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Biomedical subjects

G W Hastings

Publications and source records attributed to G W Hastings.

At least 19 recordsLinked to original sources
PubMed2000

Comparative wear ranking of dental restoratives with the BIOMAT wear simulator. Part II. An SEM evaluation.

The qualitative wear of amalgam alloys and composite resins opposing cast chromium alloys after impact-sliding wear simulation with the BIOMAT wear simulator was assessed. An impact stress of 28 MPa was adopted to allow for stresses generated during parafunctional activities. The worn specimens were examined using SEM at both impact sites and region of sliding wear. For amalgam alloys, ranking from the smoothest to the roughest surface under SEM observation was as follows: unicompositional alloy>admixed alloy>gallium alloy. For composite resins the ranking was: microfilled composite>small particle composite>hybrid composite. The qualitative SEM assessment results were consistent with our earlier volumetric wear results and supports the hypothesis that surface microstructure affects wear. Composite selection for teeth opposing cast chrome prostheses should be done with caution and knowledge of the composition of the material as three-body wear may occur.

Composite Resins↗
PubMed1999

Acid-base complex reactions in resin-modified and conventional glass ionomer cements.

Resin-modified glass ionomer cements are a recent development in which the desirable properties of glass ionomer cements and resin-composites are combined. The presence of resin may, however, retard the acid-base reaction of the ionomer component. This has led to a debate regarding the classification of resin modified materials as true glass ionomer cements, and the actual duration of the acid-base reaction after initial setting via light polymerization has taken place. To investigate this issue, a novel method employing FT-IR spectrophotometry was used to monitor the acid-base complexation reaction in a resin-modified glass ionomer cement (Fuji II LC) and a conventional, chemically cured cement (Fuji II Cap). This method involved subtraction of the background "resin" spectrum from the Fuji II LC spectra and subsequent application of a baseline to obtain the plot of absorbance area ratio in the range of 1685 to 1510 cm(-1) (complexed carboxyls) to that in the range of 1750 to 1685 cm(-1) (free carboxyls). This study demonstrates evidence of a delayed acid-base reaction for the resin-modified cement, which levels off after 168 hours of cement mixing. In contrast, the complexation reaction of the conventional glass ionomer cement was essentially complete after 24 hours.

Glass↗
PubMed1999

Comparative wear ranking of dental restoratives with the BIOMAT wear simulator.

Fundamental in vitro wear tests are important for the study of wear mechanisms, provision of data during material development and screening of materials prior to clinical trials. The aim of this project was to compare the wear of six dental restoratives using the BIOMAT wear simulator which was developed to simulate jaw movements and stresses generated in the occlusal contact areas during the chewing process. The correlation of wear to hardness of the restoratives was also assessed. Wear ranking from the least to the most volumetric wear was as follows: high copper unicompositional alloy, Tytin (T) < high copper admixed alloy, Valiant PhD (V) < microfilled composite resin, Silux Plus (S) < gallium alloy, Galloy (G) < heavily filled composite resin, Z100 (Z) < hybrid composite resin, P50 (P). The high copper amalgam alloys had significantly greater wear resistance when compared with all the composite resins. The gallium alloy, microfilled and heavily filled composite resins also exhibited significantly less wear than the hybrid resin. Wear ranking with the BIOMAT simulator was similar to that obtained in vivo. Ranking from the hardest to softest material: high copper unicompositional alloy, T < gallium alloy, G < high copper admixed alloy, V < hybrid composite resin, P < heavily filled composite resin, Z < microfilled composite resin, S. The amalgam alloys were significantly harder than the heavily filled and microfilled composite resins. There was no apparent correlation between wear performance and material hardness.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1999

Use of titanium prosthesis to bridge a vertebral gap in the spine--a preliminary experimental study.

Resection of a vertebral body for spine tumour or fracture results in a vertebral gap which has to be bridged by autogenous graft, allograft, bone cement or metal spacer. Recently, there have been several metal spacers in the market. We have designed a titanium vertebral spacer which is extensible by way of a threaded mechanism. Coating with hydroxyapatite enables bone ingrowth onto the surface of the titanium spacer. Biomechanical analysis, using the Instron biaxial electro-servohydraulic testing machine, showed that the segment bridging the spacer was rigid and stiffer than the adjacent vertebral body motion segment. Histological study showed that there was bone growth across the vertebral gap indicating fusion had taken place.

Animals↗
PubMed1998

Preparation of a chitin-apatite composite by in situ precipitation onto porous chitin scaffolds.

Composites of chitin with calcium phosphate were obtained by in situ precipitation of the mineral from a supersaturated solution onto chitin scaffolds. The chitin scaffolds were obtained by freeze drying to give a highly porous structure possessing a polar surface favorable for apatite nucleation and growth. THe extent and arrangement of calcium phosphate deposits on the chitin and substituted chitin scaffolds were explored. Up to 55% by mass of calcium phosphate could be incorporated into chitin scaffolds. Deposits on the chitin surface were a continuous apatite carpet nature while deposits on carboxymethylated chitin surfaces displayed a spherical morphology. Carboxymethylation of chitin exerts an overall inhibitory effect towards calcium phosphate deposition, but it provides for site-specific nucleation of the mineral phase. In situ precipitation can be an important route in the future production of various polymer-calcium phosphate composites.

Apatites↗
PubMed1998

Bruxing-type dental wear simulator for ranking of dental restorative materials.

An instrumented dental wear test simulator was developed to simulate jaw movement in the chewing process between two molar teeth. It simulated the natural impact with sliding masticatory action, known as bruxing (defined as the gnashing, grinding, or clenching of teeth) type of wear, in order to simulate a worst-case dental wear scenario. In vitro wear testing of dental restorative materials was performed. Impact and sliding wear were simulated on the machine, with water as the lubricant, on three metal alloys (Tytin, Valiant Ph.D., Galloy) and three composite resins (Silux Plus, Z100, P50). The impact force for each machine cycle was brought closer to the maximum natural masticatory forces by the use of a shock absorbing layer. To replicate the natural masticatory action, the specimens had a surface profile with the shape of a conical depression. Ranking of the materials' performance on the wear test simulator was seen to be consistent with published clinical ranking. Metal alloys showed greater wear resistance than composite resins. Among the different metal alloys, those with lower hardness and compressive strengths exhibited greater wear. Composite resins with large filler particles wore worse than those with small filler particles. Results were compared with previous work on impact with sliding on a flat surface without a cushioning layer. It was concluded that the magnitude of the impact force and the angle of approach during impact with sliding wear are important parameters in the in vitro wear ranking of dental restorative materials.

Bruxism↗
PubMed1998

The influence of anionic chitin derivatives on calcium phosphate crystallization.

The influence of two water-soluble anionic chitin derivatives, sodium carboxymethyl-chitin (CM-chitin) and phosphoryl-chitin (P-chitin) on the crystallization of calcium phosphate by seeded growth and turbidimetry were studied. The adsorption of these derivatives onto hydroxyapatite obtained at 37 degrees C, fitted the Langmuir isotherm. The affinity constant and number of adsorption sites were measured at 2.9 and 1.69 micromol m(-2) for CM-chitin and 11.85 and 4.23 micromol m(-2) for P-chitin. P-chitin exerted a potent inhibitory effect on the seeded growth of hydroxyapatite from a supersaturated solution, reducing the initial rate of crystallization by more than 90% at a solution concentration of 10(-4)M. Both chitin derivatives also retarded the rate of spontaneous calcium phosphate precipitation. The type of calcium phosphate precipitated was poorly crystallized, calcium-deficient apatite. The chitin derivatives were found to be incorporated into the precipitate and influenced both the phase and morphology of calcium phosphate formed.

Anions↗
PubMed1997

Hydroxyapatite modified chitin as potential hard tissue substitute material.

Calcium hydroxyapatite (HA) powder was incorporated into chitin solutions to form an intimate mixture. Upon casting of this mixture into molds of fixed dimensions with subsequent removal of solvent, HAs containing chitin flexible plates were produced. The amount of (HA) was varied from 10 to 50% by mass of HA. The elastic modulus, yield stress, and elongation to fracture, measured at a crosshead speed of 5 mm/min, of these HAs containing chitin flexible plates were evaluated. The amount of HA in the HA incorporated chitin was found to not significantly change the elastic modulus or elongation to fracture. However, a decrease in the maximum tensile stress with an increase in the HA content was found.

Biocompatible Materials↗
PubMed1997

Comparative wear ranking of dental restorative materials utilizing different wear simulation modes.

The aim of this study was to compare the wear of seven different restorative materials using two different wear simulation modes. This included a non-impact sliding wear test (rotary pin and disc) and an impact-cum-sliding wear test (masticatory simulator). The difference in wear ranking between the two wear tests was compared as well as the correlation of wear to the hardness of the materials. Hardness ranking in the order of decreasing hardness was as follows: Dispersalloy (DA), P50 (P50), Hi-Dense (HD), TPH (TPH), Fuji II LC (FJ), Dyract (DR) and Vitremer (VM). For volumetric wear using the non-impact sliding test, the following ranking in the order of decreasing wear resistance was obtained: DA, TPH, DR, HD, VM, FJ, P50. The results for volumetric wear with impact-cum-sliding wear testing in the order of decreasing wear resistance were: TPH, DR, P50, AR, FJ, VM, HD. Results showed that there is no correlation between hardness and wear resistance. There is also no correlation between impact-cum-sliding wear and non-impact sliding wear. Impact wear should be considered in future two-body wear assessment of materials.

Composite Resins↗
PubMed1996

Promotion of calcification on carboxymethylchitin discs.

A series of water-insoluble carboxymethylchitin (CM-chitin) discs of varying degrees of substitution (d.s.) has been investigated for their interaction with calcium phosphate. Discs of d.s. 0.03, 0.11, 0.14 and 0.23 were prepared by casting from solutions of CM-chitin in 90% formic acid. Calcium uptake and calcium phosphate nucleation were found to increase with the degree of substitution of the CM-chitin discs. The results suggest that water-insoluble CM-chitin may be useful as a platform for in vivo calcification.

Analysis of Variance↗
PubMed1995

Do porous calcium hydroxyapatite ceramics cause porosis in bone? A bone densitometry and biomechanical study on cortical bones of rabbits.

Porous calcium hydroxyapatite (CHA) ceramics are biocompatible and present osteoconductive properties. These ceramics are widely used in orthopaedic surgery; however, it is not yet known whether they have some adverse effects on bone and bone marrow healing. Our previous radiological study revealed possible local porosis at the adjacent sites of the CHA ceramic. Histological findings of the same study revealed bone marrow swelling and depletion at the implantation site. Osteoclasts removed particles of the implant that may be the cause of local porosis. In the present study, possible local osteoporosis was evaluated by bone densitometry analyses, and compression and three-point bending tests. CHA particles were implanted into the left limbs and a sham operation was utilized on the right limbs of 75 white rabbits. The animals were followed up for 23 weeks for bone mineral density and for 6 months for biomechanical analyses. The CHA implanted area and its distal or proximal adjacent areas were evaluated with a Hologic QDR-2000 bone densitometer. Three-point bending and compression tests were performed with an M-30 K material testing device. The results revealed a time-dependent bone density increase at the CHA implantation site and no significant porosis at adjacent areas of the implant. The stiffness of CHA-implanted bones in three-point bending is larger than that of the control group. CHA-implanted rabbit bones presented a different fracture pattern from the control group. The stiffness of the control and CHA-implanted bones generally increased with time indicating no adverse effects of porous CHA ceramics in bone and bone marrow healing. The clinical relevance of this work is that porous CHA ceramics do not cause local porosis at adjacent areas when implanted into osseous sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Microstructural characterization of glass-reinforced hydroxyapatite composites.

The influence of phosphate-based glasses and a bioactive silica glass on the sintering mechanism of hydroxyapatite was studied over a wide range of temperatures. The composites were microstructurally characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Small additions of phosphate-based glasses proved to be beneficial to the sintering process and fully dense materials were obtained. A significant improvement in mechanical properties was achieved. beta-TCP and alpha-TCP were found in the microstructure depending on the sintering temperature. Additions of bioactive glass led to the development of calcium phosphate silicate.

Biocompatible Materials↗
PubMed1993

Development of a degradable composite for orthopaedic use: mechanical evaluation of an hydroxyapatite-polyhydroxybutyrate composite material.

This study evaluates the mechanical properties of a composite material comprising polyhydroxybutyrate with hydroxyapatite added in proportions varying from 0 to 50%. Among the three methods of production, injection moulding was found to result in the most satisfactory mechanical properties. The tensile and compressive strength and the modulus of elasticity of composite produced in this way fell within the range for fresh human bone from different anatomical sites. With the additional advantages of biocompatibility, biodegradability and the potential for piezoelectric stimulation of new local bone formation, it was concluded that the injection-moulded composite material has considerable potential for use in orthopaedic surgery, both as a material to construct certain orthopaedic implants and as an alternative to corticocancellous bone graft.

Biocompatible Materials↗
PubMed1992

Development of a degradable composite for orthopaedic use: in vivo biomechanical and histological evaluation of two bioactive degradable composites based on the polyhydroxybutyrate polymer.

As a direct method for the evaluation of tissue bonding to two polyhydroxybutyrate (PHB) based composites, a mechanical push-out test was performed on implants in the femur of mature Japanese White rabbits. Three composites were tested. The first, a hydroxyapatite/PHB (HA/PHB) composite showed an increase in interfacial shear strength (ISS) up to 8 wk, after which the ISS decreased due to degradation of the implant. The second composite was an HA/glass/PHB (HGP) composite and this gave lower values for the ISS attributed to ion release from the glass causing a soft tissue reaction at the interface. The third composite was a carbon fibre reinforced polysulfone (CFRP) and this showed high interfacial shear strength values, which continued to increase with time. These conclusions were supported by contact microradiography (CMR) and histology which showed enhanced endosteal bone growth for the HA/PHB but for the HGP, no periosteal or endosteal activity was detected. Interposed soft tissue for the HGP composite was difficult to discern, histologically, but it was proposed that this was the reason for the low ISS values. It was concluded that the high ISS values for the carbon fibre control were due to surface morphology allowing deep ingrowth of soft tissue and this was confirmed by SEM.

Animals↗
PubMed1991

A pedicle screw bridging device for posterior segmental fixation of the spine: preliminary mechanical testing results.

Mechanical assessment of a new pedicle screw bridge device for spinal surgery is reported. Results are given for a series of single tests to failure and a fatigue cyclical loading test. Comparative testing of torsional and lateral bending resistance on three surgical spinal fixation systems was carried out: Luque, wired Hartshill rectangle and pedicle screwed bridge with Hartshill rectangle and pedicle screwed bridge with Hartshill rectangle. The results show the superiority of the bridged Hartshill in both rotational and lateral bending resistance. The new bridge device could also improve the versatility of the Hartshill system to cover a wider spectrum of spinal fixations. A test to determine the axial pull-out strength of three screw designs was undertaken. The differences between the forces needed were insignificant. At failure a cylinder of bone tissues greater than the major diameter of the screw was pulled out without breaking the bone.

Biomechanical Phenomena↗
PubMed1991

In vitro degradation of a PHB/PHV copolymer and a new technique for monitoring early surface changes.

The use of polyhydroxbutyrate and its copolymers as degradable materials for surgical use is showing increasing promise due to their long degradation profile. Of considerable interest were the interfacial changes and their role in affecting the overall or bulk degradation pattern. The role of pH and its effect on the degradation pattern were examined as polymer degradation significantly altered, depending on whether it was subjected to an alkaline or an acidic medium. In vitro surface changes were monitored using two techniques (scanning electron microscopy and goniophotometry); bulk changes were monitored by gravimetric, mechanical and molecular weight techniques. It was concluded that the bimodal molecular weight distribution plays a significant part in the degradation pattern and that this pattern is also considerably altered by pH.

Biocompatible Materials↗