Sean Curry

Mandibular remodeling measured on cephalograms. 1. Osseous changes relative to superimposition on metallic implants.

We report the results of a study aimed at quantifying remodeling of mandibular surfaces in a sample of growing children who represent those usually treated by orthodontists in the mixed and early adult dentition. The sample, 31 patients with metallic implants of the Björk-type, was monitored at annual intervals between 8 1/2 and 15 1/2 years of age. (Maxillary remodeling changes for the sample have been reported earlier.) The present article reports findings concerning changes at condyle, gonion, menton, pogonion, and point B as identified on lateral cephalograms. Data are reported in the Frankfort plane frame of reference with the cephalograms from different time points superimposed on the metallic implants. Mean displacement at condyle was larger than that at any other landmark and was similar in magnitude and direction to the observations of Björk when the difference in orientation of the vertical axis in the two studies is taken into account. The mean displacement of gonion was in an upward and backward direction at an angle of approximately 45 degrees to the Frankfort plane. Mean displacements at menton and pogonion were in a downward and backward direction but were very small. Mean displacement at point B was somewhat greater than that of menton and gonion, oriented in an upward and backward direction. Individual variation for most of the parameters measured was sufficiently large to warrant the inference that caution should be used when mean values are applied to the analysis of individual cases.

Mandibular remodeling measured on cephalograms: 2.*

This study quantifies the differences in the perceived pattern of mandibular remodeling when two different methods are used to superimpose roentgenographic images of the mandible. Lateral cephalograms for a group of subjects with metallic implants of the Bjork type were superimposed twice; first on the metallic implants and then independently on mandibular anatomic structures according to a common “best fit” rule. In this article, we compare the between-superimposition differences in the perceived displacements of condyle, gonion, menton, pogonion, and Point B. Mean differences between the two superimpositional techniques were smaller than had been anticipated. For the 7-year time interval between 8.5 and 15.5 years, the largest mean differences between methods were 2.70 mm in the horizontal direction at condyle, 1.90 mm in the vertical direction at condyle, and 1.52 mm in the vertical direction at gonion. None of the other between-superimposition differences had a mean value in excess of 1 mm. The individual case variability between the two methods was, however, quite considerable, a finding that we believe has bearing on the confidence that can be placed in individual case analyses in clinical orthodontics. A preliminary attempt has been made to represent and discuss the magnitude of this problem.

Dedicated Stereophotogrammetric X-Ray System For Craniofacial Research And Treatment Planning

We have constructed and brought into use what we believe to be the first dedicated coplanar craniofacial stereometric x-ray system for clinical use. Paired Machlett Dynamax 50/58 x-ray tubes with 0.3 mm focal spots are employed. Displacement between emitters is 16 inches. The focus film distance for both emitters is 66.5 inches. The mid-sagittal plane to focus distance is 60 inches. One film of each stereo pair conforms with the standards of the Second Roentgenocephalometric Workshop and can be used to make all standard two-dimensional orthodontic and cephalometric measurements. When supplemented by data from the conjugate film, a three-dimensional coordinate map can be generated as a machine operation. Specialized complementary software has been developed to increase the reliability of landmark location both in two and in three dimensions.

Establishing Quantitative Within-Subject Confidence Limits For Clinical Stereoroentgenographs

It is now quite clear that under ideal conditions, discrete points can be located on x-ray films with standard deviations of less than 50 i. However, under routine clinical conditions, such considerations as individual variation in anatomy, movement of the subject between exposures, and variations in image quality combine to produce considerable reductions in the confidence which can be placed in quantitative assessments made from stereoroentgenographic films. This paper discusses some considerations involved in designing mathematical models in such a way as to optimize the use of imperfect data in answering specific clinical questions.

Two Persistent Technical Problems In The Realtixe Analysis Of mandibular Motion

At past meetings, we have reported progress in the development of a specialized device for monitoring the motion of the mandible in real time with minimal perturbation of normal oral function. The system incorporates two sets of light emitting diodes (LEDs). By means of separate harnesses, one set of LEDs is attached to the calvarium and the other is attached to the mandible. The three dimensional displacement of the mandibular harness relative to the skull harness is monitored with six degrees of freedom by a pair of photo diode detectors interfaced to a 80386 personal computer. The computer monitor displays changes in the spatial relationship of the lower harness with respect to the upper harness at rates of thirty to fifty times per second. The positions of defined points on the lower harness can be determined relative to the upper harness to approximately 0.2 millimeters in each dimension; the orientation of the lower harness with respect to the upper harness is reported with an accuracy of approximately 0.1 degrees around each axis. During the past year, we have conducted preliminary clinical trials of the apparatus, in the course of which we have encountered two consequential technical problems. The first involves the operation of the pointer which is used to determine the locations of a triad of anatomical landmarks in each jaw with respect to its associated harness. Although the pointer is conceptually quite straight-forward, the physical implementation of the device thus far falls short of the accuracy necessary for clinical use. We believe that part of the difficulty involves line of sight problems but there may also be algorithmic difficulties.

A technique for anatomic feature extraction and tracking on sequential digital X-ray images

Abstract The Craniofacial Research Instrumentation Laboratory at the University of California, San Francisco, has been developing systems for the acquisition and display of biostereometric data. Stereo photographs and X-ray images of the head are used to analyze growth and treatment effects during orthodontic treatment and orthognathic surgery. Recent efforts have been directed towards automating anatomic feature location and tracking on series of time-separated cranial X-rays. Two tests were performed to evaluate the potential accuracies that could be achieved in feature tracking. In both tests, a series of cranial X-rays was converted to digital images using an array camera [Charge Injection Device (CID)] connected to a real-time video digitizer module or “frame grabber” installed in a microcomputer. The first test series consisted of a single X-ray image which was translated and rotated three times. The second series of images consisted of three actual cranial X-rays of a single subject, acquired over a period of approximately two years. A number of anatomic features were manually selected on the first image of each series. The features were automatically tracked on subsequent digital images, and their locations compared to those derived from manual digitizing of the original film images.

Stereoroentgenographic System With Portable Calibration Cage For Use In Clinical Medicine

For the past five years, we have been accumulating information on the performance of a stereoroentgenographic system developed for use in clinical medicine and first reported at the NATO Symposium on the Application of Human Biostereometrics. This system represents an adaptation of normal case coplanar stereometry and involves the use of a single emitter which is displaced in a controlled fashion between exposures. The system has been used primarily for the detection of applicance loosening and settling following the placement of total hip protheses and also for the detection of pseudorthosis following lumbo-sacral fusion. One major goal has been the development of a data acquisition and analysis system suitable for general hospital use which can be operated by technicians without specialized photogrammetric training. This report will focus on system design and on the delineation of technical problems encountered during routine clinical use of the system.