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Biomedical subjects

David J Wood

Publications and source records attributed to David J Wood.

At least 19 recordsLinked to original sources
PubMed2007

Biological evaluation of an apatite-mullite glass-ceramic produced via selective laser sintering.

The biological performance of a porous apatite-mullite glass-ceramic, manufactured via a selective laser sintering (SLS) method, was evaluated to determine its potential as a bone replacement material. Direct contact and extract assays were used to assess the cytotoxicity of the material. A pilot animal study, implanting the material into rabbit tibiae for 4 weeks, was also carried out to assess in vivo bioactivity. The material produced by SLS did not show any acute cytotoxic effects by either contact or extract methods. There was no evidence of an apatite layer forming on the surface of the material when soaked in SBF for 30 days, suggesting that the material was unlikely to exhibit bioactive behaviour in vivo. It is hypothesized that the material was unable to form an apatite layer in SBF due to the fact that this glass-ceramic was highly crystalline and the fluorapatite crystal phase was relatively stable in SBF, as were the two aluminosilicate crystal phases. There was thus no release of calcium and phosphorus and no formation of silanol groups to trigger apatite deposition from solution within the test time period. Following implantation in rabbit tibiae for 4 weeks, bone was seen to have grown into the porous structure of the laser-sintered parts, and appeared to be very close to, or directly contacting, the material surface. This result may reflect the local environment in vivo compared to that artificially found with the in vitro SBF test and, furthermore, confirms previous in vivo data on these glass-ceramics.

Aluminum Silicates↗
PubMed2007

Evaluation of machine-learning methods for ligand-based virtual screening.

Machine-learning methods can be used for virtual screening by analysing the structural characteristics of molecules of known (in)activity, and we here discuss the use of kernel discrimination and naive Bayesian classifier (NBC) methods for this purpose. We report a kernel method that allows the processing of molecules represented by binary, integer and real-valued descriptors, and show that it is little different in screening performance from a previously described kernel that had been developed specifically for the analysis of binary fingerprint representations of molecular structure. We then evaluate the performance of an NBC when the training-set contains only a very few active molecules. In such cases, a simpler approach based on group fusion would appear to provide superior screening performance, especially when structurally heterogeneous datasets are to be processed.

Artificial Intelligence↗
PubMed2006

Thirty-five percent carbamide peroxide application causes in vitro demineralization of enamel.

OBJECTIVES: The objective of this in vitro study was to investigate whether a high concentration 'in-office' bleaching agent affected the mineral content of enamel and dentin. METHODS: A commercially available 35% carbamide peroxide bleaching agent was applied for 2h to sectioned teeth (n=11). Specimens were then immersed in artificial saliva at 37 degrees C for a further 24h to simulate the oral environment. Tomographic images of these sections were obtained (micro-CT 80, Scanco, Switzerland) prior to and post-bleach application. Eight three-dimensional regions of interest (ROI), starting from the enamel surface extending to the dentinoenamel junction, were selected for each section. The hydroxyapatite equivalent mineral concentrations (g/cm(3)) of the ROIs were calculated. Any changes in mineral content as a consequence of the bleaching procedure were calculated in relation to each ROI. RESULTS: There was a significant reduction in the mineral content of enamel specimens post-bleach application extending to a depth of 250microm (paired t-test, p<0.05); this reduction in mineral content was greatest in the ROI's closest to the tooth surface. There was, however, no significant difference in the mineral content of dentin as a consequence of bleaching. SIGNIFICANCE: This in vitro study has shown that significant demineralization of enamel occurred following bleaching with 35% carbamide peroxide. The concept that 'in-office' bleaching is a non-destructive cosmetic procedure should be reconsidered.

Carbamide Peroxide↗
PubMed2006

The use of confocal microscopy to assess surface roughness of two milled CAD-CAM ceramics following two polishing techniques.

OBJECTIVE: To assess the effects of two polishing techniques on the surface roughness of a commercial and experimental dental ceramic for use in a chairside CAD-CAM system. METHODS: A standard onlay was reproduced fifteen times in each of the two materials. Each stub was retained and examined using confocal microscopy in reflection mode. Five random samples of each were polished with Sof-Lex aluminium oxide discs, five polished with diamond impregnated polishing wheels and five left in the as-machined state. Surface roughness parameters were measured for each material group in each condition and statistical analyses carried out to determine the efficacy of the polishing techniques for each material. RESULTS: The as-machined surfaces of both materials had a statistically similar surface finish. Polishing with Sof-Lex discs was effective at reducing surface roughness of both materials. Whilst the polishing wheels were effective in reducing surface roughness for the commercial material, there was no statistically significant difference in the surface roughness of the experimental material in the as-machined or wheel polished states. SIGNIFICANCE: Although Sof-Lex discs were effective in reducing surface roughness of the two materials examined in this study, wheel polishing should not be used to reduce surface roughness of the experimental material. This will need to be taken into consideration in any future clinical studies of this material.

Aluminum Oxide↗
PubMed2006

An investigation of the constituent elements and modes of fracture of in vivo fractured metallic posts.

OBJECTIVES: The objective of this investigation was to determine the materials used in metallic post and core construction and investigate and the modes of failure that occurred resulting in post fracture. METHODS: Eighty-five fractured metal posts were clinically retrieved over a 5-year period. The tooth with the fractured post, and relevant clinical details were recorded. Investigation of the fractured posts was undertaken to determine their constituent elements and modes of fracture using scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). RESULTS: The results showed that 77% of the posts were cast and 23% wrought. The modes of fracture were ductile (67%) or brittle (52%) although some posts exhibited both within the same specimen. In addition, evidence of fatigue was present in 20% of posts and porosity in 48%. CONCLUSIONS: A large variety of materials were used in the construction of post and cores although low-gold silver-palladium alloy most commonly encountered. Their failure was predominantly ductile in nature although a significant amount of brittle fracture was also noted. Porosity within castings also appeared to be a contributory factor in some cases and this was particularly evident in high-palladium castings. Evidence of fatigue was noted in a minority of posts.

Dental Alloys↗
PubMed2006

A kinematic and kinetic analysis of walking after total knee arthroplasty with and without patellar resurfacing.

BACKGROUND: Clarification of the indications for patellar resurfacing in total knee arthroplasty (TKA) is still necessary. Few studies of adequate power have evaluated functional differences between total knee arthroplasty with and without patellar resurfacing, in particular walking gait. This study aimed to identify clinically relevant differences in knee kinematic or kinetic parameters during level walking between total knee arthroplasty with and without patellar resurfacing, after controlling for pre-surgery gait parameters. METHODS: Kinematic and kinetic gait analysis of level walking was performed on 34 subjects (41 knees) before and 12-18 months after total knee arthroplasty with patellar resurfacing performed randomly. Linear regression analysis was used to examine the influence of patellar resurfacing upon gait variables whilst controlling for the corresponding pre-surgery measure. FINDINGS: The pre-surgery value was a moderate to strong significant predictor of all post-surgery temporal-spatial and kinetic gait parameters (p < 0.001-0.008), and most kinematic parameters (p < 0.001-0.066). The addition of patellar resurfacing to the regression models did not improve the predictive power in any case. Only one parameter, knee flexion at heel-strike, displayed a difference near statistical significance between total knee arthroplasty with and without patellar resurfacing (10 degrees versus 7 degrees respectively, p = 0.023). INTERPRETATION: Pre-surgery gait patterns are an important determinant of post-surgery gait. There are no clinically relevant differences in walking gait between total knee arthroplasty performed with or without patellar resurfacing, using the Profix design.

Aged↗
PubMed2006

No increased migration in cups with ceramic-on-ceramic bearing: an RSA study.

UNLABELLED: Ceramic-on-ceramic hip replacements might stress the bone interface more than a metal-polyethylene because of material stiffness, microseparation, and sensitivity to impingement. To ascertain whether this potentially increased stress caused an increased cup migration we compared a ceramic-on-ceramic with a metal-on-polyethylene implant for cup migration. Sixty one patients (61 hips) undergoing THA for osteoarthritis were randomized to ceramic on ceramic (Ce/Ce) or cobalt-chromium on cross-linked polyethylene bearings (PE) in the same uncemented cup shell. Migration was followed with RSA. At 2 years we observed similar mean cup translations in the 3 directions (0.07-0.40 mm vs. 0.05-0.31 mm, Ce/Ce vs. PE), as well as similar rotations around the 3 axes (0.31-0.92 degrees vs. 0.57-1.40 degrees). WOMAC and SF-36 scores were also similar and no radiolucent lines or osteolysis found. The large migration seen in some cups in both implant groups will require close monitoring to ascertain the reasons. Mean proximal wear of the polyethylene liners measured 0.016 mm between 2 and 24 months. Our data suggest there is no increased cup migration in the ceramic-on-ceramic implant compared with the metal-on-polyethylene, and they seem an equally safe choice. However, the low wear measured with the more versatile and less expensive cross-linked polyethylene makes it a strong contender. LEVELS OF EVIDENCE: Therapeutic Level I. See the Guidelines for Authors for a complete description of levels of evidence.

Aged↗
PubMed2005

Thermal conductivity through various restorative lining materials.

OBJECTIVES: Traditional teaching has advocated the placement of insulating materials under restorations to protect against 'thermal shock'. Often this involves placement of a thick zinc-oxide eugenol cement lining. The purpose of this in vitro study was to assess the heat transfer through four lining materials and dentine and to relate these findings to the temperature exposures that may be experienced in the oral environment. METHODS: Two 'traditional' linings, zinc oxide eugenol cement (ZNOE) and calcium hydroxide paste (CAOH), and two more contemporary materials, a resin modified glass polyalkenoate (RMGP) and dentine bonding system (DBS) were studied in addition to dentine itself. Seven samples of each material were tested by utilising a Lees' Disc apparatus. Incorporation of thermocouples allowed heat transfer through the sample to be recorded. Thermal conductivity (J/m/s/ degrees C) was calculated for individual samples and a mean value obtained for each material. One way ANOVA and post hoc Tukey's tests were applied to the data obtained. RESULTS: In ascending order of thermal conductivity, DBS<CAOH<RMGP<DENTINE<ZNOE. Statistical analysis revealed that the thermal conductivity of DBS was significantly less than RMGP, DENTINE and ZNOE (p<0.05); CAOH was significantly less than DENTINE and ZNOE (p<0.05); RMGP was significantly higher than DBS and significantly less than DENTINE and ZNOE (p<0.05). CONCLUSIONS: Thermal insulation is not a major consideration in cavity lining and therefore other criteria for selection of a lining material should be applied.

Analysis of Variance↗
PubMed2005

Reinforcement of poly(methyl methacrylate) denture base with glass flake.

OBJECTIVES: Since the introduction of poly(methyl methacrylate) as a denture base material, it has suffered from having relatively poor mechanical properties. Many methods of improving its strength and toughness have been investigated. Most of these have not been adopted due to: increased cost, the need for specialist processing equipment or increased laboratory time due to more complicated procedures. Glass flake has been used as a reinforcing agent in many industrial polymers, but is as yet untested with denture base acrylic materials. The aim of this study is to evaluate the effect of adding glass flake to denture base acrylic powder on the fracture toughness of the set material. METHODS: Glass flake was added in 5, 10 or 20% w/w to Trevalon denture base powder. The material was mixed, flasked, packed and processed in a manner typical for a denture base material. Fracture toughness was determined using a double torsion test technique. RESULTS: The addition of glass flake gave up to a 69% increase in fracture toughness compared to plain Trevalon material. The addition of 5% glass flake lead to an improvement in fracture toughness that was statistically significant compared to both plain Trevalon and the 10 and 20% groups. SIGNIFICANCE: The significant improvement in fracture toughness of a denture base acrylic material using glass flake is an extremely promising result. Other mechanical properties will require testing before glass flake can be recommended as a reinforcing agent for denture base acrylic materials.

Dental Materials↗
PubMed2005

Musculoskeletal tissue banking in Western Australia: review of the first ten years.

BACKGROUND: Musculoskeletal tissue allotransplantation has been used as a standard approach for reconstructive surgery. The present study has reviewed the banking of musculoskeletal tissue at the Perth Bone and Tissue Bank (PBTB) and provided evidence of quality assurance on musculoskeletal tissue allotransplantation. METHODS: All donor tissues were processed in accordance with the Therapeutic Goods Administration's relevant codes of good manufacturing practices. Microbiological monitoring at each step of manufacture and postoperative surveying of the musculoskeletal allotransplantations were both conducted. The possible contribution of contaminants in allografts to postoperative infections was also assessed. RESULTS: Of the 5276 donors obtained over the last 10 years, 1672 were rejected, giving an overall donor rejection rate of 32%. Milled femoral heads were the most frequently implanted allografts, followed by whole femoral heads. In the postoperative survey an infection rate of 4.9% was found (113/2321 recipients). The infectious agents were identified in 65 cases but for 60 of these there were no correlations with the positive culture test results for the allografts. The organism most commonly identified in postoperative infections was Staphylococcus species. CONCLUSIONS: The present study shows evidence that musculoskeletal tissue allotransplantation is a safe procedure when accompanied by high standards of quality assurance.

Australia↗
PubMed2004

Failure to clear persistent vaccine-derived neurovirulent poliovirus infection in an immunodeficient man.

BACKGROUND: Individuals who chronically excrete neurovirulent poliovirus of vaccine-origin are of considerable concern to the Global Polio Eradication programme. Chronic infection with such polioviruses is a recognised complication of hypogammaglobulinaemia. METHODS: We did a series of in-vitro and in-vivo therapeutic studies, with a view to clearing persistent neurovirulent poliovirus infection in an individual with common variable immunodeficiency, using oral immunoglobulin, breast milk (as a source of secretory IgA), ribavirin, and the anti-picornaviral agent pleconaril. We undertook viral quantitation, antibody neutralisation and drug susceptibility assays, and viral gene sequencing. FINDINGS: Long-term asymptomatic excretion of vaccine-derived neurovirulent poliovirus 2 was identified in this hypogammaglobulinaemic man, and was estimated to have persisted for up to 22 years. Despite demonstrable in-vitro neutralising activity of immunoglobulin and breast milk, and in-vitro antiviral activity of ribavirin, no treatment was successful at clearing the virus, although in one trial breast milk significantly reduced excretion levels temporarily. During the course of study, the virus developed reduced susceptibility to pleconaril, precluding the in-vivo use of this drug. Sequence analysis revealed the emergence of a methionine to leucine mutation adjacent to the likely binding site of pleconaril in these isolates. INTERPRETATION: Chronic vaccine-associated poliovirus infection in hypogammaglobulinaemia is a difficult condition to treat. It represents a risk to the strategy to discontinue polio vaccination once global eradication has been achieved.

Adult↗
PubMed2004

Mechanical compression of cartilage explants induces multiple time-dependent gene expression patterns and involves intracellular calcium and cyclic AMP.

Chondrocytes are influenced by mechanical forces to remodel cartilage extracellular matrix. Previous studies have demonstrated the effects of mechanical forces on changes in biosynthesis and mRNA levels of particular extracellular matrix molecules, and have identified certain signaling pathways that may be involved. However, the broad extent and kinetics of mechano-regulation of gene transcription has not been studied in depth. We applied static compressive strains to bovine cartilage explants for periods between 1 and 24 h and measured the response of 28 genes using real time PCR. Compression time courses were also performed in the presence of an intracellular calcium chelator or an inhibitor of cyclic AMP-activated protein kinase A. Cluster analysis of the data revealed four main expression patterns: two groups containing either transiently up-regulated or duration-enhanced expression profiles could each be subdivided into genes that did or did not require intracellular calcium release and cyclic AMP-activated protein kinase A for their mechano-regulation. Transcription levels for aggrecan, type II collagen, and link protein were up-regulated approximately 2-3-fold during the first 8 h of 50% compression and subsequently down-regulated to levels below that of free-swelling controls by 24 h. Transcription levels of matrix metalloproteinases-3, -9, and -13, aggrecanase-1, and the matrix protease regulator cyclooxygenase-2 increased with the duration of 50% compression 2-16-fold by 24 h. Thus, transcription of proteins involved in matrix remodeling and catabolism dominated over anabolic matrix proteins as the duration of static compression increased. Immediate early genes c-fos and c-jun were dramatically up-regulated 6-30-fold, respectively, during the first 8 h of 50% compression and remained up-regulated after 24 h.

ADAM Proteins↗
PubMed2003

Transgenic mice as an alternative to monkeys for neurovirulence testing of live oral poliovirus vaccine: validation by a WHO collaborative study.

OBJECTIVE: Extensive WHO collaborative studies were performed to evaluate the suitability of transgenic mice susceptible to poliovirus (TgPVR mice, strain 21, bred and provided by the Central Institute for Experimental Animals, Japan) as an alternative to monkeys in the neurovirulence test (NVT) of oral poliovirus vaccine (OPV). METHODS: Nine laboratories participated in the collaborative study on testing neurovirulence of 94 preparations of OPV and vaccine derivatives of all three serotypes in TgPVR21 mice. FINDINGS: Statistical analysis of the data demonstrated that the TgPVR21 mouse NVT was of comparable sensitivity and reproducibility to the conventional WHO NVT in simians. A statistical model for acceptance/rejection of OPV lots in the mouse test was developed, validated, and shown to be suitable for all three vaccine types. The assessment of the transgenic mouse NVT is based on clinical evaluation of paralysed mice. Unlike the monkey NVT, histological examination of central nervous system tissue of each mouse offered no advantage over careful and detailed clinical observation. CONCLUSIONS: Based on data from the collaborative studies the WHO Expert Committee for Biological Standardization approved the mouse NVT as an alternative to the monkey test for all three OPV types and defined a standard implementation process for laboratories that wish to use the test. This represents the first successful introduction of transgenic animals into control of biologicals.

Animals↗
PubMed2003

Characterization of formaldehyde-inactivated poliovirus preparations made from live-attenuated strains.

Formaldehyde-inactivated virus samples from type 1 poliovirus live-attenuated strains were prepared in the laboratory. The effect of treatment with formaldehyde on virus infectivity and immunogenicity in mice was investigated and the results compared with those from Mahoney wild-type poliovirus strain, the common type 1 component in commercial inactivated polio vaccines (IPV). Differences in the potency and specificity between these experimental vaccines were identified in both normal mice and transgenic mice expressing the human poliovirus receptor. The possible advantages/disadvantages of using live-attenuated strains for IPV production are discussed in the context of the global polio eradication initiative. A novel transgenic mouse model to study in vivo the immune protection induced by IPV preparations is described.

Animals↗
PubMed2003

A comparison of three hard chairside denture reline materials. Part I. Clinical evaluation.

Three chairside reline materials were each used to reline ten complete dentures. Comfort, fit, colour change, staining and integrity were assessed at 3, 6, and 12 months post-placement. Working and setting times were obtained using an oscillating rheometer. Tokuso Rebase Fast Set had the shortest working and setting times. It was the most colour stable, stain resistant and durable. Coe Kooliner was difficult to use due to high flow. Total Hard had the longest working and setting times, and the poorest stain resistance and durability. Severe loss of reline materials only occurred 12 months after placement, and then mostly from within lower dentures. No differences between the materials were noted for the other parameters investigated.

Acrylic Resins↗
PubMed2003

A comparison of three hard chairside denture reline materials. Part II. Changes in colour and hardness following immersion in three commonly used denture cleansers.

This study investigated the effects of daily use of three denture cleansers on three hard chairside reline materials over a 6-month period. Two controls were used; one dry and one involving storage in water. Colour and hardness were measured at 0 (baseline) and 6-months. There was no significant colour change with Tokuso Rebase Fast Set. Coe Kooliner and Total Hard changed colour more with the short acting peroxide cleanser (Steradent 3 Minutes) than with the overnight peroxide cleanser (Steradent Fresh) and the hypochlorite cleanser (Dentural). The hardness of all materials remained unchanged over the whole test period.

Acrylic Resins↗
PubMed2002

Patellar resurfacing in total knee arthroplasty: a prospective, randomized trial.

BACKGROUND: The management of the patella in total knee arthroplasty is still problematic. We aimed to identify differences in the clinical outcome of total knee arthroplasty according to whether or not patellar resurfacing had been performed in a prospective, randomized study of 220 osteoarthritic knees. METHODS: Two hundred and twenty total knee arthroplasties in 201 patients were randomly assigned to be performed with either resurfacing or retention of the patella, and the results were followed for a mean of forty-eight months (range, thirty-six to seventy-nine months) in a double-blind (both patient and clinical evaluator blinded), prospective study. Evaluation was performed annually by an independent observer and consisted of assessment with the Knee Society clinical rating system, specific evaluation of anterior knee pain, a stair-climbing test, and radiographic examination. RESULTS: Fifteen (12%) of the 128 knees without patellar resurfacing and nine (10%) of the ninety-two knees with patellar resurfacing underwent a revision or another type of reoperation related to the patellofemoral articulation. This difference was not significant (chi square with one degree of freedom = 0.206, p = 0.650). At the time of the latest follow-up, there was a significantly higher incidence of anterior pain (chi square with one degree of freedom = 5.757, p = 0.016) in the knees that had not had patellar resurfacing. CONCLUSIONS: Patients who underwent patellar resurfacing had superior clinical results in terms of anterior knee pain and stair descent. However, anterior knee pain still occurred in patients with patellar resurfacing, and nine (10%) of the ninety-two patients in that group underwent a revision or another type of reoperation involving the patellofemoral joint. Weight but not body mass index was associated with the development of anterior knee pain in the patients without patellar resurfacing, a finding that suggests that patellofemoral dysfunction may be a function of joint loading rather than obesity.

Aged↗