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Automated processing of cephalograms facial photographs and dental casts.

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TECHNICAL REPORT
Automated Processing of Cephalograms, Facial
Photographs and Dental Casts
G. w. THOMPSON A N D F. POPOVICH
Burlington Growth Centre, Faculty of Dentistry, University of Toronto,
Toronto, Ontario, Canada
KEY WORDS
Photographs.
Automation
. Craniofacial .
Dental instruments .
ABSTRACT
A n automated methodology has been developed for analyzing
cephalograms, facial photographs, and dental models. A digitizer is used as a n
input device for converting all three forms of data into Cartesian co-ordinates.
The data are stored on computer disks for data processing.
Since its inception in 1952, the Burlington Growth Centre of the Faculty of Dentistry, University of Toronto, has collected
an extensive library of craniofacial records: more than 50,000 cephalograms,
16,000 plaster dental models, and 16,000
facial photographs. Because of the numerous linear and angular relationships that
can be investigated on a single cephalogram, photograph, or dental cast, the utilization of rulers, sliding calipers, compasses,
or protractors would have been impossible.
It was necessary to utilize electronic
equipment to facilitate the data input and
output. A Gradicon digitizer, manufactured
by Instronics Ltd., Stittsville, Ontario, Canada, and sold for $25,000.00 is used to derive the Cartesian co-ordinates of points
on cephalograms, facial photographs, and
dental casts. This made it possible to collate individual serial and cross-sectional
profiles on individuals for investigations of
craniofacial growth patterns, interrelationships, and growth prediction. The results
are printed out or diagrammed on the IBM
1130 computer.
Digital output units have been used by
several investigators (Savara, '65; Walker,
'67; Miller, Hunter, and Moyers, '70; and
Miller, Dijkman, Riolo, and Moyers, '71)
for making measurements from cephalograms or cephalometric tracings. The Gradicon digitizer (fig. 1) used at the Burlington Growth Centre converts analog
information internally to a digital form and
is punched out as x and y co-ordinates on
a key punch. The cursor on the top of the
digitizing table senses a signal generated
AM. J. PHYS. ANTHROP..40. 97-104.
by a coil located beneath the digitizing
table surface. The speed, resolution ( 2
0.01 mm.), and accuracy (0.1 mm.) are
more than adequate for this type of data.
The Cartesian co-ordinates of 50 defined
anatomical landmarks and a further 318
contour points are digitized for each lateral cephalometric tracing (fig. 1 insert).
This sufficiently outlines the height and
length of the facial profile. On the other
hand, the width measurements are derived
from 40 anatomical landmarks and 246
contour points on each postero-anterior or
frontal x-ray. For any one patient at a given
age, the two sets of two-dimensional coordinates can be combined to detail the
three-dimensional construct of the face.
The facial photographs are digitized in a
similar manner by projecting film-strips
onto the digitizing table from a platform
above the table (fig. 2).
Different types of equipment such as the
modified comparator (Savara and Sanin,
'69), the microscopic Optocom unit (van
der Linden, Boersma, Zelders, Peters, and
Raaben, '72) and stereophotogrammetry
technique (Berkowitz, '71) have been used
for measuring dental casts. In co-operation
with the manufacturers, the authors have
developed a dental pencil to utilize the
aforementioned capabilities of the Gradicon digitizer. In this way, i t was possible
to establish a data processing system that
would handle not only the cephalograms
and photographs, but also the dental casts.
For dental casts, the digitizing apparatus (fig. 3) consists of the dental-cast
holder (left-hand side of figure) and the
97
98
G . W. THOMPSON AND F. POPOVICH
dental-cast digitizing pencil (right-hand
side of figure). The dental-cast holder has
upper and lower holding plates and one reference plate. The upper and lower casts
are mounted on their respective holding
plates by double-sized adhesive tape with
the occlusal plane parallel to the digitizing table or the reference plate. The holding plates are flexible in all directions so
that the casts can be easily mounted as
long as they have a flat exterior surface.
The maxillary and mandibular casts are
digitized separately relative to a common
point on the reference plate. The mandibular cast is digitized first and then the
maxillary cast is inverted and digitized.
Since the stylus of the digitizing pencil
is at the end of a plunger-like device, i t is
possible to make the mesio-distal and bucco-lingual measurements at different levels or in different planes. That is, it is
possible to locate the antero-posterior or
mesio-distal position of cusps, points, surfaces, etc. The centre of the stylus has
been machined to the centre of the electromagnetic core of the dental pencil platform. Therefore, the points that are being
located by the stylus are digitized in the
base of the dental pencil. The relative
positions of the co-ordinates of the points
in the base of the dental pencil are exactly
the same as those on the teeth.
The dental-cast holder can be positioned
flat on the digitizing table; that is, 90 degrees to its position in figure 3. In this
mode, the height as well as the mesio-distal
width measurements can be made relative
to the origin on the reference plate. A
three-dimensional construct of the dentition can be made by combining the two sets
of two-dimension co-ordinates.
Computer data files have been established to store and access the Burlington
Growth Centre data. The punch-card data
from the digitizer are fed into the IBM
1130 computer and stored on IBM 2315
disks. The data can be manipulated by
programs on the IBM 1130 or on the University of Toronto’s IBM 370-165 computer
via a synchronous communication adapter
and telephone lines to the IBM 1130. Data
for a particular case can be found by typing
in the identification number after the appropriate disk has been mounted. The data
for one or more cases can be obtained as a
printout on the typewriter or line-printer,
or as graphs or diagrams by the plotter.
For example, specific records of one or
more cases can be selected and plotted in
a desired format. The operator selects the
case and superimposition plane by entering
the numbers on the keyboard (fig. 4) and
the plotter draws the selected records of the
case with a superimposition on the sellanasion line with sella registered (fig. 5).
The entries are made again on the keyboard but this time not on the cranial base
but with superimposition on the mandibular plane with the common reference
point at the gonial angle (fig. 6).
The resolution and accuracy of the digitizer is comparable to the equipment used
by other investigators. However, the versatility of the digitizing unit makes it possible to input co-ordinate data from cephalograms, facial photographs, and dental
casts rather than using two or more separate input devices as has previously been
the case. Since all of these operations can
be made on the one machine, the data organization and subsequent manipulations
by computer are greatly facilitated.
LITERATURE CITED
Berkowitz, S. 1971 Stereophotogrammetric analysis of casts of normal and abnormal palates.
Am. J. Orthodont., 60: 1-18.
Miller, R. L., W. S. Hunter and R. E. Moyers 1970
Computer storage and retrieval system for twodimensional outlines. Jour. Dental Research,
49: 1176.
Miller, R. L., D. J. Dijkman, M. L. Riolo and R. E.
Moyers 1971 Graphic computerization of cephalometric data. Jour. Dental Research, 50: 1363.
Savara, B. S. 1965 A method for measuring facial
bone growth i n three dimensions. Human Biology, 37: 245-255.
Savara, B. S., and C. Sanin 1969 A new data
acquisition method for measuring dentitions and
tests for accuracy. Am. J. Phys. Anthrop., 30:
315-318.
van der Linden, F. P. G. M., H. Boersma, T. Zelders, K. A. Peters and J. H. Raaben 1972 Threedimensional analysis of dental casts by means
of the optocom. Jour. Dental Research, 51 : 1100.
Walker, G. F. 1967 Summary of a research report on the analysis of cranio-facial growth.
New Zealand Dental Jour., 63: 31-38.
PLATES
PLATE 1
EXPLANATION OF FIGURES
100
1
Digitizing table and console. Insert: cephalometric tracing.
2
Film projected on digitizing table.
3
Dental-cast holder and digitizing pencil.
AUTOMATED CRANIOFACIAL MEASUREMENTS
G. W. Thompson and F. Popovich
PLATE 1
PLATE 2
EXPLANATION
102
OF FIGURES
4
Craniofacial diagrams by computer.
5
Serial superimposition on anterior cranial base.
6
Serial superimposition on mandibular plane.
AUTOMATED CRANIOFACIAL MEASUREMENTS
G . W. Thompson and F. Popovich
PLATE 2
5
103
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cast, facial, dental, automaten, cephalograms, processing, photograph
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