A feedback-controlled dynamic linear actuator to test foot withdrawal thresholds in rat.

We describe a method for evaluating the threshold for cutaneous mechanical sensation in rodents, based on a stimulator that drives a probe against the plantar surface of the foot. The stimulator applies loads that can be either constant or linearly increased. We describe withdrawal responses, including forms of movement that precede foot withdrawals. With constant stimuli, response latency declines in a nonlinear fashion as stimulus magnitude is increased. With ramped stimuli the effect of loading rate is complex, reflecting both the rate of change of the stimulus and the animal's reaction time. We demonstrate the utility of using ramped stimuli in experiments that show that thresholds vary spatially across the foot and experiments that show that intradermal capsaicin injections cause allodynia but not hyperalgesia.

Water movement in tendon in response to a repeated static tensile load using one-dimensional magnetic resonance imaging.

Rabbit Achilles tendons (N = 8) were subjected to tensile loading while internal water movements were followed using NMR. The distribution of the internal water in tendons was measured using a one-dimensional proton-density map that was collected along a radial line oriented transverse to the tendon's long axis. The proton density map was created from fits to T2 relaxation data. The experimental design included two cycles of loading (7.5 N tensile load) and relaxation. The first load application was for 42.67 min: unloaded for 21.33 min, reloaded for 21.33 min, and then unloaded for 21.33 min. Water was redistributed in a time-dependent fashion upon loading: proton density decreased in the core region and increased in the rim region. In addition there was evidence that tensile loading caused water to become NMR visible. In separate, parallel experiments, we studied the mechanical behavior of tendons using identical conditions of uniaxial loading (N = 7). The time constants of water movements were very different from the time constants of mechanical relaxation, indicating that water redistribution is not the sole determining factor of mechanical behavior.

Spatial characterization of T1 and T2 relaxation times and the water apparent diffusion coefficient in rabbit Achilles tendon subjected to tensile loading.

Tendons exhibit viscoelastic mechanical behavior under tensile loading. The elasticity arises from the collagen chains that form fibrils, while the viscous response arises from the interaction of the water with the solid matrix. Therefore, an understanding of the behavior of water in response to the application of a load is crucial to the understanding of the origin of the viscous response. Three-dimensional MRI mapping of rabbit Achilles tendons was performed at 2.0 T to characterize the response of T(1) and T(2) relaxation times and the apparent diffusion coefficient (ADC) of water to tensile loading. The ADC was measured in directions both parallel (ADC( parallel)) and perpendicular (ADC( perpendicular)) to the long axis of the tendon. At a short diffusion time (5.8 ms) MR parameter maps showed the existence of two regions, here termed "core" and "rim", that exhibited statistically significant differences in T(1), T(2), and ADC( perpendicular) under the baseline loading condition. MR parameter maps were also generated at a second loading condition of approximately 1 MPa. At a diffusion time of 5.8 ms, there was a statistically significant increase in the rim region for both ADC( perpendicular) (57.5%) and ADC( parallel) (20.5%) upon tensile loading. The changes in core ADC(( perpendicular), ( parallel)), as well as the relaxation parameters in both core and rim regions, were not statistically significant. The effect of diffusion time on the ADC(( perpendicular), ( parallel)) values was investigated by creating maps at three additional diffusion times (50.0, 125.0, 250.0 ms) using a diffusion-weighted, stimulated-echo (DW-STE) pulse sequence. At longer diffusion times, ADC(( perpendicular), ( parallel)) values increased rather than approaching a constant value. This observation was attributed to T(1) spin-editing during the DW-STE pulse sequence, which resulted in the loss of short-T(1) components (with correspondingly lower ADCs) at longer diffusion times (corroborating the results from earlier spectroscopic work). The T(1) spin-editing effect was observed both in the core and in the rim regions of the tendon and hence was not solely due to the redistribution of water from the core to the rim upon loading. A measure reflective of the regional change in proton density was noted to be consistent with tensile-load-induced water transport from the central to the peripheral tendon region.

Viscoelastic properties of skin in Mov-13 and Tsk mice.

Viscoelastic properties of skin samples were measured in three types of mice (tight skin, Tsk, control and Mov-13), that are known to differ with regard to content of type I collagen. The experimental design used uniaxial stretching and measured the creep response and the complex compliance. The creep response was measured directly. The complex compliance was determined using a Wiener-Volterra constitutive model for each sample. The models were calculated from data obtained by applying a stress input having a pseudo-Gaussian waveform and measuring the strain response. The storage compliance of Mov-13 and control skin were similar and were greater than Tsk (p<0.001). The loss compliance of each group was significantly different (p<0.001) from each other group; Tsk had the lowest and control had the highest loss compliance. The phase angle of the Mov-13 and Tsk were similar and were less than the controls (p<0.001). The creep response was fit with a linear viscoelastic model. None of the parameters in the creep model differed between groups. The results indicate that gene-targeted and mutant animals have soft tissue mechanical phenotypes that differ in complex ways. Caution should be exercised when using such animals as models to explore the role of specific constituents on tissue properties.

Application of porous-media theory to the investigation of water ADC changes in rabbit Achilles tendon caused by tensile loading.

The water apparent diffusion coefficient (ADC) in rabbit Achilles tendon is anisotropic, diffusion-time dependent, and changes as a function of tensile load. Water ADC changes of tendon under mechanical load are thought to be due to the extrusion of water from the more restricted tendon core to a relatively unrestricted bulk phase at the periphery (rim) of the tendon. Tensile loading may influence water ADC values by changing the spatial separation of restricting barriers (e.g., increasing the tendon fibril packing density). To explore this issue, we have applied porous-media theory to the investigation of water ADC changes in rabbit Achilles tendon under two different mechanical loading conditions (a baseline condition with a minimal tensile stress and a second in which the tensile stress was approximately 1 MPa). Diffusion sensitivity was applied in directions parallel and perpendicular to the long axis of the tendon. The short diffusion-time behavior of the resulting time-dependent ADC curves was used to indirectly infer information regarding the average surface area to volume ratio of the space available for molecular diffusion. From these values, we estimated a 40% reduction in volume available for diffusion in the perpendicular direction after tensile loading, but only a 10% reduction in the parallel direction. These differences are consistent with the known geometry of the tendon microstructure and suggest an increase in fibril packing density upon loading. The long diffusion-time behavior of the time-dependent ADC curves was used to indirectly infer the tortuosity of the diffusion pathways through the interstitial space. The tortuosity in the direction perpendicular to the tendon long axis was approximately 2.5 times greater than that in the parallel direction. Stimulated-echo measurement of the ADC values at longer diffusion times resulted in T1 spin editing of water with shorter T1 values (and correspondingly lower ADC values). The resulting increase in water ADC with increasing diffusion time was attributed to multiple components arising from the (overlapping) distribution of T1 values in the core and rim regions of the tendon.

Properties of mouse cutaneous rapidly adapting afferents: relationship to skin viscoelasticity.

When skin is stretched, stimuli experienced by a cutaneous mechanoreceptor neuron are transmitted to the nerve ending through the skin. In these experiments, we tested the hypothesis that the viscoelastic response of the skin influences the dynamic response of cutaneous rapidly adapting (RA) neurons. Cutaneous RA afferent neurons were recorded in 3 species of mice (Tsk, Pallid, and C57BL6) whose skin has different viscoelastic properties. Isolated samples of skin and nerve were stimulated mechanically with a dynamic stretch stimulus, which followed a pseudo Gaussian waveform with a bandwidth of 0-60 Hz. The mechanical response of the skin was measured as were responses of single RA cutaneous mechanoreceptor neurons. For each neuron, the strength of association between spike responses and the dynamic and static components of stimuli were determined with multiple logistic regression analysis. The viscoelastic material properties of each skin sample were determined indirectly, by creating a nonlinear (Wiener-Volterra) model of the stress-strain relationship, and using the model to predict the complex compliance (i.e., the viscoelastic material properties). The dynamic sensitivity of RA mechanoreceptor neurons in mouse hairy skin was weakly related to the viscoelastic properties of the skin. Loss modulus and phase angle were lower (indicating a decreased viscous component of response) in Tsk and Pallid than in C57BL6 mice. However, RA mechanoreceptor neurons in Tsk and Pallid skin did not differ from those in C57 skin with regard to their sensitivity to the rate of change of stress or to the rate of change of incremental strain energy. They did have a decreased sensitivity to the rate of change of tensile strain. Thus the skin samples with lower dynamic mechanical response contained neurons with a somewhat lower sensitivity to dynamic stimuli.

Measurement of the spatial redistribution of water in rabbit Achilles tendon in response to static tensile loading.

The redistribution of water in response to static tensile loading was investigated in rabbit Achilles tendons in vitro. The distribution of water was measured along a radially oriented line, using a one-dimensional proton-density map created from fits to diffusion-weighted magnetic resonance (MR) data. Water movements were measured during application of tensile loads of 5N (N=7) and 10N (N=6). Water distribution along the line was measured before loading and up to 42 min after load application. Static loading with either 5 or 10N loads caused a steady increase in proton density in the outside edge (rim) of the tendon. The 10N load lowered the proton density in the core of the tendon, but did so in a single step that was observed when the load was applied. The 5N load caused no change in proton density in the core region. The immediate redistribution from the core was statistically significant for the 10N load, but not the 5N load application. Statistically significant within-group proton-density increases were observed in the rim after 42 min postload for all tendons irrespective of load condition. The rate of proton-density postload increase at the rim region did not depend upon load. The rate for the 5N load case was 0.010 +/- 0.002 min(-1) and 0.007 +/- 0.002 min(-1) in the 10N case. Thus, while generally consistent with an extrusion model, the data show other features that argue for a more complex model.

Comparison of responses to tensile and compressive stimuli in C-mechanosensitive nociceptors in rat hairy skin.

Mechanosensitive nociceptors with unmyelinated axons (C-fibers) were studied in a preparation of isolated skin and nerve from rat. Afferent discharges were recorded while the skin was mechanically stimulated using quantitative stretch (tension) and indentation (compression). The apparatus allowed for generating stimuli of equal magnitudes in both tension and compression. Stimulus-response functions were obtained for individual afferents relating discharge rate to tensile stress or compressive stress. A response threshold and maximal slope were obtained from each function. Thresholds did not differ significantly for compression and tension nor did the maximal slopes. We conclude that C-nociceptors are equally sensitive to tensile and compressive stress.

Wavelets of excitability in sensory neurons.

We have investigated variations in the excitability of mammalian cutaneous mechanoreceptor neurons. We focused on the phase dynamics of an action potential relative to a periodic stimulus, showing that the excitability of these sensory neurons has interesting nonstationary oscillations. Using a wavelet analysis, these oscillations were characterized through the depiction of their period as a function of time. It was determined that the induced oscillations are weakly dependent on the stimulus frequency, and that lower temperatures significantly reduce the frequency of the phase response. Our results reveal novel excitability properties in sensory neurons, and, more generally, could prove significant in the deduction of mechanistic attributes underlying the nonstationary excitability in neuronal systems. Since peripheral neurons feed information to the CNS, variable responses observed in higher regions may be generated in part at the site of sensory detection.

Computing facilities available to final-year students at 3 UK dental schools in 1997/8: their use, and students' attitudes to information technology.

OBJECTIVE: To identify computer facilities available in 3 dental schools where 3 different approaches to the use of technology-based learning material have been adopted and assess dental students' perception of their own computer skills and their attitudes towards information technology. DESIGN: Multicentre cross sectional by questionnaire. SUBJECTS: All 181 dental students in their final year of study (1997-8). RESULTS: The overall participation rate was 80%. There were no differences between schools in the students' self assessment of their IT skills but only 1/3 regarded themselves as competent in basic skills and nearly 50% of students in all 3 schools felt that insufficient IT training had been provided to enable them to follow their course without difficulty. There were significant differences between schools in most of the other areas examined which reflect the different ways in which IT can be used to support the dental course. CONCLUSIONS: 1. Students value IT as an educational tool. 2. Their awareness of the relevance of a knowledge of information technology for their future careers remains generally low. 3. There is a need to provide effective instruction in IT skills for those dental students who do not acquire these during secondary education.

Properties of sensory neurons innervating synovial joints.

While it is clear that the TMJ joint has a sensory innervation like other synovial joints, there is little specific information about the function of the innervation of the TMJ. In order to provide a template upon which future studies might build, this article briefly reviews the function of sensory neurons in other synovial joints.

Changes in ADC caused by tensile loading of rabbit achilles tendon: evidence for water transport.

Water diffusion measurements were performed on rabbit Achilles tendons during static tensile loading and tendons in an unloaded state. The apparent diffusion coefficient (ADC) was measured along two directions: parallel and perpendicular to the long axis of the tendon. Tendons were studied after being prepared in two ways: (a) after being stored frozen in phosphate-buffered saline (PBS) and (b) freshly isolated. Statistically significant directional anisotropy was observed in the ADC in all tendons. The ADC was significantly greater in the direction parallel to the long axis of the tendon than in the perpendicular direction. The anisotropy is attributed to the greater restrictions seen by the water molecules in the perpendicular direction and is consistent with the known geometry of the tendon. Storage in PBS caused tendons to swell. This increased the ADC measured along both directions and reduced the anisotropy. The existence of anisotropy in the ADC was not related to the orientation of the specimen in the magnet. The ADC increased along both directions following the application of a 5-N tensile load; the increase was greatest along the perpendicular axis of the tendon. In order to determine whether load-related changes in the ADC reflected changes in interfibrilar spacing, we used electron microscopy to measure load-related changes in fibril spacing. Load-related changes in fiber spacing could not account for the observed changes in the ADC. The increase in ADC caused by loading was attributed to the extrusion of tendon water into a bulk phase along the outside surface of the tendon. In PBS-stored samples, enough fluid was extruded that it could be visualized. The transient response of the ADC to a 5-N tensile load was also studied. The absolute ADC in both directions increased with loading and recovered to baseline upon unloading. The transient changes in ADC, for both loading and unloading, had a mean time constant of approximately 15 min. The magnitude of the load-induced transient ADC changes was comparable to that seen in the static-loading experiments.

A survey of the IT skills and attitudes of final year dental students at Bristol University in 1996 and 1997.

Surveys of final year dental students were conducted in 1996 and 1997 to see if there were any detectable differences in students' perception of their own information technology IT skills and attitudes towards information technology following the opening of a dedicated computer-assisted-learning (CAL) room. An increase was seen in students' confidence levels, with fewer assessing themselves as IT "beginners" (1996 = 36%; 1997 = 14%), and more assessing themselves as competent in some basic skills (52%; 41%). Although more students were found to be using basic computer facilities (word processing, email, the World Wide Web), there was little difference in attitudes towards these packages between the 2 years. There was a significant increase in the number of students agreeing or strongly agreeing with the statement "the use of IT had added value to this course for me" (1996 = 39%; 1997 = 67%). The main obstacle which was identified by students as a barrier to using IT was the lack of adequate training. Over half the students in both years felt that insufficient training had been provided to enable them to cope with the course without difficulty.

Responses of rapidly adapting afferent neurons to dynamic stretch of rat hairy skin.

Twenty-four rapidly adapting (RA) cutaneous afferents were recorded from a preparation of isolated, innervated hairy skin from the rat hindlimb for the purpose of identifying the mechanical variables associated with the initiation of afferent discharge. Neurons were studied while the skin was stretched dynamically along a single direction with the use of a linear actuator and a feedback controller. Input signals were load- or displacement-controlled stretches that followed either periodic or pseudorandom Gaussian noise control signals. When the tissue was actuated, loads and displacements were measured along the direction of stretch and neuronal responses were recorded. All RA afferents were activated by dynamic stretching. None had a sustained response to static stretch. Cross-correlation products, calculated between neuronal responses and either stress- or strain-related variables observed at the time of the spike, revealed a strong relationship between neuronal responses and tensile stress. Neuronal responses were observed at rates of change of stress between +1,000 and -800 kPa/s. Neuronal responses were poorly related to skin strain. Two loading conditions were used along the direction transverse to the stretch. In one condition the sides were unconstrained, so that on axial loading there was zero stress and negative strain along the transverse axis. In the other condition the sides were constrained so that when the tissue was loaded axially there was zero strain and positive stress along the transverse axis. In these two conditions the same level of axial stress was associated with two levels of axial strain. The neuronal responses were determined by the stress and not the strain. Neuronal responses were observed at stresses >5 kPa. It appears that RA afferents make little contribution to signaling limb movements or position in rat hindlimb on the basis of the behavior of rat hindlimb skin, as observed when the limb is rotated.

Computer-assisted learning in dentistry. A view from the UK.

OBJECTIVES: The objectives of this paper are to review the development and impact of computer assisted learning (CAL) in dentistry with emphasis on the UK. DATA SOURCES: This is a wide ranging review of dental, medical and technical literature. STUDY SELECTION: An attempt has been made to evaluate present knowledge in an objective manner and to make some prediction as to the future development and use of computer-based teaching methods in dentistry. CONCLUSIONS: The introduction of computers as an educational tool in dentistry and the provision of CAL is having an impact not only on how dentists are trained but also on the skills they will need to acquire in the future to keep pace with this new technology. It is suggested that there is a great potential for computer-based continuing professional education for dental practitioners, and that the Internet will provide access to such material.

A finite element based method to determine the properties of planar soft tissue.

A finite element based method to determine the incremental elastic material properties of planar membranes was developed and evaluated. The method is applicable to tissues that exhibit inhomogeneity, geometric and material nonlinearity, and anisotropy. Markers are placed on the tissue to form a four-node quadrilateral element. The specimen is loaded to an initial reference state, then three incremental loading sets are applied and the nodal displacements recorded. One of these loadings must include shear. These data are used to solve an over-determined system of equations for the tangent stiffness matrix. The method was first verified using analytical data. Next, data obtained from a latex rubber sheet were used to evaluate experimental procedures. Finally, experiments conducted on preconditioned rat skin revealed nonlinear orthotropic behavior. The vector norm comparing the applied and calculated nodal force vectors was used to evaluate the accuracy of the solutions.

Tensile and compressive responses of nociceptors in rat hairy skin.

Mechanically sensitive nociceptor afferents were studied in a preparation of isolated skin from rat leg. Each neuron was studied while the skin was subjected to tensile and compressive loading. The experiment was designed to create highly uniform states of stress in both tension and compression. Tensile loads were applied by pulling on the edges of the sample. Applied loads were used to determine the tensile stresses. Surface displacements were used to determine tensile strains. Compressive loads were applied by indenting the surface of the skin with flat indenter tips applied under force control. The skin was supported by a flat, hard substrate. Compressive stresses were determined from the applied loads and tip geometry. Compressive strains were determined from skin thickness and tip excursions. All nociceptors were activated by both tensile and compressive loading. There was no interaction between the responses to compressive and tensile stimuli (i.e., the responses were simply additive). Responses of nociceptors were better related to tensile and compressive stresses than to strains. Nociceptors responded better to tensile loading than to compressive loading. Response thresholds were lower and sensitivities were higher for tensile stress than for compressive stress. The response to compression was better related to compressive stress than to other stimulus parameters (i.e., load/circumference or simply load). Indentations of intact skin over a soft substrate such as muscle would be expected to cause widespread activation of nociceptors because of tensile stresses.

Clinical informatics and the dental curriculum. A review of the impact of informatics in dental care, its implications for dental education.

The origins of informatics lie in the development of computers and data processing techniques since the 1950s. The subsequent application of these to the practice of healthcare continues to the present day, so that information technology now holds the potential to revolutionise healthcare through more rapid and efficient management of an ever increasing quantity of clinical information. In dentistry, no less than in medicine, electronic systems can make an extremely valuable contribution to clinical practice. For these systems to be clinically useful, however, they need to be properly understood by clinicians. This review paper outlines the scope of clinical informatics and argues that a grounding in clinical informatics is now essential for today's undergraduates to equip them to meet the challenge of practice in the 21st century.

The effect of diabetes on the viscoelastic properties of rat knee ligaments.

A series of experiments was performed to determine the effect of diabetes on the viscoelastic properties of knee joint ligaments. The experimental model was collateral ligaments from spontaneously diabetic, hyperglycemic (BBZDP/Wor) rats, and various controls including nondiabetic littermates, insulin treated diabetic rats, and alloxan treated rats. Material properties were measured using a dynamic, uniaxial loading paradigm. Ligaments were subjected to load controlled, sinusoidal tensile testing, using frequencies from 0.1 to 2.0 Hz. The resulting data were used to determine the storage and loss compliances of the ligaments. Storage compliance, which reflects tissue elastic properties, did not differ between groups. Loss compliance, which reflects the viscous component of the tissue response, was increased in the hyperglycemic animals. Thus, hyperglycemic diabetes affects tissue mechanical properties through the viscous rather than the elastic component of the response to dynamic loading. Rats treated with alloxan to induce diabetes did not show an increase in loss compliance.

Stretch sensitivity of mechanoreceptor neurons in rat hairy skin.

1. Cutaneous mechanoreceptor neurons were recorded in a preparation of isolated rat skin while the skin was stretched with an apparatus that allowed the parameters of tensile stress and strain to be controlled. 2. SA2 afferents were strongly directionally selective in response to stretch. Their responses were correlated most strongly with the tensile stress along the unit's preferred direction and were related poorly to strain variables. Threshold tensile stresses required to activate SA2s were low, on the order of 5 kPa. 3. C-mechanoreceptors were stretch activated. They lacked directional selectivity and had tensile stress thresholds similar to SA2s. 4. Hair afferents had only dynamic responses to stretch. SA1 afferents were not stretch activated.