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1. Differential DiagnosisORTHODONTICS
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2. INDIAN DENTAL ACADEMY
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3. Differential diagnosis analysis
system

Merrifield ,in his effort to establish a sound diagnostic basis for his
directional force treatment using multibanded mechanotherpy
,introduced diagnostic analyses that allow clinician to determine

1)Whether & when are extractions necessary and
2)which teeth should be removed


Attainment of previously stated objectives require a through and
accurate diagnosis that specifically identifies the major areas of
disharmony.
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4. 
Thus, Weber defines diagnosis as
“ a determination of a disease from symptoms, data or tests,
and the decisions and judgment made prior to treatment”.
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Merrifield’s diagnostic philosophy can be outlined as follows:
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1.recognise and treat within the dimensions of the dentition
(non-expansion, when normal muscular balance exist.)
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2 recognize the dimension of the lower face and treat for the
maximal facial harmony & balance.
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3.recognise and understand the skeletal pattern. Diagnose and
treat in harmony with normal growth and developmental
patterns.
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5. 
Any valid identification and classification of orthodontic &
orthognatic disharmony should be based on the four major
areas of the orthodontist responsibility

1.Facial
2.Dental
3.Cranial
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4.Environmental.
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6. Facial disharmony

A study of the face & its balance or lack of it must be the first
concern during a differential diagnosis. The clinician must have
intuitive concept of a balanced face .
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There are 3 factors that influences the balanced face or lack of it
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1.the positions of teeth,
2.the skeletal pattern,
3.the soft tissue thickness.
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7. The facial balance is affected by the marked protrusion/ retrusion/
crowding of teeth. the lips are supported by the max. incisor teeth. Thus
lip protrusion is the reflection of the amt. of max. incisor protrusion.
Protruded teeth thus cause facial imbalance.
Facial disharmonies are often
the result of abnormal skeletal
relationships.
The clinician must understand
the skeletal pattern & have the
ability to compensate for
abnormal skeletal relationships
by changing the position of the
teeth.
(The FMA, is a skeletal angular
value that is crucial in diff/dia.
lower facial balance can be
dramatically improved by using
this knowledge).
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8. Facial disharmony that are not the result of skeletal or dental
distortion are generally the result of poor soft tissue
distribution. this problem needs to identified during diff/dia.
so that crucial dental compensations can be planned.

Total chin thickness
=upper lip thickness.

(if it is,< ult ,the
anterior teeth must be
positioned upright
further to facilitate a
more balanced facial
profile, because lip
retraction follows
tooth retraction.)
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9. 
Thus careful consideration of the positions of teeth, skeletal
pattern, & soft tissue overlay will give crucial information
about face & enable the clinician to determine whether dental
compensations will improve facial balance. before initiating
tooth movement.

Its impact on the overlying soft tissue must be clearly
understood.
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10. Whenever facial balance is present ,the ideal relationship of
profile line is to be tangent to the chin & the vermilion border
of both lips and should bisect the nose. This results in a
pleasing & balanced profile.
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11. 

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Similarly, on frontal view,
the vermilion border of
lower lip should bisect the
distance between bottom
of the chin & ala of nose.
The vermilion border of
upper lip should also
bisect the distance
between from the
vermilion border of lower
lip to ala of nose.
These are universally
accepted orthodontic
standards for facial
balance & harmony.
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12. Several cephalometeric standards quantify facial balance. Two that
have been found to be very useful are the1. Z angle
2.FMIA
Z angle:
This Angle was developed
to further define facial
esthetics & is an adjunct
to the FMIA.
It is the angle b/n the FH
plane and soft tissue
profile which quantifies
Facial balance.
NORMAL RANGE- 70o-80o.
(ideal value- 75o – 78o.)
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13. 
Z angle is more indicated of the soft tissue profile than FMIA
and is responsive to the maxillary incisor position.

Maxillary incisor retraction of 4 mm allows 4 mm of lower lip
retraction & apprx. 3 mm of upper lip response.

It quantifies the combined abnormalities in the values of FMA,
FMIA & soft tissue thickness and all have a direct bearing on
facial balance.

If any of the 3 above component is not within the optimal
range, differentiation can be made to determine which values
are not optimum & why

It gives immediate guidance to anterior tooth reposition.
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14. FMIA:

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Tweed believed that this
value was significant in
establishing the harmony of
the face.
Tweed established a
standard of 68o for
individual with an FMIA of
22o – 28o.
Standard should be 65o if
the FMA is 30o or more,
and the FMIA will increase
if FMA is lower.
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15. Cranial Disharmony:

A careful cranial analysis must include but if not be limited to
study and understanding of the following information.
Skeletal Analysis Factors:
FMA – It is the most significant value for skeletal analysis
because it defines the direction of lower facial growth in both
the horizontal and vertical dimensions.
Normal Range- 22o – 28o.
<FMA
>FMA
Deficient vertical growth.
Excessive vertical growth.
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16. IMPA:
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Defines axial inclination of
mandibular incisors w.r.t.
mandibular plane.
It is a good guide to use in
maintaining or positioning
of the mandibular incisors in
relation to the basal bone.
Standard value – 88o.
(indicates an upright
incisors, with a normal
FMA reflects optimal
balance and harmony of
lower facial profile)
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17. SNA:

Indicates relative
horizontal position of
the maxilla to the
cranial base.

Normal Range: 80o–
84o.
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18. SNB:

Indicates horizontal
relationship of mandible to
the cranial base.

Normal Range: 78o–82o.

<74o / >84o – Large maxillomandibular discrepancy.
(orthognathic surgery
indicated)
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19. ANB:

It indicates horizontal
relationship of maxilla to
the mandible.

Normal Range- 1o - 5o.

>10o />-3o indicative of
facial disproportion.
(possibility of surgical
assistance)
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20. AO-BO:


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This indicates relationship
of maxilla to mandible.
More sensitive than ANB
because it is measured at
the occlusal plane.
Normal Range: 0–4 mm.
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21. Occlusal Plane:

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Occlusal plane value
expresses a dentoskeletal
relationship of OP to FH
plane.
Normal Range: 8o – 12o.
Values < or > normal range
indicates more difficulty in
treatment.
In most orthodontic
corrections, the original
values should be maintained
or decreased.
An > indicated loss of control
& instability.
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22. Facial Height Index:

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Andre Horn studied the relationship of AFH to PFH,
developed Facial Height Index.
He found that Normal PFH is 0.69 or 69% of AFH.
Normal Range: 0.65 – 0.75.
If the value is < or > this range, the malocclusion is difficult
to correct.
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23. Facial Height Ratio:

Facial height change ratio is valuable in the evaluation of
treatment interval changes.

Ratio of two times as much of PFH as AFH during
treatment is ideal for correction of class II div 1.

However, even more important is the volume of the change.

Merrifield and Gebeck reported 2 to 1 increase in PFH to AFH
in the sample of successfully treated malocclusion.
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24. Jim Gramling of Jonesboro, Arkansas, research director of
Tweed foundation compiled a large sample of successful &
unsuccessfully treated Class II malocclusion by the
foundation and compared the results.
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25. 
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In the successful sample, FMA was controlled, FMIA , IMPA
In the unsuccessful sample, FMA , FMIA remained same or
decreased, IMPA or remained the same.
There was not as much Z angle increased in unsuccessful
sample.
SNA reduction was similar.
AO-BO reduction was unsatisfactory.
Y axis & SNB remained the same for both samples.
By studying the data from two samples, it can be concluded
that in unsuccessful Class II treatment, the mandibular incisor
position was not corrected or if corrected, the correction was
subsequently compromised by excessive, unreciprocated use
of Class II elastics in an attempt to estb proper AP maxillo
mandibular dental relationships.
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26. Thank You.
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