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Biomedical subjects

G J Pearson

Publications and source records attributed to G J Pearson.

At least 91 records · Page 5Linked to original sources
PubMed1993

Cuspal movement and microleakage around reinforced glass ionomer cements.

The effect of restoration of mesio-occluso-distal cavities in molar teeth with reinforced glass ionomer cements on cuspal flexure in vitro is reported. Measurements of cuspal flexure using linear variable displacement transducers were carried out for 90 min after the placement of two types of reinforced glass ionomer cement. The measurements demonstrated that no movement occurred except in cases where the materials were allowed to dehydrate. Under these circumstances the opposing cusps moved toward one another. This movement was observed to be directly related to time. Microleakage was very much less than that observed for composite materials evaluated under the same test conditions.

Composite Resins↗
PubMed1993

Sensitisation of cariogenic bacteria to killing by light from a helium-neon laser.

Suspensions of the cariogenic bacteria Streptococcus mutans, S. sobrinus, Lactobacillus casei and Actinomyces viscosus were exposed to light from a 7.3-mW helium-neon laser in the presence of toluidine blue O. A substantial killing rate (c. 10(6) cfu) of all four species was achieved with a dye concentration of 50 micrograms/ml and a light energy dose of 33.6 J/cm2. This was achieved in 60 s, an exposure time that is clinically acceptable. Exposure to laser light in the absence of the dye did not significantly affect the viability of any of the organisms. This approach may be useful in dentistry to sterilise a carious lesion prior to its repair.

Actinomyces viscosus↗
PubMed1993

The effect of temperature change on the working and setting time of two luting cements.

The effect of temperature change on the working and setting time of a glass ionomer luting cement and a resin luting cement was measured using the oscillating rheometer. The time taken for each cement to set was calculated from the chart recordings. It was observed that as the temperature increased, the working and setting time of both materials decreased. However, the reduction was much more marked for the dual curing resin cement.

Dental Cements↗
PubMed1993

SEM analyses of repaired glass-ionomer cements.

This study assessed the nature of the adhesion in repaired glass-ionomer restorative materials. Two chemically different glass-ionomer cements, Ketac Fil and Chemfil II Cap, and three different methods of conditioning the surface for repair were employed. Specimens of each material were prepared and the cut surfaces were then treated with either 35% phosphoric acid, 35% polyacrylic acid or a combination of phosphoric acid followed by polyacrylic acid. Freshly mixed material was injected against these treated surfaces and allowed to set under simulated intraoral conditions. The specimens were tested to failure in flexion after seven days storage. Assessment of the fractured surfaces was then carried out using the scanning electron microscope. The results showed the occurrence of both adhesive and cohesive failure.

Acid Etching, Dental↗
PubMed1993

An experimental evaluation of precision laser cutting of dental hard tissues and materials.

This paper examines the use of excimer laser radiation in the controlled removal of tooth tissue and three plastic restorative materials. Freshly extracted human third molar teeth were filled with three restorative materials and sectioned longitudinally through the restoratives. The cut surfaces of the materials and surrounding enamel and dentine were exposed to three laser energy densities and the dimensions and topographical details of the irradiated sites assessed using optical and scanning electron microscopy. The results showed that the radiation produced lesions of uniformly reproducible size and shape.

Composite Resins↗
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

Fissure sealants as a means of prolonging longevity of amalgam restorations--an in-vitro feasibility study.

The presence of an interface gap around the periphery of old amalgam restorations in extracted teeth was confirmed by scanning electron microscopy (SEM) and light microscopy. Two fissure sealant resins (Concise White Sealant and Delton Fissure Sealant) were placed over amalgam margins in vitro and were found to occlude this gap. SEM studies permitted assessment of the integrity of the resin in the interface defect and degree of sealant penetration toward the enamel/dentine junction. Microleakage studies using dye immersion techniques confirmed the efficacy of sealants in limiting dye penetration. This study indicates that margins of amalgams may be sealed in vivo by this method, delaying the need for replacement of the old amalgam and potentially providing protection for the tooth from secondary marginal caries.

Dental Amalgam↗
PubMed1991

Physical properties of glass-ionomer cements influencing clinical performance.

This paper considers the modern commercial glass-ionomer cements and compares their variable physical properties with specific reference to working and setting times, powder liquid ratios used clinically, finishing techniques and the effects of etching for the laminate technique. The variation in long term mechanical properties of different restorative glass-ionomer cements is examined and the hybrid glass-ionomers are assessed.

Dental Bonding↗
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↗