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Biomedical subjects

G J Pearson

Publications and source records attributed to G J Pearson.

At least 73 records · Page 4Linked to original sources
PubMed1996

Physical properties of casts prepared from disinfected alginate.

The dimensional accuracy, surface hardness and reproduction of surface detail of stone casts produced from alginate impressions treated with 4.65% sodium hypochlorite, were investigated. To test dimensional accuracy, a Reflex Microscope was used to compare casts from 10 untreated impressions with casts from 10 impressions immersed in the solution for 30 mins. Surface detail and hardness were investigated on casts produced from impressions of a master stainless steel plate with 10 micro-indentations of increasing size. Surface detail of the casts were assessed by observation and surface hardness by a Vickers Hardness Machine. The dimensional accuracy test showed no significant differences between the experimental and control groups. Surface detail was unaffected after immersion of up to 10 mins. Surface hardness decreased linearly with respect to immersion time, when this was greater than 5 mins.

Alginates↗
PubMed1995

Influence of humidity on dimensional stability of a range of ion-leachable cements.

The dimensional changes of a variety of dental restorative materials, occurring during and after setting, were investigated. The materials were tested under four different environmental conditions: 25 degrees C at laboratory humidity, 25 degrees C at 100% humidity, 37 degrees C at laboratory humidity and 37 degrees C at 100% humidity. Two materials setting by an acid-base reaction were also examined when protected with both a conventional varnish and a low-viscosity light-curable resin. The dimensional changes were recorded continuously using linear variable displacement transducers (LVDTs) over periods of up to 2 h. The materials investigated showed varying magnitudes of dimensional change. The shrinkage of conventional glass-ionomer cements (Fuji II and Opusfil) were the highest at 37 degrees C in air. This was attributed to the highest rate of water loss in the most desiccating environment. The shrinkage observed for the materials which set, even only in part, by a polymerization reaction will probably be due to the water loss and/or polymerization shrinkage. Exposure of these materials to a high-humidity environment reduced the shrinkage because of the swelling associated with water absorption. Application of the varnish and the protective resin over the cement surfaces also reduced shrinkage in Fuji II due to prevention of water exchange. The apparatus used in this study provided a simple and reliable method for measuring linear dimensional change. Data obtained in this study were comparable, where appropriate, to the values found in the literature.

Absorption↗
PubMed1995

Temperature rise in ion-leachable cements during setting reaction.

Resin-modified ion-leachable cements have been developed for use as aesthetic restorative materials. Their apparent improved physical and handling properties can make them more attractive for use than conventional glass-ionomers. However, they contain monomers which are known to contract on polymerization and produce a polymerization exotherm. This study evaluated the temperature rise during setting and the rate of dimensional change of several ion-leachable materials. The resin-modified ion-leachable cements demonstrated greater temperature rises and higher rates of contraction than conventional materials. Generally, the behaviour of these resin-modified materials was similar to that of composite resins. However, some resin-modified cements produced a temperature rise of up to 20 degrees C during polymerization which was greater than that of the composite resin. This temperature rise must be taken into account when using the materials in direct contact with dentine in deep cavities without pulp protection. Longer irradiation time than the recommended 20 s did not significantly increase the maximum temperature rise but slightly extended the time before the temperature started to decline. The temperature of the environment had a significant effect on the rate of dimensional change in some materials. The rate of polymerization contraction of light-activated cements was directly related to the observed temperature rise.

Dental Cements↗
PubMed1995

Bacteria in supragingival plaque samples can be killed by low-power laser light in the presence of a photosensitizer.

The purpose of this study was to determine whether bacteria in supragingival plaque samples could be killed by low-power laser light in the presence of a suitable photosensitizer. Plaque samples were obtained from 10 volunteers, treated with either toluidine blue O (TBO) or aluminum disulphonated phthalocyanine (AlPcS2), and then exposed to light from a helium/neon (HeNe) or gallium aluminium arsenide (GaAs) laser respectively. Following irradiation, substantial reductions were achieved in the total anaerobic count as well as in the number of viable streptococci and actinomyces present in the samples. In the absence of laser light, the sensitizers themselves had little effect on the viability of the bacteria in the plaque samples. The HeNe/TBO combination appeared to be more effective than the GaAs/AlPcS2 combination, achieving log10 reductions of 2.95, 5.40 and 3.34 in the total anaerobic count, streptococci and actinomyces respectively with a light energy dose of 1.31 J. If effective in vivo, lethal photosensitization may be useful as a means of eliminating plaque bacteria from a carious lesion prior to its restoration.

Actinomyces↗
PubMed1995

Effect of dentine and collagen on the lethal photosensitization of Streptococcus mutans.

Suspensions of the cariogenic bacterium, Streptococcus mutans were treated with either toluidine blue O or aluminium disulphonated phthalocyanine and then exposed to light from a helium-neon or gallium-aluminium-arsenide laser, respectively, after passing through demineralized dentine slices. Bacteria were also embedded in a collagen matrix prior to sensitization and exposure to the laser light. When dentine slices were interposed between the laser light and the bacterial suspension, substantial kills (10(7) CFU) were achieved at energy doses of 876, 1,752, and 3,504 mJ with the helium-neon laser and of 1,188, 2,376, and 4,752 mJ with the gallium-aluminium-arsenide laser. There was no apparent relationship between the extent of killing and the degree of demineralization of the dentine. Prolonging the exposure of the sensitized bacteria to the laser light increased the kill achieved. Substantial numbers (10(8) to 10(10) CFU) of S. mutans were also killed when embedded in a collagen matrix and exposed to 438 and 1,314 mJ of helium-neon laser light and 594 and 1,782 mJ of light from the gallium-aluminium-arsenide laser. These results imply that lethal photosensitization may be effective at killing S. mutans in a carious lesion, even when the organism is embedded in demineralized dentine.

Animals↗
PubMed1995

Effects of cyclic stressing on attachment bond strength using glass ionomer cement and composite resin.

Bonded orthodontic brackets were subjected to cyclic loading in order to simulate the effect of occlusal forces. The subsequent effect on bond strength was determined. Stainless steel, mesh-based brackets were bonded to extracted teeth with either composite resin or glass ionomer cement. A jig was designed to subject each bracket to a preselected loading level and the 24-hour shear/peel bond strength of both stressed and unstressed brackets was subsequently measured. Cyclic loading brought about a comparative decrease in bond strength when using both types of material. The potential implications of selecting these different types of bonding material for clinical use are discussed.

Acid Etching, Dental↗
PubMed1994

A survey of current practice into the use of aesthetic inlays.

In recent years there has been a concerted effort to produce an aesthetic restoration to replace amalgam, while retaining its qualities of strength and longevity. The use of porcelains and composite resins used indirectly as inlays and onlays has today improved the qualities of directly filled composites. A survey of 310 general dental practitioners in the UK known to use this type of restoration produced 162 responses to a questionnaire to evaluate their experiences to these techniques. The majority, 85%, had used a composite inlay system for about 2 years, with a 90% success rate over this period. Information collected provided details on variations in cavity design and cementing procedures.

Composite Resins↗
PubMed1994

Zinc phosphate cements: an evaluation of some factors influencing the lactic acid jet test erosion.

The lactic acid jet test was used to measure erosion rates of eight commercial zinc phosphate cements at 23 and 37 degrees C after 24 h and 2 months. Rates exceeded the ISO 9917 published limit of 0.1 mm/h when tested according to this specification (23 degrees C, 24 h), suggesting the limit should be increased. Erosion was measured by both weight loss and depth change. At 24 h erosion decreased as temperature increased, whereas after 2 months temperature had no significant effect. No trend was seen with increasing specimen maturity. Stannous fluoride may increase erosion resistance.

Hot Temperature↗
PubMed1994

Krypton fluoride excimer laser ablation of tooth tissues: precision tissue machining.

A variety of lasers using different wavelengths have been used to remove dental hard tissue. The infrared lasers produce their effects photothermally whereas ultraviolet excimer lasers remove tissue in a controlled and precise manner by photoablation. This study investigates the use of 248 nm laser radiation in the precision removal of both enamel and dentine using diffraction limited ultraviolet optics. The data showed that enamel and dentine were machined to a high level of precision (1-2 micron tolerances). The rate of removal was greater in dentine than enamel at a range of energy densities between 1.15 and 2.2 J/cm2. The method of removal of both tissues appears to be by the preferential ablation of the organic phases of each, exposing the anatomical details of their structure. An explanation of the possible method of ablation is proposed for these tissues.

Dental Enamel↗
PubMed1994

Preliminary in vitro investigation of the effects of pulsed Nd:YAG laser radiation on enamel and dentine.

Data available on the effects of pulsed near IR laser energy on dental hard tissue are limited. This study investigates the changes in dental hard tissue when exposed to short duration, pulsed IR wavelength laser light emitted from a Neodymium Yttrium Aluminium Garnet laser (Nd:YAG laser, wavelength 1.06 microns). The results showed that, after treatment with an initiator, there was superficial melting of the enamel. Dentine was altered substantially. The lesions produced in dentine were larger than the cross-section of the delivery fibre optic wand. Considerable inter-sample variation was observed. The temperature rises producing these effects were large and affected the tissue at a distance from the tip.

Aluminum↗
PubMed1994

The physical properties of a polyacetal denture resin.

A polyacetal injection-moulded resin is being marketed for the construction of retentive and supportive components of removable partial dentures (RPDs). Specimens of poly(oxymethylene) cast by commercial laboratories were tested to examine the following physical characteristics: the modulus of elasticity in compression, extension and flexure, stress relaxation, the force displacement behaviour of clasp forms, impact strength and glass transition temperature. Results showed that the material has a flexural modulus lower than that of poly(methylmethacrylate) and is insufficiently rigid to be used as a supporting element for partial dentures. Resin clasps may be resilient enough to engage undercuts for the retention of RPDs but the low flexural modulus requires that the resin be used in greater cross-sectional area than metal alloys in order to gain useful retention. This greater bulk has implications for plaque accumulation and maintenance of periodontal health.

Acetals↗
PubMed1994

Killing of cariogenic bacteria by light from a gallium aluminium arsenide diode laser.

Suspensions of Streptococcus mutans, S. sobrinus, Lactobacillus casei and Actinomyces viscosus were exposed to light from a gallium aluminium arsenide laser in the presence of aluminium disulphonated phthalocyanine and the numbers of survivors determined. Exposure to the laser light in the absence of the dye, or the dye in the absence of the laser light, had no significant effect on the viability of the organisms. However, a light-dose-related decrease in the viable count of all four target organisms was found on exposure to the laser light in the presence of the dye. The kills attributable to lethal photosensitization amounted to approximately 10(6) CFU in the case of each organisms. As appreciable kills were achieved within clinically convenient exposure times (30-90 s), these results imply that lethal photosensitization may be a useful technique for eliminating bacteria from carious lesions prior to restoration.

Actinomyces viscosus↗
PubMed1994

Repair of glass ionomer cements--methods for conditioning the surface of the cement to achieve bonding.

Two chemically different glass ionomer cements (Ketac Fil and ChemFil II Caps) and three different methods of conditioning the surface for repair were evaluated. Specimens of each material were prepared, aged and sectioned. The cut surfaces were treated with either phosphoric acid, polyacrylic acid or a combination of phosphoric acid followed by polyacrylic acid. Freshly mixed glass ionomer cement was injected against the treated surface and allowed to set under simulated intra-oral conditions. The specimens were then tested to failure in flexion after 7 days storage. The flexural strength of the repaired specimens was compared with that of control specimens of the same materials. The flexural strength of the repaired specimens was less than that of the controls. Treatment of the fractured surface with polyacrylic acid produced the weakest repair, and the use of phosphoric acid as the conditioning agent produced repaired specimens approximately 80% of the strength of the controls.

Acid Etching, Dental↗
PubMed1994

Concepts of adhesion--a review.

This paper reviews the current concepts of adhesion in restorative dentistry. Despite the numerous products available in the market, adhesion occurs in one or a combination of four ways. 1. Acid-etch and formation of resin tags. 2. Formation of strongly bonded surface precipitates, to which a resin can be chemically or mechanically bonded. 3. Chemical bonding to the inorganic components of tooth structure. 4. Chemical bonding to the organic components of tooth structure. With the success of the acid-etch technique for bonding to enamel, much of today's adhesive research has been directed towards bonding to dentine. None of the currently available dentine adhesives can achieve an ideal bond to dentine.

Acid Etching, Dental↗
PubMed1993

Effect of mixing speed on mechanical properties of encapsulated glass-ionomer cements.

It is well established that the strength of encapsulated dental amalgam is affected by the speed of mixing. An investigation into the effects of mixing speeds on the compressive strength of three encapsulated glass-ionomer cements was carried out. The working and setting time and compressive strength at 24 hours and 7 days were evaluated for the three materials at four mixing speeds. There appeared to be little variation in working and setting times at the different mixing speeds. The early compressive strength of one material, Ketac-fil, increased as the speed of mixing increased. The variation in mixing speed did not appear to affect the early compressive strengths of the other two materials. Seven-day compressive strengths of all three materials were not affected by variations in mixing time.

Aluminum Silicates↗
PubMed1993

Erosion and compressive strength of hybrid glass ionomer cements when light activated or chemically set.

It is claimed that light-activated hybrid glass ionomer cements offer advantages over the conventional glass ionomer lining materials. The compressive strengths and erosion rates of two hybrid glass ionomer lining cements, when light activated and chemically set, were compared with conventional glass ionomer cements. The results demonstrated that the erosion rates of the light-activated materials were comparable with those of the conventional materials. The conventional material, Ketac-Bond, was stronger than the light-activated hybrids. When the hybrid materials were allowed to set chemically alone, their performance was inferior to the conventional glass ionomer lining cements.

Glass Ionomer Cements↗
PubMed1993

Lactic acid jet test: in vitro erosion rates of glass ionomer dental cements containing radiopacifying elements.

The lactic acid jet test erosion rates were measured for 13 radiopaque glass ionomer dental materials obtained from a number of manufacturing sources. The erosion rate was compared with that found for the non-radiopaque restorative from the same manufacturer to determine whether the addition of an extra element had affected the resistance to erosion. Six materials were not significantly affected, six showed a significant increase in erosion rate. Only one material showed a reduced erosion rate. Materials containing a high proportion of any additive could show an increased erosion rate. Glass ionomer cements with or without radiopacifying elements had low erosion rates compared with other dental materials.

Alloys↗