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Biomedical subjects

G J Pearson

Publications and source records attributed to G J Pearson.

At least 109 records · Page 6Linked to original sources
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↗
PubMed1988

The effect of seating pressure and powder/liquid ratio of zinc phosphate cement on the retention of crowns.

The effect of three different powder/liquid ratios of one zinc phosphate cement on the early retention of a standard crown on metal and tooth dies was investigated. Two different seating pressures were evaluated. The results indicate that the effect of variation in the powder/liquid was not significant. The part played by the seating force was significant, the higher seating force resulting in a greater force being required for displacement after 1 h. Greater forces of removal were required when tooth dies were used.

Cementation↗
PubMed1988

The effects of mixing capsule geometry on the early compressive strength of dental amalgam.

Three dental amalgams were mixed in a number of different mixing capsules. Compressive strength specimens were prepared using a clinically relevant technique and tested at 1 h and 7 days. The results showed that the early compressive strength of an alloy was influenced by the mixing capsule, and suggested that internal capsule geometry may be an important contributory factor in capsule performance. With one exception, there was a marked difference between the compressive strengths produced under the present method and those reported by manufacturers under test conditions laid down in standards specifications.

Capsules↗
PubMed1987

Variations in tooth surface temperature in the oral cavity during fluid intake.

Measurements were made of the extremes in temperature which occur at different sites in the oral cavity during fluid intake. The results indicate that temperatures noted at the tooth surface, within the mouth, during fluid intake were less than the temperatures of the fluid imbibed. Variations in temperature were noted in different areas of the mouth. This may be associated with the position of the tongue during swallowing and the effect of the tissues of the oral cavity as heat absorbers. The range of temperatures noted at the tooth surface and the duration of the temperature changes were at variance with those utilized in many thermocycling studies. It is suggested that closer alignment with the clinical situation is desirable.

Adult↗
PubMed1987

Cusp movement in molar teeth using dentine adhesives and composite filling materials.

Forty extracted molar teeth were stored in saline. After MOD cavities were prepared and the dimensions of each cavity recorded, the teeth were restored with either a microfine or hybrid composite in conjunction with a dentine adhesive. Cusp movements were recorded from two linear variable displacement transducers attached to the cusps. Three types of movement were identified, one in which the opposing cusps moved towards one another, the second where no movement occurred at all, and the third where both cusps moved in the same direction. The degree of movement observed with the microfine material was nearly double that recorded with the hybrid. The movement appeared to relate to the polymerization shrinkage values of the materials and to the failure of the adhesive bond between the tooth and the composite-adhesive complex.

Adhesives↗