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Biomedical subjects

D F James

Publications and source records attributed to D F James.

16 recordsLinked to original sources
PubMed1995

Force and moment distributions among osseointegrated dental implants.

Distributions of force, bending moment and torque are determined by structural analysis for an osseointegrated dental implant system. The system is a dental prosthesis rigidly connected to bone by implants. Since the implants have the lowest flexural rigidity of the structural components, they are considered to be the only elastic components of the system. In the analysis, the number and position of the implants are variable and the magnitude, direction and location of the applied load are arbitrary. The distributions found by force and moment balances are in the form of simple algebraic equations, a form which is useful for clinicians in determining the number and location of implants so that forces and moments are shared equitably. One immediate result of the structural analysis is that the bending moment due to the vertical component of the applied load--a moment which has previously been neglected--can produce stresses in the implant which are an order of magnitude larger than the direct axial stresses.

Biomechanical Phenomena↗
PubMed1995

Measurements of shaft speed while drilling through bone.

PURPOSE: This study investigated the effect of force on drill speed and measured the energy consumed during the drilling process. MATERIAL AND METHODS: Applied force, drill speed, and energy consumed were measured during drilling in bovine cortical bone specimens. A commercial surgical drill was fitted with a custom-designed speedometer for measuring the rotational speed. The handpiece was attached to a laboratory drill press and positioned above a bone specimen mounted on a load cell. To apply steady loads, weights were placed on the drill platform, and tests were conducted for forces between 1.5 and 9.0 N and for free-running speeds from 20,000 to 100,000 rpm. RESULTS: The simultaneous measurements of speed and load for the electrically powered instrument showed that the average operating speed changed with the force applied: at low starting speeds, the speed increased slightly with force; at high starting speeds, the speed decreased with force by as much as 50%. The measurements of electric power showed that the total energy consumed generally decreased with speed and force, primarily because of decreased drilling time. CONCLUSION: The decrease in energy suggests that drilling at high speed and with a large force may be desirable because bone temperature is reduced.

Animals↗
PubMed1993

Fractures of the fixture component of an osseointegrated implant.

The cause of mechanical failure of the fixture component of an osseointegrated dental implant was investigated. The surfaces of five clinical specimens that had fractured were compared to those of new specimens fractured in the laboratory under monotonic and cyclic loads. Scanning electron microscopy revealed striations on the fractured surfaces of the clinical specimens, similar to striations on the laboratory-fatigued specimens and in contrast to the dimpled surfaces on the overloaded specimens. The investigation demonstrated that fractures of the fixture component of this dental implant occurred by fatigue under physiologic loads, with marginal alveolar bone loss around the fixture.

Alveolar Bone Loss↗
PubMed1991

Load transfer to abutment teeth by two non-metal adhesive bridges.

Recently, two alternatives to the etched metal, Maryland-type bridge have been proposed for anterior applications. These are the all-ceramic bridge and the composite resin framework, ceramic veneered pontic bridge. Both designs use acid-etched winged retainers for adhesion. The purpose of this study was to evaluate the load transfer to abutment teeth by these two designs using photoelastic modeling.

Composite Resins↗
PubMed1982

Forces in the metacarpophalangeal joint due to elevated fluid pressure--analysis, measurements and relevance to ulnar drift.

The mechanics of the metacarpophalangeal joint are analyzed, with a view to understanding why the finger moves in the direction of ulnar drift when the intra-articular pressure in the joint is increased. The first step is the in situ measurement of stiffness of the various tissues surrounding the joint, and the data show that (a) the two collateral ligaments are the major component and (b) the ulnar ligament is the stiffer. This latter result, combined with finding the centre of pressure at the base of the phalanx, reveals how increased intra-articular pressure produces ulnar deviation. Flexion, the other component of ulnar drift, is produced because of the volar side attachment of the ligaments. The mechanics are evaluated quantitatively by the measurement of forces at the finger tip for various pressures; the data agree reasonably well with predictions using the measured joint properties in a simplified mechanical model of the joint.

Biomechanical Phenomena↗
PubMed1982

The hydrodynamic resistance of hyaluronic acid and its contribution to tissue permeability.

An experimental system was developed to measure flow rates and pressure drops across hyaluronic acid solutions. The solutions were contained by membranes in a test cell, and solvent was perfused through the cell at flow rates comparable to physiological conditions. The pressure drop was found to be proportional to a steady flow rate for concentrations up to 1.5%, confirming that Darcy's Law for porous media is valid for hyaluronic acid solutions (and indicating that the polymer chains did not pile up at one end of the test cell). From the flow data, the hydrodynamic permeability of each solution was calculated and found to be 50 times higher that whole tissue having the same hyaluronic acid concentration; hyaluronic acid on its own, therefore, is not the source of resistance to flow in tissue. The results for hyaluronic acid were then used to show that all the glycosaminoglycans together cannot cause the high resistance of ground substance in tissue, and it is argued that mucoproteins are the most likely source. A hydrodynamic model of the polymer chains was developed to predict solution permeability; the theoretical values agree closely with the experimental data.

Biomechanical Phenomena↗
PubMed1980

Analysis of the urethral pressure profile using a mechanical model.

Using a model of the urethra designed to ensure a predictable pressure profile along its length, we investigated optimal parameters for gas and water profilometry. In gas profilometry, the response characteristics of the machine, attributable to the highly compressible nature of gas, were shown to be the most important determinants of accuracy. Gas and water profilometry have drawbacks that make clinical results inaccurate. However, if all measuring parameters are carefully recorded and considered when a pressure profile is analyzed, system error can be decreased from 62 to 5% by using the optimal pull and flow rates determined by this study.

Hydrostatic Pressure↗
PubMed1978

Intra-articular pressure as a factor in initiating ulnar drift.

To determine the possible relevance of intra-articular pressure in the production of ulnar drift, metacarpophalangeal joints of fresh cadaver specimens were injected with water to increase the intra-articular pressure. Of the thirty-two joints tested, ulnar deviation was produced in twenty-three, flexion in twenty-four, and simultaneous ulnar deviation and flexion (ulnar drift) in nineteen. In two or three instances, the displacement was in extension or radial deviation. These results suggest that elevated intra-articular pressure may be a factor in the initiation of ulnar drift in patients with rheumatoid arthritis.

Aged↗
PubMedDate not supplied

An experimental evaluation of spinal flexibility with respect to scoliosis surgery.

Lateral flexibility of the spinal column was investigated by mechanical analysis and by experiments on fresh cadavers. The work was undertaken with the aim of improving the surgical treatment of scoliosis by quantifying the effects of ribs and transverse processes on lateral spinal flexibility. To this end, flexibilities before and after removal of the bony elements in cadavers' spines were compared. A portable instrument was built to apply loads to the spines. Generally, the spines were tested in the following sequence of conditions: intact, resected ribs on one side, resected ribs and transverse processes on the same side. The results from nine cadavers indicate that only rib resection on the tension side of the induced curve (scoliotic concavity) significantly increased spinal flexibility. It is concluded that the surgical correction of scoliotic curves with instrumentation and fusion is maximized with rib osteotomy or resection.

Biomechanical Phenomena↗
PubMedDate not supplied

Temperature rise during drilling through bone.

Temperature was measured during drilling in bovine cortical bone specimens. A surgical drill fitted with a custom-designed speedometer and mounted on a drill press was used to drill holes at one speed, 49,000 rpm, and at forces in the range of 1.5 to 9.0 N. The resulting temperatures were recorded by thermocouples placed at various locations. The distribution of maximum local temperature rise (delta T) was best fitted by the function delta T = aR-b, where R is the distance from the center of the drilled hole and a and b are constants that were found by regression analysis. It was also found that the temperature increased with force, up to about 4.0 N, and then decreased at forces greater than that because of decreased drilling time. A separate series of tests revealed that temperatures were higher in the longitudinal direction than in the circumferential direction; this difference was attributed to the anisotropic thermal properties of bone.

Acceleration↗