded & used to
attach arch wires for the correction of teeth not covered by
RME. Commonly used appliances are
1) Derichsweiler type : Tags are
welded & soldered to the palatal
aspects of the bands to provide
attachments for the acrylic which
is also extended to the palatal
aspects of all non-banded teeth
Hass type :
A thick stainless steel wire of 1.2mm
diameter is soldered on the buccal
lingual aspects connecting the premolar and
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
which has a midline screw.
• The plate does not extend over the rugae area.
•Inflammation of the palatal tissue is an additional complication.
Isaacson type :
This is tooth borne appliance without
any acrylic palatal covering.
This design makes use of a spring
loaded screw called MINNE expander.
Metal flanges are soldered on to the
bands on the buccal and lingual sides.
The expander consists of a coil spring
having a nut which can compress the
The coil spring is made to extend
between the lingual metal flanges that
have been soldered.
Expander is activated by closing the nut
so that spring gets compressed.
Biedermann type or Hyrax type:
This appliance also required a special
screw either Hyrax, Leone 620 or Unitek.
These have extensions in heavy guage
wire which are welded and soldered to the
palatal aspects of the bands.
Mandibular dental decompensation
The Schwarz is a horseshoe shaped removable
appliance.Inferior border of the appliance
extendsa below the gingival margin and contacts
the lingual gingival tisue.
A midline expansion screw is incorporated into the
acrylic and also there a re ball clasps that lie in
the interproximal spaces inbetween the deciduous
and permanent molars.
The appliance is activated ince per week producing
about 0.25m of expansion.It is expanded for 3 or
4 months, depending upon the degree of incisor
crowding, producing 3-4 mm of arch length
Purpose of Schwarz appliance is to produce
orthodontic tipping of the lower posterior teeth.
Mandibular passive expansion
♦ A removable appliance that attaches to buccal tubes located
on the lower first molar bands.
A lip bumper is made from .036” SS and available in
avariety of preformed sizes.
Useful in patients who have very tight buccal and labial
The lip bumper should lie at the gingival margin of the
lower central incisors .
Increases arch length passively by lateral and anterior
expansion and also by distalisation of molars.
Made of .036”SS wire.Extends along the mandibular dentition
from first molar to first molar.
An adjustment loop can be placed in the lingual arch in the
Acrylic splints :
Made of poly methyl metha-acrylate
A wire framework may be adapted
around the teeth to reinforce the
Mondro et al (1977)have described
an all acrylic form of cap splints and
inter connection with a screw
embedded in the midline.
These splints are bonded to a teeth
using either GIC (or) other bonding
adhesive, after adequate etching.
Description of a typical expansion screw :
• A typical expansion screw consists of an oblong body divided into two
• Each half has a threaded inner side that receives one end of the double
• The screw has a central bossing with four holes. These holes receive a
key which is used to turn the screw.
Commercial Expansion screws
1. Bilateral symmetrical expansion screws
Most commonly used.Can have a double guide pin or a single
2. Mandibular bow screw.
3. Encased expansion screw.
This restricts accidental recoiling of the screw.
4. Sectional expansion screw.
Used for moving single tooth or groups of teeth.
5. Trapezoidal expansion screw.
It is used in cases of narrow maxillary arch where the
anterior part of the arch is narrower than the posterior.
6. Radial expansion screw
Used where anterior region should be expanded more than
the posterior region.
7. 3-dimensional expansion screw
Brings about movements in 3 directions.
8. Spring loaded expansion screw
Springs are changed periodically each time
with one having more tension.
9. Traction screw
Used for closure of extraction space.Works
by closing the screw.
10. Telescopic screw
11. Piston spring screw
For moving a single tooth in labial or
Bala is a lova
The turning of the screw by 90° (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.
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 patient, they recommended two turns
each day for 4-5 days and later one turn each
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 next 5-7 days and
one turn every alternate day till the desired
expansion is achieved.
Nearly parallel opening by a rigid appliance is required (or) the dento-alveolar
elements will tilt too far buccally and consequently curtail expansion of basal
This undesirable condition arises if the appliances is to flexible (or) teeth held
in a manner that allows rotation b/w’n them and the appliance.
quirements will generally dictate the type of appliance used and also the choice
of many other components (eg., Bands or splints).
2). Tooth Utilization: ( No.of teeth included in appliance)
a). Load distribution :
As the entire lower portions of the maxilla are to be moved laterally, it would
be best to incorporate as many teeth as possible & thus spread the load over the
entire alveolar length instead of applying it only at a few isolated points
Bands can be cemented simultaneously only to a few teeth because of
difficulties of multi alignments whereas splints can be adapted to all teeth.
b). Appliance retention:
Retention of an appliance against accidental dislodgment during RME
depends on a no.of factors, but especially the area of adhesion / interface b/w’n
the teeth & appliance, the precision of fit (or) thickness of the adhesive agent &
shape of clinical crown www.indiandentalacademy.com
Bands may be superior to capsplints in view of their closer adaptation.
Bands may be pressed into the gingival sulcus where the clinical crowns are
3). Expansion : (Dilating unit & action)
The dilating mechanism can be a spring (or) a screw but a spring reduces the
rigidity & control.
A screw is far better but should have a thread of sufficient length to complete
the expansion without interruption.
Changing the screw i.e removing the fully open one & replacing it with a new
one (or) the same one that as closed, only jeopardises rigidity & wastes time
4). Economy :
a). Time : The use of capsplints keep the clinical time to a minimum with good
laboratory backup. Chairside work is limited to taking of impressions & bite
b). Material : The appliance which makes the least intrusion into the oral space
will be best tolerated by patient. Here the banded appliances have a distinct
advantage over the bulky capsplints
5). Hygiene :
The form which produces the minimal covering of the dental and palatal
mucosal tissues consists of bands and least amount of interconnecting material.
But this design as the inherent disadvantage of too much flexibility.
The criteria of hygiene given the lowest priority, because any deleterious
effects are superficial & reversible and the well manage patient.
Cap splints should be fixation of choice, especially where
rigidity is important & bands have their place, where there are difficulties in
Clinical Management of RME :
a).Fitting the appliance :
The clinician must examine the appliance & satisfy about the quality laboratory
work. In the case of Cast cap splints, attention must be paid to cleanliness
especially the fitting surface to secure good adhesion.
Check the direction of the screw for opening. it should be backwards when
viewed from lingual aspects the appliance should slip on to the teeth with
sufficient friction to hold it in place.
Incorrect seating may caused by a high spot on the casting and is revealed by
rocking, if the spot can be located it can be removed easily
b). cementation of appliance :
Only when the clinician is satisfied without causing pain (or) discomfort he
should then only proceed with cementation.
Ames black copper cement is used, in addition to its good adhesive quality, it
has a germicidal property which assists oral hygiene. Setting time 20 to 30sec.
Allow the cement to become hard for atleast 1/2 hr. to assure complete setting,
before strain is imposed by activation
C. Instructions : (Initial)
The parent & child should be told about the appearance of midline diastema
which can be disconcerting to them.
If the patient has never worn an orthodontic appliance before, the usual
inherent difficulties in speech and mastication must be mentioned together with
points on oral hygiene.
Most expansionists advocate 180° rotation per day, which will provide up to
10mm of expansion in 4 weeks.
In order to simplify instructions patients have been classified into 3 age groups.
The recommendations must be regarded only as provisional and subject to
modification in light of symptoms expressed at subsequent visits.
1). Upto age 15 years :
Includes most patients receiving RME and 180° daily rotation can be
met with turn of 90° both morning & evening.
The easiest way to rotate the screw is to have to long handled keys to
work extraorally. One key is straight and other has a bend of 45° near
the end so that 90° is achieved with successive turns of 45 ° from each of
While the person responsible for turning the screw is being instructed,
the clinician must demonstrate the action precisely & then the person is
invited to do it as shown, having first returned the screw to 0.
Only when the clinician is sure that the instructions of fully
understood, patient to be send and called after one week.
2). Age 15 to 20years :
Increasing resistance for maxillary separation may cause a force
buildup & pain to patients in this age group with turns of 90°.
It is possible to maintain an overall daily rotation of 180° if the total is
broken down into 4 turns of 45°.
Ideally, the divisions should follow 4 equal time lapses but here one
may run into difficulties of organization, However, the tension disperses
fairly quickly & only a comparatively short break may be needed b/w
Such patients are also asked to return after one week
3). Over age 25 years:
The mid palatal suture often is opened surgically which relives much of
the tension. Here it may not be necessary to reduce the overall rate of
expansion in these patients.
In this age group the clinician is more (or)less feeling his. way and
mindful of the probable painful symptoms about which the patient is
Revisit within 3 -4 days
Pain to be reviewed during active RME, before continuing with patient
management during subsequent visits.
D). Pain during RME:
Completion of the desired expansion in the short time allotted requires strong
forces which often produces painful effects.
The clinician metering treatment by rate of expansion has only the modality of
pain as a monitor and indication of excessive force buildup that may lead to
possible tissue damage.
The threshold levels of pain very among individuals, the cause being the force
buildup from resistance to maxillary separation.
2 factors generally are
1. Rigidity of facial skeleton
2. Mechanical interlocking and synostosis of mid palatal suture.
As the facial skeleton becomes progressively stiffer the tension is relieved by
dispersion. By the teens, the suture will be interlock mechanically.
Persistent pain normally is the product of an unyielding suture because the
tension disperses and pain disappear as the maxilla separate.
Suture opening is confirmed by first checking that there has been expansion
by the appearance of some of the threaded portion of screw & than noting
superior median diastema.
Only if the clinician is satisfied the suture is opening should RME be continued,
never should be the appliance be regularly activated for a period longer than 1
week against an unyielding suture in the hope of achieving maxillary separation.
The rate can be modified, when patients report episodes which indicate
excessive force buildup by the following adjustments to schedule of rotation.
1. Reduce the angle of rotation but increase the frequency .
2. Reduce the rate of expansion, which will stop the accumulation of residue
E). Instructions : (Subsequent)
First ask the patient & person turning the screw if there were any difficulties.
This information may be volunteered as any persistent pain certainly will be.
Then check the central incisors for diastema.
Then examine the screw to see how much thread is exposed, which indicates
regularity in turning.
If all is well, ask the patient to continue with the same instructions & return in
The patients who complaints of pain when the screw is turned should be
asked how long it lasts; it generally disappears if the suture is open.
Advice that 2nd 45° turn of screw not be made before the pain generated
by the first has dissipated.
With patients overage 20 years it is difficult to differentiate b/w the
pain from on unopened suture & that from skeletal rigidity. In event of
non opening of suture, surgical freeing should be considered.
Should difficulties (or) minor illnesses arise during the active
expansion phase, it may be stopped & resumed later.
F). How much to expand:
The reports from Krebs (1964), Stockfish (1969), Timms (1976) &
Linder-Aronson et al (1979) show that b/w one - third & one-half of the
expansion was lost before stability was eventually reached.
General guideline :
Expansion should stop when the maxillary
palatal cusps are level with the buccal cusps of the mandibular teeth.
During active expansion it is useful to know how much of the screw
thread is still available & when the limit is near, so that its is not
completely exhausted, the halves of the appliance must not be allowed to
disengage, that would lead to collapse.
At the cessation of active expansion, the patient enters the fixed
retention phase & is required to attend only for check-ups once each
During this phase, it should be unnecessary to ligate (or) apply coldcuring acrylic to lock the screw as the angular thrust creates sufficient
friction to hold it.
After 3 months, the fixed appliance is removed & replaced with a
C. Retention :
The objective of retention is to hold the expansion while all those forces
generated by expansion have decayed away
First 2.1/2 years after expansion to be critical & it is essential that in the
first 3 months the fixed expansion appliance acts as a retention
appliance. Then this can remove and the mouth left without any
appliance & without fear of relapse for a few days to permit recovery of
The first removable retention plate is made with patient waiting &
delivered with in hour. It consist of fully fiting base-plate of cold cure
acrylic with 4 adams clasps (2on 1st molars & 2 on 1st pre molars)
In the mixed dentition stage a retention plate with only 2 adams
clasps (on 1st permanent molars) is fitted and fixed retention phase is
longer, up to 6 months when using an all metal expansion appliance.
Long retention period of atleast 2 yrs after removal of expansion
appliance is needed.
Even with the appliance worn according to instructions there can be
slippage & creep it some relapse
About 9 months after expansion, wear of retention plate can be
reduced from full time to half time (usually evenings & nights)
A palate covering retainer is
satisfactory but may be some what
awkward in combination with a
fixed appliance to align the teeth
as 1st stage of treatment proceeds.
An alternative is a heavy labial
archwire placed in the headgear,
which will maintain the lateral
expansion while light resilient
archwires are being used to align
the teeth (or) lingual arch can be
RME in cleft palates
RME is carried out only in those cases where cleft has been closed
Appliances : The basic principles of design apply equally to clefts, the
idiosyncrasies of these malocclusions usually call for more complicated
The most common problem, is the anterior collapse, so that parallel (or) near
parallel expansion is undesirable
To restrict the posterior expansion, the left and right, portions of the
appliance should be tethered at the back, leaving the anterior aspects to
expand fully. This may be done with a hinge (or) omega spring, the
latter is probably better as this puts the point of rotation well back in the
Differential expansion puts considerable flexural strain on the screw in
the horizontal plane & there are limits which if exceeded, will result in
fracture of the screw (or) displacement of the appliance.
If an appliance is required to provide a vastly greater expansion
anteriorly than posteriorly, some form of articulation b/w’n the left &
right sides is advised
Unfortunately very few articulated screws are available and these seem
to have neither the length (nor) the strength for much of this work.
The greater the collapse, the less space available for the screw, where
the longest possible length of thread is needed
• As the palate in cleft palate patients is usually flat, the screw
can be mounted near the level of crowns & due to limited
availability of clinical crowns, bands are preferred to cap
RME in young children, springs might be easier to use
eg: ‘W’ Porter (or) Quad helix
Normally RME is done before extraction (or) other forms of appliance therapy.
Often some alignment of incisors is done early. Eg., at age 7-8 yrs & RME
RME usually produces less discomfort then in normal palate subjects of
No mid palatal suture, & less force is required to separate the maxilla.
The usual 3 months of fixed retention phase with expansion appliance left insitu
The only undesirable situation which may arise from RME is the opening of
oro-nasal fistula, which can be so find that inter collapsed state of the maxillae
they do not readily pass fluids but can cause inconvenience when opened by
• RME IN CLASS III
Treatment with RME /FM therapy for 10 months induces a
significant response of the craniofacial skeleton in terms of
forward movement of the and downward and backward movement
Although Class III craniofacial characteristics were
re-established in the posttreatment period, postpro-traction
Overall, RME/FM therapy has been shown to be an
effective treatment for correcting skeletal Class III
malocclusion in the long term
The favorable skeletal effects induced before the puber-tal
growth spurt with orthopedic facemask therapy led to the
establishment of a positive overbite and overjet
The occlusal relationships gen-erally withstood subsequent
Class III craniofacial
growth throughout attainment of skeletal maturity as
assessed by the CVM method.
SURGICALLY ASSISTED RAPID PALATAL EXPANSION
Surgical freeing of the maxilla
Age at surgery :
Resistance in the maxilla to separation may be traced to 3
1. Mid palatal synostosis
2. Mid palatal inter locking
Generally the commencement of synostosis corresponds with the cessation of
growth in the middle to late teens, as spicules of bone appear b/w’n the palatal
These thin early bridges may be removed by osteoclasts to suit local
physiological needs. There after this rather slow sutural obliteration increases
more rapidly in the twenties.
All RME patients of age 25 yrs & over are to be supported with surgery. B/w’n
20-25 yrs must be treated with utmost respect for early sutural closure.
Surgical option cannot be dismissed fully in 15-20 yrs range, because the force
buildup can be quite high & produce some pain with sutural opening.
Some overexpansion is suggested to counteract the relapse effect of
buccal tipping of the posterior teeth
that takes place during Surgically assisted rapid maxillary expansion
treatment in the mixed dentition.
It is a form of expansion which involves increase of arch width by movement of
few teeth (or) many teeth.
Slow expansion has traditionally been termed dento-alveolar expansion,
although some skeletal changes can be observed.
Expansion is at a rate of 0.5-1mm per week.
Differences between slow expansion and RME
1. Bio Mechanical
2. Type & Amount of
3. Effects on tissues
5. Duration of
6. Arch Perimeter changes Lesser
7. Inter- canine width
the posterior expansion
8. Mandibular rotation
Skeletal mainly &
Lesser than RME
0.65 times the
Using Jack screws
Using Functional Appliances
Ni-Ti palatal expander
Fan Shaped Expander
Light Continous Force Expander
By Arch Wires
The various jack screws incorporated in the appliances described for rapid expansion can
be used for slow expansion, but with a more spread out activation schedule.
The screws used for slow expansion have a smaller pitch than those used in RME.
Coffin spring :
This appliance was designed by Walter Coffin around the beginning of this
It is a removable appliance capable of slow dento-alveolar expansion.
The appliance consists of an omega shaped wire of 1.25mm thickness, placed
in the mid palatal region.
The free ends of the omega wire are embedded in acrylic covering the slopes of
The spring is activated by pulling the two sides apart manually (or) by 3 prong
Coffin spring is believed to bring about a dento-alveolar expansion. However
use of this appliance in younger patients is believed to bring about some amount
of skeletal expansion. www.indiandentalacademy.com
‘W’ arch :
Use to correct the bilateral constriction in primary dentition.
Made of 36mil steel wire soldered to molar bands.
The lingual wire should contact the teeth involved in cross bite &
extend not more than 1-2mm distal to banded molars to eliminate soft
Lingual wire should remain 1-1.5 mm away from marginal gingival &
the palatal tissue.
Accelerates the rate of normal expansion of the mid palatal suture in a
The appliance delivers proper forces levels when opened 3-4 mm
wider than passive width & should be adjusted to this dimension before
Quad helix :
It is said to have evolved from the original Coffin loop.
It exerts a palatal suture widening effect.
It is slower, but separate the suture in pace with the speed of new
formation of bone.
It consist of 4 helices that increase the wire length. Therefore the
flexibility and range of action of this appliance is more.
The appliance is constructed using 0.038 inch Elgialloy 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 b/w’n the two anterior helices is
called the anterior bridge.
The wire b/w’n the anterior and posterior helices is called the palatal
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.
Activation : It can be pre activated by stretching the two molar bands
apart prior to cementation or by using three prong pliers after
1). All cross bite in which upper arch needs to be widened.
2). Cases needing mild expansion in the mixed / permanent dentition which
will frequently exhibit lack of space for upper laterals & in which long
range of forecast is available.
3). Cases of class II in which upper arch needs to be widened & upper
molars rotated distally.
4). Class III conditions in which upper arch needs to be widened &
advanced with class III elastics.
5). Cleft palate conditions either unilateral (or) bilateral.
Nickel Titanium palatal expander : (JCO Mar 1993).
To overcome the limitations of conventional expansion appliances Wendell V
.Arndt, developed a tandem- loop, Ni-Ti temperature activated palatal expander.
It has the ability to produce light, continuous pressure on mid palatal suture while
simultaneously uprighting, rotating & distalizing the maxillary 1st molars.
This fixed removable appliance has adjustable stainless steel extensions and is
inserted into standard horizontal lingual sheaths that are spot welded to the molar
Action of appliance is consequence of Ni-Ti shape memory & transition
Expanders come in 8 different intermolar widths ranging from 26mm-47mm that
generate forces of 180 - 300gms.
The clinician determines the appropriate size by measuring the amount of
expansion needed & then adding 3mm for over correction.
♦ Freeze -gel packs, provided in the expander kits, can be placed around the
expander assembly while the band cement is being prepared. This will cool the
appliance enough to allow easy insertion into lingual sheaths
Expander should be handled by molar attachments during placement to avoid
warming the Ni-Ti.
When appliance begins to stiffen in mouth, it may cause some discomfort at
first. The patient can alleviate this by sipping a cold liquid, which will
temporarily make the Ni-Ti slightly more flexible.
It can be alloyed to produce a metal with specific transition temperature. At
temperatures below the transition temperature interatomic forces weaken,
making the metal much more flexible & above the transition temperature the
interatomic forces bind the atoms tighter & metal stiffens.
Ni-Ti as transition temperature of 94°F, when it is chilled before insertion, it
become flexible & can easily be bent to facilitate placement.
As the mouth begins to warm the appliance, the metal stiffens, the shape
memory is restored and the expander begins to exert a light continuous force on
the teeth & mid palatal suture.
The Spring Jet for Slow Palatal Expansion
(JCO Sep 1999)
It is a new appliance designed to achieve fully controllable mechanics
for slow maxillary expansion.
Appliance Design :
The active components of the spring Jet are soldered or attached to the
molar bands as with any traditional expander.
The transpalatal arch is replaced by a telescopic unit with a nickel
titanium coil spring and a lock screw.
Activation of the coil spring is achieved simply by moving the
lockscrew horizontally along the telescopic tube.
A ball stop on the transpalatal wire allows the spring to be compressed.
The telescopic unit is placed high in the palate, about 5mm up from the
center of the molar bands, so that the line of force passes close to the
center of resistance of the maxillary teeth.
While the higher placement avoids irritating the tongue, the Spring Jet
should be kept atleast 1-1.5mm away from the palatal soft tissue as well.
Two different coil springs are available 1). using the 240g spring in the
mixed dentition and 2). the 400g spring in the permanent dentition.
Because the force level of the spring tends to decrease as it opens, the
lockscrew is designed to maintain full spring compression, assuring a
constant level of force throughout expansion.
Unfortunately, with previously available appliances, whether stainless
steel or nickel titanium, it has been virtually impossible to maintain a
constant force of expansion as the palatal arch rebounds to its passive
The simple and comfortable Spring Jet allows a constant expansion
force to be applied as long as necessary. After correction, the appliance
can easily be inactivated and kept in place as a retainer.
Butterfly Expander for Use in the Mixed Dentition
(JCO Oct 1999)
RPE have been shown to create undesirable side effects such as dental
extrusion and tipping. A new RPE appliance, called a “butterfly
expander”, that is used to treat patients in the mixed dentition was
Appliance Design :
The butterfly expander follows the basic design of Hass, with a few
A high midpalatal jackscrew (A0620) is attached to a butterfly-shaped
stainless steel framework that extends forward to the palatal surfaces
of the deciduous canines.
The appliance is soldered to bands on the second deciduous molars.
A high -powered laser is used to weld the two arms to the screw
housing, ensuring perfect, one-piece joints and eliminating any
possibility of detachment.
The rigidity of the appliance and its location high in the palatal vault
allow the transverse force to be delivered closer to the center of
resistance of the posterior teeth than with conventional expander.
The butterfly design thus minimizes posterior tipping and extrusion.
Activation of the screw is begun with a complete turn (four quarter
-turns) immediately after cementation of the appliance.
The parents should be instructed to activate the screw a quarter-turn
three, times a day (morning, afternoon, and evening).
Active expansion takes seven to nine days, depending on the degree of
Transverse expansion is usually deemed sufficient when the posterior
crossbite is over corrected by 2-3 mm.
Screw is then blocked, and the appliance is left in place as a passive
Occlusal and anteroposterior x-rays should be taken at this point to
confirm the expansion.
♦ It allows early treatment of a skeletal problem that commonly manifests itself in
the primary dentition and will not-self-correct. Because the butterfly expander is
applied to the primary molars, it will not cause root resorption of anchored
premolars and permanent molars after RPE
Fan-shaped Maxillary Expander
(JCO Nov. 1999
Patients with narrow maxillae, sometimes require differential expansion of the
anterior and posterior segments, as in cleft lip and palate cases. Schellino &
Modica have designed a “ spider screw” that works asymmetrically to produce
The expander is made of medical -grade stainless steel, with the spider screw as
the active component.
There are three pivot points; a posterior one, which allows the “fan” opening,
and two anterior ones, which counteract the torquing forces produced during
Four arms, two mesial and two distal, are welded to the expander and to bands
on the teeth. The type of expansion produced depends on the angulation and
length of the arms.
If the arms are mesially inclined (acute
anterior angles with respect to the
screw), the interarm distance will
increase both anteriorly and posteriorly
during expansion, but more in the
If the arms are perpendicular, only the
anterior interarm distance will increase ,
with no appreciable change in the
•With distally directed arms (obtuse anterior angles with respect to the
screw), there will be a contraction in the posterior interarm distance, with
no anterior change.
• Shortening the arms will decrease any of these effects.
•Placement of the fan-shaped expander is similar to that of the traditional
rapid palatal expander.
• After a bite registration is taken with the bands in place, the screw is
adapted and welded to the bands by the laboratory technician.
• A screw with asymmetrical action can produce expansion, contraction,
or conservation of the anterior or posterior transverse dimensions.
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