Determining locations of intracerebral lesions for proton radiotherapy.

Using an external view of the head, the ability to direct a proton radiotherapy beam at an intracerebral lesion is described, using a biostereometric (BSM) technique. The positions of markers, recognizable on computed tomography (CT) or magnetic resonance (MR) images, at known locations on the skin of a patient's head are related to the site of the lesion seen on the images. The markers' positions are determined by a BSM device, incorporating six video cameras coupled to a computer. A transformation from a coordinate system, defined by the CT or MR images, to another coordinate system, that of the BSM device, allows the proton beam to be directed towards the lesion. Markers used in this work were solid steel spheres for CT and plastic spheres containing oil for MR images.

Analysis of motion of the head.

This study was undertaken to determine the geometric form of the surface on which a fixed point on the head moves as a result of neck motion. Motion of a retroreflective marker on the glabella of six normal subjects was stereoscopically recorded by two video cameras, during a variety of neck motions, performed on command. Near real-time computer analysis in three dimensions of the video images showed the marker moved on a surface that very closely approximated an elliptical paraboloid (with tendency to a hemisphere), after extraneous shoulder motion had been eliminated. Parameters defining the elliptical paraboloids were obtained. Using a reflex microscope, the shape of the articular facets on skull base and superior facets of C1 and C2 of 6 normal subjects were examined. The shapes of all these facets were calculated and also found to be elliptical paraboloids.

Absence of association between a preferred chewing side and its area of functional occlusal contact in the human dentition.

Preference for a particular chewing side may be influenced by several factors, one of which could be the functional contact area on each side of the dentition. In this study, interocclusal wax records were made for each of the 30 subjects. A digital image of the transilluminated wax record was analysed to group 'grey' values into categories of wax thickness. The total area for tight and intermediate tooth contacts was calculated for both the left- and right-hand sides of each subject. The chewing-side preference was recorded. No correlation was found between the area of occlusal contact on one side and the preference for chewing on that side. Occlusal contact area does not appear to be a determinant of chewing-side preference.

Dimensions of the temporal glenoid fossa and tooth wear in prehistoric human skeletons.

Both the mandibular condyle and the glenoid fossa remodel in response to changes in the dentition during life, although the precise relationship between teeth and joint is not clear. This study was undertaken to ascertain changes, if any, occurring in the glenoid fossae in skeletons with much tooth wear. In a collection of skulls from an excavation site on the South African coast, occlusal wear was measured using the scale devised by Molnar. The dimensions of the glenoid fossae were measured using a reflex microscope. Profiles of the glenoid fossa at right angles to a line through its medial and lateral poles provided estimates of the slope of the articular eminence in three places: centrally, and midway between this slope and each of the poles. The mediolateral profile gave an estimate of the height and gabling of the fossa. Central and lateral slope angles showed weak correlation with molar wear, and the medial but not the lateral angel was significantly different from the central. The fossa appears to remodel in response to patterns of forces generated during function, but compared to the condyle, is not as strongly influenced. This may be accounted for if the relative load-bearing areas of the condyle and fossa are considered.

An indirect in vivo method for quantification of wear of denture teeth.

A method using a reflex microscope to undertake direct and highly precise three-dimensional measurements of denture casts for the purpose of mapping and determining the volumetric loss of material over a period of time has been developed. The wear that occurred in tooth 46 after clinical use for one year was measured and found to be 7.2 mm3. This technique has proved to be an accurate and objective quantification of what has previously often been a subjective impression.

Novel proprioceptive action in stepping down.

A hypothesis is offered which extends the concept of proprioception to use information necessarily obtained during the first part of a complex motion (stepping down) to facilitate the second part. It is suggested that, when the leading foot of a normal person stepping down arrives at its destination, relevant proprioceptive information is used by the following foot in its descent, to render its movement more efficient. Analogy to another effort-minimizing proprioceptive mechanism and a possible mechanical manifestation of the hypothesis are given.

A stereo-photogrammetric method to measure the facial dysmorphology of children in the diagnosis of fetal alcohol syndrome.

In diagnosing a child with fetal alcohol syndrome (FAS), anthropometric measurements of the face are conventionally performed by highly trained dysmorphologists using a hand-held ruler. This renders the screening of large populations of children for the facial features characteristic of FAS very time-consuming and costly. This study proposes a new, cost-effective, and non-intrusive method to measure in three dimensions the facial dysmorphology of children using stereo-photogrammetry. The face of each child is photographed in a control frame simultaneously by a pair of high-resolution digital cameras mounted 1.04 m from the child and 0.26 m apart. Software has been developed to calibrate the images and to compute the three-dimensional object-space coordinates of any point on the face from a measurement of the point on each of the images. The palpebral fissure lengths, inner canthal-, and interpupillary distances of 44 subjects were measured in this manner independently by two investigators and compared with measurements obtained by clinical specialists in the conventional manner. There was found to be no statistically significant difference between palpebral fissure lengths determined using the two techniques (paired Student's t-test p-values are 0.29 and 0.18, respectively). It has also been demonstrated that facial measurements can be performed with greater consistency from a pair of stereo photographs than direct measurements from live subjects.

The effects of arterial interruption on bone growth in a rat model.

A controlled study was undertaken to examine the effects of temporary arterial interruption on bone growth in a laboratory rat model. Under general anaesthesia, the right external iliac artery (EIA) was exposed in each of 80 male rats weighing 110-120 g. Twenty of the rats served as sham controls while three groups of 20 rats each underwent ligation of the artery for 6, 24 and 48 hours respectively. All rats underwent measurement of right and left femoral and tibial length 12 weeks after artery ligation. Measurements were performed in vivo using three-dimensional stereoscopic analysis, the method of which is described. Results revealed that EIA ligation for 6 hours had no effect on bone growth but that ischaemia for 24 hours and 48 hours produced leg length discrepancies equalling 3.1% and 3.6% respectively. We conclude that a time-dependent relationship may exist between ischaemia and compromised bone growth in a developing animal.

Tooth wear measurements using a reflex microscope.

The resistance to wear of composite resins is an important feature of their suitability for use as posterior restorative materials. The in vivo clinical evaluation of new materials requires an accurate and reliable method of assessing tooth wear. The purpose of this study was too investigate the possibility of using a new stereometric measuring instrument for this purpose. Tooth wear was experimentally produced on a lead cast. The volume and average depth lost was measured using a reflex microscope. A gravimetric method of wear measurement was used as a control. When the results of both methods were compared it was found that the mean difference in depth of wear measured between the two methods was 10 microns. The reflex microscope appears to be ideally suited to making objective comparisons between the wear characteristics of composite resins.

A photogrammetric method for monitoring changes in the residual alveolar ridge form.

Resorption of the residual alveolar ridge calls for regular attention to the fitting surface of a denture. In the case of distal extension partial dentures, changes which occur in less than a year may require attention. These changes are apparent, though difficult to measure using radiographic techniques. Stereophotogrammetry is a means of recording and measuring contours of land masses. A short focus non-metric camera was used in this study to produce stereoscopic paired pictures of four casts of the same partial dentition. Additional casts were made 2 and 12 months after a partial denture had been made. A stereophotogrammetric plotting instrument was used to map the alveolar ridge area of each cast. A prescribed area for each map was traced out and the volume above a reference height was calculated. The percentage error between the four columns for the pre-treatment casts was +/- 2%. A 10% loss of ridge volume was observed after wearing a partial denture for 2 months. The same area observed 12 months later revealed an 18% volume reduction. Short range stereophotogrammetry may be applied to study changes in alveolar ridge morphology which may result from wearing a partial denture.

Accuracy of a replication technique for biostereometric evaluation of clinical tooth wear.

The accuracy of a replication system for biostereometric analysis of denture tooth wear was examined. The differences observed were less than 0.32 per cent which serves to illustrate the degree of accuracy of this technique.

Designing a transmandibular implant with the aid of biostereometric analysis.

A biostereometric survey of severely resorbed dry mandibles was used to determine whether it was possible to design a transmandibular implant that could be used for the majority of clinical situations. Computerized profiles of the relevant mandibular areas were generated and superimposed to examine the feasibility of a universal shape. It would appear that the crestal shape of the mandible between the mental foramina is on the circumference of a circle and that the surface of the inferior border is so variable that a flat surface would have to be used for a transmandibular implant. A design of a transmandibular implant is proposed on the basis of the common anatomic features of the mandible.

The relationship between clinical denture tooth abrasion and morphologic features of the mandible.

Biostereometric evaluation of denture tooth wear in 25 subjects was used to determine whether there was a relationship between the gonial angle, mandibular length, Frankfort-mandibular angle, and abrasion of denture teeth. The results of this study indicated no correlation could be demonstrated between any of the factors.

Biostereometric quantification of clinical denture tooth wear.

In this study the wear of mandibular acrylic resin teeth opposed by porcelain maxillary teeth arranged in a lingualized occlusal scheme over a period of 3 years was measured. Six edentulous subjects received complete dentures as above and with three baseline markers of amalgam. At yearly intervals casts were made of the mandibular occlusal surfaces, including markers, and plotted by stereophotogrammetry. Volumetric loss of material was quantifiable. Ranges of 0.62-3.33 mm3/mm2 on the left side and 0.71-1.64 mm3/mm2 on the right were recorded. Friedman two-way ANOVA test indicated significant wear on teeth 35, 36, 45 and 46 but not on 34 and 44. A one-sided chewer displayed greater wear on the contralateral side, a finding difficult to explain.

Postural adaptations to workbench modifications in standing workers.

Surveys have shown that many workers operate under conditions that require constrained standing. The aim of this study was to investigate postural adaptations in constrained standing to facilitate the development of design guidelines for standing workspaces. Standing postures were observed in six different workspaces that were designed using combinations of task distance (which was either constrained or unconstrained) and foot position (which was constrained, unconstrained or employed a footrest). Subjects at work were recorded stereophotogrammetrically and postural variables were obtained in three dimensions. Postural adaptation to increased task distance was found to be characterized by increased trunk flexion and increased hip flexion while adaptation to close work was found to be characterized by increased neck flexion and increased thoracic kyphosis. Constrained foot position resulted in increased hip flexion accompanied by increased plantar flexion. Although use of the footrest resulted in some reduced lumbar lordosis, it increased trunk flexion and was not associated with significantly less discomfort than any of the other workspaces.