Tweeds analysis & wits appraisal / dental crown & bridge courses

INDIAN DENTAL ACADEMY
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CONTENTS
• Introduction
• TWEED’S Analysis
Diagnostic Facial Triangle
Cepahlometric correction
Studies on Tweed’s analysis
• Shortcomings of ANB
• WITS Appraisal
Wits Appraisal of jaw disharmony
Related Studies
• Conclusion
• Bibliography

INTRODUCTION
• With the development of cephalometrics some 30yrs.
ago, profound changes occurred & are still occurring in
clinical orthodontics
• After W.B.Downs (1948), who introduced a method for
measuring, recording & analyzing the individual
dentofacial pattern indicating whether dysplasia present
in facial skeleton or dentition or in both
• Steiners (1953), published his analysis based on what
compromises in incisors position would be necessary to
achieve normal occlusion, when ANB angle was not
ideal

• TWEED (1954): his analysis & treatment procedures
are based mainly on the following:
1. A good visual clinical examination
2. The diagnostic facial triangle
3. A knowledge of facial growth trends

DIAGNOSTIC FACIAL TRIANGLE
• There are four essential
angle that has to be
discussed for clinical
orthodontic procedure:
 Frankfurt mandibular
plane angle(FMA)
 Mandibular incisor plane
angle(IMPA)
 Frankfort mandibular
incisor plane angle
(FMIA)
 Point A-Nasion-Point B:
(ANB)

• Frankfurt mandibular
plane angle:
• established: by
connecting a point 4.5mm
above the geometric
center of ear rod & an
orbitale point midway
between left & right lower
border of orbits.

• Mandibular Plane:
• Drawn along the lower
border of mandible & is
extended posteriorly to
connect with Frankfort
plane
• Anteriorly: connects with
Menton
• Posteriorly: bisects
distance between right &
left lower border of
mandible in region of
gonial angle www.indiandentalacademy.com

• Third Plane of Triangle:
• Made by extending the
long axis of mandibular
central incisor downward
to mandibular plane &
upward to FHP.

• These planes together form the following angles: FMA,
IMPA,& FMIA.
• In addition another plane S-N plane will also be
discussed & it is a plane that connects the geometric
center of Sella turcica & Nasion.
• Angle ANB : very important as it expresses the
mesiodistal relationship of maxillary & mandibular basal
bones
• 100 sample was collected- satisfactory facial esthetics-
range founded to be 50
to -20
, with 65% samples had
range between 30
& 00.

• He selected four treated cases head films
• Drawn a triangle
• FHP : connected a point 41/2
mm above geometric center
of ear rod with the lower border of the orbit
• FMPA: connected Frankfurt plane with mandibular plane
• IMPA: constructed by drawing the line through apex &
incisal edge of the mandibular central incisor, extending
it to intercept the frankfurt & mandibular planes to form
the triangle

• Angles were measured & noted as:
• FMIA: 650
, 660
, 64.50
& 650
, all very close to 650
• FMPA: considered normal variation range between 200
& 300
, midway between these two values would be 250
,
which he called the norm for that angle
• IMPA: considered range between 850
to 950
with 900
being designated as norm for this angle
• Therefore, if FMA is 250
& 900
is taken for inclination of
mandibular incisor (IMPA) when related to the lower
border of the mandible, then the norm for the third angle
automatically becomes 650
i.e. FMIA

• But after seeing the work done by Down’s,
Brodie & others & the norms given by
them, he thought that norms given by him
is not as accurate as they might be
• So, again did study: 45 samples
• Founded: norms FMA: 250
FMIA: 650
IMPA: 900

CEPHALOMETRIC CORRECTION
• To determine the correct location of mandibular central
incisal edge & the correct degree of inclination of that
tooth in relation to the mandibular border, cephalometric
correction has to be done:
• FMA that varied from120
to 200
, rarely displayed IMPA
greater than 940
,therfore FMIA ranged from 680
to 800
.
• FMA fell between 210
& 300
had FMIA’s varied from 700
to
750
when FMA read 210
to FMIA’s of 650
when FMA
approached 300
• FMA ranged upward from 300
presented FMIA’s that
averaged 650

STUDIES ON TWEED’S
ANALYSIS
• Savadi S.C.
• Karnataka population
6-9 yrs. 10-13
yrs.
14-17
yrs.
18-21
yrs.
FMA 28.70
27.75 27.4 26.55
FMIA 62.150
51.75 53.5 56.4
IMPA 93.650
100.0 98.6 98.0

• Sarkar .P.
• Sample size: 50
• Male:25, Female: 25
• Age group: 16-25
• Ethnic group: Kerala-
Trivandrum
Population Mean SD Range
FMA 27.81 4.31 17.40
FMIA 52.75 6.59 41.0-68.5
IMPA 99.46 6.05 86-114.5www.indiandentalacademy.com

• Valiathan.A.- 1976
• Sample size: 20
• Male: 10, Female: 10
• Age group: Mean- 30 yrs.,
Range: 20-48 yrs.
• Nationality/ Ethnic group:
Indian Adults
• Mean SD Range
FMA 21.6 6.0 13.5-3.30
FMIA 51.87 8.19 32.5-66.5
IMPA 106.5 10.51 88.0-129.5

SHORTCOMINGS OF ANB

The anteroposterior spatial
relationship of nasion relative to
jaws
• Anthropologists
studying faces
traditionally use
NASION as a
reference point from
which to measure
prognathism

• Anteroposterior relationship of maxillary & mandibular
denture bases may be measured by relating these bases
to Nasion.
• The relative A-P position of denture bases in craniofacial
complex in turn may directly influence the ANB reading.
• Examples shows that with the change of position of both
the jaws in relation to nasion will also has the effect on
ANB reading
• With forward position of both jaws in relation to nasion
will increase ANB reading (despite relationship of jaws to
each other remain unchanged) & vice –versa.

Effect of short & long cranial bases on the ANB
angle

Rotational effect of jaws
• Clockwise or counterclockwise rotation of
the jaws relative to cranial reference
planes also affects the ANB angle reading.

• The relationship of the
jaws to each other is
unchanged, but the jaws
are now rotated in a
counter clockwise
direction relative to the
SN plane.
• The rotation has had the
effect of producing a
Class III type of jaw
relationship.
• The ANB angle had been
reduced from 2 degrees
to 5 degrees.

• A clockwise rotation of
the jaws relative to the
cranium or the SN
reference plane produces
the opposite effect; that
is, a Class II type of jaw
relationship.
• The relative clockwise
positioning of the jaws
has increased the ANB
angle reading from 2 to 8
degrees in spite of the
jaws maintaining an
identical relationship to
each other.

• In cases of class I molar relationship i.e. normal
occlusion , it may show increased ANB angle but wits
appraisal shows normal standards
• Inspite of its shortcomings, it is still used by many as an
absolute determination of sagittal skeletal disharmony
• Shortcomings were recognised as early as in 1955 by
JENKINS, who elected to use the functional occlusal
plane as a reference base for measurement of jaw
disharmony.

• He said this as traditionally this plane used as a primary
plane of orientation, since all masticatory forces are
focused on this plane & intimately related to it
• He argued that even Angle used this plane as a plane of
reference for his classical classification of malocclusion

• He established the “a”
plane drawn through
point A at right angles to
the occlusal plane & then
measured from the “a”
plane to point B,
gnathion& mandibular
incisor edge.
• To predict the extent of A-
P jaw dysplasia, he
formulated range of
values for these
measurements from the
“a” plane

• TAYLOR(1969): pointed out that ANB angle did not
always indicate true apical base relationship.
• Varied horizontal discrepancies of point A&B could give
the same ANB measurement because variation in
vertical distance from nasion could compensate for other
variation
• A relative forward / backward position of nasion would
likewise change ANB reading as forward / backward
position of maxilla & mandible

• BEATTY(1975): pointed out that ANB angle is not
always an accurate method of establishing the actual
amount of apical base divergence
• As an alternative to ANB angle, he devised the AXD
angle, where point X is formed by projecting point A
onto a perpendicular to the SN line & point D is located
in bony symphysis

He also introduced a linear measurement AD, to describe the anteroposterior
relationship of the jaws. Point D is the point that represents the shortest
distance from point A on a line perpendicular to SN passing through D

• Two variables Nasion & Point B were eliminated
• Ten years after publication of Wits appraisal & 30yrs.
following Jenkins comments on occlusal plane
• JARVINEN: mentioned variation in ANB angle
• He stated that “the use of apical base should be
replaced by a better method to determine sagittal apical
base difference”.
• He suggested Wits appraisal, as a possible
alternative for this angle.

WITS APPRAISAL
• Given by Alexander Jacobson (He was head of
the orthodontic department at the University of
Witwatersrand known as Wits, hence the name
“Wits” analysis).
• Purpose: to identify instances in which the ANB
reading does not accurately reflect the extent of
A-P jaw dysplasia. It reflects the relationship of
jaws to each other & to the cranial base
(AJO 2003Vol. 124, No.5)

• The “Wits” appraisal of jaw disharmony, however,is not
an analysis rather, it is intended as a diagnostic aid
whereby the severity or degree of anteroposterior
jaw disharmony can be measured on a lateral
cephalometric head film.

The “Wits” appraisal of jaw
disharmony
• The “Wits” appraisal of jaw disharmony is a measure of
the extent to which the jaws are related to each other
anteroposteriorly
• Assessment of degree / extent of jaw disharmony:
perpendicular lines should be drawn on a lateral
cephalometric head film tracing from points A and B on
the maxilla and mandible, respectively, onto the occlusal
plane (drawn through the region of maximum cuspal
interdigitation / region of overlapping of cusps of first
premolars & first molars).

• The points of contact
on the occlusal plane
from points A and B
are labeled as AO
and BO, respectively

• In a sample series of 21 adult men, found that point BO
was approx. 1mm ahead of point AO
• Calculated mean reading= -1.17mm
• SD = 1.9(range -2 to 4mm)
• In a sample series of adult women, found that point AO
& BO generally coincides
• Calculated mean reading= -0.10mm
• SD = 1.77 (range -4.5 to 1.5mm)
• Therefore, average jaw relationship wits reading is
-1.0mm (men) & 0mm (women)

Related Studies
• Since the introduction of Wits appraisal,
various papers addressing the subject
have been published

• Guido Ferrazzini : studied more than 200 patients cephalometric
head film, determined that what other factors influence the ANB
angle, besides the anteroposterior distance of the apical bases that
the ANB angle must measure.
• Maxillary prognathism: i.e. anteroposterior position of the upper jaw
in relation to cranial base, measured by SNA angle
• Maxillary inclination: reffered to the angle formed by the nasal
plane(ANS-PNS) & the cranial base(S-N)
• Concluded: that the angle ANB not only depended on the
anteroposterior relationship of the jaws but also on the inclination of
the palatal plane, maxillary prognathism & vertical facial dimension.
Also stressed that ANB angle should not be considered as absolute
measurement for anteroposterior relationship of the jaws rather
other variables should also be considered.

• Binder RC: arbitrarily varied the positions of points,
lines, and angles on cephalometric drawings, &
recognized the geometric effects on ANB angle.
• Concluded: that for every 5-mm anterior displacement
horizontally, the ANB angle changed 2.5 degrees.
A 5-mm upward displacement of nasion altered the ANB
angle 0.5 degrees
A downward displacement of nasion changed the ANB
angle 1 degree.

• Samir E Bishara et al: (1) determine the changes in the ANB angle
and Wits appraisal between 5 years of age and adulthood in both
male and female subjects and
• (2) determine whether the changes in the ANB angle and Wits
appraisal are significantly different from each other.
• Subject was obtained from the Facial Growth Study at the University
of Iowa. Lateral cephalograms were obtained biennially between the
ages of 5 and 12 years and annually through age 17. A final set of
records was taken in adulthood at a mean age of 25.5 years.
• Following parameters were examined (1) the anteroposterior
angular relationship of the maxilla to the mandible and cranial base
as described by ANB, and (2) the anteroposterior linear relationship
of the maxilla to the mandible

• Showed the effect on the ANB
angle of moving nasion
forward or backward 0.5 inch
(12.7 mm), and vertically up or
down by the same amount.
• Position of nasion with points
A and B held constant.
• 1. Horizontal positioning of
nasion results in these ANB
angles: 1 = 2 degrees, 2 = 8.5
degrees and 3 = —4.5
degrees.
• 2. Vertical positioning of
nasion results in these ANB
angles:1 = 2 degrees, 2 = 1
degree, and 3 = 0 degrees.

• Concluded:The ANB angle changes significantly with
age, while the Wits appraisal indicates that the
relationship between points A and B does not change
significantly with age.
• No significant differences were observed in the changes
between male and female subjects for either ANB or
Wits values between the ages of 5 years and adulthood.
• To arrive at a more accurate diagnosis of anteroposterior
apical base relationship, both the ANB angle and the
Wits appraisal should be used.

• Roth and Martina et al: recognized the ANB angle as
an invalid measure of sagital skeletal disharmony
because of its being affected by rotations and variations
in the sagittal and vertical jaw dimensions relative to the
cranial base.
• The interdependency of the Wits appraisal and the
vertical dimensions of the jaws might be expected
because of the geometric relationship between the
distance A—B and angle A—B/Occlusal
• The mean value of the measured Wits appraisal,
according to Roth, is 0.27, which corresponds to the
mean value of zero found in the original 1975 Jacobson
study.

• Two factors that Roth suggests
will affect the Wits reading
• The occlusal plane angle and
the vertical alveolar
dimensions.
• The positive summation effect
of increasing the distance A—
B and decreasing the occlusal
plane angle are demonstrated
in . Alteration of the vertical
jaw relationships (increasing
the distance between points A
and B) leads to a further
increase in the A—B distance
or Wits reading.

Roth modifications
• Roth contends that it would be
interesting if the anteroposterior
effect of the Wits appraisal of
treatment changes in the occlusal
plane could be used for
determining, or predetermining,
changes in molar relationship
relative to the occlusal plane.
• The alteration of Wits appraisal
applied to the molar relationship,
and assuming an
identical.alteration of the occlusal
plane (—10 degrees), the
anteroposterior molar relationship
is positively correlated with the
length of the distance A—B if the
upper molar moves on an arc (RA)
with-the anterior point A, and the
lower molar on the arc (RB) with
the center point B. Starting from a
Class .1 molar relationship
(shaded blocks),-the Class II
effect in the molar region is larger
with the greater distance A—B
(right) than with the smaller
distance A-B (left).

• Rushton et al: did study to compare the reproducibility & reliability
of the Wits appraisal & the angle ANB
• 27 lateral skull radiographs, following points were determined A,B,S
& N, functional occlusal plane (FOP) taken as line of maximal
intercuspation between premolars & first molars, angles
SNA,SNB,ANB & the Wits values were recorded
• Concluded: that the ANB method relies on the base of the skull and
is affected by the rotation of the jaws and the position of nasion.
• In the Wits appraisal they stress correct location of the occlusal
plane, stating that ‘the greatest error occurs in the location of
functional occlusal plane”
• A correlation between angle ANB & Wits would not be expected
because they each involve an exclusive point or plane which are not
necessarily biologically related

VARIOUS OCCLUSAL
PLANES
• Functional occlusal plane: (Steiners &
Wits): plane passes through maximum
intercuspation of molars & premolars
• Occlusal plane: plane passes midway
between the cusp tips of maxillary molars
& mandibular molars and bisecting
through the incisor overbite
• Bisecting occlusal plane(M.M.Bisector,
1994): taken palatal & mandibular plane

• Meet both planes posteriorly
• Bisected the angle formed by these two
planes
• Plane passes through this bisecting point
will form the bisecting occlusal plane

Shortcomings of Wits
• Change in degree of occlusal plane will
have the effect on Wits reading i.e.
decrease in occlusal plane will increase
the Wits reading
• Increase in the vertical distance between
point A & B will also effect Wits reading
i.e. it will also increase the Wits reading
• Tracing error of occlusal plane will also
effect the Wits reading

CONCLUSION
Assessment of anteroposterior apical base discrepancy by applying
the Wits appraisal is largely dependent on correct location or
representation of the Occlusal plane.It is a linear measurement and
not an analysis . It is simply an adjunctive diagnostic aid that may
prove useful in assessing the extent of anteroposterior skeletal
dysplasia and in determining the reliability of the ANB angle.
No single parameter in cephalometry should be relied on entirely
and interpreted as an absolute value. Conventionally used angular
and linear measures are highly correlated and overlap to the extent
that two or more measures often reflect the same underlying
anatomic condition in slightly different terms. It is not proper to treat
all angular or linear measures as if they were equally reliable.

BIBLIOGRAPHY
• Alexander Jacobson. Radiography Cephalometry. Quintessence
Co,1995,26-33,39-62,165-173,175-184.
• Charles H.Tweed. Clinical Orthodontics; The C V Mosby company,
1966,Vol. One Pgs.1,2,3,5,6,7,8.
• Indian Cephalometric Norms. Indian Orthodontic Society, dental
Department C.M.C.Hospital, Vellore.
• Ferrazzini G. Critical evaluation of the ANB angle. AJO
1976;69:620-626
• Bishara SE, Fahl JA, Peterson LC. Longitudinal changes in the ANB
angle & Wits appraisal. AJO 1983;84:133-139
• Rushton R, Cohan AM, Linney AD. The relationship & reproducibility
of angle ANB & the Wits appraisal. BJO 1991;18:225-231
• Charles H.Tweed. The Frankfurt- Mandibular Incisor Angle (FMIA)
In Orthodontic Diagnosis, Treatmant Planning & Prognosis. July
1954
• A. Jacobson. The “Wits” appraisal of jaw disharmony. AJO
2003;124:470-479.

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