STEREO X-RAY PHOTOGRAMMETRY APPLIED TO 
ORTHODONTIC MEASUREMENTS 
By 
Francis H. Moffitt 
Professor of Civil Eng 
o 
University of California, Berkeley 
Invited Paper Prepared for Working Group II, Commission V o£ the 12th Congress of 
the International Society for Photogrammetry, Ottawa, Canada. July 1972 
Introduction 
There have been many and varied approaches to obtaining three-dimensional 
information from x-ray films of a subject's head 25, (2), (3), (4), (3). Some 
of these techniques have been moderately successful. However, they have suf- 
fered from being either too cumbersome, too complex, or too time-consuming from 
the standpoint of routine clinical evaluation of treatment of the subject patient. 
The development to be discussed here has been prompted by the need for a 
relatively simple, straightforward, rapid, and reliable method for.evaluating 
relapse tendancies which have been observed to follow orthodontic treatment, in 
particular, the surgical correction of mal-relationships of the jaws and teeth. 
Previous dento-cranial measurements have been made using independently-obtained 
skull x-ray films, plaster casts of the teeth and jaws, and facial photographs. 
The main difficulty has been a lack of a satisfactory method for the precise 
quantitative integration of information from these three sources. And yet, 
evidence is very strong that none of the three sources, taken by itself, con- 
tains information accounting for a sufficient portion of the total system vari- 
ance to be clinically predictive. 
An Overview of the System 
The photogrammetric portion of the system used for the clinical study of 
orthodontic treatment can be viewed as three different stereo sub-systems. The 
first of the three, which is of the greatest interest, is the configuration of 
x-ray emitters used to take two stereoscopic pairs of head films of the patient. 
These stereo-pairs of x-ray films register artificial radiopaque landmarks some 
of which have been placed in the patient's mouth, and some of which have been 
placed on the surface of his face prior to the x-ray exposures. These land- 
marks will be discussed in detail. 
The second sub-system is at present a pair of 35-mm cameras mounted so as 
to make the two focal planes coplaner. This stereo camera arrangement is used 
to obtain a pair of stereo photographs of plaster casts of the patient's upper 
and lower teeth and gums which have been prepared by the orthodontist. The 
plaster casts contain acrylic inserts each.of which cóntain three or more radi- 
opaque points. These points, which appear in the stereo pair taken with the 
35-mm. stereo-camera, are the artificial landmarks which have been placed in 
the patient's mouth prior to exposing the x-ray head films. This set of photo- 
graphs can then be related to.the x-ray head films by means of the images of 
the common landmarks.