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Biomedical subjects

G J Pearson

Publications and source records attributed to G J Pearson.

At least 55 records · Page 3Linked to original sources
PubMed1998

Long-term flexural strengths of resin-modified glass-ionomer cements.

The use of resin-modified glass-ionomer cements (RMGICs) in restorative dentistry has expanded since their introduction about seven years ago. These materials have been shown to possess superior initial mechanical properties to those of the conventional glass-ionomer cements. However, studies on the strength of RMGICs as a function of storage time are limited. This in vitro study investigated the effects of long-term storage of RMGICs in two storage media, distilled water and artificial saliva, at 37 degrees C on their four-point and bi-axial flexural stengths for a period up to 1 yr. All materials, except Fuji Lining LC, were weak at 5 min after light exposure but reached the maximum strengths within 7 d. Subsequently, there was a small decline in strength. Generally, the specimens aged in distilled water and artificial saliva had similar strength values. The bi-axial strengths of RMGICs were significantly greater than those obtained from the four-point flexure tests by a factor of approximately three. More variations in strengths of RMGICs with time were also observed from the four-point flexure test than from the bi-axial flexure test.

Biocompatible Materials↗
PubMed1998

Long-term flexural strength of three direct aesthetic restorative materials.

OBJECTIVES: This investigation evaluates the long-term flexural strength behaviour of three different glass-ionomer cement (GIC) based materials. METHODS: The materials under investigation were a conventional GIC (Opusfil), a metal-reinforced GIC (Opus Silver) and a resin-modified GIC (Fuji II LC). Flexural strength specimens of the materials were prepared according to the relevant manufacturers' instructions for clinical use. After 10-min maturation at 37 degrees C, the specimens were placed in water, also at 37 degrees C, until required for testing. Specimens were tested under four-point bend at intervals between 7 and 130 days after manufacture. RESULTS: Opusfil increased in strength up to day 56, but was significantly weaker after this time. Opus Silver was strongest on day 7, although there was no further decline in strength after day 14. Fuji II LC increased in strength up to day 14, but there was deterioration in strength after day 100. Opus Silver had the highest early strength of the three materials, but after day 7 there was no significant difference in strength between the three materials under test. CONCLUSIONS: The three cements tested did not exhibit the continued increase in strength with time that has been attributed to glass-ionomer cements. Each material behaved differently, but they all appeared to be adversely affected by storage in aqueous media. Materials formed by the inclusion of metal or the incorporation of resins into the glass-ionomer cement formulation should be regarded as separate sub-classes of materials in their own rights.

Dental Cements↗
PubMed1998

The uptake and release of fluoride by ion-leaching cements after exposure to toothpaste.

OBJECTIVES: The cariostatic action associated with the glass-ionomer cement (GIC) is usually attributed to its sustained release of fluoride. However the ability of the GIC to act as a fluoride reservoir, taking it up from an external source (e.g. toothpaste, mouthwash) and subsequently releasing it over time, may also be a contributory factor. This study investigated the reservoir effect of various recently introduced ion-releasing cements: two resin-modified glass-ionomer cements (Fuji II LC, Vitremer), a compomer (acid-modified composite resin) (Dyract), and a recently introduced conventional glass-ionomer (Fuji IX). METHODS: Specimens were exposed to a fluoridated toothpaste after 28 and/or 58 days. The release of fluoride into the storage water, both before and after exposure, was monitored using a differential electrode cell. RESULTS: There was no significant difference in the fluoride releases from Vitremer and Fuji II LC. These materials released significantly more fluoride than Fuji IX and Dyract. All the materials released more fluoride on the day after exposure to an external fluoride source compared with the day before exposure. Release rates returned to baseline within 3 days. Within the time periods of the study, only the uptake/re-release of Fuji IX was adversely affected by late exposure. All the materials showed an enhanced uptake and release on repeated exposure to the external fluoride source. CONCLUSIONS: All the materials under test (Dyract, Fuji II LC, Vitremer and Fuji IX) released significant amounts of fluoride and reacted positively to exposure to an external fluoride source.

Cariostatic Agents↗
PubMed1998

Long-term surface micro-hardness of resin-modified glass ionomers.

OBJECTIVES: The presence of a resin component in resin-modified glass-ionomer cements (RMGICs) results in considerable water sorption which may affect the surface hardness of the materials. This study investigated the effect of long-term storage in aqueous solutions on the surface hardness of RMGICs. METHODS: The surface micro-hardness of four RMGICs stored in either distilled water or artificial saliva was measured using the Wallace microindentation tester at regular time intervals up to 360 days. RESULTS: There was a substantial increase in hardness during the first day of storage when RMGICs were kept in distilled water. All RMGICs except one liner/base material reached their maximum hardness within 7 days and maintained their hardness for up to 1 year. RMGICs stored in artificial saliva were relatively softer and showed a decrease in surface hardness with time. CONCLUSIONS: The post-hardening reaction overcame the plasticising effect of water when RMGICs were stored in distilled water. However, progressive and high water uptake of specimens stored in artificial saliva resulted in a decrease in their surface hardness.

Analysis of Variance↗
PubMed1998

Long-term strength of aesthetic restoratives.

Glass-ionomer cements have established an important role in clinical dentistry since their introduction over 20 years ago. More recently, in an attempt to enhance the strength of the material, resin additions have been made to conventional glass-ionomer cements. This study established the long term flexural strength of two hybrid glass-ionomer cements, by use of a bi-axial flexural strength test (Shell test), and compared the values with those obtained for a light curing composite resin and a conventional glass-ionomer cement. The results demonstrated that those materials with a high resin component relying on polymerization as the main method of setting had a greater initial flexural strength than those with little or no resin addition. Those materials where the glass-ionomer acid-base reaction provided a substantial contribution to the setting reaction showed an increase in strength as they matured, whereas a decline in strength with time was observed for those materials where the resin setting reaction predominated.

Acrylic Resins↗
PubMed1998

A comparison between the wear resistance of three types of denture resin to three different dentifrices.

This study compares the abrasive effects of three dentifrices on three different denture base resins, a heat cured acrylic resin, a self cured acrylic resin and a light activated urethane dimethacrylate-based resin. Specimens of the resins were subjected to a regimen of mechanical brushing using measured amounts of paste on standard toothbrushes driven by a reciprocating device. The apparent wear of each specimen was assessed qualitatively using scanning electron microscopy and quantitatively using profilometry and reflex microscopy. The study showed that cleaning pastes play a significant role in the wear of conventional acrylic resins, the relative abrasivity of the dentifrices being substrate related. However, wear was less evident on the light activated urethane dimethacrylate resin. Brushing with water alone produced no detectable wear on any of the specimens.

Acrylic Resins↗
PubMed1998

Effect of moisture protective coatings on the strength of a modern metal-reinforced glass-ionomer cement.

The strength of a modern, low metal:glass ratio, metal-reinforced glass-ionomer cement was measured evaluating a number of protective barriers: one light-cured resin, two solvent-based dental varnishes and petroleum jelly. The cement was exposed to water at 10 and 60 min from start of mix. The results obtained with these protecting agents were compared with those obtained where no protection was applied. A comparison of uniaxial flexural strength and biaxial flexural strength showed the latter to be more discriminating. Proprietary dental varnishes were superior to petroleum jelly, producing similar strengths of 50 MPa. Petroleum jelly was, however, preferable to no protection. Moisture protection during the first 30 min was found to be beneficial, thereafter no further strength increase was found. A second material, a cement which has a high metal:glass ratio, was found to be more moisture resistant but weaker in strength than the modern material, with a biaxial strength of 39 MPa.

Cermet Cements↗
PubMed1998

Dye penetration at a cobalt-chromium alloy--composite resin interface.

This study examined microleakage along the interface of resin systems bonded to cobalt-chromium alloy; a microfine resin with adhesive properties based upon methacrylic acid, and a hybrid resin containing an adhesive phosphate monomer. Specimens were thermocycled between 4 degrees, 37 degrees and 60 degrees C over 1000-10,000 cycles and placed in 0.1% neutral red dye for 7 days. Each was cut diagonally and the interfaces photographed using an optical microscope. Dye penetration was expressed as a percentage of the total length of each edge. The hybrid resin showed significantly less microleakage than the microfine resin.

Chromium Alloys↗
PubMed1997

A laboratory evaluation of the construction of resin-bonded cast restorations.

OBJECTIVE: To compare the effect of two construction techniques and two pattern materials on the fit of resin-bonded cast restorations. DESIGN: In-vitro study carried out by one operator. SETTING: Postgraduate university hospital. SUBJECTS AND METHODS: 65 nickel-chrome castings were constructed using refractory die and lift-off techniques with wax and acrylic resin pattern material. They were cemented onto master silver dies, embedded in self-curing acrylic resin and sectioned along their long axes. Interfacial distance between the master silver die and casting was measured. RESULTS: A significant different between the range of figures in each group (Mann-Whitney Test, P < 0.01) was found. Construction techniques can be ranked in order of fit of castings: 1. Refractory die, wax patterns: 42.6 microns (SD 12.03). 2. Refractory die, acrylic resin patterns: 53.7 microns (SD.16.06).3. Conventional technique, acrylic resin patterns: 85.5 microns (SD 31.62). 4. Lift-off technique, wax patterns: 139 microns (SD 53.15).5. Lift-off technique, acrylic patterns: 172.8 microns (SD 74.04). CONCLUSIONS: Castings constructed using refractory die technique and subsequently cemented resulted in a more accurate and less variable fit than those produced with the lift-off technique. Wax patterns lead to more accurate castings than acrylic resin and locating indentations may interfere with the cementation of castings when lift-off techniques are used.

Acrylic Resins↗
PubMed1997

Water sorption characteristics of resin-modified glass-ionomer cements.

When restorative materials take up water, their dimensions and structural integrity may be affected. This study determined, using gravimetric measurements, the water sorption characteristics of four resin-modified glass-ionomer cements (RMGICs) immersed in either distilled water or artificial saliva. The dimensional changes on water storage were also determined. The RMGICs exhibited differing characteristics as they absorbed water. Percentage water uptake and solubility of the liner/base RMGICs were significantly greater than those of the restoratives. Higher rates of water uptake, i.e. higher values of sorption diffusion coefficients, were found in the materials from one manufacturer. The desorption diffusion coefficients of the four cements were not significantly different from one another, but were significantly higher than the sorption coefficients, indicating rapid water loss from the desiccated cements. All the cements expanded on immersion in water and contracted during desorption. Greater weight increase and greater volumetric expansion were observed on long-term storage in artificial saliva than in distilled water.

Chemical Phenomena↗
PubMed1997

Adhesive composite resins for artificial teeth: a laboratory investigation of bond strength to a cobalt-chromium alloy.

Adhesive resin systems are reported to improve the bond strength between resins and cast cobalt-chromium alloy. This investigation compares the behaviour of three resin systems. Cylinders and beams of cobalt-chromium, with 0.6-mm-diameter retention beads regularly cast onto the bonding surfaces, were air-abraded and ultrasonically cleaned. Resin veneers 4 mm deep on the cylinders and 2 mm on the bars were polymerized by heat and pressure or by light. Specimens were water-stored for 7 or 90 days, including thermocycling between 4, 37 and 60 degrees C, before testing in a Universal Testing Machine to examine the shear bond strength or the effect of the bonded resin spine on the flexural strength of the beams using a three-point bend test. Specimens were examined with an optical microscope to attempt to determine the nature of the failures that occurred. The investigation showed that, overall, the heat- and pressure-cured urethane dimethacrylate resin with and adhesive based upon methacrylic acid performed significantly less well than a conventional acrylic resin, or a hybrid composite resin with and adhesive monomer.

Chromium↗
PubMed1997

High throughput PCR detection of HCV based on semiautomated multisample RNA capture.

An amplification procedure based on a semiautomated 60-sample RNA capture, including combined reverse transcription/polymerase chain reaction (RT-PCR) and nested PCR/Taqman amplicon detection. is described. It can be completed within a working day and is suitable for the development of a fully automated system. HCV RNA-specific capture is independent of the sequence variations as it targets the poly(U) tract commonly present at the 3'-end of the HCV genome (U-capture). The type specificity of the assay determined in a panel of 56 confirmed HCV antibody-positive samples (genotypes 1-6) was slightly better when compared to a commercial assay. The sensitivity evaluated on serial dilutions of representative samples was equal for genotypes 1, 2, 5, 6, or increased for genotypes 3 and 4 with the U-capture assay.

Automation↗
PubMed1996

An in vitro microleakage study of three restorative techniques for Class II restorations in posterior teeth.

Microleakage associated with a silver reinforced restorative glass ionomer cement used alone and also as a laminate restoration with a composite resin and dentine adhesive in extracted premolar and molar teeth was evaluated. The influence of artificial saliva, thermal and load cycling was also determined. The composite and dentine adhesive alone were used for comparative purposes. The results showed that the composite resin/dentine adhesive restorations showed substantial microleakage at both the cervical and occlusal margins of the Class II restorations, whereas the glass ionomer alone showed little or no leakage after storage in water for seven days at 37 degrees C. These results were confirmed when the restorations were thermo-cycled and load stressed. The addition of glass ionomer as a base to the composite forming the laminate restoration reduced the leakage substantially and in certain conditions the leakage was less than that observed with glass ionomer restoratives alone.

Dental Leakage↗
PubMed1996

In vitro investigation of fluoride ion release from four resin-modified glass polyalkenoate cements.

Conventional glass ionomer cements are known to release fluoride ions to the surroundings. Recently, resin-modified glass ionomer cements have been produced. These have differing chemical formulations and this may affect their ability to release fluoride ions. The study evaluates both the fluoride release and compressive strength of one conventional and four resin-modified glass ionomer cements with respect to time. The results showed that the formulation of the resin-modified materials influenced the fluoride release. One resin-modified glass ionomer (PhotacFil) released more fluoride than all other materials, while Vitremer, Fuji II LC and Chemfil Superior release similar amounts. Variglass had a very much smaller elution of fluoride ions. This suggests that there is considerable variation in fluoride release between materials of similar generic origin. The compressive strength of these materials was not affected with time.

Biocompatible Materials↗
PubMed1996

Method for enhancing the fluoride release of a glass-ionomer cement.

The cariostatic action of the glass-ionomer cement has been attributed to its sustained release of fluoride. The fluoride in the set cement originates from the glass particles which are eroded, in part, during the setting reaction. In this study a water-activated glass-ionomer was mixed with sodium fluoride (NaF) solutions of different concentrations (0%, 2% and 4%). The different cements were used to prepare discs which were stored individually in demineralized water at 37 degrees C, the fluoride concentration of the storage solutions were measured, at intervals, until the specimens were 80 days old. The effect of the different mixing solutions on the working and setting times and compressive strength were also determined. It was found that the cement mixed with the 4% solution of NaF released significantly more fluoride than the water mixed control. The fluoride solution mixed materials had longer setting times than the control, but there was no significant difference in the compressive strengths. All the materials became progressively stronger on storage. Mixing the cement with a 4% solution of NaF increased the initial fluoride release of the glass-ionomer without seriously affecting other physical properties.

Delayed-Action Preparations↗
PubMed1996

Factors contributing to the temperature rise during polymerization of resin-modified glass-ionomer cements.

Part of the setting reaction of a resin-modified glass-ionomer cement (RMGIC) is a photoinitiated polymerization. As a result of the polymerization exotherm, the temperature of the cement may rise during setting. This study investigated the temperature rise for two liner/base- and two restorative-type RMGICs. The effects of factors such as specimen thickness, exposure time and environment temperature were investigated. The thermal diffusivity of the cements was also evaluated. Temperatures were measured using a thermocouple embedded in the centre of 6-mm diameter specimen discs of 1, 2, or 3 mm thickness. The exposure times used to cure the specimens varied from 15 to 60 s. The test were carried out at either 25 or 37 degrees C. The temperature rises attributable to the polymerization reaction ranged from 11 to 26 degrees C for the liner/base cements and from 8 to 17 degrees C for the restorative cements. Increasing the specimen thickness reduced the temperature rise only when inadequate exposure times were used. Raising the environmental temperature resulted in a smaller temperature rise. The thermal diffusivities were determined from cylindrical specimens. These ranged from 1.9 x 10(-3) to 2.5 x 10(-3) cm2 s-1, the lining cements showing lower values than the restorative materials.

Chemical Phenomena↗
PubMed1996

An in vitro microleakage study of a new multi-purpose dental adhesive system.

Despite the advances made in the field of adhesive dentistry, microleakage still remains an area of concern, as a secure seal to dentine and cementum still cannot be achieved with certainty. This project compared the effectiveness of a new adhesive, Scotchbond Multi-Purpose Dental Adhesive System (SBMP) with an established product, Gluma Bonding System (Gluma) in preventing microleakage and the influence of storage, thermal and load cycling on microleakage patterns. In uncycled specimens, Gluma Bonding System had significantly less leakage (P < 0.01) at both occlusal and cervical margins. Thermocycling of composite restorations utilizing SBMP resulted in a significant decrease (P < 0.05) at the occlusal margins but had no effects on cervical leakage. Mechanical loading had no influence on leakage patterns either cervically or occlusally. Three months' storage and combined treatment resulted in a significant decrease in leakage (P < 0.05) at the occlusal margins.

Chi-Square Distribution↗