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Biomedical subjects

A G Erdman

Publications and source records attributed to A G Erdman.

10 recordsLinked to original sources
PubMed1992

6R instrumented spatial linkages for anatomical joint motion measurement--Part 2: Calibration.

The six-revolute-joint instrumented spatial linkage (6R ISL) is often the measurement system of choice for monitoring motion of anatomical joints. However, due to tolerances of the linkage parameters, the system may not be as accurate as desired. A calibration algorithm and associated calibration device have been developed to refine the initial measurements of the ISL's mechanical and electrical parameters so that the measurement of six-degree-of-freedom motion will be most accurate within the workspace of the anatomical joint. The algorithm adjusts the magnitudes of selected linkage parameters to reduce the squared differences between the six known and calculated anatomical position parameters at all the calibration positions. Weighting is permitted so as to obtain a linkage parameter set that is specialized for measuring certain anatomical position parameters. Output of the algorithm includes estimates of the measuring system accuracy. For a particular knee-motion-measuring ISL and calibration device, several interdependent design parameter relationships have been identified. These interdependent relationships are due to the configuration of the ISL and calibration device, the number of calibration positions, and the limited resolution of the devices that monitor the position of the linkage joints. It is shown that if interdependence is not eliminated, then the resulting ISL parameter set will not be accurate in measuring motion outside of the calibration positions, even though these positions are within the ISL workspace.

Algorithms↗
PubMed1992

6R instrumented spatial linkages for anatomical joint motion measurement--Part 1: Design.

Six-revolute-joint instrumented spatial linkages (6R ISLs) have become often-used devices to measure the complete six-degree-of-freedom motion of anatomical joints. Accuracy of motion measurement depends on ISL design and calibration technique. In this paper, a design process is outlined that uses computer graphics and numerical methods as aids in developing 6R ISLs that (i) physically assemble within the desired range of motion of the joint; (ii) do not collide with either the experimental apparatus or the subject joint; (iii) avoid singular linkage configurations that can cause forces to be applied to the joint; and (iv) measure selected anatomical motions most accurately. It is found that a certain subgroup of 6R linkages are suitable for accurate measurement of specific motions, and can be the basis for new ISL designs. General guidelines are developed that can assist in the generation of unique linkage designs for different anatomical joints. The design process is demonstrated in the creation of an ISL to measure knee motion.

Computer Simulation↗
PubMed1991

CAD/CAM for dental restorations--some of the curious challenges.

Computer-aided design and manufacturing for dental restorations has opened a new world of possibilities--some that appeal to engineers and clinicians and some that have created some interesting challenges. The objective of this overview is to briefly describe a system being developed by the Universities of Maryland and Minnesota which is capable of producing dental crowns. Some of the challenges and difficulties that have arisen during the development activities will be addressed. The final focus will be on some of the questions that, because of the new technology, can now be addressed and are presenting new challenges.

Computer Graphics↗
PubMed1985

Treatment-induced errors in occlusion following orthognathic surgery.

Posttreatment occlusion following orthognathic surgery is often different from that predicted in the treatment plan. Differences between intended and actual occlusion may be treatment-induced occlusal errors caused by mismatches between the centers of rotation of the mandible and of the articulated models. Discrepancies in the position of the articulator center of rotation (relative to the position of the center of rotation of the patient's mandible) influence the magnitude of occlusal errors. A computer model was developed to quantify these errors. As the center of rotation of the articulated models becomes more divergent from the patient's center of rotation, the magnitude of the occlusal errors increases. This magnitude increases most rapidly along the line that is perpendicular to the line joining the patient's center of rotation and a preselected mandibular landmark (incisor tip or molar cusp, for instance). For small changes in vertical dimension, clinically insignificant errors result, independent of the degree of mismatch between the centers of rotation. Clinical implications of these findings are discussed.

Computers↗
PubMed1985

Working condylar movement and its effects on posterior occlusal morphology.

The movement of the mesiolingual cusp of the maxillary left first molar was studied in the frontal and horizontal planes. The movement was studied while varying the top wall, rear wall, and incisal guidance on the articulator. It can be concluded that the top wall inclination may significantly influence movement of the mesisolingual cusp of the maxillary first molar during working mandibular movement, the rear wall inclination has less influence than top wall inclination on cusp movement during a working mandibular movement, and the working side condylar movement should be considered when evaluating or restoring the dentition.

Dental Articulators↗
PubMed1980

Growth contributions to class II corrections based on models of mandibular morphology.

Various morphologies of human models are modeled with various growth patterns to demonstrate the role of mandibular morphology on growth contributions to Class II corrections. Growth patterns are described by centers of mandibular rotation relative to the cranial base. Centers of rotation are used to determine several parameters of growth generated by a computer programmed to show growth effects. The direction and amount of condylar growth are held constant. With condylar growth constant, various centers of rotation of the mandible reveal that maximum Class II molar correction is present when the condyle is vertically located farthest from the molar. Of lesser importance, Class II corrections are greater when the condyle is anteroposteriorly closest to the molar.

History, 18th Century↗
PubMed1978

Mechanics, growth, and class II corrections.

Growth of the orofacial region is quantitatively described by locating the center of mandibular rotation relative to the cranial base. The center of mandibular rotation is positioned by the ratio of vertical facial growth (AFH/PFH) and the direction of condylar growth. Appliance therapy is associated with changes in the means of both of these parameters. These changes reduce or stop favorable anterior mandibular rotation and redirect the mean condylar growth vector more posteriorly. When appliance therapy is stopped, these parameters return toward their resting values. The mean direction of the condylar growth vector became even more anteriorly directed after treatment than the pretreatment mean value. These data support the hypothesis that orthodontic appliances significantly alter the facial growth pattern and when they are stopped, the growth pattern tends to rebound to or beyond the pretreatment values.

Activator Appliances↗