1. The document discusses arch form considerations and management in orthodontic treatment. It reviews literature on ideal arch forms and notes variations among individuals. 2. Three basic arch forms - tapered, square, and ovoid - are presented as part of the MBT technique. The ovoid arch form is preferred as it provides stability with minimal relapse. 3. Customizing arch wires to a patient's original arch form reduces relapse risk and improves esthetic outcomes compared to using a single arch form for all patients. Management of arch form throughout treatment is important for stability.

1. SYSTEMIZEDORTHODONTICTREATMENT
MECHANICS
M.B.T.
Presenting by:
Dr.Rahul Tiwari

2. • TOPICS :
1. Arch Form
2. Anchorage Control During Tooth Leveling And
Aligning
3. Arch Leveling And Overbite

3. ARCH FORM

4. INTRODUCTION:
• In order to properly manage arch form in a modern orthodontic practice,
there needs to be a balance between efficiency (a single arch form for all
patients) and accuracy (the customizing needed for case stability). In this
presentation, a short literature review will be presented to support the need
for this balance, followed by the description of a practical system for arch
form management.

5. ARCH FORM CONSIDERATIONS FOR
STABILITY AND ESTHETICS:
• Bonwill and Hawley in 1905,suggested the geometric method of
constructing the ideal arch form.
- The lower six anterior teeth lie along a circle whose radius equaled
their combined widths.
-From this circle an equilateral triangle is created,the base of which
represented the condylar width.
-Premolars and molars should lie along these extended lines.

6. In 1907 Angle-
- The form of line from the premolars and molars should resemble a
parabolic curve.
-He proposed the need for natural curvature in molar region.
In 1934 Chuck-
-Noted variation in arch form –square, oval, tapering.
-The premolar region should be wider than canines to prevent excessive
expansion of the canines.
In 1963 Boone –
-Superimposed Bonwill-Hawley arch form on a millimeter grid and
used Angles method for construction.
-Thus Bonwill-Hawley arch form is used as a template in edgewise.

7. Boone arch formBonwill and Hawley

8. Braun et al,1998
-Reported that the human arch form could be represented by a complex
mathematical formula,known as the Beta function.
-This was calculated by entering measurements of dental landmarks on
orthodontic models into a computer curve-fitting program.

9. •The Catenary curve is formed by extending a chain from two fixed points.
•Many of the tapered arch forms provided by orthodontic manufactures today
are based on Catenary curve.
THE CATENARY CURVE

10. Relapse tendency after changing arch
form:
• in 1969, in a chapter on retention in Graber's text, Riedel reviewed previous
studies on the stability of arch form. he cited numerous authors who had
reported that when intercanine 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. He cited only one author who had reported the
stability of a slight increase in mandibular inter-canine width after all retention
had been removed for what was termed an 'adequate period'. Riedel postulated
that 'arch form, particularly in the mandibular arch, cannot be permanently
altered during appliance therapy.
• The paper by Burke et al confirms the overall message from the orthodontic
literature, thai if arch form is changed during orthodontic treatment, in many
cases there will be a tendency for relapse to the original dimensions. This is
particularly true of inter-canine width. Changes in inter-molar width seem to be
more stable.

11. Cases where expansion of lower
intercanine width may be stable:
• In 1974, Shapiro reported on changes in arch length and inter-molar width
in 22 nonextraction cases and 58 extraction cases after treatment and post-
retetlion. He concluded that mandibular inter-canine width showed a
strong tendency to return to its pre-treatment dimension in all groups, with
the exception of Class II/2 cases. Expansion of inter-canine width in
treated Class II/2 cases showed significantly greater stability than Class I
or Class II/1.
• Cases where rapid maxillary expansion is indicated in the upper arch and
this expansion is maintained post-treatment.

12. The four components of archform:
• ANTERIOR CURVATURE
Based on inter-canine width. Its shape becomes more tapered when
inter-canine width is narrow and more square when inter-canine width is
wide.
• INTER-CANINE WIDTH
This appears to be the most critical aspect of arch form,because
significant relapse occurs if this dimension is changed.

13. POSTERIOR CURVATURE
In the posterior area a gradual curvature between canine and second
molars are preferred.
INTER-MOLAR WIDTH
Treatment changes in this dimension is more stable. Arch form in the
inter-molar region can be widened or narrowed , depending on the needs of
the case.

14. MBT ARCH FORM
The three basic arch forms are tapered, square and ovoid.
When superimposed they vary mainly in inter-canine width, giving a range of
approximately 6mm.
Inter-molar widths are similar ,but the molar areas can be widened or
narrowed as needed, by easy wire bending.
•THE TAPERED ARCH FORM
•THE SQUARE ARCH FORM
•THE OVOID ARCH FORM

15. THE TAPERED ARCH FORM
•Indicated for patients with narrow ,tapered arch form and gingival recession
in canine and premolar regions.
•Cases undergoing single arch treatment, in this way no expansion of treated
arch occurs.
THE SQUARE ARCH FORM
•Indicated in cases with broad arch form.
•Cases that require buccal uprighting of the lower posterior segments and
expansion of the upper arch.
•After over-expansion has been achieved ,it may be beneficial to change to
the ovoid arch form in the later stages of treatment.

16. THE OVOID ARCH FORM
•It is the most preferred arch form. The ovoid arch form has proved to be
good, reliable arch form for high percentage of cases treated with PAE
• Treated cases have shown good stability, with minimal amounts of post-
treatment relapse.

17. ARCH WIRE SEQUENCING:
EARLY IN TREATMENT -
.015”/ .0175” multistranded /.014” SS
OR
.016” HANT. Less effect on arch form , so ovoid arch form indicated for all
cases.
MID TREATMENT –
.014”/.016”/.018” SS
OR
.019x.025” Rec. HANT. stocks of three arch forms
LATE TREATMENT-
.019x.025”SS.

18. ARCHWIRE COORDINATION:
•It is important throughout treatment.
•Most critical with heavier round wires and .019x.025 SS.
•Arch form templates can be used for coordination.
•The upper wire should superimpose approximately 3mm outside lower wire.
•This is representative of overlap of the upper teeth relative to the lower teeth.

19. ARCH FORM DURING FINISHING AND
DETAILING:
•Phase of settling is preferred with lighter wires.
• -Lower arch- .014”SS or .016” NiTi
• - Upper arch- .014”SS sect.,with light triangular elastics.
•Teeth adjacent to extraction sites lightly tied together.
•An upper removable plate is required to maintain maxillary expansion.
•In Class II/1 cases to prevent overjet relapse, a full .014”SS arch wire with
bendbacks is advocated.

20. Summary of the issues facing the clinician
Research papers and clinical observations are giving clear messages:
• There are extensive variations among human arch forms.
• As a result of these variations, there does not seem to be any single arch
form that can be used for all orthodontic cases.
• If the patient's original arch form is changed during treatment, there is a
strong tendency (in as much as 70% of cases) for the arch form to return to its
original shape after appliances are removed.
•Customization of arch wires reduces the risk of relapse and helps to achieve
good esthetics.
•If a broad arch form is used for an individual with a narrow facial
appearance, for example, there will be a risk of relapse and an unnatural look
to the smile. It is therefore desirable for the clinical orthodontist to have a
system of customizing the arch form for each patient.