Arch lengthening and expansion

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Arch lengthening and expansion
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Arch lengthening

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

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Arch expansion

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

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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

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Arch expansion
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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

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• Preparation for a bone graft in a cleft alveolus
• Child with lt 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

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• 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

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Clinical points

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

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• 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

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• 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

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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

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complications

• Over expansion can cause scissors bite
• Possible periodontal damage
  (equivocal evidence)
• Increase in MMP angle and lower face height thus
  worsening AOB

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Appliances used for maxillary expansion
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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

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Rapid maxillary expander

• Design consists of an active plate, which
  incorporates a jackscrew which is attached to the
  teeth with wirework or acrylic
• Patient 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
  appliances
• There is evidence that mid palatal suture does
  split producing maxillary expansion

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RME contd.

• Limitations are
• Amount of available bone for expansion
• Controversial evidence Î periodontal breakdown
  compared with URA
• Care in choosing age for RME, due to Î resistance
  to maxillary base expansion which needs prolonged
  retention

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RME contd.

• Bonded acrylic RME has occlusal coverage to
  reduce tipping and extrusion of molars
• No significant differences between bonded and
  banded RME

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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 screw
• Claims
• Less periodontal support loss ------
  unsubstantiated
• Increase in nasal air flow ------ unsubstantiated

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• 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

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Quad /tri /bi helix

• Bi-helix used in mandibular arch in grossly
  narrowed or distorted arches, or to aid
  correction of a severe scissors bite
• Some differential expansion of inter-molar width
  possible (however changes in patients original
  archform may not be stable)
• Quad helix / tri helix fixed or removable, are
  useful in cleft cases
• Activated by half a tooths width on either side
• Provides some differential expansion and can
  derotate molars
• May produce less dental tipping than URA
• Unlike URA ,fixed quad helix is not reliable on
  patients compliance

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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

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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

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Arch lengthening
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indications

• Non 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
  minimum
• Half unit CL II molar relationship in a
  non-extraction case
• Correction of incisal relationship in CL III case
  by proclination if upper incisors
• Regain space lost by early loss of deciduous
  teeth
• Correction of retroclined mandibular incisors in
  CL II/2 cases,or CL II/1 cases with mandibular
  incisors trapped in palate

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Arch lengthening procedures

• Distalisation of upper buccal segments
• Distalisation of lower buccal segments
• Proclination of upper or lower incisors

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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
  worn
• Distalising super elastic Nickel titanium coil
  springs
• Magnets supported with CL II traction
• Active palatal arch (TPA)

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Distalisation of lower buccal segments

• Lip bumper not well tolerated
• Removable appliance and HG

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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 incisors
• Labial crown torque ( rectangular wire in FA )
• Avoiding the use of lace backs in CL III
  maxillary incisors
• Side effect of some FA is to procline the
  mandibular incisors if there is no incisal
  capping