Permissible limit for mandibular expansion

Permissible limit for
mandibular expansion
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 Mandibular expansion is brought about by lateral tipping
of the molars.
 Excessive expansion may result in excessive buccal
tooth inclination which may disturb the occlusal
relationship.
 Inclination movement was used as a clinical index to
determine the permissible limit of mandibular expansion.
 Inclinations in occlusal surface of the first molar and
intermolar width was measured before expansion, after
expansion and before edgewise treatment.
ABSTRACT

 Average change in intermolar width was 5.42mm and the average
angle of buccal tooth inclination was 10.16˚.
 No significant correlation was found between age prior to treatment
and treatment period when they were compared with intermolar
width increments and inclination angles.
 Significant positive correlation between retention duration and
amount of expansion.
 According to the study 1mm of expansion is accompanied by 5˚ of
moalr lateral tipping.
 The regression coefficient of the angle of buccal tooth inclination to
the increment of the intermolar width was 0.2.

 According to Hass,mandibular expansion is
localised to the alveolar bone and is brought
about by tooth inclination.
 Adequate occlusal contact relationship provides
normal stomatognathic functions.
 The occlusal relationships are related to the
mesiodistal and buccal-lingual tooth inclination.
 Mandibular expansion can result in excessive
tooth inclination and disturb normal occlusal
functions.

 Control
-11 children
-4 boys
-7 girls
-Angle’s class I malocclusion.
-minimum crowding
-no restorations covering the cusp
tips.
 Subjects
29 subject
-10 males
-19 females
-age ranged from 6 yrs 10 months
to 11 yrs 7 months.
-With Angle’s class I malocclusion
with posterior crossbite.
-Some crowding in the lower arch.
-No restorations covering the
cusp tips.
Subjects and methods

 Appliance used in this
study for expansion-
Schwarz appliance

 Reference plane –the lower occlusal plane including the midpoint of the
tips of the right and left central incisors along the mesiobuccal cusp tips
of the right and left first molars.
 Occlusal surface of the molars was defined as a plane including the
mesiobuccal ,mesiolingual and distobuccal cusp tip of the molars.
 Angle of inclination-difference between the two angles.

 The 3D measurements
were made using a
contact 3D measuring
system.
 All measurements were
made ny one examiner to
reduce intra examiner
errors.

 Statistical analysis
 The data obtained were analysed using a
statistical software package
 Treatment changes pretreatment, post-
treatment,and before start of edgewise
treatment were measured in the treatment group
and control group.
 A index to estimate the permissible limit of
mandibular expansion was obtained.

Inference from the analysis
 The increase in intermolar width with the expansion plate
was 5.42mm
 Mean molar inclination change-10.16˚during treatment.
 Relapse was observed despite using a maintenance
plate.
 Molar width decreased to 4.12mm and molar inclination
decreased to 8.26˚
 Expansion at the beginning of edgewise treatment was
76% of the expansion achieved.
 Longer retention period can maintain a greater amount
of expansion.

 Regression coefficient of the angle of buccal tooth
inclination to the intermolar width increment =0.2
 Permissible limit for mandibular expansion=
=(θr+θl)×0.2
θr and θl are the angles of the occlusal surface of
the first molars to the occlusal reference plane.

An experimental study on mandibular expansion –
increase in arch width and perimeter-Motoyosi et
al, EJO 2002
 Using 3D simulation the increase in arch width and perimeter
was measured.
 A space of 1.43mm opened between the canine and the first
premolar with an increase in arch perimeter of 2.86mm.
 The tip of the mesiolingual cusp moved 3.88mm laterally with
an increase in intermolar width of 7.76mm.
 A 1mm increase in arch width increased the arch perimeter by
0.37mm.

Stability of transverse expansion in
the mandibular arch AJO2003
 An expanding lingual arch used for less than 6 months
with the mandibular fixed edgewise appliance caused an
increase in both the transverse and sagittal dimensions
of the mandibular dental arch.
 Transverse expansion was more stable in the posterior
region of the mandibular dental arch than in the anterior
region.
 Mandibular intercanine width increase could be
maintained only by fixed retention.
 Although the maxillary and mandibular incisors were
advanced and proclined, lip protrusion did not occur.

Increase in arch perimeter due to
orthodontic expansion. AJO 1991
 Increase in midline arch width length by incisor
advancement was four times more effective than molar
expansion.
 Combination of molar-canine expansion and canine
incisor expansion yields results
comparable to the total effect of expanding individual
teeth.
Combined molar canine expansion created increase in arch
perimeter that was slightly less than those generated by
incisor advancement alone.

Treatment of Brodie bite by lower
lateral expansion-a case
reportJCPD1998
 A brodie bite is a unilateral posterior scissor bite.
 A patient 4 yrs 4 months was given a schwarz
appliance to expand the lower arch.
 The treatment duration was one year 2 months.
 At the end of treatment the patient achieved
good occlusion, muscle function and the function
of the tmj improved.

Modified mandibular Schwarz
appliance-JCO 1998
Traditional schwarz
appliance made patient co-
operation difficult
The clasps did not fit well
in the undercuts.
The pyramidal shape of
the crowns produced an
occlusal riding effect when
the screw was activated.
Provided exceptional
overall retention.
Reduces breakage.
Maximum lingual
extension to enhance
alveolar expansion.

The relationship of arch length to
alterations in dental arch width-
AJO2000

Permissible limit for mandibular expansion

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Permissible limit for mandibular expansion