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At least 91 records · Page 5Linked to original sources
PubMed1979

A simple model for anatomic bone scanning studies.

A simple anatomic model for studying the scintigraphic appearance of various skeletal structures is described. The technique makes use of the fact that technitium pyrophosphate uptake in bone occurs by chemisorption to the surface of crystals in the bone matrix. By soaking clean bones in solutions of technetium pyrophosphate they can be rendered radioactive and subsequently studied by various imaging techniques.

Bone and Bones↗
PubMed1992

A new oral surgery teaching model.

An anatomical model for teaching the practical aspects of routine oral surgery in a clinical or laboratory environment, is described. Replaceable sections allow the model to be rapidly re-used so that successive students may practise procedures such as incisions, flap reflection, bone removal, tooth removal, apicectomy and suturing. Keeping the cost per procedure to a minimum was considered to be of fundamental importance and this has been achieved through the use of 'factory produced' replacement parts.

Equipment Design↗
PubMed2002

Jumping in frogs: assessing the design of the skeletal system by anatomically realistic modeling and forward dynamic simulation.

Comparative musculoskeletal modeling represents a tool to understand better how motor system parameters are fine-tuned for specific behaviors. Frog jumping is a behavior in which the physical properties of the body and musculotendon actuators may have evolved specifically to extend the limits of performance. Little is known about how the joints of the frog contribute to and limit jumping performance. To address these issues, we developed a skeletal model of the frog Rana pipiens that contained realistic bones, joints and body-segment properties. We performed forward dynamic simulations of jumping to determine the minimal number of joint degrees of freedom required to produce maximal-distance jumps and to produce jumps of varied take-off angles. The forward dynamics of the models was driven with joint torque patterns determined from inverse dynamic analysis of jumping in experimental frogs. When the joints were constrained to rotate in the extension-flexion plane, the simulations produced short jumps with a fixed angle of take-off. We found that, to produce maximal-distance jumping, the skeletal system of the frog must minimally include a gimbal joint at the hip (three rotational degrees of freedom), a universal Hooke's joint at the knee (two rotational degrees of freedom) and pin joints at the ankle, tarsometatarsal, metatarsophalangeal and iliosacral joints (one rotational degree of freedom). One of the knee degrees of freedom represented a unique kinematic mechanism (internal rotation about the long axis of the tibiofibula) and played a crucial role in bringing the feet under the body so that maximal jump distances could be attained. Finally, the out-of-plane degrees of freedom were found to be essential to enable the frog to alter the angle of take-off and thereby permit flexible neuromotor control. The results of this study form a foundation upon which additional model subsystems (e.g. musculotendon and neural) can be added to test the integrative action of the neuromusculoskeletal system during frog jumping.

Animals↗
PubMed1999

Conceptualization of anatomical spatial entities in the Digital Anatomist Foundational Model.

Anatomical spatial concepts are indispensable in educational and clinical discourse, yet a system for representing these concepts has not been proposed. Guided by explicit principles and definitions of the Digital Anatomist Foundational Model, we developed an ontology of spaces, surfaces, lines and points that are associated with anatomical structures. Ontologies for Anatomical Structure and Anatomical Spatial Entity were instantiated for the thorax, abdomen, pelvis and perineum. Representing the concepts in--part of--hierarchies as well, provided formative evaluation of the classification. We invite empirical evaluation of the Foundational Model through its use for educational and clinical applications.

Anatomy↗
PubMed1989

Quantitation of human shoulder anatomy for prosthetic arm control--I. Surface modelling.

Anatomical data and models for the human shoulder musculo-skeletal system are developed with the intent of quantifying physiological subcomponents of a model-based multi-axis prosthetic limb control scheme which has heretofore been implemented empirically. Part I presents the controller formulation, the surface descriptions of the muscles (and bones), and the centroidal trajectory data of the muscles. The data partially quantify the muscle modelling components of the controller, and set the stage for the analysis of the force-to-moment anatomical conversion factors of Part II.

Arm↗
PubMed2001

A framework for predictive modeling of anatomical deformations.

A framework for modeling and predicting anatomical deformations is presented, and tested on simulated images. Although a variety of deformations can be modeled in this framework, emphasis is placed on surgical planning, and particularly on modeling and predicting changes of anatomy between preoperative and intraoperative positions, as well as on deformations induced by tumor growth. Two methods are examined. The first is purely shape-based and utilizes the principal modes of co-variation between anatomy and deformation in order to statistically represent deformability. When a patient's anatomy is available, it is used in conjunction with the statistical model to predict the way in which the anatomy will/can deform. The second method is related, and it uses the statistical model in conjunction with a biomechanical model of anatomical deformation. It examines the principal modes of co-variation between shape and forces, with the latter driving the biomechanical model, and thus predicting deformation. Results are shown on simulated images, demonstrating that systematic deformations, such as those resulting from change in position or from tumor growth, can be estimated very well using these models. Estimation accuracy will depend on the application, and particularly on how systematic a deformation of interest is.

Biomechanical Phenomena↗
PubMed2001

Stress distribution around maxillary implants in anatomic photoelastic models of varying geometry. Part I.

STATEMENT OF PROBLEM: It is unclear which implant inclination and position are most favorable in relation to the supporting anatomy and loading direction in the maxilla. PURPOSE: This study was designed to examine stress distribution around implants in a 2-dimensional photoelastic anatomic model. MATERIAL AND METHODS: Two 2-dimensional photoelastic models were prepared with opposing 8-degree cylinder metal implant and molar teeth analogues. A frontal anatomic sectional plate model based on a CT section at the first molar was symmetrically loaded through its long axis. A midfacial rectangular model based on the same section was loaded in a different direction with varying supporting geometries. RESULTS: Stress distribution around the maxillary implant was highest in the buccal concavity at the apical buccal third and in the lingual concavity on intercuspal loading. No stress concentration occurred at the implant apex under the sinus for axial and nonaxial loading in both anatomic model geometries. On lateral loading, stress concentration was observed at the buccal concavity and at the implant neck. In the midfacial block model, principal stresses were concentrated at the maxillary implant neck on nonaxial loading and at the apex on axial loading. CONCLUSION: This 2-dimensional skull model showed different patterns of stress distribution among the maxillary implant, mandibular implant, and teeth. The highest principal stress concentration was seen at the buccal concavity of the maxillary implant; this may play a role in osseointegration with highly angled implants in the posterior maxilla. Differences in stress distribution between anatomic and nonanatomic models showed how the supporting geometry (for example, sinus/nasal anatomy), boundary conditions, and loading direction influence stress distribution.

Birefringence↗
PubMed2001

Stress distribution around maxillary implants in anatomic photoelastic models of varying geometry. Part II.

STATEMENT OF PROBLEM: Insufficient buccal bone volume can be a significant problem when loading dental implants in the maxilla. Increased potential for buccal fenestration and dehiscence can result in an exposed implant surface, mucosal irritation, decreased support, and potential implant failure. PURPOSE: The objective of this study was to model the stress distribution around maxillary implants by comparing simulated occlusal loading of maxillary implants in a 2-dimensional photoelastic anatomic model and a dry skull model. MATERIAL AND METHODS: Two model systems were used. First, a 2-dimensional photoelastic anatomic frontal skull sectional model was prepared in the first molar region. Left and right maxillary metal cylinder implant analogues inclined at 0 and 25 degrees to the sagittal plane were loaded in simulated intercuspation. Second, a dry skull lined with a photoelastic coating on the buccal aspect over an embedded cylinder implant was prepared in the first molar region. Principal stress concentration was photographed on axial and nonaxial implant loading. RESULTS: On simulated intercuspal loading, maximum stress concentration occurred at the buccal concavity in both the 2-dimensional anatomic photoelastic and skull models. There was no stress concentration at the apices of the maxillary implants in the 2-dimensional model. On lateral loading of the skull model, stress was distributed along the entire buccal aspect of bone adjacent to the implant, with a higher concentration at the buccal concavity. CONCLUSION: Preservation of buccal supporting bone volume is desirable to obtain a physiological modeling response and to enhance the facial plate. Insufficient bone volume may result in buccal fenestration or dehiscence, which can precipitate mucosal irritation, decreased support, and potential implant failure.

Birefringence↗
PubMed1995

Cells and circuits contributing to functional properties in area V1 of macaque monkey cerebral cortex: bases for neuroanatomically realistic models.

Anatomical and physiological data obtained from investigations of area V1 of the macaque monkey visual cerebral cortex have been used in 3 models outlining possible circuitry underlying functional properties of the region. The 3 models use, respectively, a fully implemented computer neural network, a mathematical formulation of interactions in a descriptive model of anatomical circuitry and a purely descriptive account of circuitry that could underlie particular functions. The 1st 2 models involve as part of their design an interpolation principle where afferents of opposite physiological property establish spatially offset but adjacent terminal fields and the postsynaptic neurons' dendrites have a continuum of different degrees of overlap into the 2 afferent pools and therefore different synaptic weights from the 2 afferents; this creates a functional and spatial gradient of response properties in the postsynaptic neurons between the properties of the different sets of afferents. The 3rd model examines lateral excitatory and inhibitory interactions in such gradients. Model 1 addresses the transformation of distinct thalamic axon properties to a gradient of response properties in postsynaptic spiny stellate neurons in layer 4C of V1. Model 2 proposes circuitry producing orientation specificity in V1 that begins by generating specificity of responses to orthogonal orientations; this is achieved by means of orthogonally oriented lateral axon projections made by the layer 4C spiny stellate neurons; this is followed by generation of a full cycle of orientation specificities by means of pyramidal neuron dendritic overlap across spatially separated fields of spiny stellate neuron axons responding preferentially to orthogonal orientations. Model 3 describes a circuitry to explain inhibitory and facilitatory interactions observed to occur in single unit responses when the classical receptive field is stimulated concurrently with the surround region. All the proposed models make predictions that can be tested by further anatomical and physiological experiments in the real visual cortex.

Animals↗
PubMed1985

Photoelastic effects of maxillary protraction on the craniofacial complex.

The conventional treatment of anterior crossbites has been the application of orthopedic force to the mandible to redirect its growth. However, in the patient with an underdeveloped maxilla, this treatment alone is not sufficient. Therefore, the purpose of this investigation was to study the orthopedic effects of maxillary protraction appliances in the treatment of anterior crossbites. A three-dimensional anatomic model of a human skull was fabricated with birefringent materials for photoelastic analysis. Three maxillary protraction appliances that utilized different anchorage units were used. The protraction forces placed on these appliances were parallel to the occlusal plane, a downward vector 20 degrees to the occlusal plane, and a combination of these two vectors. The resulting stress patterns were observed. The effects of the forces produced by the three appliances were transmitted to the maxilla and distant craniofacial structures. Both a parallel traction and a 20 degrees downward pull to the occlusal plane caused a constriction of the anterior portion of the maxilla. The parallel traction caused a counterclockwise (opening) rotation of the molar tooth and palatal plane. A 20 degrees downward force to the occlusal plane decreased this effect.

Bicuspid↗
PubMed2001

Calculation of induced current densities for humans by magnetic fields from electronic article surveillance devices.

This paper illustrates the use of the impedance method to calculate the electric fields and current densities induced in millimetre resolution anatomic models of the human body, namely an adult and 10- and 5-year-old children, for exposure to nonuniform magnetic fields typical of two assumed but representative electronic article surveillance (EAS) devices at 1 and 30 kHz, respectively. The devices assumed for the calculations are a solenoid type magnetic deactivator used at store checkouts and a pass-by panel-type EAS system consisting of two overlapping rectangular current-carrying coils used at entry and exit from a store. The impedance method code is modified to obtain induced current densities averaged over a cross section of 1 cm2 perpendicular to the direction of induced currents. This is done to compare the peak current densities with the limits or the basic restrictions given in the ICNIRP safety guidelines. Because of the stronger magnetic fields at lower heights for both the assumed devices, the peak 1 cm2 area-averaged current densities for the CNS tissues such as the brain and the spinal cord are increasingly larger for smaller models and are the highest for the model of the 5-year-old child. For both the EAS devices, the maximum 1 cm2 area-averaged current densities for the brain of the model of the adult are lower than the ICNIRP safety guideline, but may approach or exceed the ICNIRP basic restrictions for models of 10- and 5-year-old children if sufficiently strong magnetic fields are used.

Biophysical Phenomena↗