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Biomedical subjects

G J Fleming

Publications and source records attributed to G J Fleming.

At least 19 recordsLinked to original sources
PubMed2001

The influence of mixing ratio on the toughening mechanisms of a hand-mixed zinc phosphate dental cement.

OBJECTIVE: A range of mixing ratios occur for zinc phosphate cements in clinical usage and trials. The compressive strength of these cements is dependent on mixing ratio and at a critical ratio, a sudden rise in compressive strength is known to occur. This study investigated the mechanisms behind the cement curve behavior in an attempt to explain the strength increase with mixing ratio. METHODS: Crack propagation from indentations produced in cements were examined to identify if any variation in toughening mechanism existed over the range of mixing ratios investigated (1.7-3.2g/ml). Pore distribution within the cylindrical specimens was determined using an image analysis technique. RESULTS: Increasing the powder content from 2.3 to 2.4g/ml increased the number of powder agglomerates formed in the cement mix over individual particles. The likelihood of introducing pores in excess of 42 microm diameter was enhanced when the ratio exceeded 2.6g/ml. SIGNIFICANCE: It is proposed that crack deflection by agglomerates in the cement reduces the energy of the crack fronts emanating from indentations more than would occur with individual powder particles. This decreases the cracks ability to progress and is likely to result in the marked strength increase from 2.3 to 2.4g/ml identified previously. It is suggested that cement pores in excess of 42 microm diameter were probably generated on filling the sample molds with more viscous cements. These results emphasise that the properties of cements manipulated under optimum conditions provide little information on the cement characteristics present in clinical practice.

Compressive Strength↗
PubMed2001

A comparison of the mechanical properties of a gallium-based alloy with a spherical high-copper amalgam.

OBJECTIVES: The aim of the present study was to investigate how the mechanical properties of a palladium free gallium-based alloy (Galloy) compare with a leading spherical high-copper amalgam (Tytin). METHODS: Cylindrical specimens were mechanically condensed, according to the ISO 1559:1986 standard, to measure compressive strength, Vickers hardness, static creep and dimensional change on setting. Disc and beam shaped specimens were manually prepared to assess the diametral tensile and flexural strengths of the investigated alloys. RESULTS: The mean hardness, 1h compressive fracture strength, 24 h diametral tensile and 24h flexural strengths of Galloy were significantly lower (P<0.001) than Tytin. No significant differences in modulus of elasticity, creep, dimensional change on setting, 24 and 168 h compressive fracture strength for the two alloys were identified. SIGNIFICANCE: The significant reduction in the 1 h mean compressive fracture strength and hardness identified for Galloy compared with Tytin possibly indicate a slower setting reaction in the gallium-based alloy. Manual condensation of the gallium-based alloy produced specimens with inferior mechanical properties possibly due to the increased likelihood of introducing voids within the test specimens. Previous reports indicating poor corrosion resistance and moisture sensitivity of gallium-based alloys highlight the need for further research to investigate the effect of the oral environment on the gallium-based alloy.

Compressive Strength↗
PubMed2001

An evaluation of the technique sensitivity of a hydrothermal low-fusing dental ceramic.

OBJECTIVES: To investigate the technique sensitivity in the manipulation of Duceram Low-Fusing Ceramic, a hydrothermal dental veneering material by employing bi-axial flexure tests. METHODS: Disc shaped specimens of Duceram-LFC dentine powder were condensed from varying powder contents manipulated with 0.33 ml of liquid. Bi-axial flexure (ball-on-ring) testing was employed to determine the mean bi-axial flexure strength, standard deviations and Weibull modulus (m). Apparent solid density and apparent porosity were also measured. RESULTS: Mean bi-axial flexure strengths and standard deviations of specimens condensed from 0.82 g of powder were 66.47 and 9.62MPa (m=7.23, 1.32) compared with 59.12 and 13.62 MPa (m=4.19, 0.77) and 63.91 and 14.51MPa (m=4.46, 0.81) for powder contents of 0.78 and 0.86 g, respectively. A decrease in apparent solid density and an increase in apparent porosity were also associated with increasing or decreasing the powder content of slurry consistencies. CONCLUSIONS: A slurry consistency was identified for Duceram-LFC specimens where the reliability of fracture strength data increased. The technique sensitivity in the manipulation of Duceram-LFC would appear to be confirmed due to the relatively small amount of powder required to complete the transition from a 'fluid' to a 'thick' slurry consistency compared with a conventional veneering dental porcelain.

Analysis of Variance↗
PubMed2001

Crocodilian anesthesia.

With declining crocodilian populations worldwide, a greater interest in the conservation of these animals in the wild and in captivity is ongoing. This effort has created a demand for safe and effective ways to handle and immobilize crocodiles for transport and relocation. With the advent of new anesthetic protocols, working with crocodilians has now been made safer for both the animal and the handler. Unfortunately, current anesthetic protocols have been limited to a few species and further application of these protocols need to be undertaken with new species.

Alligators and Crocodiles↗
PubMed2001

The effect of antiretroviral therapy on the prevalence of oral manifestations in HIV-infected patients: a UK study.

OBJECTIVE: The purpose of this study was to compare the prevalence of oral manifestations in human immunodeficiency virus (HIV)-infected patients on monotherapy, dual therapy, or triple therapy with the prevalence of those not on antiretroviral therapy (ART). STUDY DESIGN: A cross-sectional study of the oral manifestations of HIV was carried out on 284 HIV-infected patients, 89 of whom were undergoing ART (12 on monotherapy, 41 on dual therapy, and 36 on triple therapy) and 195 who were not undergoing ART. Oral manifestations were recorded by using established presumptive clinical criteria. Chi-square statistical tests and separate bivariate analyses were conducted by using the Spearman rank correlation to describe the relationship between the prevalence of oral lesions and ART. RESULTS: The detection of oral manifestations was significantly decreased in subjects on dual therapy and subjects on triple therapy in comparison with patients on monotherapy (P <.05) and those on no ART regimen (P =.014). Oral manifestations were also significantly increased, with CD4 counts <200 cells/mm(3) and a viral load >3000 copies/mL (P <.001). CONCLUSIONS: Compared with the non-ART group, subjects on combination ART had significantly fewer HIV-related oral manifestations-probably as a result of an expression of their reconstituted immune system.

Adolescent↗
PubMed2001

Materials for restoration of primary teeth: I. Conventional materials and early glass ionomers.

This paper demonstrates how the treatment of primary dentition may present the clinician with increased difficulties compared with the preparation and placement of restorations in adult dentition. Established dental materials (dental amalgam and conventional glass ionomer cements) and less well established alternative materials (copper cements) are reviewed. The use of amalgam to restore primary dentition is the subject of concern amongst the dental profession in terms of lack of adhesion and potential toxicity concerns, while the low tensile strength of traditional glass ionomer cements make them less suitable for the restoration of primary dentition.

Child, Preschool↗
PubMed2000

An assessment of the influence of mixing induced variability on the bi-axial flexure strength of dentine porcelain discs and the implications for laboratory testing of porcelain specimens.

OBJECTIVES: The proportions of dentine powder and modelling fluid employed to produce a "creamy" porcelain slurry consistency used in veneer construction are assessed by the technical experience of the operator so that variability is inevitable. The present study investigated the implications of mixing variability on the slurry consistency used in the manufacture of dentine porcelain disc specimens for laboratory testing. METHODS: Vitadur-Alpha dentine porcelain was fabricated into disc specimens and the mean fracture strength, standard deviation and associated Weibull Moduli (m) were determined by fracturing sets of 30 specimens prepared to different powder contents for a constant 0.33 ml of liquid using bi-axial flexure (ball-on-ring). RESULTS: The strength data showed variation in magnitude and consistency ranging from 85.1 +/- 12.9 MPa (m = 7.2 +/- 1.3) at 0.82 g to 87.3 +/- 11.9 MPa (m = 8.0 +/- 1.5) at 0.91 g and 81.9 +/- 13.2 MPa (m = 6.7 +/- 1.2) at 1.0 g of powder. Increasing or decreasing the powder content of the slurry (compared with specimens condensed using 0.91 g of powder) resulted in an increase in porosity and a decrease in the apparent solid density. SIGNIFICANCE: No significant decrease in the mean bi-axial flexure strength or reliability of the fracture strength data was identified for the slurry consistencies investigated, however, the results suggested that an optimum consistency existed wherein consistent reproducibility of test results was achieved. A comparison between materials can only be achieved if specimen preparation occurs consistently between test centres and therefore these results appear to have implications for the laboratory testing of materials.

Algorithms↗
PubMed2000

A sedation technique for implant and periodontal surgery.

OBJECTIVE: Evaluation of a sedation technique which involved titrating intravenous midazolam to an 'ideal' sedation end point, followed by a continuous infusion of propofol. This technique might be a satisfactory alternative to general anaesthesia for implant surgery in anxious patients or when procedures exceed 60-min duration. MATERIAL AND METHODS: 20 patients were treated on 23 occasions. A 2-mg bolus of midazolam was injected intravenously followed after 90 s by 1 mg increments until the patient was adequately sedated. 30 min after this induction with midazolam, a propofol infusion was started at a rate which varied between 0-300 mg/h (0-30 ml/h). The actual infusion rate was adjusted in order to maintain the optimum sedation level which had been achieved using midazolam. The quality of sedation was assessed using Ellis and Sedation scores. RESULTS: Midazolam dosage varied between 5 and 14 mg. The initial propofol infusion rate was 200 mg/h (20 ml/h) for 21 of the 23 implant surgery treatments. CONCLUSION: The sedation technique described takes advantage of the differing pharmacokinetic properties of midazolam and propofol. Initial sedation was achieved using midazolam, this was then maintained using a variable propofol infusion. The shorter distribution and elimination half-lifes of the latter drug made matching the level of sedation to the patient's needs easier and also provided good short-term recovery.

Adult↗
PubMed2000

Multiple Stafne bone cavities: a diagnostic dilemma.

Salivary gland inclusions in the mandible are relatively uncommon. If defects occur they are generally unilateral, although bilateral cases have been reported. This article describes an unusual case in which the dental panoramic tomogram revealed three radiolucent areas in the mandible. The diagnosis of the two posterior radiolucencies was confirmed as Stafne's bone cavities but a definite diagnosis for the parasymphyseal lesion remained elusive, even after surgery. However, Stafne's bone cavities are known to occur in this region and this diagnosis remains the most probable.

Diagnosis, Differential↗
PubMed2000

Oral midazolam for adults with learning disabilities.

This paper demonstrates how oral midazolam can be employed as an alternative method of behaviour management to general anaesthesia for the dental treatment of people with learning disabilities. A range of treatments, from scaling to root canal therapy, can be carried out successfully using the sedation technique outlined. The advantages of sedation include reduced morbidity and mortality. Treatment outcomes are also likely to be improved as root canal therapy and periodontal care can be carried out over a number of visits rather than a single treatment session under general anaesthesia. Oral sedation with midazolam should improve the scope of dental treatment available to patients with disabilities.

Administration, Oral↗
PubMed2000

The management of occupational exposures to blood and saliva in dental practice.

Accidental injuries when handling sharp or rotating instruments can allow inoculation of a dental team member by the patient's blood or saliva. The risk of transmission of HIV from occupational exposure among dental workers is low and to date no occupational exposure has resulted in HIV transmission. However, hepatitis B and C have a high morbidity and mortality and are more infectious than HIV. This paper demonstrates how occupational exposures to blood and saliva could be managed in general dental practice and outlines the legal responsibilities of a dentist in the management of these exposures.

Accidents, Occupational↗
PubMed1999

The influence of clinically induced variability on the bi-axial fracture strength of cemented aluminous core porcelain discs.

OBJECTIVES: Zinc phosphate cements are supplied in powder/liquid form so that a range of mixing ratios are naturally generated in clinical practice. However, these cements are known to have a deleterious effect on dental ceramics and the impact of variations in cement mixing on the strength of dental porcelain was investigated in the present study. METHODS: Vitadur-N core porcelain was fabricated into discs (15 mm diameter and 2 mm thickness), zinc phosphate cements of different mixing ratios were applied to the discs to produce a luting cement thickness and the samples were stored for 24 h prior to testing in a water-bath at 37 +/- 1 degrees C. The mean fracture strength, standard deviation and associated Weibull moduli (m) of the coated porcelain discs were determined as a function of mixing ratio using bi-axial flexure (ball-on-ring) by fracturing sets of 30 specimens coated with cements manipulated at different mixing ratios. RESULTS: The strength data for the coated porcelain discs showed little variation in magnitude and consistency ranging from 108 +/- 8.3 MPa (m = 14.0 +/- 2.6) at 1.7 g/ml to 112 +/- 8.5 MPa (m = 14.6 +/- 2.7) at 2.6 g/ml and 108 +/- 8.1 MPa (m = 14.4 +/- 2.6) at 3.2 g/ml. However, the plots of survival probability against strength for coated specimens prepared using mixing ratios below that recommended by the manufacturers' for luting purposes (2.6 g/ml), appeared to develop an asymmetry at the lower values of strength. SIGNIFICANCE: It was proposed that the increased corrosive acidic environment for cements prepared at mixing ratios below 2.6 g/ml may have extended pre-existing flaws in the porcelain discs thereby possibly producing the asymmetry in the survival distributions.

Aluminum Oxide↗
PubMed1999

The influence of clinically induced variability on the distribution of compressive fracture strengths of a hand-mixed zinc phosphate dental cement.

OBJECTIVES: Conventional approaches to comparing dental cements use standard property tests under manufacturers' specified conditions. Zinc phosphate cements are supplied in powder/liquid form and manipulation frequently involves mixing the components by eye so a range of mixing ratios will inevitably occur in practice. Unfortunately, the physical, chemical, biological and mechanical properties of cements are known to be dependent on the mixing ratio. METHODS: Forty dental nurses prepared a series of three cement samples to a luting consistency they considered acceptable for use in practice. RESULTS: It was found that each dental nurse produced consistent cement mixes, although, the mixing ratios varied from 1.7 to 3.2 g/ml between nurses. The mean compressive strength, standard deviation and associated Weibull Moduli (m) of the cements were determined as a function of this mixing ratio range and showed considerable variation ranging from 33.5 +/- 3.2 MPa (m = 11.0) at 1.7 g/ml to 71.4 +/- 8.4 MPa (m = 8.6) at 2.6 g/ml and 42.5 +/- 10.0 MPa (m = 5.0) at 3.2 g/ml. SIGNIFICANCE: An analytical approach was adopted which facilitated an integrated analysis of the mixing ratio variability with the strength data. It was found for the test group of dental nurses that 25% of cement mixes produced would have achieved strengths below 40 MPa whilst strengths below the standard value were produced in at least 70% of mixes. These results indicate that a simple analysis of the properties of cements manipulated under optimum conditions, provides little information on the material characteristics obtained in practice because of clinically induced variability.

Analysis of Variance↗
PubMed1999

Encapsulated verses hand-mixed zinc phosphate dental cement.

Zinc phosphate cements are commonly supplied as two components, powder and liquid, and the proportions of the constituents are determined by operator experience. A capsulated system which is mechanically mixed has been marketed and this study investigated the performance of the encapsulated cement system. The mean fracture strength, standard deviation and associated Weibull Moduli (m) of encapsulated cements were determined by compressive fracturing 20 cement specimens filled directly from the mixing syringe or from narrower cement tubes. Pore distribution within the cylindrical specimens was determined using image analysis to assess the influence of the method of mould filling with the cement. The strength data showed variation in magnitude and consistency ranging from 44.6+/-13.7 MPa (m = 3.18+/-0.71) for cements filled directly from the syringe to 61.0+/-7.8 MPa (m = 8.35+/-1.87) for cements filled from cement tubes. Larger pores were found in specimens consolidated directly from the cement syringe. Mechanical mixing of the encapsulated cement resulted in air entrapment in the cement mix which manifested itself as large pores (over 200 microm diameter) within the cylindrical specimens. The smaller orifice of the cement tube compared with the syringe was considered to be responsible for eliminating the majority of the air entrapped in the cement mass during mixing. Whilst mechanical mixing of encapsulated cements is quicker and more convenient, the encapsulated specimens consolidated according to the manufacturers instructions from the syringe offered no significant advantage in terms of reliability or strength over hand-mixed cements in this investigation.

Biocompatible Materials↗
PubMed1999

The influence of clinically induced variability on the bi-axial fracture strength of aluminous core porcelain discs.

OBJECTIVE: The proportions of the constituents required to produce a porcelain slurry used in crown construction are assessed by experience so that variability is inevitable. The present study investigated the strength dependence of porcelain specimens on slurry consistency. METHODS: Vitadur-N core porcelain was formed into discs and the mean fracture strength, standard deviation and associated Weibull Moduli (m) determined as a function of slurry consistency using bi-axial flexure (ball-on-ring) by fracturing sets of 30 specimens prepared to different powder contents for a constant 0.4 ml of liquid. RESULTS: The strength data for the porcelain discs showed variation in magnitude and consistency ranging from 145 +/- 16.5 MPa (m = 9.7 +/- 1.8) at 1.2 g to 155 +/- 13.8 MPa (m = 12.3 +/- 2.2) at 1.4 g and 142 +/- 13.7 MPa (m = 11.7 +/- 2.1) at 1.6 g of powder. Increasing or decreasing the powder content of the slurry (related to specimens condensed using 1.4 g of powder) resulted in an increase in the apparent porosity and a decrease in the apparent solid density. CONCLUSIONS: There was no significant decrease in the mean bi-axial flexure strengths for the slurry consistencies investigated. However, the reliability of the fracture strength data did vary significantly. The results suggested that an optimum consistency exists (wherein consistent reproducibility of test results was achieved) and appears to have implications for laboratory testing of materials since a comparison between materials can only be achieved if specimen preparation occurs consistently between test centres for all the materials under investigation.

Aluminum Oxide↗
PubMed1993

Practice management--warts and all.

A recent survey, part of a Practice Management Study, asked 100 doctors how their businesses were going. From the responses, it was evident that there were many areas of concern, including working long hours looking after patients; no time for the family; the accountant does the tax, but that's all; and accountants, solicitors and consultants are too expensive. This article sets out some of the issues raised in the survey.

Australia↗