Arch Form in orthodontics /certified fixed orthodontic courses by Indian dental academy

ARCH FORM
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


INTRODUCTION




The achievement of a stable,
functional and esthetic arch form has
long been one of the prime
objectives of orthodontics
Despite numerous investigations,
there is little agreement as to the
best size and shape for an ideal
orthodontic arch form.





Various authors have used different
curved mathemetical models,but
stability of these arch forms has not
been established
The mandibular dental arch is
considered as a reference element of
diagnosis and therapy in dentofacial
orthopedics.

DEFINITION


ARCH FORM-position and relationship the
teeth have
with each other
in all 3 dimensions


-It is the collective response of all
teeth to all of the environment forces
and their resultant positions in the
oral cavity (Brader-1974)




-dental arch form is made up of
teeth which assumes unique
positions along a compound curve
representing an equilibrium at all
points and delimited by the
counterbalancing force fields of the
tongue and of the circumoral
tissues(Brader)

DETERMINATION OF
ARCH FORM


Determined by
-skeletal pattern
-muscular forces
“ neutral zone”
( Mills 1968)


TYPES OF ARCH FORM


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

BONWILL
HAWLEY
ELLIPSE
PARABOLA
CHUCKS –ARCH FORM
CANTENARY CURVE
BRADER
PENTAMORPHIC
COMPUTER PRIDICTION
VARI-SIMPLEX DESIGN
ROTH TRUE ARCH
STRAIGHT WIRE
M.B.T
BEGG ARCH FORM
LINGUAL ARCH FORM

BONWILL


In 1885, he noted the tripod
shape of the lower jaw and
declared that it formed an
equilateral triangle with the base
extending from condyle to
condyle and the sides extending
from each condyle to the midline
of the central incisors.



He stated that this triangle
existed for the proper
functioning of the teeth.
Importantly, he noted that the
bicuspids and molars formed a
straight line from the cuspids to
the condyles.


HAWLEY




In 1905, Hawley employed some of
Bonwill’s principles in proposing a
geometric method for constructing
the ideal arch form.
Hawley suggested that the six
anterior teeth be made to lie along a
circle whose radius equaled their
combined widths. From this circle he
created an equilateral Triangle, the
base of which represented the intercondylar width.





It was proposed that the
bicuspids and molars should be
aligned along these extended
straight lines.
Hawley did, however, advised
against the strict use of this
method for determining arch
form, and that it be used only as
a guide in establishing arch form.







Arch form is constant for all
induviduals
The radius of the arch varied
depending on the size of the anterior
teeth
This arch form is no longer
recommended

CONSTRUCTION


PARABOLA


Angle , 1907, - Defined “line of
occlusion”, as being “the line
with which, in form and position
according to type, the teeth must
be in harmony If in normal
occlusion”. The form Of this line
was said to resemble a Parabolic
curve but one that varied greatly
due to race, type, temperament,
etc. of the individual.

PARABOLA


By E.H.Angle in 1906

Fits as well as any ideal arch
Ignors narrowing of arch form over the
second molars






In describing the First order bends,
Angle objected particularly to the
straight line proposed from cuspid to
third molar.
Angle stated that a straight line
existed from the cuspid to the mesiobuccal cusp of the first molar,
however, there was a natural
curvature needed in the molar region.



Landmarks
A,D,D’,E,E’


GRAY


In 1942, Gray’s Anatomy stated :

“The maxillary dental arch forms
an elliptical curve...The
mandibular dental arch forms a
parabolic curve”


CHUCK




Chuck -In 1934, noted the variation in
human arch form and pointed out that
arch forms had been referred to as
square, round, oval, tapering.
He stated that while the BonwillHawley arch form was not suitable for
use in each patient, it could serve as a
template for the construction of
individualized arch forms.





Chuck superimposed this arch form on
a millimeter grid and used this
template for archwire construction
according to Angle’s method.
Chuck suggested that the bicuspid
regions should be wider than the
cuspids to prevent excessive
expansion of the cuspids.


DRAWBACKS OF PARABOLAELLIPSE ARCH FORM




MacConaill -1949, stated that, in
considering the line of occlusion, it
would be impossible for an ellipse and
a parabola to meet one another at
every point.
He concluded that the ellipseparabola description of the two dental
arches, although elegant, had no
immediate relation to function.

BLACK


In 1902, he stated that the upper
teeth are arranged in a semiellipse and that the lower teeth
were arranged similarly on a
smaller curve.


CATENARY CURVE



Mcconnail and scher -1949
He stated that the catenary
curve, fit so many cases with
exactness that it could be taken
as the “ideal curve” of common
occlusions.






Shape formed by a length of chain
held at each end and allowed to drop
Catenary curve could be described as
a central core or central perimeter
around which teeth arrange
themselves






Ignores narrowing of archform over
the second molar
The length of the chain and the
distance between the supports
determine the precise shape of the
curve






Catenary curve fits the dental arch
form of the premolar-canine-incisor
segment of a arch very nicely for
most individuals
The curve doesn’t fit accurately if it
is extended posteriorly, because the
dental arch normally curves lingually
in the second and third molar region







Catenary curve a better
representation of mandibular dental
arch
Ellipse or parabola represents
maxillary arch (Neilans-1968)
Catenary curve is a good fit in
27%of the samples studied (White
LW-1977)



In 1957, Scott also supported the
concept of the catenary curve as
the shape of the human arch
based on the developmental
anatomy of the dental arches and
surrounding anatomic structures.




He pointed out that the basal
bone of the maxilla and mandible
remains much more constant in
form in all mammals and forms a
foundation on which a great deal
of variation in form of alveolar
processes are constructed




Burdi and Lillie in 1966 stated
that the basic bony arch is
established as early as 9.5 weeks
in utero and that this form was
that of the catenary curve.






Musich, in 1973, supported the
concept of the catenary curve as the
ideal arch form and suggested the use
of the catenometer as a reliable
device for construction of arch
perimeter.
The catenary curve creates a rather
tapered arch form and many of the
tapered arch forms provided by
orthodontic manufacturers today are
based on the catenary curve.

BRADER ARCH FORM




By Brader-1972
He stated that dental arch form was
made up of teeth which assume
unique positions along a compound
curve representing an equilibrium at
all points and delimited by the
counterbalancing forces of the tongue
and circumoral tissues.






Also called as trifocal-ellipse
Arch form is similar to cantenary
curve but tapers over the second
molar
Several manufacturers use Brader
arch form




The geometry of the curve of the
dental arch form was said to be
best approximated by a closed
curve with the curvilinear
properties inherent in the trifocal
ellipse, with the teeth occupying
only the portion at the
constricted end of the curve.







Brader recommended an arch guide
with five arch forms.
The selection of the proper arch form
was based on arch width at the
second molars as measured at the
facial, gingival surface.
The maxillary archform was selected
one size larger than the mandibular
arch form.






They differ in size as dictated by
width of second molar
The maxillary arch form is always
one size larger than the mandibular
arch form






It differs from a cantenary curve in
producing greater width across
premolar
The Brader arch form will more
closely approximate the normal
position of the second and third
molars

SELECTION OF ARCH WIRE




Measure the
greatest intermolar
diameter in
millimeter
This measurement
gives the optimum
arch curve on
guide chart






The unique geometry of the Brader
arch is that it forms a superior dental
arch form
The primary determinants of arch
form morphology are the tissue force
in resting state





The geometry of the dental arch
form is so related with the resting
forces of the tongue
PR=C






The lips and cheek exert inward
counterbalancing tension against the
teeth

PI=Pe+t{1/R+1/R’}




Arch form characteristics are such
that the form is stabilized and dental
equilibrium is attained whenever
C=T


DRAWBACK OF BRADER
ARCH FORM


Many clinicians found that this
arch form created excessive
narrowing in the cuspid region of
many patients and led to
excessive wear of the incisal
portion of the cuspids.


VARI-SIMPLEX ARCH FORM




By Dr Garland McEvain-baylor
university
He studied 102 treated cases of Dr
Alexander and found 2 arch form
which fits to all his cases “u” form
and”v” form




The anterior section of Vari-simplex
arch forms is flatter than PAR arch
forms and more pointed compared to
roth arch forms


TYPES OF ARCH FORM






Vari simplex arch form serves merely
as treatment guide, they never
intended to be final arch wire
Final mandibular arch wire is always
fitted to the original study model








Care is taken to determine that
cuspids are not expanded
Mandibular expansion occures in
molar and premolar region
The maxillary arch form is built to fit
the mandibular arch form





Dr Alexander does not correlate arch
form to the facial type to keep the
cuspid stable.
He does not use Tweeds concept of
co-relating upper and lower arch
wires since similar arch wires are not
placed in upper and lower arch at the
same time

PENTAMORPHIC ARCHES



By Ricketts
Atleast 10 factors needed to be
taken into account in the research of
arch form




This includes
-Arch correlation
-Arch size
-Arch length
-where the arch to be measured
-contact details
-final determination of the bracket
location



Twelve arch forms were originally
identified, these were narrowed
down to 5 by ricketts and are called
as pentamorphic arches




They are
-narrow ovoid
-ovoid
-normal ideal
-tapered
-narrow tapered


NARROW OVOID


OVOID

NORMAL IDEAL


TAPERED

NARROW TAPERED


ROTH TRU-ARCH FORMS




The Roth Tru-Arch form was derived from
his extensive clinical testing and recording
of jaw-movement pattern in treated
patients who were out of retention and
had stable results
Comparison with arch form derived by
Andrews from measurement of his 120
normal cases shows that the Roth arch
form is wider by few millimeter in the
bicuspid region





Roth notes that superimposition of
his Tru-Arch form on Ricketts normal
form shows that they coincides
almost exactley
The Roth Tru-Arch form actually
overcorrects the arch width
slightly;over correction is part of
roths goal



Arch width varies with facial type
the brachyprosopic arch is seldom
more than 2-3mm wider than the
dolichoprosopic arch, but the
individual jaw width may wary more
and the arch wire should be adjusted
to harmonize




The widest point in the entire arch is
at the 1st molars, but in the front part
of the arch, the widest part is in the
bicuspids and not cuspids




There are actually 5 arcs in the arch
-1) the arc acros front
-2,3) another arc in each cuspid ,
bicuspid region
-4,5)a uniform curve in the buccal
segment


TYPES




TAPERED
OVOID
SQUARE


STRAIGHT WIRE TECHNIQUE


The arch wire used in this technique
is slightly expanded in the bicuspid
region to allow proper functional
movements and it is close to roth
arch forms


M.B.T ARCH FORM




M.B.T technique uses arch form
used by chuck(1932)
Classified by chuck in 1932
Tapered (narrow)
Ovoid (normal)
Square (broad)


TAPERED




Ovoid arch form
has the narrowest
inter canine width
Used in
-gingival recession
in canine and
premolar region
-single arch
treatment cases


OVOID





Preferred arch form
Has resulted in
good stability
When
superimposed with
tapered arch form
there is 6mm
difference in canine
region


SQUARE




Used in cases with
broad arch forms,
Useful atleast in
part of the
treatment in cases
requiring
expansion of upper
arch, buccal
uprighting of lower
posteriors


ANDREIKO THEORY OF ARCH
FORM



By Andreiko et al -1994
Shape of the mandible should
dectate arch form,with the teeth
aligned and contained with in the
limits of the mandibular bone




ADVANTAGES
-The arch form are derived from
the skeletal and dental anatomy and
are therefore designed to be closer
to an anatomic ideal than
mathemetical ideal
-Individualized treatment is
simplified

ARCH FORM CONSIDERATIONS
IN BEGG TREATMENT


Dr BEGG –each patient is an entity
unto himself, as far as the most
favorable arch form should bear in
relation to rest of the face and skull






MOLLENHAUER-There has not been
the rigorous teaching of arch form in
begg technique as in edgewise.
Neglect-due to the belief that use of
light wires could not alter the
patients original arch form ( but this
is not true)




An arch wire as light as 0.016” can
alter the arch form if kept in the
brackets for few months


METHOD TO DRAW INDIVIDUAL
ARCH FORM


The arch form consists of 3
segments – an anterior segment
between the two canine teeth, and 2
posterior segments from canine to
molars on either side




The dimensions and curvetures of
these segments depends on
1)-anterior tooth materialdetermines the anterior segment
length from one canine cusp to the
other canine cusp


2)-width across the cusp tips of 33,43,
mesio buccal cusp of 36,46 and disto
buccal cusp of 37,47 determines the
transverse dimension of the arch


3)-arch length measured as
perpendicular distance from the mid
point between 31,41 to the line
joining the tips of disto buccal cusps
of 37-47,determines the sagittal
dimension of the arch


DRAWING A ARCH FORM





Obtain the above said measurements
from patient
Draw a midline on a graph paper
Transfer the canine locations on the
graph paper on either side of the
arch midline




Take a 4” long 0.016” s.S wire.Mark
on it the length of the anterior
segment,the wire is flexed such thar
these pointslie on the canine location
in graph,the wire gives the anterior
curvature






Location of mesio buccal cusps of
first molars are marked exactely and
the canine marking is extended to it
using a straight or curved line
The upper arch form is drawn
parallel to and outside the lower arch
form keeping a distance of 2-3 mm


COMPUTER PREDICTION



Schulof-1975
Various other arch form have been
constructed using algebraic
equations




Arch form are produced from
measurements of intermolar width,
intercanine width and arch depth
from labial surface of incisors to last
standing molars


OTHER ARCH FORMS


Williams -1917 described anterior
teeth as lying on the arc of a circle
with its centre midway between the
buccal grooves of 1st molar






Sicher-1952-upper arch-elliptical,
lower arch-parabolic
Baz -1958 determined normal arch
size by a geometric construction
based on measurements taken from
patient’s face






Kato-1964 no great disparity
between arches, same arch form
may be classified differently by
different workers
Lu 1964 dental arch could be
described by a polynomial equation
of the 4th degree


THE RELAPSE TENDENCY INHERENT IN
ARCH FORM CHANGES


MCCAULEY,STRANG,GRABER,AND
ERSON,HUGGINS,MILLS,LUDWIG
--numerous authors who had
reported that when inter-cuspid
and inter-molar width had been
changed during orthodontic
treatment, there was a strong
tendency for these teeth to
return to their pre-treatment
position.





Walter- reported the
maintenance of slight increase in
mandibular inter-cuspid width
after all retention had been
removed for what was termed an
adequate period.
.






Steadman also reported similar
results.
Arnold later pointed out that at
least five years must elapse
before an apparent maintenance
of increase in inter-cuspid width
could be accepted




In 1976 Gardner studied intercuspid, inter-first bicuspid, intersecond bicuspid and inter-molar
widths, as well as arch length
changes in 103 cases, 74 of
which were treated nonextraction, and 29 of which were
treated with extraction of four
first bicuspids. His conclusions
were as follows:





1. Inter-cuspid width was expanded
during treatment but had a strong
tendency to return to or close to its
original pre-treatment width in both
non-extraction and extraction cases.
2. It would appear that the inter-first
bicuspid width showed the greatest
treatment increase in width with only
a minimal amount of post-treatment
width decrease.





3. Second bicuspid width for nonextraction cases showed a
significant amount of increase
with a slight tendency for postretention decrease.
4. Second bicuspid width for
extraction cases showed a
decrease with treatment and a
slight continued decrease postretention.



5. The inter-molar width of
nonextraction cases showed
significant increase in width
with treatment and the
extraction cases showed a
significant decrease with
treatment, However there were
no changes in either extraction
or non-extraction cases postretention.



6. The incisor to inter-molar
distance decreased with
treatment and had a slight
tendency to continue to decrease
post-retention.




In 1995 De La Cruz, et al.,
studied the long term changes in
arch form of 45 Class I and 42
Class II Division 1 cases after
orthodontic treatment and a
minimum of 10 years post
retention.






They concluded that arch form
tended to return toward the pretreatment shape after retention
and that the greater the
treatment change, the greater
the tendency for post-retention
change.
They suggested that the patient’s
pre-treatment arch form
appeared to be the best guide for
future arch form stability,

NORMAL GROWTH AND
DEVELOPMENT


Arch dimensions changes with
growth, it is therefore necessary to
distinguish changes induced by
appliance therapy from those that
occur from natural growth




MOORREES-has pointed out that
considerable individual variations in
arch form will occur with normal
growth, with a general tendency
towards an increase in the intermolar
width during the change over from
the decidous to permanent dentition.




It is difficult to predict the growth
potential in induvidual patients, but
information is available on the
average changes in arch dimension
in centered samples




The average changes reported by
Moyers et al shows changes in arch
width vary between males and
females and that more growth in
width occurs in upper than the lower
arch, this growth occurs mainly
between 7 to 12 years of age, after
12years growth in width is seen only
in males



SINCLAIR et al have confirmed that the
increase in molar width after age 12 is
statistically different in males and females.
-Male arches grow wider than female
arches
-Lower intercanine width increases
significantly in the change over dentition
but does not increase in permanent
dentiton after 12 years of age


-upper and lower inter molar width
increase spontaneously to a
considerable extent between ages of
7 and 18 in males
-little changes in arch width occurs in
the premolar region after age of 12




-changes in arch width may not be
accompanied by changes in arch
length,there is a tendrncy towards a
decrease in arch depth in third and
forth decades


APPLIANCE INDUCED GROWTH


It is difficult to determine the
contribution of appliance, as a
normal growth change would be
expected for each individual




McNAMARA and BURDON-it seems
logical to consider increasing arch
size at a young age so that
skeletal ,dentoalveolar, and muscular
adoptations can occur before the
eruption of permanent dentition.




An appliance inserted in an actively
growing patients, shows a favorable
response,however this response may
have occurred in the absence of
treatment,the relative contribution of
appliance being difficult to determine




SPILLANCE and McNAMARA
-Examined the records of PATIENTS IN
THE Michigan study who presented with
narrow arch forms and compared them
with the average sample. result show that
those with initially narrow arch forms tend
to become more average, and ppliance
therapy is therefore more likely to achieve
a stable change

INTER CANINE WIDTH


LEWIS & LEHMAN & BAUME have
shown that the inter canine width
increases during eruption of
permanent incisors and again during
eruption permanent canines




DUTERLOO and BIERMAN show that the
alveolar crest is relatively inactive after
the deciduous teeth erupt, but it is most
active during eruption of permanent teeth
and then becomes relatively inactive again
after the permanent teeth have erupted.
Therefore if mandibular lateral expansion
is ever to be considered, the optimal time
is prior to and during eruption of
permanent teeth

FACIAL FORM VS ARCH FORM




dolicocephalic form --longer but
narrower and deeper maxillary arch
and palate.
Brachy cephalic type --wider but
shorter and more shallow palate and
maxillary arch.


ROLE OF SOFT TISSUE MATRIX
IN MAINTAINING ARCH FORM;


Frankel postulates that the increase
in crowding is the result of
hypertonic muscles in the buccinator
mechanism restricting the lateral
growth of teeth and their supporting
tissues.







The equilibrium theory states that
the positions of the teeth are
determined by the balance between
the intrinsic forces of tongue, lips,
dental occlusion, and periodontal
ligament
Supported by Tomes-1873
Opposed by Scott-1967





ORAL RESPIRATION- Ricketts has
shown that mouth breathing tends to
lead to narrow arches, cross bites
and increased crowding
Linder-Aronson and backstrom report
that children scheduled for
adenoidectomy generally have
longer, more narrow faces than
control children

AJO 1980 January

Anoop Sondhi, John F. Cleall and
Ellar A. Be Gole

Distal movements of canines during
treatment does not ensure stable
increase in mandiular inter canine
width.

Analysis of change in arch form
with premolar expansion




Ellen A.BeGole, Cyril Sadowsky (Ajo1998)
The arch forms of 38 cases in which
expansion, while maintaining arch
form, were analyzed before
treatment, after treatment, and an
average of 6 to 8 years after
retention.



Significant stable expansion of the
premolar and molar widths may be
possible in both the maxillary and
mandibular arches in nonextraction
cases.


Upper dental arch morphology of adult
unoperated complete bilateral cleft lip and
palate
 Omar Gabriel, daSilva Filho.(Ajo
1999)
 Cast model analysis of the maxillary
dental casts of 31 adult persons with
unoperated complete BCLP and those
of a matched sample of 31 noncleft
patients indicate the following:




· Gender has a differential effect on
the maxillary arches of cleft and
noncleft patients; significant
differences are present in the
noncleft group (wider and longer
arches in males), but not in the
unoperated cleft group.






· BCLP results in an anteriorly
progressive constriction of the upper
dental arch in both genders.
· The BCLP group has a significantly
longer maxillary dental arch, which is
attributed to the premaxillary
anterior projection.


CONCLUSION


Clinicians should be cautious when
treating to mathematically derived
arches, since studies have not
determined conclusively what that
shape might be


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