arch expansion 1-ortho / orthodontic courses by indian dental academy

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ARCH EXPANSION

Contents IntroductionArch dimensional changes with ageNeed for arch expansionChanges possible with orthodontic/orthopedic

treatmentMaxillary expansionMandibular expansionConclusionReferences


Introduction Arch expansion and frequency of extraction

have very close but inverse relationship with each other.

To Edward Angle and his followers in the early

20th century, extraction was anathema.


In their concept, extraction destroys the possibility of ideal occlusion or ideal esthetics, both of which require presence of all the teeth in any case.

Hence any space required for aligning

dentition was achieved by expansion of arches.


As it became clear that arches could and did collapse after expansion despite efforts to produce ideal function, extraction was reintroduced in the 1930s in an attempt to overcome relapse problems


Why did the first premolar extraction percentages declined dramatically in the last few decade?

Various long term studies demonstrated not

much difference between extraction and nonextraction/expansion group regarding esthetics, stability and occlusion.


In Class I crowding cases, nonextraction treatment increases the prominence of the lips, extraction decreases it.

For satisfactory esthetics,

some patients require extraction, some require nonextraction treatment, and a considerable group in the middle could have acceptable esthetics with either approach.


In the treatment of Class I crowding, stability probably is greater with extraction than nonextraction treatment, but the difference is not as great as was believed at the height of enthusiasm for premolar extraction.

As with esthetics, some patients require extraction for reasons of stability, some require nonextraction, and a large group in the middle could have satisfactory outcomes with either approach.


Satisfactory occlusal function for the great majority of patients, including consideration of TMD, has little to do with the presence or absence of premolars.

A few patients would require extraction or nonextraction treatment for occlusal reasons, but for almost all, either approach is satisfactory from an occlusion point of view.


How much dental arch dimensions can be permanently changed by orthodontic treatment ?

If the limits are tightly set by genetic control, then long-term expansion is unlikely to be successful.

Hence, tooth size jaw size ratios would be

a major diagnostic criterion. www.indiandentalacademy.com

On the other hand if arch dimensions are greatly influenced by environment as Angle believed, then major changes should be possible.

This view has reappeared in recent years supported by studies that show little genetic determination of occlusal variations. (Corrucini, Sharma , Potter, 1986).


It is difficult to know how much change is possible regarding arch width, but a strong possibility of arch expansion certainly encourages attempts of nonextraction treatment.


Arch width changes with age

There are clinically significant differences in the magnitude and manner of width changes in the maxilla and mandible.

Dental arch width increases correlate with

vertical Alveolar process growth, whose direction is different in the upper than in the lower arch.


Maxillary alveolar processes diverge while the mandibular alveolar processes are more parallel.

As a direct result, maxillary width increases

more than mandibular arch due to vertical alveolar development , a important clinical point.


The maxillary permanent cuspids are placed further distally in the arch than their primary counterpart and erupt pointing mesially and labially.

Hence their arrival is another important

factor contributing to expansion of maxillary dental arch.


The intercanine diameter increases only slightly in the mandible, and some of this increase is the result of the distal tipping of the primary cuspids into the primate space, since the mandibular incisors are not normally moved labially through time.


Furthermore, dental arch width changes are closely related to the events of dental development rather than endocrinally mediated events of overall skeletal growth such as the adolescent spurt in stature.


Bicanine width increments versus dental age

age. 0 = moment of arrival of first permanent incisor.


Need for arch expansion

To correct lateral Malrelationships of Dental Arches

Failure of the two dental arches to occlude normally in lateral relationship, known as lateral or posterior crossbite, may be due to localized problems of tooth position or alveolar growth, or to gross disharmony between maxilla and mandible.


Dentoalveolar crossbite with good apical base width (left) and crossbite with a deficient apical base width (right).


Lack of harmony between the maxillary and mandibular widths usually is due to a bilateral constriction of maxilla.

In such cases, the muscles shift the

mandible to one side to acquire sufficient occlusal contact for mastication, causing unilateral crossbite though the constriction is bilateral.


Rarely, there may be true unilateral crossbite due to asymmetric lateral growth of maxilla e.g in case of hemifacial microsomia.


A more severe condition is that in which the mandibular denture occludes completely within the maxillary arch


When lateral problem is combined with a skeletal Class II / Class III malocclusion, lateral discrepancy get exaggerated because of antero-posterior morphology of mandible.


The effect of anteroposterior position of the arches on buccal overjet is shown when a normal occlusion (B) is shifted to a Class II molar position (A) that increases buccal overjet and to a Class III molar position (C) that decreases buccal overjet.


Dimensional Changes possible with Orthodontic Therapy

It is relatively simple to increase the maxillary dental arch width and length, but difficult to increase and retain the mandibular dental arch width.


Maxillary expansion CLASSIFICATION

1 Orthopedic: width of underlying basal bone is increased by means of splitting mid palatal suture.

Orthopedic expansion may be rapid or slow depending on rate of expansion.

2. Orthodontic: Expansion produced by conventional fixed appliances or removable expansion plates. The crowns of involved teeth are tipped buccally with resultant lingual tipping of roots. Resistance of muscular envelope may lead to relapse.

3. Passive: When the muscle forces (buccal & labial) are shielded away from the dentition, a widening of dental arches occurs. This expansion is a result of intrinsic forces produced by tongue.

Ex. F.R. Appliance, Lip Bumper


Rapid maxillary expansion HISTORICAL BACKGROUND

The problems associated with a narrow maxilla and the need for expansion has been recognized since long time.

In 1860, E.C. Angell successfully splitted maxilla

using a jack screw appliance. He is considered the father of rapid maxillary expansion.

However his work failed to gain popularity in the orthodontic community.


In 1877, Walter coffin introduced coffin spring for arch expansion. This spring was believed to cause separation of the mid palatal suture in young children.

Farrar (1888) and Clark C. Godard (1893) also discussed the feasibility of lateral expansion with mid palatal suture opening.

Around beginning of 20th century, ENT surgeons showed interest in this technique of orthopedic expansion of maxilla.


EyselL, a rhinologist believed that rapid expansion could bring about a change in nasal configuration and airflow.

Wright in 1912 reported a 6.5mm widening of

nasal cavity with rapid maxillary expansion.

During early 1970’s, Hass started using rapid maxillary expansion extensively.


HAAS (1980) evaluated the stability of maxillary expansion achieved with rapid palatal expansion.

He wrote “totally stable 4 and 5mm intercanine

expansions in the lower arch many years out of retention.… and upper buccal teeth expanded 9 to 12mm with the expansion remaining absolutely stable.”


Mid palatal suture Latham (1971) believed that growth at the

midpalatal suture ceases at the age of 3 years.

By means of implants, Björk and Skieller (1974) found that growth at the suture might be occurring as late as 13 years of age.


Persson and Thilander (1977) in a study on cadavers found that 5% of the suture was obliterated by age 25 years, yet the variation was such that a 15-year-old cadaver had an ossified suture, while a 27-year-old cadaver had an unossified suture.

Epker and Wolford (1980) stated, “In patients

over the age of 16 years, attempted orthopedic rapid maxillary expansion is frequently associated with significant difficulties.”


Difficulty is usually the resultant fusion of various craniofacial sutures, which results in a lack of suture opening on expansion.

Most important effect is produced by zygomatic buttress which resist lateral movements of two maxillae.

The optimal age for expansion is, therefore, before 13 to 15 years of age.

Although it may be possible to accomplish expansion in older patients, the results are neither as predictable nor as stable.


INDICATIONS FOR R.M.E According to Haas, the following five conditions

are recognized to be primary indications for RME:

1. Transverse maxillary discrepancy resulting in posterior cross bite.

2. A-P maxillary deficiency cases with negative ANB that would benefit from maxillary protraction. In such cases RME is required to loosen the maxilla.


3. Cleft palate cases with collapsed maxilla.

4. Cases of nasal stenosis characterized by mouth breathing & constricted nasal aperture.

5. Moderate arch length problems in patients of 14-16 yrs age.


CONTRAINDICATIONS1. Periodontally compromised dentition2. Single tooth cross bite3. Ossification of suture is completed4. Poor patient co-operation


APPLIANCES USED FOR EXPANSION Removable appliance – removable plate with jack screw Fixed appliances: Fixed tooth & tissue borne appliances - Derischsweiler type - Haas type Fixed tooth borne appliances - Isaacson type - Hyrax appliance


Removable plates These appliances usually consist

of an expansion jack screw with palatal coverage & claps for retention of appliance.

They are general advocated

during deciduous / early mixed dentition to bring about desired skeletal changes.

Retention during expansion procedure is difficult as they easily get dislodged. Patient co-operation is essential.


Derischsweiler expander In this type of expansion

device, the screw is embedded in acrylic which covers the palatal vault & alveolar ridges. The first premolars & molars are banded.

Wire tags soldered to the palatal aspect of the bands to facilitate attachment of acrylic.

The acrylic extends to the palatal aspect of all non banded teeth except incisors.


Haas expander The first premolars & first molars are banded. 1.2 mm diameter stainless steel wire is soldered

onto the buccal & palatal surfaces of these bands connecting the premolar to the molar.

Disadvantage of Hass type expander is pressure

necrosis of palatal mucosa under acrylic


The lingual bar is over extended anteriorly and posteriorly and is bent palatally to aid in attachment to palatal acrylic.

A midline screw is incorporated in the split acrylic base plate.

The acrylic falls short of the rugae anteriorly and lingual gingival areas.

Haas type expander


FIXED TOOTH BORNE APPLIANCES

Isaacson type: This appliance uses a special spring loaded

screw called Minne expander. The Minne expander is soldered on to the metal

flanges running from banded first premolar and first molar.


Spring is activated by

turning the adjustment screw, thereby compressing the coil spring.

Disadvantage of minne

expander is poor oral hygiene.

Minne expander


Hyrax appliance. (hygienic rapid palatal expander)

A fixed wire appliance cemented to the first permanent molars and first premolars with centrally located jackscrew.

Banded Hyrax


Tooth extrusion, dental tipping, and an increase in the vertical dimension are often encountered with expansion appliances.

Bonded Hyrax using interocclusal acrylic

may control the vertical dimension and expand the maxillary halves in a more bodily and symmetrical fashion.


A. Hyrax appliance design.B. Bonded Hyrax design.


In one study (Steven Asanza, George J. Cisneros, Lewis G. Nieberg. 1997) , the results suggest that :

1. The bonded RME appliance displayed less inferior movement of the posterior aspect of the palate as measured by SN-PNS in mm.

2. The bonded appliance showed less anterior displacement of the maxilla than the Hyrax appliance as measured by S-A pt. in mm.

3. The Hyrax appliance showed a greater increase in vertical facial height as measured by ANS-Me in mm.

4. Both appliances resulted in tipping of the posterior teeth, which was highly variable and asymmetric.


Expansion screw A typical screw consists of an oblong body

divided into two halves, each half has a threaded inner side to receive one end of a double ended screw.

The screw has a central bossing that has four holes. These holes receive a key to activate the screw.

A single adjustment of the screw brings about 1/4 revolution causing 0.18mm linear movement.


ACTIVATION SCHEDULE

Zimring & Isaacson: In young growing patients, two turns each day for 4-5 days and later

one turn per day till desired expansion is achieved.

In adults (non growing patients) two turns each day for first two days, one turn per day for the next 5-7 days and one turn every other day till desired expansion is achieved.

Timms: 1. Up to 15 yrs : 90° rotation once in the morning & once in the evening

2. 15-20 yrs : 45° activation 4 times a day


Period of retention: The objective is to maintain the expansion

achieved while all forces generated during the procedure have decayed.

Hass : Recommends 2 yrs of full time retention followed by 1/1/2 - 2 years of part time retention.

Isaacson :Use RME appliance for retention. The screw is immobilized with acrylic.


Chaconas and Caputo (1982) compared these expansion appliances with respect to force delivered and change in width of appliance.

The Haas and Hyrax appliances delivered very high orthopedic forces that were similar.


The removable appliance, when fully and firmly seated, delivered the highest force of all appliances tested.

When unstable, however, the removable appliance was only capable of much lower forces, similar to those of the Minne-expander.


Pattern of stresses produced during RME

Stresses produced by appliances are concentrated in the anterior and posterior regions of the palate.

Darker shading represents areas of higher stress.


Stresses radiate from the junction of the palatine bones to deeper structures via the perpendicular plates of the palatine bone.



Stresses radiate from the maxillary tuberosity to the base of the medial pterygoid plate.



Concentration of stresses at the zygomatico-temporal suture.



Concentration of stresses at the junction of the nasal and lacrymal bones.



Displacement of various structures during RME

Movement of Maxillary teeth Anteriors : Appearance of space between

the maxillary central incisors is the earliest clinical evidence that midpalatal split is occurring.

It is estimated that the incisors separate

approximately half the distance the screw is opened (Haas).


Clinical features

X-ray picture before expansion, after expansion, and three months later.


Posteriors:

Initial bending of alveolar process & compression of periodontal ligament is accompanied by change in long axis of posterior teeth (buccal tipping).

This is also partly due to the tipping of teeth in the alveolar bone and partly because of extrusion of maxillary posteriors.


Direction of palatal split In the frontal view, the suture separates in a

triangular fashion with base towards the oral cavity & apex towards nasal cavity.

From occlusal view, the split occurs in a wedge shaped manner with maxilla opening anteriorly. This resembles the opening of a fan evident on an occlusal radiograph.


A. Triangular pattern of maxillary expansion in the frontal plane includes orthopedic and orthodontic movement. Orthopedic changes may involve separation at sutural sites with a lateral rotation or tipping of the palatal halves, widening of the nasal processes, and subsequent bony remodeling. Orthodontic changes may involve lateral tipping and bodily translation of maxillary teeth, transient midline diastema, and mild expansion of mandibular teeth.

B, Occlusal view of maxillary expansion illustrating midpalatal suture opening with greatest separation occurring anteriorly, lateral rotation of palatal halves, bony remodeling of maxillary elements, and lateral/rotational movement of the maxillary teeth.


Effect on alveolar bone The alveolar process being resilient, RME forces

initially leads to its lateral bending. This is due to the arcing of the bones themselves and some amount of lateral tipping of teeth.

Walters, however contradicted these findings and

reported a lateral & upward rotation of the maxilla itself.


Effect on Palatal vault

Haas & Krebs reported lowering of the palatine process due to outward tilting of the alveolar processes.

This contributes partly in straightening of DNS (Korkhaus), widening of nasal floor & flattening of palatal vault.


Effect on palatal mucoperiosteum & PDL tissues.

As the maxillary halves separate, the

palatal mucoperiosteum is stretched. During the post-expansion period, recoil of the stretched fibers causes a decrease in the inter-molar angulation.


Surgically Assisted Rapid Palatal Expansion

Surgically assisted palatal expansion is an method of reducing the resistance of ossified midpalatal suture to facilitate expansion by mechanical procedures.


Surgical Procedure A paramedian incision is made under local

anesthesia. After the mucoperiosteum is released,

midpalatal suture is separated with a midline cut, about 3mm deep but not reaching the foramen incisivum.

The mucosal and bony cuts should not overlap.


Surgical procedure: Mucosal (solid line) and bony (dashed line) cuts on palate (A) and lateral maxillary buttress (B).


Two bony cuts each about 4mm long, are then made on each side of the lateral maxillary buttress above the root apices and parallel to the occlusal plane.


After the osteotomy, the maxillary segments are not fully detached, but can be separated by rapid expansion with a jackscrew appliance.

The expansion appliance should be cemented in place before surgery and activated three or four quarter-turns by the surgeon after the bony cuts are made.

The rest of the expansion is achieved in daily increments for about two weeks after surgery. Overcorrection of about 2.5mm per side (5mm total) is usually advisable.


Modular Palatal Disjunctor Appliance (Jean-luc pruvost, 1989)

Development of a modular, easily

removable palatal expander was prompted by the need for increased precision and working comfort during maxillary surgery.


The appliance is made of cast, etchable nickel chromium, which has a high resistance to breakage and torsion.

The three parts of the appliance can be

joined by Allen screws.


Rapid Maxillary Expansion in Cleft Lip and Palate Patients

Because of their tendency toward skeletal segmental collapse, bilateral complete cleft lip and palate patients often require rapid maxillary expansion.

As in normal individuals, the pattern of

expansion is triangular with a greater opening in the anterior region


In cleft patients, however, the separation occurs in the suture between the maxilla and the premaxilla, with no osseous gain.

The increase in maxillary arch width and the orthopedic effect can correct the transverse maxillomandibular relationship.


In growing cleft palate individuals, the

opening of the sutures can displace the maxilla forward and downward, opening the bite and moving Point A anteriorly.

In most instances, however, these effects

are only temporary.


Activation schedule in cleft patients

The appliance is first activated with four quarter-turns 24 hours after placement.

For the next four days, the screw is activated two quarter-

turns in the morning and two quarter-turns in the evening.

At this point, the orthopedic force should be sufficient,

and activation can be reduced to a more comfortable one quarter-turn in the morning and one in the evening.


The average activation period is from one to two weeks, depending on the degree of maxillary constriction and the resistance of the patient's maxillofacial structures.

A 2-3mm overcorrection at the molars is

recommended to counteract a relapse that has been reported to reach 30-50%, or even 75% at the canines.


A. Upper arch before expansion. B. Haas-type expander in place.


After full expansion


Once the desired expansion is obtained, the screw is immobilized by acrylic.

The appliance is kept in place for three months

of retention, which further reduces the possibility of relapse.

The expander is then removed, and impressions

are taken.


A removable palatal plate, without clasps that might interfere with any remaining orthodontic movement or with proper tongue position, is worn as a retainer until the end of treatment.


Nickel Titanium Expander Unlike normal patients, one has to be very

careful regarding force level in cleft patients.

A tandem-loop, nickel titanium, temperature-activated palatal expander with the ability to produce light, continuous pressure is very useful tool for arch expansion in cleft patients.


A Degree of compression when prototype appliance was chilled to 20° below transition temperature.

B. Effect of shape memory when appliance was warmed to body temperature.


This fixed-removable appliance has adjustable stainless steel extensions and is inserted into standard horizontal lingual sheaths that are spot-welded to the molar bands.

A locking indent on the lingual attachment securely fastens the expander to the molar band to ensure patient safety.


A. Passive appliance. B. Initial activation and

insertion for expansion and distal molar rotation.

C. After expansion and rotation correction.


SLOW MAXILLARY EXPANSION

Initially, RME was believed to cause more skeletal than dental expansion.

However, when the expansion is completed and bone is filling in the defect, orthodontic tooth movement continues causing skeletal relapse.

Hence although total expansion is maintained, the % due to tooth movement increases & skeletal expansion decreases.


With slow expansion, the total expansion is half dental/half skeletal from beginning. The final outcome of rapid versus slow expansion at 10weeks is similar.


The rate of expansion in slow expansion is 1 mm per week compared to about 1 mm per day with RME.

Slow expansion is achieved by activating a

spring to give 2-4 Ibs of force in contrast to about 10 lbs force with RME.


Quad-helix Quad-helix or W expansion appliance was

popularized by Ricketts. Depending on age of patient, quad helix can produce dento-skeletal (SME) or dental effects.

It is fabricated from .040" blue Elgiloy wire and is

either soldered to the upper first molar or bent to fit into a lingual sheath. The lingual arm of the appliance extends to the premolar or cuspid.


The posterior helix is beveled slightly to lay against the palatal vault and is as close to the upper molar as possible to prevent impingement on the palatopharyngeus muscle.

The anterior helices are brought as far forward as possible.


The anterior segment of the W expansion should be as wide as possible so that the appliance is maintained away from the swallowing position of the tongue.

All of the helices should roll to the top and should be tightly wound to increase their mechanical efficiency


Initial activation of quad-helix appliance during insertion.

In Class II cases, most of

the arch form change should occur in the anterior portion of the buccal segments.

As the upper molars are expanded approximately 1cm per side, the anterior segments are expanded approximately 3cm overall.


Intra-oral activation of quad-helix appliance.

When an intraoral bend is made in the anterior segment to increase the amount of overall expansion, a reciprocal bend must be made in the posterior section in order to compensate for the tendency for mesial rotation of the upper molars.

Therefore, three intraoral adjustment bends are usually made at each activation.


Modifications of the quad-helix appliance.


Schwarz Appliance: The appliance basically

consists of an acrylic plate with a midline split incorporating one / two expansion screws, the acrylic does not cap the occlusal surface / incisal edges.

The appliance in addition has a labial bow & is retained by means of Adam's / ball end clasps.


Y plate: The acrylic sectioning is

done in a Y shape. The appliance incorporates two screws on each side.

The incisor segment is

expanded anteriorly whereas the posterior segment moves laterally


Coffin spring (Walter coffin 1877)

Removable appliance incorporating omega shaped loop.

The appliance is retained by means of Adam's clasps. The free ends of the spring as well as retentive arms of clasps are acrylised.

Activation is done by using three pliers.


Porter lingual archwire. This appliance is usually used for

correction of posterior crossbite in the primary dentition.


Mandibular expansion


Historical background

Lack of adequate space in the mandibular arch is often a critical factor in the decision of whether to extract teeth or not.

In this regard, expansion of the mandibular

arch has gained interest in non-extraction treatment


Reidel (1952) stated that arch form, particularly in the mandibular arch, could not be altered by appliance therapy.

Intercanine and intermolar widths tend to decrease during the post-retention period, especially when expanded during treatment


In one study (Housley, Dale, Ram S. Nanda, Frans Currier, 2003), only 8% of the arch width increase at the canines was maintained after retention, but, at the premolars and the first molars area, about 60% to 70% of the expansion remained stable.


Haas (1970), using a midpalatal suture-opening appliance without any treatment in the lower arch, observed that the mandibular arch tended to follow the maxillary teeth by tipping laterally.


He claimed that mandibular intercanine width can be increased in the non growing individuals if the apical base of the maxillary complex is permanently widened.


According to Sandstrom, Klapper, and Papaconst (1998), this stability of the expanded mandibular arch width may be the result of an altered muscular balance exerted on the dentition by the buccinator muscles, which have been carried laterally by the maxillary expansion.


Gardner (1978) has shown that the cuspids are the greatest limiting factor in arch expansion, but the very adjacent tooth i.e first premolars offered great opportunity for expansion regarding stability.


Lestrel (1978) proposed a formula determining the ideal dimension of the lower arch at the distal contact of the cuspids. The formula is as follows:


incisor mass: sum of mesio-distal diameters of the four lower incisors

mandibular width: the distance between the left and right antegonial notches.

Frankfort mandibular plane angle.facial angle: Angle between facial plane

and Frankfort plane.


norms


The formula shows that a patient with a brachyfacial pattern (wide mandible + low mandibular plane angle) will have a wider mandibular arch than the dolichofacial pattern (narrow mandible and a high mandibular plane angle)


Therefore under certain circumstances, expansion of lower arch is possible.

Till recently before the introduction of distraction osteogenesis technique, it was impossible to widen mandibular basal dimensions.


Mandibular expansion appliances

Mandibular Schwarz appliance The original mandibular Schwarz appliance

retained with ball end clasp is effective in dentoalveolar expansion, but often retention is problem.


Traditional mandibular Schwarz appliance with ball clasps for retention.


Whether Adams clasps, C clasps, or ball clasps are used as the primary method of retention, the appliance is unstable because the clasps do not fit well in the undercuts of the lower deciduous molars.


Warren Hamula (1993) modified Mandibular Schwarz Appliance to increase both retention and strength of appliance by means of wire reinforment. Posterior framework of .028"

round wire.


Modified mandibular Schwarz appliance.


Buccal Shield Appliances for Mandibular Arch Expansion

- The lip bumper - Frankel's buccal shields These appliances are most effective for increasing the

arch width during the eruptive phase of dentition.


Lip bumpers The lip bumpers are made

of malleable, 0.040" stainless steel wire with posterior adjustment bends to allow anteroposterior adjustments.

About 3mm of clearance is recommended between the bumper and the teeth to allow proper lip contact with minimum discomfort.


A.Displacement of buccal mucosa by typical lip bumper.

B,C. Buccal mucosa may

roll over or under wire, preventing arch expansion by contacting teeth.

Hence for arch expansion, vestibular appliances are better


This problem of limited shielding effect by lip bumper wire does not happen with buccal shields of Frankel appliance.


The functional matrix and the Fränkel appliance

OO, Obicularis oris. B, Buccinator. PMR, Pterygomandibular raphe. SPC, Superior pharyngis constrictor. LP, Labial pad. VS, Vestibular shield.

The functional regulator provides a larger functional matrix than the teeth. The buccinator mechanism will grow and adapt to whichever functional matrix (soft-tissue capsule) is present in the mouth.

This adaptation occurs primarily during growth. After growth is complete, very little, if any, change can be expected.www.indiandentalacademy.com

Schematic view of the influence of vestibular shields on eruptive path and dentoalveolar

development.

Dense stippling shows alveolar apposition prompted by the vestibular shield, whereas lighter stippling shows the more lateral position of the permanent tooth.


The vestibular shield creates tension at the depth of the mucobuccal fold in a lateral direction. This tension is directed at influencing the erupting permanent teeth to erupt further laterally than normal, thereby resulting in arch expansion.

Notice that less influence is seen on fully erupted teeth, as shown by the open arrow. www.indiandentalacademy.com

Distraction osteogenesis

Distraction osteogenesis (DO), originally developed by Russian orthopedic surgeon Ilizarov, has produced significant results in limb lengthening.

Mandibular symphyseal DO introduced by Guerrero, provided a new paradigm for increasing transverse dimension of mandible, which once thought to be impossible.


Distraction protocol A latency period is critical for DO. Without

allowing time for a callus to form, callus manipulation cannot occur.

Without a good callus, the quality of the

regenerate bone can be adversely affected, possibly creating bone of poor quality and other complications.


The latency period is typically seven days.

In young children, healing is accelerated, and may require a shorter latency period.

Older patients may require a slightly increased latency period because of a slower rate of healing.


The rhythm of distraction refers to the number of increments required to reach the preplanned daily rate of distraction. The rate of 1mm/day can be performed all at once or in various smaller increments.

A clinically efficient rhythm has been 0.25 mm four times a day or 0.50 mm twice a day.


Post DO retention A fixed lower canine-to-canine wire will

adequately maintain the canine width and anterior alignment, but cannot be expected to aid in maintaining any posterior expansion.

Consequently, a Hawley retainer with integral

lingual support wire is a good form of mandibular retention.


Conclusion

There is clear reversal swing of pendulum towards non extraction treatment modality.

Most of the borderline cases which once were considered for extraction are now being attempted through non extraction approach with required space being provided by arch expansion.


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