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 intermolar 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
stable
Stable expansion of lower intercanine
width unlikely unless canines lingually
displaced
Expansion 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 pretreatment 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 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
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
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” screw
Claims:
 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 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 patient’s
original archform may not be stable)
Quad helix / tri helix fixed or removable, are
useful in cleft cases
Activated by half a tooth’s 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
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
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 nonextraction 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
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 worn
Distalising super elastic Nickel titanium coil
springs
Magnets supported with CL II traction
Active 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 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