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Biomedical subjects

G J Pearson

Publications and source records attributed to G J Pearson.

At least 19 recordsLinked to original sources
PubMed1992

The comparative strengths of commercial glass-ionomer cements with and without metal additions.

Metal reinforced glass-ionomer cements are said to possess superior mechanical properties when compared to non-metal reinforced glass-ionomer cements. However, the literature to date does not always support this view, owing to the variety of materials and test methods employed. In this study the mechanical properties of three reinforced and three standard materials were tested using the standard specification tests of compressive and diametral strength in addition to tensile strength using the four point bend test. The tensile strength was also measured using the shell test in order that this test, which on theoretical grounds is more suited to these materials, may be evaluated. Six specimens of each material were prepared for each of the test modalities resulting in the conclusion that the addition of metal to glass-ionomer cements can markedly increase the strength of the materials. However, the method of fusing the metal to the glass rather than by simple addition does not produce any advantages in strength. In this evaluation one reinforced material was significantly stronger than all other materials in all four test modalities. The compressive strength test which appears in most standards does not appear to be very discriminatory. Of the tensile tests, which have more clinical significance, the results of the diametral strength tests, which are included in some standards, appear to be at variance with the other two tensile tests, suggesting that the flexural or shell test would be more appropriate.

Cermet Cements↗
PubMed1992

In vitro erosion of 20 commercial glass ionomer cements measured using the lactic acid jet test.

The lactic acid jet test has been proposed for incorporation in international standards for dental cements, since results correlate well with in vivo erosion. In the literature, jet test results have been reported on only six glass ionomer cements. This study examines three types of glass ionomer, restorative, luting and metal reinforced, twenty materials from six manufacturers. A wide range of erosion rates was found particularly for restorative cements. The hypotheses put forward by previous workers to explain differences in erosion rates found on their limited range of glass ionomers do not apply to the wider range that we tested.

Biocompatible Materials↗
PubMed1992

Case report: treatment of blastomycosis with fluconazole.

The authors present two cases of systemic blastomycosis successfully treated with fluconazole. In one case, the disease involved the respiratory tract, and the central nervous system was presumed to be involved. The second case consisted only of pulmonary blastomycosis. Both patients were treated with oral fluconazole 200 mg twice per day for 9 and 6 months, respectively. Treatment with this new triazole antifungal agent resulted in the complete resolution of the disease in both patients. They have remained asymptomatic for more than 6 months after the completion of therapy.

Adult↗
PubMed1992

Microleakage studies comparing a one-visit indirect composite inlay system and a direct composite restorative technique.

Problems related to leakage have been observed with direct-filled composite restorations. The development of indirect system of fabrication followed by cementation should theoretically reduce this phenomenon. The present study compares the leakage around directly placed composites with composite inlays prepared by a surgery-based system. The results indicate that the amount of leakage is reduced with the inlay system, but that it is not eliminated.

Acrylic Resins↗
PubMed1991

Long-term flexural strength of glass ionomer cements.

The flexural strength of five glass ionomers was measured at intervals ranging from 1 h to 3 months after mixing. The pattern of change in flexural strength is material-specific with two water-activated materials having significantly higher long-term flexural strengths than the others. This may be attributable to the different polyacrylic acids used or to changes in the glass formation in the different materials.

Biocompatible Materials↗
PubMed1991

The effect of etching on glass polyalkenoate cements.

The effect of acid etching on the surface appearance and flexural strength of four glass polyalkenoate cements was investigated. Specimens were etched for intervals of 10-60 s, both at the recommended time after mixing and after a 24-h delay. The surface texture was examined microscopically. Further specimens were subjected to a 4-point bend test following etching 1 h and 24 h after mixing. Deterioration of the surface appearance occurred as the etching time was increased beyond 10 s following immediate etching. Etching after 24 h reduced surface damage, but a 10-s etch still gave the most favourable surface appearance without loss of particulate material. Etching beyond 10 s significantly reduces flexural strength.

Acid Etching, Dental↗
PubMed1991

Finishing of glass-ionomer cements.

Glass-ionomer cements offer considerable advantages in certain areas over other restorative materials. These result from their cariostatic properties, their inherent dimensional stability and their adhesive properties both to enamel and to dentine. However, because they derive from silicate cements they are prone to desiccation and require protection during the setting phase of the material. This article describes the relationship between the setting time and finishing. The effects of various types of finishing on the surface of the restorative material are also discussed.

Dental Polishing↗
PubMed1990

Variation in powder/liquid ratio of a restorative glass-ionomer cement used in dental practice.

This study investigates the powder/liquid ratios of a glass-ionomer restorative (ChemFil II, Dentsply) mixed in clinical practice. Twenty-two dental surgery assistants (11 from general practice; 11 from a dental hospital) mixed this cement as they would for clinical use. Samples were taken of three mixes from each assistant and the powder/liquid ratios were derived from weight loss on dehydration. A wide range of ratios were obtained, but in no case was the manufacturer's recommended ratio of 6.8:1 achieved. The consistency measured in accordance with BS 6039 showed the cement at 6.8:1 to be less fluid than the requirements of the standard and other glass-ionomer restoratives. When tested at the mean ratio used in practice, 5.0:1, the consistency complied with BS 6039, but the compressive and diametral strengths did not, being about half the values found at 6.8:1. It was concluded that this restorative was often mixed in practice at much lower powder/liquid ratios than that recommended by the manufacturer and that this would impair the cement's mechanical properties.

Glass Ionomer Cements↗
PubMed1990

The effectiveness of dentine adhesives as demonstrated by dye penetration and SEM investigations.

A previous investigation identified three types of cuspal movement that occur as a result of polymerization shrinkage when extracted molar teeth are filled with a microfine or hybrid composite used in conjunction with a dentine adhesive. That investigation was extended further by dye penetration and SEM studies of the margin, involving assessment of the degree of dye penetration and marginal integrity around the restoration. These studies indicate that there may be a failure of the adhesive bond between tooth and composite/adhesive complex which correlates with little or no cuspal movement. Failure within the tooth structure itself was also observed in a number of cases.

Acrylic Resins↗
PubMed1990

Aspects of the use and abuse of aesthetic restoratives. 2. Dentine adhesives and glass-ionomer cements.

Modern materials offer great promise in the aesthetic restoration of teeth. However, their performance in practice may not fulfil this promise. This is often because of inadequate understanding of the scientific principles behind the new materials, leading to misuse. In Part 1 of this article the author reviewed some of the physical properties of composites, and explained both their proper use and their limitations. In Part 2 he looks at dentine adhesives and glass-ionomer cements.

Dental Bonding↗
PubMed1990

Aspects of the use and abuse of aesthetic restoratives: 1. Composite materials.

Modern materials offer great promise in the aesthetic restoration of teeth. However, their performance in practice may not fulfil this promise. This is often because of inadequate understanding of the scientific principles behind the new materials, leading to misuse. In this two-part article the author reviews some of the physical properties of the new materials, and explains both their proper use and their limitations. Part 1 examines the composites, Part 2 will look at dentine adhesives and glass-ionomers.

Chemical Phenomena↗
PubMed1989

Cusp movement of molar teeth with composite filling materials in conventional and modified MOD cavities.

One hundred and twenty caries-free molar teeth were stored in saline. Three types of cavities were prepared in these teeth: conventional MOD, parallel-sided MOD with no buccal or lingual extensions, and a slit cavity. Cavity dimensions were recorded. Each group of teeth were restored with either a microfine or conventional composite, used in conjunction with a dentine adhesive. Cusp movement was recorded via two linear variable displacement transducers attached to the cusps. Using dye penetration studies, the marginal adaptation of the material to the teeth was assessed. In a small number of cases, the amount and type of cuspal movement and the degree of dye penetration was variable, depending on cavity design and the composite used, but generally cusp movement was unaffected by variation in cavity outline.

Acrylic Resins↗
PubMed1989

The flexural strength of repaired glass-ionomer cements.

The flexural strength of three glass-ionomer-type cements was measured by means of a four-point bend test. Specimens were tested at one hour and seven days after being mixed. The maleic copolymer materials showed similar strengths at one hour and seven days, while the water-based polyacrylic acid material showed a reduction in strength over the seven-day period. For assessment of the capacity of fresh glass ionomer to bond with old material, further half-length specimens of all materials were prepared and additions made at one hour and seven days. These specimens were tested at one hour and seven days after the addition. There was a considerable reduction in the strength of all specimens where additions had been made. The degree of reduction varied with the type of material. All fractures on the addition specimens occurred at the junction between the two sections.

Dental Bonding↗
PubMed1989

Water sorption and solubility of resin-based materials following inadequate polymerization by a visible-light curing system.

The water sorption and solubility of three hybrid and one microfine composite are reported. The values obtained are dependent on composite type and resin system. Incomplete polymerization of the two materials resulted in increased solubility and sorption due to incomplete conversion of the monomer. The marked increased in both parameters will have clinical significance on the durability of the material.

Absorption↗
PubMed1989

Local dental anaesthesia and evidential breath testing: the effect of injection of local anaesthetic on lip seal.

The effect of local anaesthetic infiltration on the ability of subjects to provide adequate specimens of breath for analysis using an evidential breath testing device was assessed. The results showed that in ten out of the fourteen cases there was no impairment of the ability to provide the specimens of breath at any time. Within two hours of the administration of a local anaesthetic all subjects were able to provide the requisite samples.

Adult↗
PubMed1988

Evaluation of dye penetrations around two resin-based materials used as fissure sealants.

Two materials, based on Bis GMA resin, which may be used as fissure sealants were evaluated for dye penetration between sealant and enamel. The conventional fissure sealant (Durafil Flow) showed the greatest degree of dye penetration in the largest number of specimens. The penetration of the dye was less extensive when a filled resin (P30) was used. The use of a dentine adhesive together with the filled resin further reduced the penetration of the dye. The number of teeth exhibiting leakage with this treatment was the smallest noted.

Acrylates↗