Controversies in cephalometrics /certified fixed orthodontic courses by Indian dental academy

Controversies in Cephalometrics

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INDIAN DENTAL ACADEMY
Leader in continuing dental education


Orthodontics as a science is still very
young and a major part of the
development of this profession has
been raised on trial and error
approaches rather than deductive
research. Controversies have thus
sprung up within the field of
Orthodontics.

Natural head position
Natural head position is a standardized and
reproducible orientation of the head in space
when one is focusing at a distant point at eye
level.
German anthropological society in 1884 –
Frankfort Agreement. The plane which passes
through the left and right porion landmarks and
the left orbitale achieved uniformity in
craniometric research.

Downs – timely warning. It was he who had shown that
discrepancies between cephalometric facial typing and
photographic facial typing disappear when the Frankfort
plane is not horizontal but tilted up or down.


Bjorks studies of facial prognathism also illustrates the
unreliability of intra cranial reference lines on
cephalograms.
Two adult Bantu men were selected to represent
maximum and minimum facial prognathism relative to
the S-N plane.Bjork illustrates the greatest variation in
the inclination of the cranial base rather than the
greatest differences in prognathism.


The simplest procedure to obtain facial photographs
and head radiographs is to instruct patients to sit
upright and look straight ahead to a point at eye level
on the wall in front of them.
The conventional use of two ear rods to stabilize the
head in radiographic cephalometry is based on the
assumption that the transmeatal axis of humans is
perpendicular to the mid sagittal plane.
The relationship of the left and right ears in their
vertical and horizontal relation is frequently
asymmetric.

The insertion of ear rods will obviously result in
vertical and/or horizontal rotation of the head ,which
introduces a deficient and misleading image.
Thereby,the attempt to determine facial asymmetry
of a patient generally results in a compromise rather
than as an exact definition.
Only the left ear rod should be used in radiographic
cephalometry both for the lateral and frontal
projection.
The right ear rod should merely be inserted against
any part of the ear.

Reliability of Landmark identification and
Head Film Measurement.
Head film measurements like all
measurements involve error which falls into
two categories.
• Errors of Projection
• Errors of Identification

Errors of projection:
Results because headfilm is a two dimensional depiction of
a three dimensional object.
Since the rays that produce the image are not parallel and
originate from a small source , headfilms are subject to
distortion.- the side nearer the x ray source is enlarged
more than the side closer to the film.
While meaningful systematic corrections for projection
errors are obtainable by using a real time video subtraction
stabilization procedure , this is impractical for routine
clinical use.


Error of identification:
Involves the process of identifying specific
landmarks on headfilms.
To test landmark identification reliability , 4
instructors and 3 orthodontic residents were
requested to select and plot four high quality
radiographs.
They were provided with a list of landmarks and
definitions of each and were asked to identify them
using a pencil point on a clean sheet of acetate
paper on the radiograph.

The porion, condylion , orbitale and basion were
less readily identified than some of the other
landmarks.
Condylion was less readily identified and Gnathion
more accurately identified.
Baumrind and Frantz demonstrated marked
differences in magnitude and configuration of
envelope of error found among different
landmarks.Other factors that can influence
landmark identification are film density and
sharpness.

Reliability of cephalometric analyses:
Fundamental to orthodontics is the need to
determine the relationship of the various skeletal
components, particularly those of the jaws to each
other and to the rest of the cranium in the cranio
facial complex.
The interpretation of the measurements continues
to be the subject of much debate.


Wylie et al compared five analyses in ten individuals
who underwent various surgical corrections.Pre
treatment cephalometric radiographs of the ten patients
were selected to illustrate different dentofacial
deformities , each of which was corrected with a
different surgical procedure.
The pretreatment cephalometric radiographs were
blindly assessed by one investigator who used the
criteria for each of five popular analyses.
The results of the analyses ( diagnoses ) were then
compared to one another and to the actual surgery
performed.

The outcome of the study revealed that performance of the
analysis in relation to actual surgery was generally poor.
In the case with mandibular advancement there was 35 %
agreement on the surgery performed.
For maxillary advancement - 20 %
For maxillay superior positioning 100%
For maxillary advancement and mandibular reduction- 20%
For bimaxillary protrusion – all analyses agreed that the
teeth were protrusive and that the lower third of the face
was too long.
This illustrates the unreliability of cephalometric analyses.

Limitations of traditional superimposition methods:

No points or planes in the craniofacial complex
are stable and all move relative to each other
during growth. Orthodontic analyses, in effect ,
relates relatively stable areas as depicted by
arbitrarily selected points or planes to more
remote but less stable landmarks.


While the primary errors are biologically induced ,
the secondary errors are entirely mathematically
defined, since they are related to the primary
errors.
Errors in tracing superimposition can be
compounded by the method of superimposition
used in interpreting the findings.
A study conducted by Ghafari et al demonstrated
differences in interpretation of facial changes by
comparing four traditional cephalometric methods
of superimposition.( best fit on anterior cranial
base anatomy,sella-nasion,registration point with
bolton nasion planes www.indiandentalacademy.com
parallel and basion- nasion

The results of their study showed differences among all
paired methods to be statistically significant.

Growth behavior of an individual as recorded on a
sequential set of roentgenograms has been shown to
differ greatly when studied using different
superimposition methods. Nothing is known of the
growth behavior of the individual parts in the
continuum of the discrete points studied.

Because of the inability of conventional cephalometry
to apprehend curved forms, it is limited to landmark
indices.

Reference planes:
The various reference lines still compete with each
other.One system is more or less as good or poor as
any other and none is completely reliable because
each is subject to large individual variability.
What can be done to diminish this problem?
The answer is to choose measurements that are based
on different reference planes, in this way it is hoped to
compensate for pronounced variations in one or the
other reference lines.


True vertical plane:
The problem of a constant reference plane can be
solved if the true vertical plane is used. The true
vertical is a constant and is perpendicular to the true
horizontal.
Some clinicians have acknowledged this fact and
developed a cephalometric assessment based on this
reference plane.
(Michielis and Tourne,1990;Viazis,1991)
Viazis analysis was based on Bolton standards in which
natural head positionwas never a serious
consideration.Thus there was a shortcoming of lack of
equivalent norm data.

The analysis we feel comfortable at present is
divided into four fields or areas.
• Sagittal base relationships
• Vertical base relationships
• Dento alveolar relationships
• Memos ie important evaluations without proper
measurements.
A criticism could be that readers do not agree with
some of the abbreviations selected. ( SN – SGn
instead of Y axis etc ).

Advantages:
• Enhances communication
•Could be speculated that these measurements
have some merits since they have been used for a
long time.
• Further, it is easy to reckon that the idea of
different reference planes was indeed realized: the
Steiner angles are related to the SN plane, those of
Downs to the FH plane , Wits appraisal to the
occlusal plane and the Holdaway soft tissue
evaluation like NA-Apog angle to the extension of
the skeletal base onto the forehead, the chin and
upper lip.

Cross evaluation with different reference planes is
important and can be demonstrated with the ANB
angle.
If one takes only the ANB angle to measure the relative
position of maxilla and mandible to each other ,one
must realize that any different horizontal or vertical
position of point N and the location of the points A and
B in the vertical plane will have an influence on the size
of this angle and not on the actual sagittal relation of
the two jaws.
( Hussels and Nanda ,1984 ).

The same holds true for a rotation of the
occlusal plane: backward rotation of the
occlusal plane has a decreasing effect on the
ANB angle, though sagittal basal relationships
remain constant.


Shortcomings of ANB angle:
Taylor in 1969 pointed out that ANB angle did not
always indicate true apical base relationship.
Varied horizontal discrepancies of points A and B
could give the same ANB measurement because
variation in the vertical distance from nasion could
compensate for other variation.
Beatty in 1975 reported that ANB angle is not
always an accurate method of establishing the
actual amount of apical base divergence.As an
alternative to ANB angle for measuring apical base
discrepancy , he devised the AXD angle,where
point x is located by projecting point A on to a
perpendicular to SN line.

Point D is located in the bony symphysis as described
by Steiner.


-Frankfort horizontal basis for cephalometric analysis
Lundström and Lundström- AJO 1995

No difference was found between the variability
of the Frankfort horizontal and the sella-nasion
line with regard to the horizontal plane. The
large variation of both intracranial reference
lines, related to NHP, as well as to NHO,
confirms their relative unsuitability as
cephalometric references for clinical purposes.
Findings indicate that a horizontal line, related to
natural head position, adjusted to natural head
orientation when indicated, presents the most
reliable basis for cephalometric analysis.

AJO-DO on -DO, 1980 Variability between the
optic plane and Frankfort horizontal – Tremont

Frankfort horizontal is commonly constructed
on a lateral cephalogram from the top of the ear
rod to orbitale. Ear rod positioning and
identification of orbitale present obvious
variables with such a reference plane. The optic
plane has been proposed as a more accurate
representation of Frankfort horizontal.

The optic plane, was significantly
different from anthropologic Frankfort
horizontal. Also, the optic plane did not
vary significantly less from anthropologic
Frankfort horizontal than from ear rod
to orbitale Frankfort horizontal.


The optic plane was constructed, as defined by
Sassouni, by drawing the supraorbitale plane
(a line tangent to anterior clinoid and the roof
of the orbit), drawing the infraorbital plane
(line tangent to the inferior of sella turcica and
the floor of the orbit), and then bisecting the
angle formed by their intersection to obtain the
optic plane.

Cephalometrics for you and me – Steiner – 1953
AJO
Porion and Orbitale are not accurate for our use as
we are not dealing with dry skulls.
Points S and N are clearly visible in the X ray
pictures and can be located easily and accurately.
Emphasizes that points S and N are located in the
mid sagittal plane of the head and therefore they are
moved a minimum amount whenever the head
deviates from the true profile position and that the
points are located on hard non yielding tissue.

Point A revisited – Jacobson- AJO 1980
Point A cannot be accurately identified in all
cephalometric radiographs. In instances where this
landmark is not clearly discernible, an alternative
means of estimating the anterior extremity of the
maxillary base is shown.
A point plotted 3.0 mm. labial to a point between
the upper third and lower two thirds of the long axis
of the root of the maxillary central incisor was
found to be a suitable point - (estimated point A)
through which to draw the NAE line and one which
most closely approximates the true NA plane.

Steiners analyses:
Acceptable compromises:
Steiner clearly recognized that cephalometric standards
are merely gauges by which to determine more
favorable compromises as a treatment goal.He
developed a chart that reflects a number of average
measurements of normal dentofacial relationships.
Steiner recognized variations in antero posterior jaw
relations to each other.
The compromise describes the anticipated axial
inclinations of the maxillary and mandibular incisors to
the NA and NB lines at various ANB relationships.

The Steiner compromises are geometric
resultants of morphogenetic variations and their
resulting treatment possibilities.


Method of appraisal of jaw disharmonyWitts
The Witts appraisal is the extent to which the
jaws are related to each other.
The occlusal plane is drawn through the region
of the overlapping cusps of the first premolars
and first molars.The point of contact on the
occlusal plane from points A and B are labeled
AO and BO respectively.
The average jaw relationship according to Witts
is – minus 1 mm for men and 0 mm for women.

Schudy described the occlusomandibular plane angle
(OM angle )as another method of evaluating skeletal
divergency and thus an indication of skeletal pattern.A
variation in the range of OM angles is from 7 to 21
degrees.
As the OM angle approaches 21
degrees,hyperdivergency of skeletal pattern is more
likely.
Smaller OM angles indicate hypodivergency.


A-Po line and cephalometric correction- Ricketts
The A-Po line is another method used in
cephalometric analyses to assess the position of
mandibular incisor tooth.
A range of –2mm to +3mm is considered a satisfactory
incisor position,with + 0.5 mm lower incisor tip to APo line being an idealized position.
Downs credits Ricketts for suggesting relating the
lower incisor to the profile,specifically the lower face
using A-Po.

Cephalometric correction describes a method to
determine mandibular dental arch crowding or spacing
by assessing mandibular incisor position on a
cephalometric radiograph in concert with mesiodistal
dimensions of mandibular teeth and mandibular arch
circumference.
The rationale is that by advancing or retracting the
mandibular incisor 1mm will result in a 2mm gain or
a 2 mm reduction in the available space for
mandibular arch.


Calculations have indicated that tipping the lower
incisor tooth forward by 3 degrees results in total
dental arch length increase of 2.5mm.
Conversely, retracting the mandibular incisor 3
degrees will encroach on the lower arch length by
2.5mm.
Ricketts stresses the significance of utilizing linear as
well as angular measurements in these assessments.
All cephalometric measurements must be evaluated in
concert with other measurements and must include
clinical and diagnostic judgement.

Mc Namara analyses:
For determining the anteroposterior relationship to
maxilla and mandible , mid facial length is measured
from condylion to point A. The effective length of the
mandible is measured from condylion to gnathion.
Birte Melsen suggests that there are displacements of
condyle,pogonion,menton and point B relative to
superimposition on implants at a study done on annaual
intervals between 8.5 yrs and 15.5 yrs of age.


Soft tissue analyses- Holdaway
Legan and Burstone suggest using a constructed
horizontal.This is a line drawn through nasion at an
angle of 7 degrees to the SN line.
A vertical reference line can be traced passing through
sub nasale (SnV) or glabella.
Naso labial angle – formed by two lines namely the
columella tangent and an upper lip tangent.Arbitrary
value is 90 to 110 degrees.
Legan and Burstone report a mean value of 102 +/- 4
degrees.

Scheidman et al drew a postural horizontal line through
subnasale and further divided the naso labial angle into
columella tangent to postural horizontal ( -25 degrees)and
upper lip tangent to postural horizontal ( -85 degrees).
They argue that each of these angles must be assessed
individually in as much as they vary independently.


E line: Drawn from tip of nose to soft tissue
pogonion.Normally the upper lip is about 4 mm
behind this reference line while the lower lip lies about
2 mm behind it.
Ricketts admits that considerable variation exists in
terms of age and sex.He therefore advises that adult
lips should be contained with nose – chin lip line.
S line:- Steiner line is a line drawn from soft tissue
pogonion to the mid point of the S shaped curve
between sub nasale and tip.


H line: The harmony line is tangent to the
chin point and the upper lip. The H line
angle formed between this line and the soft
tissue nasion – pogonion line.The H line
angle measures either the degree of upper
lip prominence or the amount of
retrognathism of the soft tissue chin.


Conclusion:
A combination of various cephalometric norms
and variables should be compiled to arrive at a
proper diagnosis.Although innumerable
controversies exist in the field of
cephalometrics, it is still a very significant &
effective diagnostic tool.


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Controversies in cephalometrics /certified fixed orthodontic courses by Indian dental academy

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