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4. 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
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5. 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
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7. 3. Black -1902
Upper teeth are arranged in a
semi-ellipse
&
lower
teeth
arranged on a smaller curve.
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were
8. 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.
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9. 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
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10. LINE OF OCCLUSION
•Upper
Molar – central fossa
Anterior- cingulum
•Lower
Molar – buccal cusps
Anterior –incisal edges
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11. 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.
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13. 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.
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14. 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.
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15. 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
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16. 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
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17. Disadvantage of Catenary curve
Does not give a good fit in the
II & III molar region
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18. 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.
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20. 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.
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22. 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
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23. 12. Rocky mountain Data systems –
Computer derived Arch design
• Inter molar width
• Inter cuspid width
• Arch depth
• facial type
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27. 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.
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30. 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
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32. 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
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33. Facial form Vs Arch form
Leptoprosopic – Narrow dental arches
Euriprosopic - Broad, round arches
Mesoprosopic – Average/ parabolic
arches
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35. Malocclusion
Class II – Narrow & Tapered maxillary
arch form
- Ovoid mandibular arch form.
Class III- Tapered mandibular arch form
- Ovoid maxillary arch form.
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36. 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
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37. Habits
Thumb sucking – Narrow dental
arches
Tongue thrusting – Narrowing of
the
maxillary arch
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39. Basic components
• The anterior curvature
• Inter cuspid width
• Inter molar width
• Curvature from cuspids to II molars
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40. VARI SIMPLEX DISCIPLINE ARCH
FORM
•Not based on clinical examination
•Result of research by Dr. Garland
McElvain
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41. 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
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42. Roth – Tru Arch form
•Modified catenary curve
•5 separate radii
•Over correction concept
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43. 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.
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44. TAPERED ARCH FORM
•Narrowest intercanine width
•Indications
narrow arches
gingival recession
single arch Rx
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47. 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.
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48. 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
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49. 3M UNITEK
• Tapered
archform –Orthoform I
• Square archform –Orthoform II
• Ovoid archform
-Orthoform III
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50. Nojima et al – AO, 1971
Caucasian sample
Japanese sample
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51. 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
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individualization.
52. DIAGNOSIS OF ARCHFORM
1. Clear templates - Early indication
TAPERED
OVOID
SQUARE
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53. 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
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56. Riedel- 1969
Arch form, particularly in the
mandibular arch, cannot be permanently
altered during appliance therapy.
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57. 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.
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58. 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.
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59. 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.
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60. 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
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for post- retn decrease.
61. 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
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62. Felton et al, AJO- 1987
70% of the dental arches returned
to their original shape during the post
Rx period.
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63. 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.
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64. 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.
65. Thank you
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