Guide to Dental Arch Forms

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


OVERVIEW
•INTRODUCTION
•REVIEW OF LITERATURE
•ANATOMY
•FACTORS AFFECTING ARCH FORM
•PREFORMED ARCHWIRES
•DIAGNOSIS
•STABILITY & RELAPSE

INTRODUCTION
The

achievement

of

a

stable,

functional & esthetic arch form has
long been one of the prime objectives
of orthodontist from the period of
Edward Angle.

SEARCH FOR IDEAL ARCH FORM
1. Bonwill –1885
 Tripod shape of lower jaw
 Equilateral triangle
Base – Condyle to Condyle
Sides – Condyle to midline
 Bicuspids & molars formed a straight
line from cuspid to condyle
2. Hawley -1905

Bonwill -Hawley Arch Formula
 Anterior teeth should be made to lie
along a circle whose radius
equaled their combined widths
 Equilateral triangle
Base – Intercondylar width
 Should be used only as a guide in
establishing arch form

BONWILL – HAWLEY CHART


3. Black -1902

 Upper teeth are arranged in a
semi-ellipse

&

lower

teeth

arranged on a smaller curve.


were

4. Broomel -1902
The teeth are arranged in the jaws in
the form of two parabolic curves, the
superior arch describing the segment of
a larger circle than the inferior , as a
result of which the upper teeth slightly
overhang the lower.

5. Angle –1907 – Line of occlusion
Definition
The line with which, in form & position
according to type, the teeth must be in
harmony if in normal occlusion.
• This line resembles parabolic curve
but varies due to
Race
Type
Temperament of the individual

LINE OF OCCLUSION
•Upper
Molar – central fossa
Anterior- cingulum
•Lower
Molar – buccal cusps
Anterior –incisal edges

Angle -1907
Bonwill –Hawley Arch form- General
approximation of the
true line of occlusion
Objected the straight line from
cuspid to third molar
Straight line existed from the cuspid to
the MB cusp of the I molar,however,
there was a natural curvature needed in
the molar region.

6. Grays Anatomy -1942
Maxillary dental archform- Elliptical
curve
Mandibular dental archform- Parabolic
curve


7. Chuck, 1934-AO –Ideal arch form
Square
Round
Oval
Tapering
•BH archform – not suitable for every
patient, can be used as a template
•Bicuspid region should be wider than
the cuspids to prevent excessive
expansion of the cuspids.

8. Boone AO-1963
Similar superimposition of the BH
archform on a mm template.

9. Mac Conaill & Scher 1949
It is impossible for an ellipse & a
parabola to meet one another at every
point.

Mac Conaill 1949
Catenary curve – Ideal curve of common
occlusion
Catenary curve is formed by suspending
a chain or flexible cable of appropriate
length from two points of varying width


Scott 1957
Shape of the human arch - Catenary
curve

Broodie & Lillie 1966
Basic bony arch is established as
early as 9.5 weeks in utero & the arch
was of a catenary design

Disadvantage of Catenary curve
Does not give a good fit in the
II & III molar region


10. Musich –1973, AJO
Catenometer –Device for construction
of arch perimeter

11. Brader –1972-AJO
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.

CATENOMETER


Brader arch form
The geometry of the
dental arch form was best
represented by a Trifocal
ellipse, with the teeth
occupying the portion at
the constricted end of the
curve.

BRADER ARCHFORM


Brader arch form
 Arch guide with 5 arch forms
 Selection of proper form –Arch width
at the II molars
 Maxillary arch form is selected one
size larger than the mandibular arch
form
Drawback – Excessive narrowing in the
cuspid region & excessive wear of the
incisal portion of the cuspids

12. Rocky mountain Data systems –
Computer derived Arch design
• Inter molar width
• Inter cuspid width
• Arch depth
• facial type

SURESMILE TECHNOLOGY
Dr. Rohit sachdeva, JCO- 2000.
DIGITAL ARCHWIRES


LINGUAL ORTHODONTICS
Mushroom archwire


STANDARD ARCHFORM


Functional anatomy
Although bone is the hardest tissue in
the body, it is one of the most responsive
to change when there is an alteration in
the musculature.
The dental arch form is initially shaped
by the supporting bone & following
eruption of teeth, by the musculature &
intraoral functional forces.

Buccinator mechanism
Tongue


Buccinator mechanism


Balance of muscle forces & Arch form
•Between the tongue and perioral
musculature, there is no balance of
force
• During swallowing tongue pressures
are considerably greater than those
exerted by the cheeks & lips

EQUILIBRIUM ???


 Buccal forces operate constantly
throughout the day.
 Occlusal forces also help to maintain
the equilibrium.
Dental equilibrium – Dynamic equilibrium
Posterior teeth may be moving buccally
during swallowing, but the forces of
the cheeks return them to a more
lingual position, occlusal forces also
produce buccolingual movements

Facial form Vs Arch form
 Leptoprosopic – Narrow dental arches
 Euriprosopic - Broad, round arches
 Mesoprosopic – Average/ parabolic
arches

FACTORS AFFECTING ARCH
FORMS


Malocclusion
Class II – Narrow & Tapered maxillary
arch form
- Ovoid mandibular arch form.
Class III- Tapered mandibular arch form
- Ovoid maxillary arch form.


Stanley Braun et al –AO, 1998
Class II
Maxillary arch – Narrower
Mandibular arch –

z

width & Depth

Class III
Maxillary arch

–

Arch width

Mandibular arch -

Arch width
Arch depth


Habits
Thumb sucking – Narrow dental
arches
Tongue thrusting – Narrowing of
the
maxillary arch

PREFORMED ARCHWIRES


Basic components
• The anterior curvature
• Inter cuspid width
• Inter molar width
• Curvature from cuspids to II molars

VARI SIMPLEX DISCIPLINE ARCH
FORM
•Not based on clinical examination
•Result of research by Dr. Garland
McElvain


Final arch form
•Fitted to the original study model of
the mandibular arch
• cuspids should not be expanded.
• Wax bite of the maxillary arch is
examined
• Mandibular II molars – toe in


Roth – Tru Arch form

•Modified catenary curve
•5 separate radii
•Over correction concept


MBT ARCH FORMS
Arch forms
[Chuck-1934 ]

– Tapered
Square
Ovoid

MBT - 3 Archforms in early treatment
Individual archform in final stages
These archforms vary mainly in interPm,
intercanine width of 6mm.

TAPERED ARCH FORM
•Narrowest intercanine width
•Indications
narrow arches
gingival recession
single arch Rx


SQUARE ARCHFORM
•Indications
Broad arches
Buccal uprighting &
expansion of post
To maintain expansion


OVOID ARCHFORM

•Most preferred
•Good stability &
•Minimum relapse

CUSTOMIZING ARCHWIRES
 Done according to the lower arch
 Upper archform –3mm wider in all areas
After the rectangular HANT wires
in approximate form for the patient as
determined using the clear template.

INDIVIDUALIZED ARCHFORM
PROCEDURE
Wax template is molded over the lower
arch
19x25 ss arch wire is bent to the
indentations
Compared with starting lower model
Checked for symmetry
Xerox copy of the wire is made & stored

3M UNITEK
• Tapered

archform –Orthoform I

• Square archform –Orthoform II
• Ovoid archform

-Orthoform III


Nojima et al – AO, 1971
Caucasian sample

Japanese sample


PRE FORMED ARCHWIRES
The normal variation in arch form, are
not reflected in the preformed arch wires
presently available & it is important to
keep in mind during orthodontic
treatment that if preformed arch wires
are used, their shape should be
considered a starting point for the
adjustments necessary for proper
individualization.

DIAGNOSIS OF ARCHFORM
1. Clear templates - Early indication
TAPERED

OVOID

SQUARE

2. Hassan Noroozi et al, AO-2001
Defined arch forms using the following
parameters
•Inter II molar width
•Inter canine width
•II molar depth
•Canine depth

Square archform
Inter canine width/ Inter IImolar width
Canine depth / Molar depth

Tapered archform
Canine depth / Molar depth
Intercanine width / Intermolar width

STABILITY
&
RELAPSE

Riedel- 1969
Arch form, particularly in the
mandibular arch, cannot be permanently
altered during appliance therapy.

Strang , AO- 1949, AJO- 1946
Howes, AJO- 1960
Inter molar width was normally
decreased during extraction Rx,
however, that if cuspids were moved
distally into extraction sites, they
could be expanded buccally to limits
offered by their new distal location.

Amott-1962, Arnold-1963,Welch-1956
Bishara AJO-1973
With regard to extraction cases,
intermolar width decreased post Rx, but
inter cuspid width which retained its
original dimension did not show an
increased arch width as was previously
thought.


Shapiro AJO-1974
Mandibular intercuspid width
demonstrated a strong tendency to
return to its pre Rx dimension in all
groups except cl II, div 2.
 Mandibular arch length decreased
substantially in every group during
post- retention period.

Gardner , AJO-1976
Inter cuspid width was expanded
during Rx but had a strong tendency to
return to its original pre Rx width in
both ext & nonext cases.
Inter I pm width showed the greatest
Rx increase in width with only a minimal
post Rx reduction
II pm width for nonext cases showed a
significant increase with slight tendency
for post- retn decrease.

II pm width for ext cases showed a
decrease with Rx & a slight continued
decrease post- retention
Inter molar width
Non ext cases –increase in width with Rx
Extraction cases – decrease with Rx
Post retention

- no change


Felton et al, AJO- 1987
70% of the dental arches returned
to their original shape during the post
Rx period.


De La Cruz et al, AJO 1995
 Arch form tended to return toward
the pre Rx shape after retention & that
the greater the Rx change, the greater
the tendency for post- retention change.
 Patients pre Rx arch form
appeared to be the best guide for
future arch form stability.

CONCLUSION
The search for an ideal arch form, suitable
for every patient, has been an unrealistic
goal because of the wide individual variation.
The basic principal of arch form in
orthodontic Rx is that within reason, the
patients original arch form should be
preserved.
Retention should certainly be an important
consideration when original arch form is
changed during www.indiandentalacademy.com
Rx.

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Guide to Dental Arch Forms

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