Reprinted from AMERICAN JOURNAL
OF PHYSICAL ANTHROPOLOGY
Vol. 40, No. 1, January 1974 © The Wistar Institute Press 1974 TECHNICAL REPORT
Automated Processing of Cephalograms, Facial
Photographs and Dental Casts
An automated methodology has been developed for analyzing cephalograms, facial
photographs, and dental models. A digitizer is used as an 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 by a coil located beneath the digitizing table surface. The speed, resolution (? 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, it 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 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, it 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.
Fig. 5 Fig. 6
Berkowitz, S. 1971 Stereophotogrammetric analysis of casts of normal and abnormal palates. Am. J. Orthodont.,60: 1 - 18.
Miner, 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. Dukman, M. L. Riolo and R. E. Moyers 1971 Graphic computerizationofcephalometric data. Jour. Dental Research, 50: 1363.
Savara, B. S. 1965 A method for measuring facial bone growth in 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 ret port on the
analysis of cranio-facial growth. New Zealand Dental Jour., 63: 31 - 38.