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1. TWEED’S ANALYSIS
INDIAN DENTAL ACADEMY
Leader in continuing dental education
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2. Background
• In 1930, with the death of Dr. Angle
• the introduction of the cephalometric
headplate by Dr. Broadbent,
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3. Charles H Tweed (1895~1970)
• Dr. Tweed
established the
diagnostic facial
triangle
• Based primarily on
deflection of
mandible as
measured by FMA
and position of the
lower incisors
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4. Planes Used for Tweeds Facial Triangle
Frankfort Horizontal Plane
Long Axis of
Lower Incisor
Mandibular plane
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5. Frankfort Horizontal Plane
• Adopted at 13th German Congress of
Anthropologists – the Frankfort Agreement
at Frankfort am Main , 1882
• Finally accepted by the International
Agreement for the Unification of
Craniometric and cephalometric
Measurements in Monaco, 1906
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6. Frankfort Horizontal Plane
• A horizontal plane represented in the
profile by a line between the lowest point
on the margin of the orbit to the highest
point on the margin of the auditory meatus
• Tweed took the Porion as a point 4.5 mm
above the geometric center of the
mechanical ear rods
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7. Mandibular plane
• Tangent to the lower border of the
mandible
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8. Angles of Tweeds Facial Triangle
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9. Angles of Tweeds Facial Triangle
Variable
Mean
Value
Range
Frankfort Mandibular
plane Angle (FMA)
250
160-350
Incisor Mandibular Plane
Angle (IMPA)
900
850-950
Frankfort Mandibular
Incisor Angle (FMIA)
650
600-750
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10. Objectives
• Determines the position the lower incisor
should occupy at the end of treatment
– Useful information for treatment planning
– Planning of Extraction
• Prognosis of treatment result
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11. • People agreed that extraction was often
necessary.
• Tweed’s reasons for extraction seem to
have prevailed
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12. When extraction is done, one is
inevitably reminded of Newton’s
third law
Newton’s third law
“For every action,
there is an equal
and opposite
reaction.”
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13. Newton’s Law in Orthodontics
• In orthodontics this means that when
retracting front teeth, one will be faced
with the problem of having to minimize the
tendency of the posterior teeth to move
forward
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14. Anchorage & Anchorage
Preparation
• The minimization of such force is called
“Anchorage”
• Dr. Tweed introduced en-masse
anchorage preparation
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15. Determining Growth Pattern
• When FMA<25
– Horizontal Growth Pattern
• When FMA>25
– Vertical Growth Pattern
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16. Prognosis???
 If FMA 160 to 280
PROGNOSIS IS GOOD
at 160 IMPA should BE 900+50 = 950
0
0
at 25 IMPA should be 90
at 280 IMPA should be 900-50 =850
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 Approximately 60% of malocclusion have
0
0

17. Prognosis???
• If FMA 280 to 350
PROGNOSIS IS FAIR
at 28 0 IMPA should be 90 0-95 0
at 35 0 Extraction necessary in majority of
cases
IMPA should be 80 0 -85 0
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18. Prognosis???
• If FMA above 350
PROGNOSIS IS BAD
• Extraction usually complicates the
problem
• Tweed stressed the importance of the
FMIA angle recommending that it be
maintained at 65° to 70°
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19. Thank You
Qu
Any
•
ns??
estio
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