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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. - PowerPoint PPT Presentation
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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
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