Arch lengthening and expansion

Arch lengthening

Increasing the arch length using distal movement of posterior teeth or proclination of incisors

Arch expansion

Management of “narrow” arches by increasing the upper or lower intercanine, inter-premolar and/or inter-molar width

Arch width changes with age

Male arches wider than female

Lower intercanine width increases up to change to permanent dentition

Upper and lower inter-molar width increases between ages 7 to 18

Little change in premolar width after age 12

Arch expansion

Indications for arch expansion

Correction of posterior cross-bite

Elimination of a displacement

Avoiding creation of a cross-bite in cases needing distal movement of upper buccal segments

“V” shaped arch in a thumb-sucker

Preparation for a bone graft in a cleft alveolus

Child with < 31mm of inter-molar width at age 7 yrs. Is unlikely to attain adequate arch dimensions through normal growth alone

Minimal crowding in upper arch (1-2 mm)

Interceptive orthodontics

Mobilization of maxillary sutural system for orthopedic correction of early CL III

Initial preparation for functional jaw orthopedics (FR III), facial mask therapy and orthognathic surgery

Clinical points

Expansion where posterior teeth are tilted lingually may be expected to be stableStable expansion of lower intercanine width unlikely unless canines lingually displacedExpansion more likely to be stable in absence of extractions

Correction of bilateral cross-bites is controversial: they may be left untreated if there is no displacement – the decision will depend on the pre-treatment inclination of the teeth and width of the underlying maxilla

Over-expansion is advisable in anticipation of some relapse

Increase in inter-molar width produces linear reduction in arch depth

1mm of arch expansion causes 0.3mm reduction in arch length ( equates to 0.6 mm space creation within the arch)

Claims that expansion improves nasal respiration equivocal

relapse

Up to 40 % relapse has been found with all forms of active expansion

Occurs via lingual tilting of molars

Relapse less with fixed retainer than URA

complications

Over expansion can cause scissors bite

Possible periodontal damage (equivocal evidence)

Increase in MMP angle and lower face height thus worsening AOB

Appliances used for maxillary expansion

URA

Design consists of an acrylic base plate which incorporates springs and retention clasps

Relies on patient to turn screw two quarter turns per week

Needs adequate seating and retention to produce expansion as the main effect is that of tipping

Coffin springs are less well tolerated and retained but can provide differential expansion laterally and anteroposteriorly

Coffin springs provide a continuous as opposed to interrupted orthodontic force

Rapid maxillary expander

Design consists of an active plate, which incorporates a jackscrew which is attached to the teeth with wirework or acrylicPatient turns a “Hyrax” screw once a day (0.2-0.5 mm/day) for 1-3 weeks (midline diastema develops quickly)May produce more bodily movement than other appliancesThere is evidence that mid palatal suture does split producing maxillary expansion

RME contd.

Limitations are :Amount of available bone for expansionControversial evidence: Î periodontal

breakdown compared with URACare in choosing age for RME, due to Î

resistance to maxillary base expansion which needs prolonged retention

RME contd.

Bonded acrylic RME has occlusal coverage to reduce tipping and extrusion of molars

No significant differences between bonded and banded RME

Surgically assisted RME

To overcome problems of expansion in non growing patients Use buccal corticotomy or Le Forte 1 osteotomy and/or midpalatal splits in conjunction with “hyrax” screwClaims:

Less periodontal support loss ------ unsubstantiated

Increase in nasal air flow ------ unsubstantiated

Evidence :Surgical and non-surgical techniques ;

no difference in stability of expansion after one year

Non-surgical expansion allows sufficient expansion in adults

Problems : Surgical procedure associated with

morbidity and risks Risk of nasal septum deviation

Quad /tri /bi helixBi-helix used in mandibular arch in grossly narrowed or distorted arches, or to aid correction of a severe scissors biteSome differential expansion of inter-molar width possible (however changes in patient’s original archform may not be stable)Quad helix / tri helix fixed or removable, are useful in cleft casesActivated by half a tooth’s width on either sideProvides some differential expansion and can derotate molarsMay produce less dental tipping than URAUnlike URA ,fixed quad helix is not reliable on patient’s compliance

Fixed appliances

Limited amount of expansion possible with fixed appliance alone

Requires rectangular wire to prevent unfavorable dental tipping

Unilateral expansion possible but requires placement of buccal root torque on correct side to prevent tipping

Functional appliances

Produce active expansion ( usually with either expansion screw or palatal arch) to prevent cross bite formation whilst a CL I relation is being obtained

Frankel appliance produces passive expansion only by removing influence of buccal tissues with buccal shields

Arch lengthening

indicationsNon extraction cases with only very mild crowding (1-2 mm)Any change in original arch form is likely to collapse, so lengthening must be kept to a minimumHalf unit CL II molar relationship in a non-extraction caseCorrection of incisal relationship in CL III case by proclination if upper incisorsRegain space lost by early loss of deciduous teethCorrection of retroclined mandibular incisors in CL II/2 cases,or CL II/1 cases with mandibular incisors trapped in palate

Arch lengthening procedures

Distalisation of upper buccal segments

Distalisation of lower buccal segments

Proclination of upper or lower incisors

Distalisation of upper buccal segments

HG with URA ( palatal finger springs to upper 6s, bite plane, HG to 6s tubes)HG with no URA – HG to 6s tubes only. May take longer as there is no finger springs to prevent to prevent relapse during the day when HG is not wornDistalising super elastic Nickel titanium coil springsMagnets supported with CL II tractionActive palatal arch (TPA)

Distalisation of lower buccal segments

Lip bumper ; not well tolerated

Removable appliance and HG

Proclination of upper or lower incisors

URA ( split screw anteriorly, “Z” springs or “T” springs)ELSA (expansion and labial segment alignment appliance); recurved spring or “wiper” arms to procline incisorsLabial crown torque ( rectangular wire in FA )Avoiding the use of “lace backs” in CL III maxillary incisorsSide effect of some FA is to procline the mandibular incisors if there is no incisal capping