Evaluation of an improved orthognathic articulator system. 2. Accuracy of occlusal wafers.

The errors produced by occlusal wafers constructed on casts of the teeth mounted on a standard articulator and an improved orthognathic articulator were investigated by carrying out simulated orthognathic surgery on plastic skulls. The wafers were used to relocate the position of the maxillae of the skulls. The vertical and horizontal displacements of the maxillae were determined from measurements of the positions of markers on the skull and teeth. Comparison of the magnitudes of the actual and intended movements showed that wafers constructed on the standard articulator had systematic prediction errors of up to 5mm, but the improved orthognathic articulator showed much smaller random errors. There was a statistically significant improvement in overall accuracy in predicting maxillary Le Fort I position with the use of the improved orthognathic articulator which the authors recommend for clinical use.

Evaluation of an improved orthognathic articulator system: 1. Accuracy of cast orientation.

A systematic study was carried out using plastic model skulls to quantify the accuracy of the transfer of face bow registration to the articulator. A standard Dentatus semi-adjustable articulator system was compared to a purpose built orthognathic articulator system by measuring the maxillary occlusal plane angles of plastic model skulls and of dental casts mounted on the two different types of articulators. There was a statistically significant difference between the two systems; the orthognathic system showed small random errors, but the standard system showed systematic errors of up to 28°.

Errors in orthognathic surgery planning: the effect of inaccurate study model orientation.

The results of orthognathic surgery may differ significantly from the planned outcome using dental models. The orientation of dental models mounted on articulators using conventional face bows does not accurately replicate the orientation of the patients' teeth and jaws, but introduces a systematic error. A mathematical analysis showed that the misalignment of the maxillary model introduces errors in the perioperative wafers, which may lead to the incorrect surgical positioning of the maxilla reported in the literature. The results of the mathematical analysis were validated by image analysis of photographs of mounted maxillary models, used to simulate five orthognathic procedures. No significant difference between the experimental results and the theoretical predictions from the mathematical equations was noted. Planning for maxillary forward and upward movement produced more advancement and only 50% of maxillary impaction. Planning for maxillary forward and downward movement produced less advancement and more inferior displacement in relation to horizontal and vertical reference planes.

Mandibular elongation by automatic distraction osteogenesis: the first application in humans.

We report the case of a 65-year-old man who was the first person to have the right ramus of his mandible lengthened by 20mm by automatic continuous distraction osteogenesis. The device consists of two units: a component that is implanted into the bone, and an external component that is distant from the surgical site and mounted on a battery-driven portable syringe driver or infusion pump. A non-compressible drive cable connects the two.

Mechanical testing of recombinant human bone morphogenetic protein-7 regenerated bone in sheep mandibles.

A new method was developed in this study for testing excised sheep mandibles as a cantilever. The method was used to determine the strength and stiffness of sheep hemi-mandibles including a 35 mm defect bridged by regenerated bone. Recombinant human bone morphogenetic protein-7 (rhBMP-7) in a bovine collagen type-I carrier was used for the bone regeneration. Initial tests on ten intact sheep mandibles confirmed that the strength, stiffness and area beneath the load-deformation curves of the right and left hemi-mandibles were not significantly different, confirming the validity of using the contra-lateral hemi-mandible as a control side. Complete bone regeneration occurred in six hemi-mandibles treated with rhBMP, but the quality and mechanical properties of the bone were very variable. The new bone in three samples contained fibrous tissue and was weaker and less stiff than the contra-lateral side (strength, 10-20 per cent; stiffness, 6-15 per cent). The other half had better-quality bone and was significantly stiffer and stronger (p < 0.05), with strength 45-63 per cent and stiffness 35-46 per cent of the contra-lateral side. Hemi-mandibles treated with collagen alone had no regenerated bone bridge suggesting that 35 mm is a critical-size bone defect.

A new capillary viscometer for small samples of whole blood.

A new capillary viscometer is described in which a column of blood is discharged under a constant pressure, producing a variety of shear stresses during a single test. Measurement of the viscosity of Newtonian sucrose solutions showed good agreement between the viscosity determined from the new system and the expected values. The viscosity of whole blood was measured in a cone-and-plate viscometer at a wide range of shear rates and characterized using a power law model; good agreement was obtained between the capillary and rotational results at low and medium shear rates. High shear rate results could also be obtained by increasing the driving pressure. The new viscometer proved to be simple to use, utilized a small test volume and produced reliable results.

The use of artificial intelligence in the design of an intelligent cognitive orthosis for people with dementia.

Dementia often reduces a person's ability to perform activities of daily living because he or she becomes confused and cannot remember the sequence of steps to perform. The current solution is to have a caregiver continually supervise and assist the person using verbal reminders or cues. This loss of privacy and increased dependency may cause the affected person to become embarrassed and agitated. We propose that this situation might be improved by using a computerized device that monitors progress and provides the reminders needed. The COACH is a first prototype of such a device. It uses artificial intelligence to observe a user, learn from his or her actions, and issue prerecorded cues of varying detail. The device was developed using a personal computer and a video camera that unobtrusively tracked the user. Preliminary testing with subjects who simulated confused behavior as they washed their hands showed that the device was performing its functions with an efficacy of approximately 95%. More extensive clinical testing and evaluation has begun, and the results will be reported in future publications.

A new capillary viscometer for whole blood viscosimetry.

A new capillary system was developed, incorporating infrared sensors, which allowed the determination of whole blood viscosity over a wide range of shear stresses. Flow conditions were defined by the geometry of the capillary and the sample pressure head. Whole blood was considered to be a power law fluid and a modified Mooney's formula was used for the calculation of the related invariants. The new viscometer proved to be very simple in use, requiring one run, had a short measuring time and utilised a small test sample volume. However it can be used for whole blood viscosity measurements only at medium and high shear stresses.

Investigation into the tensile properties of collagen/chondroitin-6-sulphate gels: the effect of crosslinking agents and diamines.

Artificial skin substitutes based on autologous keratinocytes are being developed for grafting onto burns patients. In order to be used successfully in the clinic, these skin substitutes need to have sufficient strength to allow ease of handling. This may be achieved by crosslinking the collagen substratum on which the cells are cultured. The influence of potential crosslinking agents on the tensile properties of acellular collagen gels has been investigated, including the glycosaminoglycan, chondroitin-6-sulphate (Ch6SO4), the water-soluble carbodiimide crosslinking agents 1-ethyl-3-(3-diaminopropyl) carbodiimide (EDAC), and 1,1-carbonyldiimidazole (CDI), and the polyamines, putrescine and diaminohexane. Values for Young's modulus, maximum load, stress, displacement and percentage strain at maximum load were generated by subjecting the samples to a tear propagation test. Incorporation of 20% Ch6SO4 into collagen gels caused a significant increase in the Young's modulus, maximum load and stress at maximum load. Crosslinking treatment with EDAC, CDI or polyamines had little further benefit, and in many cases resulted in a decrease in particular parameters. In terms of mechanical strength, the best crosslinking combination proved to be the combination of CDI and diaminohexane, with results either improved or maintained when compared with the control no treatment variants. However, previous experience suggests that the use of CDI as a crosslinking reagent may inhibit infiltration and proliferation of fibroblasts in the substratum and it may be necessary to reach a compromise to obtain the best combination of biological and mechanical properties for artificial skin substitutes.

A new ambulatory monitoring instrument of posture and mobility related activities.

Long-term ambulatory monitoring of posture and mobility related activities provides useful information about the extent of disability and the outcome of rehabilitation. The aim of this project is developing an instrument which could distinguish between a set of selected mobility-related physical activities and produce parameters characterising the subjects' activity pattern; The selected activities are lying, sitting, standing and walking. A novel activity transducer and a data logger with 1MB memory are employed in the system configuration. Analytical algorithms and program are developed. The subject's whole day activity pattern and the histogram of each activity event are successfully obtained.

Direct measurement of the optical properties of human breast skin.

The optical properties of thin tissue samples are obtained using goniometric apparatus. Direct measurements of the scattering of 633 nm light by 20-120 microns thick samples of in vitro human breast epidermis and dermis are numerically integrated to obtain values for the scattering and absorption coefficients mu s and mu a, respectively, and the anisotropy parameter g. The total attenuation coefficient mu t is obtained from transmission measurements. The Beer-Lambert law is found to be sufficiently valid for congruent to 100 microns thick samples to be used as the basis of the numerical integration. However, normalisation errors involved with the integration mean that only approximate values of mu a could be obtained. Values of congruent to 40 mm-1 are obtained for mu t and mu s, with the value of mu a estimated as 1 mm-1. The optical properties of human breast epidermis and dermis are found to be similar at 633 nm, and the two could be considered as a single layer for modelling light propagation at this wavelength. Further, the intersubject variability seen in this study suggests that a model that uses a range of values for each optical property may be more useful in a clinical situation.

Peroneal stimulator; evaluation for the correction of spastic drop foot in hemiplegia.

OBJECTIVE: The objective of the study was to assess the orthotic and therapeutic value of the peroneal stimulator (PS) for adult hemiplegic patients. DESIGN: This was a two-period crossover study lasting 11 weeks. After recruitment each patient had a 4-week control period followed by a 4-week treatment period. The patients were assessed before the control period, after the control period, and after the treatment period. SETTING: Nineteen patients were recruited from physiotherapy departments in the Glasgow area; 2 subsequently dropped out before the treatment period. PATIENTS: All patients had hemiplegia as a result of cerebrovascular accident (CVA) and were greater than 3 months but less than 36 months post-CVA. Average time since stroke was 7 months. MAIN OUTCOME MEASURES: The patients' gait was assessed over smooth linoleum, carpet, and uneven ground. Gait was evaluated using a switch-based portable system. Outcome measures were the temporal gait parameters of speed, symmetry, heel strike, and foot inversion during stance. The gait evaluation was repeated on 5 separate days at each assessment. The Barthel Index was applied to each session. RESULTS: There was a significant orthotic improvement in inversion on all surfaces and for symmetry on linoleum (AN-OVA, p = .05). There was no significant improvement in patients' gait when not using the PS. There was a significant improvement in the Barthel Index over the treatment period (Wilcoxon, p = .05). CONCLUSION: Use of the PS an an orthotic device late in the rehabilitation program would be appropriate for a selected subpopulation of patients.

A body-worn gait analysis system for evaluating hemiplegic gait.

This paper describes a system for measuring the temporal parameters of hemiplegic gait. This system uses shoe insoles with sensors, acting as switches, placed under the heel, head of the first metatarsal, head of the fifth metatarsal and the big toe. This system is able to monitor gait for up to 10 min and can be used by the patient over any surface. Parameters for evaluating hemiplegic gait are defined, including scuffing during swing and the degree of inversion during stance.

Improvements in bandaging technique following training.

Effective compression bandaging is critical for leg ulcer care. The bandaging technique of 18 nurses was assessed using a pressure monitor and the assessment repeated after training with feedback from the monitor. The use of a bandage marked with a tension indicator resulted in a small, insignificant improvement in bandaging technique. The combination of training and feedback significantly improved the nurses' bandaging technique. This improvement was sustained on retesting two weeks later.

Poly(vinyl chloride) formulations: acute toxicity to cultured human cell lines.

Two quantitative cytotoxicity assay methods (cytoplasmic retention of carboxyfluorescein and mitochondrial cleavage of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT)) have been used to evaluate the response of two cultured human cell lines; HepG2 (hepatoma) and W138va13 (transformed lung fibroblasts) to extracts of a range of poly(vinyl chloride) (PVC) formulations. Two plasticizers; di(2-ethylhexyl)phthalate (DEHP) and di-isooctyl phthalate and a range of tin and non-tin stabilizers were incorporated in the study. Only those formulations containing both a plasticizer and a tin-based stabilizer produced extracts which were toxic. Extracts of those formulations which contained both plasticizer and dibutyl tin dimaleate stabilizer were toxic to both cell lines in both assay methods. Extracts of a formulation containing plasticizer and a dioctyl tin mercaptide were toxic to both cell lines in the carboxyfluorescein assay but were only toxic to the WI38va13 cells in the MTT assay. The WI38va13 cells were generally more sensitive to the extracts than the HepG2 cells. When serial dilutions of the extracts were evaluated, the carboxyfluorescein assay proved to be the more sensitive of the two. The acute toxicity of extracts of these PVC formulations cannot be directly attributed to the plasticizers or to the tin stabilizers. It is likely that a synergistic mechanism, such as plasticizer facilitated extraction of the tin stabilizer, exists.

Mechanics of native bovine pericardium. I. The multiangular behaviour of strength and stiffness of the tissue.

Native bovine pericardial samples have recently been reported to be mechanically anisotropic in both biaxial and uniaxial tests. We present results of multiangular tensile tests conducted on strips from native pericardial samples. These tests were needed in order to establish the nature of the anisotropy, in other words identify the class of the material symmetry. We also examine the possibility of describing the multiangular behaviour of the ultimate tensile stress and stiffness of the tissue by using a theory pertinent to composite structures comprised of linear elastic elements. This application was in general successful and should contribute towards a better understanding of the mechanics and deformations of natural materials with a woven fabric (structure).