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At least 397 records · Page 22Linked to original sources
PubMed1990

Masticatory efficiency determined with direct measurement of food particles masticated by subjects with natural dentitions.

The size of soya particles masticated by 10 subjects with natural teeth were directly measured by means of a graphic digitizer and a computer at a varied number of masticatory strokes. The statistical parameters were calculated by computer and a test of normality was used for estimating the frequency distribution. It was found that the frequency distribution of chewed particle size was a positive skew state; its shape was asymmetric, wide, and flat. After natural logarithm transformation the distribution tended toward normal. Increasing the number of masticatory strokes decreased the mean and median of the distribution (p less than 0.01) and did not change the coefficient of variation, skewness, and kurtosis (p greater than 0.05). The results show that the distribution of chewed particle size tends toward a normal logarithmic distribution; the distribution shapes at various numbers of strokes are the same; these parameters can be used for determining masticatory efficiency. Direct measurement of the particles is more convenient and reliable than dyeing particles or fractionating the particles in a sieve system.

Adult↗
PubMed1991

Stereophotogrammetric analysis of abutment tooth movement in distal-extension removable partial dentures with intracoronal attachments and clasps.

This study applied the three-dimensional measurement technique of stereophotogrammetry to measure abutment tooth movement under occlusal loading as a function of intracoronal attachment and clasp design. Six distal-extension removable partial denture designs were studied: (1) RPI-mesial occlusal rest, proximal plate, buccal I-bar; (2) cast circumferential clasp; (3) P.D. locking semiprecision attachment; (4) Thompson dowel nonlocking semiprecision attachment; (5) McCollum precision attachment; and (6) Stern G/L precision attachment. The movement in microns was determined by computer analysis. The Thompson dowel semiprecision attachment generated the most abutment movement in a gingival direction. The clasp-retained designs generally had less total movement than the attachment designs. Clasps and attachments for the abutment teeth adjacent to the distal-extension bases generally moved more than the abutment teeth.

Analysis of Variance↗
PubMed1994

An in vitro investigation into the wear effects of unglazed, glazed, and polished porcelain on human enamel.

Abrasive wear tests were performed on unglazed, glazed, and polished porcelain stud specimens using human enamel as the opposing plate specimens. The wear tests were carried out on a wear machine that was specifically designed to simulate the masticatory cycle. The amount of enamel wear produced by both glazed and unglazed porcelain was similar; however, that produced by polished porcelain was substantially less. Investigation of the glazed porcelain surface showed that the glaze was removed in less than 2 hours of wear on the machine.

Dental Enamel↗
PubMed1984

High-voltage electron microscopy of capillary endothelial vesicles.

Conventional electron microscopy of thin sections through capillary walls is inadequate to discern the relationships between endothelial vesicles and their association with the cell surface. High-voltage electron microscopy of thick sections through diaphragm muscle capillaries has been employed to visualize the three-dimensional structure of the vesicular system. Stereopairs of thick sections provide for direct three-dimensional observations of samples several vesicle diameters deep. A variety of simple and compound vesicular forms are present but not all are conjoined or maintain connections with the endothelial cell surface. This contributes to the concept of a dynamic interaction between free and attached vesicular structures where fission and fusion events compartmentalize and reconnect repeatedly. Such interactions would provide for a discontinuous pathway across the capillary wall but with a higher degree of complexity than a simple shuttling mechanism.

Animals↗
PubMed1988

Changes in mandibular position during treatment with disk-repositioning onlays: a roentgen stereophotogrammetric study.

Seven patients with temporomandibular joint disk displacement were treated with disk-repositioning onlays, and changes in the mandibular position were studied by means of roentgen stereophotogrammetry. A wide range of changes in mandibular position was seen at cementation of the onlays and during the observation period. On an average, recapturing of the disk and cementation of the onlays lowered the mandible by 2.5 mm and protruded it by 0.5 mm. During the observation period of 7 months the mandible had a tendency to resume its original position. The relapse was 80% in the sagittal plane, 70% in the transverse plane, and 12% in the vertical plane. It was concluded that disk-repositioning onlays can be used to lower the mandible with a relatively small relapse. Changes in the horizontal plane, however, seem to be less stable.

Adolescent↗
PubMed1990

The accuracy of osteosynthesis repositioning of the mandible--a stereophotogrammetric study.

The accuracy of repositioning of wire and plate osteosyntheses is measured by means of close-up stereophotogrammetry on cadaver mandibles. An increase of the intercondylar distance, which increases by an average of about 3.3 mm after plate osteosynthesis and by about 1.9 mm after a wire suture, is characteristic for both methods of osteosynthesis. In addition, there is a tendency to displacement of the articular condyle to caudal in osteosyntheses at the base of the mandible.

Bone Plates↗
PubMedDate not supplied

Early detection of glaucomatous damage. I. Psychophysical disturbances.

In summary, automated perimetry and other psychophysical tests currently provide the most sensitive, reliable and reproducible means of clinically detecting early glaucomatous changes. Compared to optic disk and nerve fiber layer evaluation, such procedures provide a consistent, quantitative method of distinguishing between early abnormalities and normal variations.

Glaucoma↗
PubMedDate not supplied

Early detection of glaucomatous damage. II. Changes in the appearance of the optic disk.

Once we understand that an increase in the size of the optic disk cup is due to loss of optic nerve fibers combined with some physical tissue rearrangements, it is quite clear that cupping begins as soon as nerve loss begins. Methods to detect cupping are more sensitive to the earliest glaucoma damage than are present field testing methods. This conclusion is supported by large clinical studies and histological demonstration of nerve fiber loss prior to field loss in eyes with abnormal cups, asymmetric cupping, or nerve fiber layer abnormalities. While automated perimetry is likely to increase the sensitivity of detection, better test methodologies are needed to combine with the objectivity of computer-assisted machines. Disk hemorrhages, nerve fiber layer defects, and color vision abnormalities are early signs of damage, supporting the conclusion that damage is present before field loss. A number of other methods await further testing to determine their effectiveness. The idea that the disease glaucoma is defined by a certain visual field finding on the Goldmann perimeter is not valid if we define glaucoma as an eye with a history of elevated IOP and optic nerve damage. While such field loss is a convenient means of defining a particular stage of damage in glaucoma, there are clearly earlier stages of damage, whether we can always detect them or not. No patient should be told that he or she does not have glaucoma, but rather has ocular hypertension, based on a particular visual field finding. As testing and examination methods improve, so, hopefully, will our ability to determine whether damage is present. As this occurs, we will be better enabled to select most rationally those patients who will benefit from therapy. The idea that field testing is relatively insensitive to the earliest glaucoma damage might lead the skeptic to conclude that perimetry is not worth the trouble. This review has indicated that none of our present methods, ophthalmoscopic, psychophysical or otherwise, is perfect. But to omit using any of them (especially field testing) does a great disservice to the glaucoma patient. The greatest usefulness of the new automated instruments is that adequate field testing is now available in a cost-effective form to every ophthalmic office. We need to strive for better detection and follow-up of glaucoma damage to prevent needless blindness.

Color Perception Tests↗
PubMed1985

Aliasing in human foveal vision.

An improved laser interferometer allows forced choice contrast sensitivity measurements that are relatively unaffected by optical blurring in the eye. At spatial frequencies above about 60-70 c/deg, the regular bars of the interference fringe are no longer visible; observers report a pattern resembling zebra stripes centered on the line of sight. The characteristics of this pattern are consistent with the hypothesis that it is a moiré pattern resulting from aliasing by the foveal cone mosaic. Properties of this moiré pattern allow an assessment of the regularity of the foveal lattice, the spacing between cones, and the light-catching area of individual cones.

Form Perception↗
PubMed1988

Biostereometric analysis for breast cancer detection.

A measurement technique has been developed for noninvasive breast cancer detection. The process involves the use of close-range stereophotogrammetry as a data acquisition device for the determination of breast surface concavities. We report the methodology used to detect these surface depressions, the rationale for the study, and our preliminary findings.

Algorithms↗
PubMed1992

Performance of a 7-parameter DLT method for the calibration of stereophotogrammetric systems using 1-D transducers.

A method is presented for calibrating stereophotogrammetric systems which are based on 1-D cameras, i.e., able to record only one of the two coordinates relative to the projection of the target point onto the image plane of a camera. This procedure is based on the Direct Linear Transformation, DLT, introduced by Marzan and Karara. The present version (7DLT) is different from the standard 11-parameter DLT (11DLT); it avoids certain non-orthogonality problems arising in usual DLT implementations, whose correction can be obtained by modifying the basic algorithm, at the expense of its simplicity (MDLT). The accuracy assessment of the 7DLT method was carried out both by a computer simulation of a two-camera stereophotogrammetric system, and on real data from three 1-D optoelectronic cameras. The computer simulation permitted us to compare the performance of 7DLT with 11DLT and MDLT. The reconstruction accuracies of the three algorithms were quite similar. When using real 1-D data, a reconstruction accuracy of 0.66 mm RMS error was obtained (mean value for X, Y, Z coordinates) for 18 target points used as calibration control points. The extrapolation accuracy was 1.85 mm RMS for 180 target points lying outside the calibration structure.

Animals↗
PubMed1993

Stereoradiogrammetric technique for estimating alignment of the joints in the hand and wrist.

A method and apparatus for quantitative measurement of the alignment and motion of the joints of the hand in three dimensions has been developed using stereoradiogrammetric principles. Alignment in planes of flexion-extension and radial-ulnar deviation can be determined to within 2.5 degrees; rotation about the long axis of the metacarpals or phalanges is more difficult to determine, and can be measured to within 7 degrees. Stereo views subtending angles in the range of 40 degrees were found to optimize the total system accuracy.

Calibration↗
PubMed1993

Precision and accuracy of bone landmarks in characterizing hand and wrist position.

Characterization of the motion of the hand and wrist requires reference to the underlying bones which, for three-dimensional analyses, are assumed to be rigid bodies. Stereoradiogrammetric techniques involving the identification of prominent bone landmarks have been used as the standard against which surface markers used for in vivo testing have been evaluated. The precision and accuracy with which the 3D positions of bone landmarks in the hand and wrist could be determined was evaluated in a small inter-observer and inter-cadaver study and compared to the precision and accuracy with which implanted lead markers could be located. A subset of landmarks suitable for evaluating wrist and metacarpal-phalangeal joint motion was identified; the mean precision for identifying these points was better than 1.1 mm in all hand positions with a mean inter-observer accuracy of 2.3 mm. These values show that the average uncertainty in locating bone landmarks is at best roughly twice that for implanted markers.

Bone and Bones↗
PubMed1987

Changes to the lower third facial profile following mandibular sulcoplasty with free skin grafting.

The lower third facial profile changes following anterior sulcoplasty with free skin grafting and bilateral mylohyoid ridge resection have been assessed. Nineteen patients were selected and were photographed prior to and at one month, 6 months and 1 year following surgery. The patients were photographed from an anterior and lateral position using a telecentric optics system designed to overcome geometric distortion. The patients were photographed both wearing and not wearing their complete dentures. Marked facial profile changes were found following surgery. There was a flattening of the labial mental fold and an increase in the bulk and prominence of the chin. The wearing of dentures enhanced this profile change. The changes were most marked in those patients in whom a larger labial sulcus extension was attempted.

Cephalometry↗
PubMed1988

Accuracy of the oblique lateral transcranial projection, lateral tomography, and x-ray stereometry in evaluation of mandibular condyle displacement.

Condylar displacement similar to that occurring during and after mandibular ramus osteotomies was simulated in an in vitro study. Three different radiographic methods were used to measure the displacement, and the accuracy of the methods was compared. The stereometric method was more accurate than the plain radiographic methods and permitted measurements in all three dimensions. The oblique lateral transcranial projection was more accurate than lateral tomography, possibly because identification of measurement points in lateral tomography was complicated by the substantial displacement of the condyle.

Craniotomy↗
PubMed1995

A new three-dimensional treatment algorithm for complex surfaces: applications in surgery.

PURPOSE: Recent advances in computer technology enable automatic reconstruction of surface models using digitized contour lines and three-dimensional (3D) representation on a graphic terminal. This work was aimed at obtaining 3D reconstructions of facial bones to help guide oral surgery and complex dental implantology procedures. MATERIAL AND METHODS: The starting point was a computed tomographic examination. The limits of the cortical bone were automatically outlined and then digitized using a special computer program. The resulting data were then compiled for computer-aided design (CAD) purposes, and a virtual 3D model of the bone was mathematically computed. This model was next transferred to a computer program that piloted a CAD/computer-aided manufacture (CAM) machine that guided a laser stereolithography process. RESULTS: The early results of the use of 3D images, as well as solid models, for clinical and surgical purposes, indicate a high degree of reliability in morphologic diagnosis, determining the surgical procedure, and establishing the subsequent prognosis.

Algorithms↗
PubMed1991

Comparison of a novel photogrammetric technique and modified USPHS criteria to monitor the wear of restorations.

This paper describes monitoring the wear of restorations borne by partial dentures over a 12 months period using a novel photogrammetric technique and modified United States Public Health Service (USPHS) criteria. The performance of Class II restorations of Dispersalloy was compared with that of similar restorations of either KetacFil or Occlusin. The photogrammetric technique highlighted differences in performance not detected by the modified USPHS criteria. It is concluded that the photogrammetric technique should prove valuable in the in vivo assessment of the performance of restorative materials but that further refinement of the method is required particularly with regard to the orientation of replicas for sequential measurements.

Composite Resins↗