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Alex Vo

on 11 September 2013

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Transcript of Tweed

Charles H. Tweed
Tweed 's Focus
1) The position of the MD incisors as related to the medullary bone of the body of the MD (basal bone or dental base)

2) Normal facial esthetics and their deviations

Tweed Philosophy
"Treatment involving class I and class II and bimax protrusion types of malocclusion, where the growth pattern of the face is not too abnormal, the MD incisors must always be positioned upright on the alveolar process and over medullary bone"

Tweed Method of Diagnosis, Classification, Treatment Planning, and Prognosis
The Frankfort and mandibular planes, which when extended into space meet and form the Frankfort-mandibular plane angle
The location of the point of interception is somewhere distal to the auditory meatus

Dr. Herbert Margolis- Commentator
Uprighting the incisors is in direct harmony with evolutionary trend. Tipping them forward orthodontically is “evolution in reverse”
FMA – shows basic principle necessary in practicing orthodontics, no more “by guess and by God formulas”
Non-prognathous face cannot always be achieved orthodontically. IMPA should serve as a guide

Normal range of the inclination of the MD incisors as related to the plane parallel with the lower border or base of the MD in sagittal view is approx +/- 5 degrees (d) with 90 d as the norm when the incisors stand at right angles to the plane parallel with the lower border or base of the MD (MD plane)

Tweed Principle
*Developed based on Dr. Tweed's study of individuals possessing normal occlusion (Angle's definition of the line of occlusion)
Tweed Philosophy
His theories on normal range of incisor position applies to cases where growth is:
Approximately normal
Slight jaw-tooth size discrepancies, without growth direction disruption
Dental crowding present
Reduction of the mesial-distal dimension of the dental arch is needed to obtain a normal tooth-base relationship with normal facial esthetics

The above does not apply to true Class III cases or where the growth vector is too much downward and not enough forward

Tweed Philosophy
Broadbent, Brodie, Margolis and other have found that the MD plane and the gonion angle (when related to a fixed point and constant plane) always remain approximately parallel to one another

During growth, the planes formed by the base of the MD at various ages after 3 months and older always remain the same

Margolis was the first to relate axial inclination the of the central MD incisor with the sagittal plane tangent to the most dependent points on the lower border or base of the MD

Incisor Mandibular Plane Angle
"As man fulfills his evolutionary destiny we find the cranium becoming increasingly larger and the face correspondingly smaller in their relative proportions to each other in the skull"

While this is going on, the MD incisors are becoming less procumbent

The dentition remains stable once it reaches a state in malocclusion the forces become neutralized, resisting changes.
When the malocclusion is treated orthodontically by expanding teeth into protrusive relationship to the bony base, the forces become unbalanced and treatment collapses.
Angle vs.
Tweed Philosophy
"The face is a study of symmetry and beauty of proportion...Every feature is in balance with every other feature and all the lines are wholly incompatible with mutilation [charged synonym for extraction] or malocclusion" - Angle
Apollo Belvedere
Angle believed that proper occlusion of the dentition required a full complement of teeth "as Nature intended" and therefore was against orthodontic tooth extraction
Tweed rejected Angle's non-extraction philosophy

Angle's clinical practice resulted in dentition that was:
Protrusive and overexpanded due to non-extraction methods
Unstable dentitions (relapse)

Facial esthetics & occlusion are closely linked together
Normal growth pattern dictates facial esthetics
Facial esthetics are better with a dentition in balance

Discrepancy between tooth size-bony base growth is fairly common
Size of tooth pattern cannot be influenced by adverse health conditions after age 3
Childhood illness may negatively affect osseous growth, between 3rd to 25th years. This loss may never be regained

*Orthodontists cannot increase jaw growth with any orthodontic appliances
Teeth are Irregular
Growth of the Mandible
Generalized growth of the body of the MD is over by the time the patient reaches 12
Growth that does occur is restricted to areas other than the canine or lateral incisor region
In Brash, Schour and Brodie study using alizarine dye injections in monkeys
The growth is restricted to the posterior borders of the rami, the alveolar process, the border of the sigmoid notch, and the head of the condyle

To try and align crowding would push teeth off medullary bone
Tweed illustrates with multiple case studies that the incisor mandibular plane angle coincides with his own clinical findings
Margolis found that in most white children with normal dentitions and nonprognathous faces, the MD incisors were at 90 degrees and the variation was less than 5 degrees either way in 90 percent of 300 children examined

Most balanced dentition is when it’s closest to human’s evolutionary pattern
Dental balance relies on osseous growth balance
Stable dentition -> best facial esthetic results
Position of mandibular incisors (IMPA) -> determines facial balance
Normal growth pattern (FMA) -> important concept showing growth pattern

Using FMA as a predictor of facial growth pattern and orthodontic treatment outcomes
Brodie and others have shown growth pattern is constant and resists change whether normal or abnormal

There is support by the fact that parallelism of the lower borders of the mandible continues even in an abnormal direction during growth (i.e. from condylar fracture)
Angle Orthodontist 1941, Broadbent paper on his growth study:
From records of 3,500 white Cleveland children

1) The composite representing the children in the 3.5 yr bracket shows the incisor mn plane angle to be 90 degrees
2) for 7 yo 81*
3) for 14 yo 87.5*
4) for adults 91.5*
The average for all the cases was 87.9*

Measuring FMA:
Salzmann Maxillator used to take measurements directly from the patient
Take a sagittal x-ray
Profile photograph

FMA 16-28º
Ideal, prognosis is good
FMA 28-35º
Growth factor not favorable, will require extraction
Prognosis is good (28º), fair (32º), poor (35º)
FMA >35º Poor prognosis
FMA 45-55º prognosis is nil,
May not benefit from orthodontic treatment, extraction may further complicate things

Incisor Mandibular
Plane Angle
Am J Ortho and Oral Surgery 1946;32:175-230

+5° Incisor position applies to FMA near 16°
0 ° Incisor position applies to FMA near 22°
-5° Incisor position applies to FMA near 28°

Above FMA of 35°, the +/- 5° formula cannot
be applied as the incisor position will be from
-5° to -10°
If FMA lies 8 inches or more posterior to tragion
Prognosis is excellent
Growth pattern normal
If FMA lies around 4 inches posterior to tragion
Prognosis is good
Growth pattern normal
If FMA lies around 3 1/2 inches posterior to tragion
Prognosis is fair
Growth pattern not favorable
If FMA lies around 1 1/2 inches posterior to tragion
Prognosis is poor
Growth pattern abnormal
Tend to be Class III malocclusion
The +5° formula applies toward the 10 inches posterior to tragion, while the -5° applies toward the 3 1/2 inches posterior to tragion

Really high FMA may signify true bimaxillary prognathism. Therefore, needs more analysis of anatomic structures:
Height of ramus
Gonial angle
Length of inferior border of mandible
Height of mandible from molar to inferior border compared to height of mandible from incisal edge to inferior border

Dr. Herbert Margolis- Commentator
Tweed Conclusion
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