Template analysis /certified fixed orthodontic courses by Indian dental academy

Template Analysis
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


Contents
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Introduction
History
Mooree’s Mesh diagram
Mesh coordinate system study
Template Analysis
Proportionate Analysis
Conclusion

Introduction
• The cephalometric technique has been used in
the field of orthodontics for over 60 years and
has become an important diagnostic aid in the
formulation of diagnosis and treatment plan as
of today.
• Cephalometric standards have been useful
guidelines but many of their limitations were
unrecognized and ignored.

• Many a times clinicians take statistical mean as
the norm and tend to treat the patients
according to them which in all cases may not be
the ideal treatment.
• Hence the orthodontic profession has been
criticized as a millimeter profession. To
overcome this a template analysis was
developed.

• A cephalometric template is a set of oriented
rulers that permit size and position to be
measured in terms of years of development.


History
• The grids superimposed on the face of a horse
rider and the edentulous man by Leonardo da
Vinci (1490) demonstrate the artist's keen
appreciation of proportion.
• Focus on the proportionate representation of
man's face dates back to ancient records from
Egypt, and India.


• As early as 1917, D'Arcy Wentworth Thompson
studied growth and form of primate skulls
comparing them to a human skull by using
Cartesian coordinate system.
• Lucien de Coster of Belgium, one of the
pioneers of contemporary cephalometric
methods, led transformation of a mesh
coordinate system as early as 1939 for analysis of
radiographs in norma lateralis of orthodontic
patients.

• But the earliest grid analysis that was developed
in a standardized and coordinated manner to
assist in a clinical situation giving a clearer
perspective for assessing the treatment
objectives was originally developed by Moores
in 1953. Later more norms were added to this
mesh in 1976.


Mooree’s Mesh Diagram
• Standardized lateral head radiographs of 46 men
and 47 women from the greater Boston area,
representing a broad range of normal occlusal
variation, were used to construct male and
female norms for the mesh diagram. These
radiographs were obtained as part of the
Longitudinal Studies of Child Health and
Development by the Department of Maternal
and Child Health, School of Public Health,
Harvard University.

• The Mooree’s mesh can be used to compare
growth changes in longitudinal studies where
proportions can be visualized rather than the
amount of growth. It also helps in
circumventing the great variation in facial
dimension.


Mesh Coordinate System Study


• Data from longitudinal studies of twins
conducted at the Forsyth Dental Center was
used. All head radiographs at the Forsyth Dental
Center were taken in natural head position.
• Extracranial vertical could be used as reference
line for cephalometric analysis.


• When serial records were available for an
individual, one radiograph was used to
standardize the natural head position on all
other serial records of that individual, by
superimposing the tracings on the cranial base
area.
• Skeletal landmarks used were based on the
standard and classic anthropometric definitions
of Martin-Saller.

Construction of the Mesh Diagram
• Upper face height, and the length of the anterior skull
base (NS), determine the size of the core rectangle
within the mesh.
• The construction of the grid's core rectangle involves
drawing a vertical through nasion, parallel to the
extracranial reference line and two horizontal lines
perpendicular to this vertical, one at nasion and the
second through the anterior nasal spine (ANS). The
fourth line is drawn parallel to the vertical at a distance
from nasion equal to (NS).

• The sides of the core rectangle are divided into equal
parts to provide the scale interval for all the horizontal
and vertical grid lines needed to construct the mesh
diagram.
• One vertical line is added at the front and at the back of
the core grid rectangle. One horizontal line is added
above the core grid rectangle and three under it. The
face is thereby inscribed in a rectilinear coordinate
system composed of 24 small rectangles

• Preference has been given to the female norm,
because the vertical through nasion intersects
point A and the tip of the mandibular incisor.
The anterior and posterior nasal spines are both
located on the same horizontal, and a horizontal
also intersects both the tip of the mandibular
incisor and the anterior aspect of the line
representing the functional occlusal plane.

• Individual variation in the position of facial
landmarks and teeth implied that the facial
configurations of the subjects studied differed
markedly in the degree of prognathism and in
facial shape. The contour ellipses illustrating
these individual differences at 50% confidence
limits showed various shapes.


• The amount and direction of this variation in
the location of a given landmark were reflected
in the lengths of the major and minor axes of
the corresponding ellipses. A very narrow ellipse
indicated that most of the variation in the
location of the landmark was concentrated along
the major axis of he ellipse.


• No variance occurred at nasion because his
point served as the origin of the coordinate
system. Likewise, no variance occurred for ANS
along its Y coordinate because the projection of
ANS on the vertical through nasion served to
scale the vertical coordinates of the grid. The
horizontal coordinates were scaled on the
anterior skull base depth (nasion-sella).

• Therefore, the variations in the position of sella
turcica reflected individual differences in its
cephalo-caudal (vertical) position relative to
nasion, ie, the biologic variation in the
inclination of the anterior skull base. The small
component of variance along the X axis for
point sella was contributed by individuals with
pronounced caudal (downward) inclination of
the anterior skull base.

• To determine the need for separate age norms
of children at various ages, a mesh diagram
analysis was undertaken on the purely
longitudinal sample of male and female twin
pairs defined in the materials section.


• Although the size of the mesh rectangles at 8
and 16 years varied, the average proportionate
location of the anatomic landmarks in the mesh
coordinate system at 8 years of age, when
plotted in the mesh coordinate system of the
same individuals at 16 years, showed that the
location of landmarks at both ages was
remarkably close for all landmarks in the upper
face and for the soft tissue profile outline.

Procedure for Mesh Distortion
• The vertical and horizontal location of
landmarks in the mesh diagram are compared to
the location of corresponding landmarks in the
norm. The mesh coordinates are subsequently
distorted to display differences in the
proportionate location of each landmark in the
individual's mesh. This objective is
accomplished in two steps:

– By locating the median proportionate position of
each landmark in its respective grid rectangle of the
patient's mesh diagram, just as in the norm. For
example, the mean location of gonion within its
small grid rectangle is horizontally at 14% from the
anterior vertical line and vertically at 27% from the
upper horizontal line. The deviation of the patient's
gonion from its median location is represented by an
arrow that depicts the displacement factor.

– Distorting the grid lines of the specific small mesh
rectangle to reflect the deviation of each landmark
from its normal proportional location. The sides of
some rectangles will be elongated while others will
be shortened, indicating the sites of facial
disproportion or disharmony. The amount of grid
transformation is equal to the distance between the
actual location of the landmark and its normal
proportional location within its mesh rectangle.

• When a mesh rectangle contains two landmarks,
the procedure becomes more complex and
consequently two sets of normalizing factors
pertain. After the location of all landmarks has
been evaluated, distortions are drawn through
the points marked on the tracing for various
landmarks.


• These distortions are smoothed and thereby
constitute trend lines revealing the differences in
the individual's facial pattern with respect to the
norm. The grid lines are not changed when all
landmarks on the tracing and the norm are in
the same proportionate position within their
respective mesh rectangles.


• To interpret the mesh diagram of a patient, the
reader should realize that sagittal dimensions are
proportional to the length of the anterior skull
base (nasion-sella turcica). Vertical dimensions
are proportional to upper face height (nasion to
the projection of the anterior nasal spine on the
vertical through nasion).


• When the mesh is drawn on the tracing of the
lateral cephalogram of an individual patient, it is
important to compare first the size of the
individual's small individual rectangles with the
size of the small rectangles of the norm. These
differences express the shape of the individual
patient's face.


• If the height is smaller the face is short in
comparison to its depth. If the height is greater,
the face is longer.
• If the length is greater the face is deep. If the
length is shorter, the face is shallow.
• If both dimensions of the small rectangles are
larger or smaller than those of the norm, but
maintain their ratio as in the norm, the
individual's face is simply bigger or smaller than
the norm face without any proportional
difference.

Template Analysis
• It was intended initially to use clear plastic
templates inscribed with standardized facial
outlines.
• Templates
– Numeric standards for the sex specific templates
were charted out based on the data published by
Riolo et al. from the University of Michigan
Elementary and Secondary School Growth
Study(1974).

– Non-standard enlargement of 13% and so these
templates were adjusted to the 6% to 7%
magnification which was comparable to the
Broadbent-Bolton cephalostat.
– Admixture of Class I and Class II malocclusion.
– These norms were similar to the Bolton standards
(Broadbent et al., 1975) except that they were more
retrognathic. They were considered normative rather
than ideal.


Analysis
• Each template is a compact set of oriented rulers
graduated in years(6 to 16 years).
• So a single template can be used for the analysis.
• There are no millimeter measurements or
degrees.
• It becomes easy to rapidly duplicate the essence
of any type of analysis.

Cranial base Superimposition
• Any localized deviation from the apparent
baseline age can be explained by a detailed
regional superimposition.
• So any kind of comparison must be done with
some kind of superimposition.
• Commonly used reference planes are SN and
FH plane.
– FH greater variation
– Other planes that may be used Ba-N, PMV, ANSPNS

• Measurements and methods of superimposition
are chosen to evaluate the general relationship of
the various landmarks to the age scales on the
template.
• Point to point matching is not sought but an
overall balance is checked for.
• Once this is evaluated the nature of the faulty
unit can be assessed by regional superimposition

Regional Superimposition
• To determine relative size (measured in years) of
any given craniofacial dimension, the template is
placed over the cephalogram and the pairs of
points describing the measurement to be taken
is compared with the template scales at
symmetric ages until a match is achieved.


• Some points to be compared will be registratio
points which in the event will not require age
matching.


Suggested Cephalometric Measurements
• Cranial Base length
Anterior

Posterior
Total

Register on S, read age
at N
Register at S and read
age at Ba
Ba to N at symmetric
ages

• Facial height
Upper anterior

ANS to N /SN/FH

Upper posterior

PNS to S/SN/FH

Lower anterior

ANS to Go

Anterior

N to Gn

Posterior

S to Go

• Maxillary Size
Length
Effective length

PNS to ANS or Point
A
Ar to Point A*


• Mandibular size
Ramus height

Ar to Go

Body length

Go to Pog/Gn/Point B

Overall

Ar to Go/Pog/Point B

Effective length

Ar to Gn

• Dental position
Maxillary dentition

Orient the template on palatal plane
and register at Point A, and read the
molar position at the upper contact
point dots and incisor position at
1/1

Mandibular dentition

Orient the template on mandibular
plane (Go-Gn) and register at Point
B, and estimate the molar position
by interpolation at the lower
terminal points M and incisor
position at 1/1


• Dental extrusion
Maxillary

Mandibular

Palatal plane registered at
Point A to Down’s
occlusal plane (DOP), M
or 1/1
Mandibular plane (GoGn) registered at Point B
to DOP or 1/1

• The given set of values must be treated as
examples.
• Many of the dimensions an orthodontist can
think of can be easily visualized using these
templates.
• Angular measurements can be visualized as a
qualitative or a semi-quantitative measure rather
than a quantitative measure.
• Experience will prove that many popular
analyses can be easily duplicated.

Proportionate Template
• The proportionate template is designed for use
on adults and is used mainly in treatment
planning associated with orthognathic surgery.
• Angular measurements rather than linear
measurements are used when comparing
individuals to “normal” and individuals of
different sizes.
• Linear measurements are mainly used when the
distances 'measured are minimal and can be
conveniently measured in millimeters

• A practical and convenient method of
identifying dental and skeletal disharmonies is
direct visual comparison.


Philosophy of the Template
• The proportionate template is based on the principle of
the visual comparison of lateral cephalometric tracings
with average normal tracings.
• It may be argued that a single template cannot be used
for all individuals because of variations in body height.
• But since body (or craniofacial) proportions of all
individuals should be similar regardless of height, only
templates of different sizes would be needed for
comparison.

• To compare lateral head film tracings of persons
with craniofacial skeletal dysplasia, a template
having average skeletal proportions was
developed from the data of Broadbent and
coworkers. These data were based on the
recordings of 5,000 individuals.


• To accommodate variations in skull size, four
templates were designed. The average template
was developed by averaging geometrically the
dimensions of the sample. The large template
was intended for larger than average persons,
and the small template for persons with smaller
than average craniums and jaws. In addition, an
extra-large template was designed for much
larger than average individuals.

• There were no separate templates made for men
and women as the spatial arrangement of the
skeletal components and their relation did alter
much.
• Difference:
– Larger frontal sinuses, supraorbital ridges and noses
– Prominent chin


Cephalometric Landmarks and Planes


Method of Application
• Select the appropriate template
• Method 1
– The mid S-J point of the template is superimposed
on that of the tracing, and the template is adjusted to
the point where the Ba-N lines on the template and
the tracing are parallel to each other.


• Method 2
– Points basion and nasion in the correctly selected
template will approximately overlie the same points
on the tracings. When superimposing Ba-N, both S-J
lines will be parallel to each other. The template is
then raised or lowered, keeping the Ba-N lines
parallel until both of the mid S-J points are
equidistant from the Ba-N line.


• Method 3
– Any other plane or points for reference must be used and
adjusted and moved around to identify the offending agent.

• Interpretation
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The relative spatial position of maxilla and mandible
Length of maxilla.
Length of mandible.
Vertical dimensions
Incisor inclination.
Cant of mandibular plane.

Summary
• The expanding scope of temporary orthodontic
treatment would seem to demand meaningful
diagnostic procedures. Template analysis
provides a simple and flexible alternative to the
conventional methods.
• It demands the active participation of the
clinician. It forms more of a “decision tree”
when compared to the conventional numerical
analyses.

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Template analysis /certified fixed orthodontic courses by Indian dental academy

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