Colin H. Daly

Interface shear stresses during ambulation with a below-knee prosthetic limb.

Shear stresses on a residual limb in a prosthetic socket are considered clinically to contribute to tissue breakdown in below-knee amputees. When applied simultaneously with normal stresses, they can cause injury within the skin or can generate an abrasion on the surface. To gain insight into shear stresses and parameters that affect them, interface stresses were recorded on below-knee amputee subjects during walking trials. On the tibial flares, resultant shear ranged from 5.6 kPa to 39.0 kPa, while on the posterior surface it ranged from 5.0 kPa to 40.7 kPa. During stance phase, anterior resultant shears on a socket were directed toward the apex while posterior resultant shears were directed downward approximately perpendicular to the ground. Waveform shapes were usually double-peaked, with the first peak at 25% to 40% into stance phase and the second peak at 65% to 85% into stance. Application of these results to residual limb tissue mechanics and prosthetic design is discussed.

Duration of nocturnal tooth contacts during bruxing

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Clinical measurement of normal and shear stresses on a trans-tibial stump: Characteristics of wave-form shapes during walking

Stresses on the surface of a stump within a prosthetic socket during walking can potentially traumatise stump tissues. To gain insight into stresses and design parameters that affect them, normal and shear interface stresses were measured on three unilateral trans-tibial amputee subjects during walking trials. During stance phase repeated characteristics in wave-form shapes from different subjects were apparent. They included “loading delays”, “high frequency events (HFEs)”, “first peaks”, “valleys”, “second peaks”, and “push-off”. Characteristics did not necessarily occur at the same time from one step to the next but their timings matched well with events in shank force and moment data which were collected simultaneously. For “plantarflexion” and “dorsiflexion” alignment changes, the above wave-form characteristics were still pesent but their timings within the stance phase changed. The physical meaning and relevance of the characteristics to stump tissue mechanics are discussed.

Measurement of stresses in three orthogonal directions at the residual limb-prosthetic socket interface

Transducers were developed to measure stresses in three orthogonal directions applied on a below-knee amputee residual limb within a prosthetic socket during walking. Strain-gage measurement techniques were used for all three orthogonal directions. Instrumentation error for four transducers averaged less than 4.2% full-scale output (FSO) for the normal direction and less than 0.9% FSO for shear directions. Measurements from amputee subjects collected during walking trials are presented. >

Interface pressures and shear stresses: sagittal plane angular alignment effects in three trans-tibial amputee case studies

Interface pressures and shear stresses at different sagittal plane angular alignment settings were measured on 3 trans-tibial amputee subjects ambulating with patellar-tendon-bearing total contact prostheses. Substantial socket-shank angular alignment modifications in the sagittal plane had minimal effect on stance phase peak interface pressures, though more substantial effects on stance phase peak resultant shear stresses. No consistent trend of a greater stress at misaligned vs nominally aligned settings was identified. Changes in interface stresses from session to session tended to be greater than those for different alignment settings, suggesting that subjects compensated well for misalignments but less well for session differences.

The response of the human periodontal ligament to torsional loading—I. Experimental methods

Abstract A test technique is described in which torsional loads are applied to human maxillary central incisors in vivo . The central axis of the incisor is located by a stereoscopic X-ray method and the tooth loading device is adjusted by means of a setting jig so that torque is applied about this central axis. The maximum torque which can be applied is ± 0·05 Nm and the maximum rotation of the tooth is ± 0·02 radian (± 1·2). A servo-control system allows one to apply any desired torque or deflection history. e.g. a creep or stress relaxation test or a cyclic load of any waveform. Initial results obtained with this system are presented and show that the torque vs rotation response is initially linear but becomes highly nonlinear at higher torques. Creep tests and cyclic loading tests indicate that the periodontal ligament is viscoelastic in nature. Periods of cyclic loading separated by rest periods of 1–20 min show that the commonly observed decrease in tissue stiffness during the initial few load cycles is not a permanent effect in this in vivo test. Recovery to the initial stiffness takes place rapidly. e.g. 50 per cent recovery in 5 min at zero load.

Root Surface Measurement Using a Digital Computer

An accurate method is presented for the determination of the area of the periodontal ligament attached to teeth. This method requires the use of digitizing equipment for an accurate determination of tooth cross sections and a digital computer for final manipulation of the area calculations. The procedure is general and is not restricted to single-rooted teeth.

Bone-titanium implant response to mechanical stress

The purpose of this study was to investigate the nature and strength of any bond which may develop between alveolar bone and titanium allow implants. Implants were placed in a previously prepared edentulous region in the mandibles of dogs. The implants were conical in shape with circumferential grooves to provide axial retention. Five months later the implants were rotated. No indication was found of an adhesive bond being broken.

Indicator pastes: Their behavior and use

Indicator pastes were subjected to a laboratory investigation and a clinical trail. The tests showed: 1. An increase in temperature increased the rate of flow of the pastes. 2. An increase in applied pressure increased the rate of the flow of the pastes. 3. Pastes containing a small percentage of filler were compressed to a smaller thickness than those containing a greater percentage of filler. 4. The zinc oxide-hydrogenated oil mixture demonstrated a biphasic flow pattern. Pressure Indicator Paste demonstrated a simple flow pattern. 5. Similar tests did not give identical results. However, the characteristics of flow curves for similar tests were consistent. 6. A clinical trial using eight subjects showed no marked differences between three indicator pastes but did show significant differences between the interpretations of paste patterns by four dentists. This evidence suggests that the nature of the suspension medium affects both the type of flow and the rate of flow of an indicator paste. The percentage composition of filler affects both the final film thickness and the rate of flow. Improved criteria for the interpretation of paste patterns must be developed before clinical differences in paste behavior are noted.

Normal and shear interface stresses in lower-limb prosthetics

Instrumentation for measuring normal stresses and biaxial shear stresses at the residual-limb/prosthetic-socket interface during ambulation is presented. Three-directional force transducers were designed using strain-gage technology. With an amplifier gain of 4000, shear and normal sensitivities are 0.132 V/kPa and 0.0259 V/kPa, respectively. Nonlinearity, crosstalk, noise, and drift are reported to be within acceptable levels. Transducers were calibrated in the shear direction by static loading in the sensing surface plane. At a gain of 4000, the sensitivity was 0.132 V/kPa. Nonlinearity was less than the quantization error of the data acquisition system. Crosstalk between shear directions was measured to be less than 1% full-scale. Normal direction calibration with or without a 2.38-mm-thick silicone rubber sheet between a metal loading plate and the Pelite surface showed a sensitivity of 0.0259 V/kPa at a gain of 4000. Nonlinearity was less than 2% full-scale. The principal source of noise was from cable motion during ambulation. The estimated error introduction was 5%. Drift and electronic noise were minimal.<<ETX>>