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Biomedical subjects

R Strang

Publications and source records attributed to R Strang.

At least 37 records · Page 2Linked to original sources
PubMed1994

Fluoride uptake and release characteristics of glass ionomer cements.

The aims of this study were firstly to investigate the fluoride-releasing characteristics of five commercial glass ionomer materials: Ketac Fil, Chemfil Superior, Fuji II LC, Aquacem and Vitrebond. The second aim was to assess the fluoride uptake and subsequent release from the same range of materials. In both tests, ten discs, 6 mm in diameter with a thickness of 1.5 mm, were made for each material. The initial fluoride release was assessed over a 60-day period for all materials. Each disc was immersed in 2 ml of de-ionised water within a plastic vial. The solutions were changed daily up to day 15, and thereafter every 3 and 4 days until the end of the test. All of the materials released measurable amounts of fluoride throughout the test period, with a considerable range on day 1 (15.3-155.2 ppm F). The concentration of fluoride released on the 2nd day fell sharply for all materials (range 6.3-44.3 ppm F). By day 60 all materials continued to release fluoride, albeit to a lesser extent (range 0.9-3.99 ppm F). With regard to the uptake and release of fluoride, a similar protocol was employed, although all samples were immersed in 1 litre of de-ionised water for 60 days to allow the majority of the fluoride to leach out from the materials. The ten pellets for each material were divided into two groups, five samples as control and five samples as test. Each day over a 20-day period all test samples were exposed to a 1000-ppm F solution for 2 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylic Resins↗
PubMed1992

The plane of fracture and shear bond strength of three composite inlay systems.

Composite inlays have been introduced to overcome some of the problems encountered with direct placement techniques. However, some doubt has been expressed about the strength of the bond between the inlay surface and the composite luting cement due to the decreased number of C = C bonds remaining following supercuring of the inlay. This study investigated the bond strength of three composite inlay systems to etched bovine enamel and recorded the plane of fracture of the samples. The bond strength of one system was significantly greater than that of the other groups and was increased by the application of an unfilled resin enamel bonding agent. Unfilled resin application did not significantly alter the other systems tested. In only one of the systems tested was the inlay/composite cement bond found to be the weak link in the bonding procedure. In this group, the application of the manufacturer's specially formulated bond enhancer did not lead to an increase in bond strength.

Acrylates↗
PubMed1992

An in situ enamel section model for assessment of enamel re/demineralization potential.

An enamel-section-carrying intra-oral appliance to predict the results of double-blind anti-caries studies has been developed. Initial validation was against the F concentration effect attained in a clinical trial where three sodium monofluorophosphate (SMFP) dentifrices were used. Original appliance-based work showed significant differences in remineralization between non-F and F dentifrices, but not between different F dentifrices. However, it was shown later that acidified gel-prepared lesions were not as responsive as solution-prepared lesions to de- and remineralizing processes, and lesion remineralization rates were found to be dependent on initial lesion size. An in situ cross-over study was then repeated with use of acid-solution-created lesions, and seven volunteers completed the project. Each brushed twice daily x 2 min with either 0, 1000, or 2500 ppm F, as SMFP dentifrice. After a two-week wash-out, subjects wore the appliances for four weeks. Enamel mineral content was assessed at 0, two, and four weeks via microradiography/microdensitometry, and a statistically significant dose-response was obtained between non-F and F as well as between 1000 and 2500 ppm F pastes, i.e., as per the three-year clinical trial data. Hence, the model's suitability for pre-clinical screening was confirmed. It has also been used in caries microbiological studies, in root caries investigations, and currently in chewing gum cariogenicity experiments.

Dental Enamel↗
PubMed1992

The effect of chewing gum use on in situ enamel lesion remineralization.

Two independent cross-over studies investigated the possibility of enhanced early enamel lesion remineralization with the use of chewing gum. The first study involved a sorbitol-containing chewing gum, and the second, which had an identical protocol, tested a sucrose-containing chewing gum. In each study, 12 volunteers wore in situ appliances on which were mounted enamel sections containing artificial caries lesions. Subjects brushed twice daily for two min with a 1100-ppm-F (NaF) dentifrice (control and test) and in the test phase chewed five sticks of gum per day for 20 min after meals and snacks. Microradiographs of the enamel lesions were made at baseline and at the end of the seven-week experimental period. In the sugar-free gum study, the weighted mean total mineral loss (delta z) difference [(wk7-wk0) x (-1)] was 788 vol.% min. x micron for the gum, corresponding to remineralization of 18.2%, vs. the control value of 526 vol.% min. x micron, 12.1% remineralization (p = 0.07). There were no significant differences for the surface-zone (p = 0.20) and lesion-body (p = 0.28) values. In the sucrose-containing gum study, the delta z difference was 743 vol.% min. x micron for the gum, corresponding to a remineralization of 18.3%, vs. the control value of 438 vol.% min. x micron, 10.8% remineralization (p = 0.08). The surface-zone values were not significantly different (p = 0.55). For the lesion body, however, the sucrose-containing gum value of 6.11 vol.% min. was significantly different (p = 0.01) from that of the control (2.81 vol.% min.).

Adult↗
PubMed1992

Microleakage of a composite inlay system.

This study investigated the marginal seal of resin composite inlays in dentin and enamel when either unfilled resin or a second or third generation dentin bonding agent is used. Standardized mesial and distal inlay cavities were cut in 135 human third molar teeth. The teeth were randomly divided into 9 groups and inlays fabricated in a hybrid resin composite inlay material. Each group of teeth was then treated with one of 8 dentin bonding agents or an unfilled resin and cemented with a dual curing resin cement. Each group was stored in deionized water for 1 week, thermocycled between 5 degrees C, 37 degrees C and 55 degrees C for 500 cycles, then placed in 2% methylene blue solution for 15 hours. Following this the teeth were sectioned and scored for the degree of leakage observed. Marginal microleakage was minimal at enamel margins, however there was marked leakage, even when a dentin bonding agent was used, on the dentin side. Only two dentin bonding agents proved more effective than unfilled resin and in only one case was the leakage not significantly worse than in enamel.

Analysis of Variance↗
PubMed1991

Silane effects on luting resin bond to a Ni-Cr alloy.

This study investigates the effect of a silane coupling agent on the shear bond strength of four commercially available resin luting systems (two of which rely on mechanical retention and two which have a chemical bond to metal) when bonding a prepared Ni-Cr alloy to etched bovine enamel. Silane application reduced the bond strengths of the two chemically adhesive resins and increased the bond strength of one of the mechanically retained resins. For the other mechanically retained resin, silane application did not significantly increase the bond strength but the plane of fracture changed from resin/metal to resin/enamel: from this an increase in metal resin bond strength can be inferred.

Acid Etching, Dental↗
PubMed1991

Clinical application of computerized continuous-infusion pressure-monitored sialography.

The clinical application of computerized continuous-infusion pressure-monitored sialography using an aqueous contrast medium during the investigation of 296 salivary glands is described. A comparison between the pressure changes and the sialographic features revealed a significant (P less than 0.001) correlation between raised filling pressure (greater than 60 mmHg) and the presence of an obstructive lesion (stricture, mucous plug, sialolith). Occasionally a raised filling pressure was observed although the associated sialography films were normal. The sensitivity of the technique was 86.4%. It is concluded that the monitoring of pressure changes occurring during sialography can alert the clinician to the presence of high filling pressure and may also provide additional evidence of obstructive changes within salivary glands.

Adolescent↗
PubMed1991

Effect of Mirage Bond primer on microleakage of resin composite restorations.

This in vitro study assessed the microleakage of Class V restorations using Mirage Bond (NPG-PMDM) with a hybrid light polymerized resin composite. Restorations were inserted in cavities prepared in extracted human premolars using either bulk or incremental packing and with or without an intermediary unfilled resin. The enamel margin of each tooth was etched only with the primer. The teeth were stored for 1 week at 37 degrees C, thermocycled, and the restorations examined for leakage using methylene blue dye. The teeth were sectioned mesiodistally through the restorations and the microleakage assessed visually. All groups exhibited leakage at the gingival margin, but there was a significant difference between the cavities restored by bulk packing of the resin composite. Application of the intermediary resin did not diminish microleakage (P less than 0.01). Nevertheless, there were no other significant differences in microleakage between the groups (P greater than 0.05).

Acid Etching, Dental↗
PubMed1991

The effect of silane on shear bond strengths of etched cast metal restorations.

This study investigated the effect of a silane on the shear bond strength between an electrolytically etched Ni-Cr alloy and bovine enamel. The effect of time delay after etching and after silaning was also investigated. The results showed there to be a significant increase in bond strength when silane was used and bonding carried out immediately following silaning. However, a delay in bonding of even one hour after silaning significantly reduced bond strength. For periods up to one week, delay in silaning after etching had no effect on bond strength.

Animals↗
PubMed1991

Shear bond strength of Mirage Bond to enamel and dentin.

This study determined the shear bond strength of resin composite to bovine enamel etched with Mirage Bond primer containing 2.5% nitric acid. These results were compared with 37% orthophosphoric acid gel. In addition, the bond strength of resin composite to dentin was determined following treatment with the same primer. Resin composite was applied with and without an intermediary unfilled resin, and the specimens were stored for 1 week and then thermocycled prior to testing. The bond strength to enamel was substantially greater than to dentin (P less than 0.001). The results for enamel revealed that there was no significant difference between the etchant regimes (P greater than 0.05) but the intermediary resin significantly improved bond strengths (P less than 0.05). The presence of an intermediary resin also significantly improved the bond strength to dentin (P greater than 0.05).

Acid Etching, Dental↗
PubMed1990

Effect of fluoride concentration on remineralization of carious enamel: an in vitro pH-cycling study.

An in vitro pH-cycling experiment was carried out to investigate the effect of fluoride concentration on enamel demineralization and remineralization. Artificial caries lesions were formed in an acid-buffered solution and subjected daily to a 3-hour acid attack, a 5-min immersion in the test NaF solution (0, 1, 250, 500, 1,000, 1,750 and 2,500 ppm F), and to 21 h in an artificial saliva. Changes in mineral content were assessed weekly for 5 weeks using microradiography/microdensitometry. The lesions in the control group (0 ppm F) and the 1-ppm F group demineralized. Remineralization was significantly higher in the 500-ppm F group compared to the 250-ppm F group. However, higher fluoride concentrations did not produce any further significant increase in remineralization. Laminations were apparent in lesions subjected to the 250- and 500-ppm F solutions.

Bicuspid↗
PubMed1990

Effect of composite resin placement and use of an unfilled resin on the microleakage of two dentin bonding agents.

The purpose of this study was to assess, in vitro, the microleakage of Class V restorations using two third generations dentin bonding agents, with a hybrid light polymerized composite resin. One of the bonding agents was of the NPG-PMDM type and the other was a polyhexanide. Restorations were placed in cavities prepared in extracted human premolars using either a bulk or incremental packing technique. The NPG-PMDM-based agent was used with and without an intermediary unfilled resin. The teeth were stored for 1 week at 37 degrees C, thermocycled for 1500 cycles between 55 degrees C, 37 degrees C and 5 degrees C and the restorations examined for leakage using methylene blue dye. The teeth were sectioned through the restorations and the degree of microleakage assessed visually. All groups of restorations showed some degree of leakage at the gingival margin. Statistical analysis showed that there were significant differences in the amounts of leakage (P less than 0.001). There was no difference in leakage between any of the groups that had been restored using the NPG-PMDM system (P greater than 0.05). There was, however, less leakage of the incrementally filled group compared with the bulk-packed group with the polyhexanide agent (P less than 0.05). When the two bonding agents were compared, there was no significant difference in leakage (P greater than 0.05) except for the incrementally-packed polyhexanide and the incrementally-packed NPG-PMDM with unfilled resin (P less than 0.05). Only one specimen in any of the groups leaked at the enamel margin.

Adhesives↗