Biomedical subjects

G J Pearson

Publications and source records attributed to G J Pearson.

At least 37 records · Page 2Linked to original sources

PubMed2002

The glass ionomer cement: the sources of soluble fluoride.

This study aimed to investigate certain processes of fluoride production which enable glass ionomer cements to leach fluoride. Two fluoroaluminosilicate glasses, G338 and LG26 were used. The free and total fluoride which could be dissolved from the glasses was measured, before and after acetic acid washing. Both glasses contained appreciable amounts of soluble fluoride prior to any acid treatment. The latter process reduced the amount to some 75% of the original levels. Replacing the customary polymeric acid with propionic acid produced a cement which disintegrated in water allowing the amount of fluoride generated by the cement forming process to be measured. Cement production increased soluble fluoride by a further 3%. Both glasses behaved similarly when undergoing the various processes. G338 produced significantly greater quantities of fluoride, of the order of 10, compared with LG26 although containing only three times the amount of fluoride in the glass formula. A substantial proportion, over half, of the total fluoride was complexed especially after contact with cement and when G338 was used. During the period of the experiment, 21 days, total fluoride release did not seem to depend on the square root of time.

Acetic Acid↗

PubMed2002

Assessment of new onset postcoronary artery bypass surgery atrial fibrillation: current practice pattern review and the development of treatment guidelines.

BACKGROUND: The incidence of postcoronary artery bypass graft (CABG) atrial fibrillation (AF) is 22.5% at the QEII Health Sciences Centre and the mean length of stay is 5.5 days greater than for those patients who do not experience this complication. Appropriate pharmacological management is important to prevent the potential morbidity from AF, such as thromboembolism, congestive heart failure, cardiogenic shock and coronary ischemia. This project compared current practice patterns in the management of post-CABG AF with local practice pattern beliefs and evidence from the primary literature. Subsequently, treatment guidelines were designed to help guide a rationale treatment approach. OBJECTIVE: To promote appropriate treatment strategies for post-CABG AF and increase local practitioner awareness of drug-use outcomes by developing consensus treatment guidelines. DESIGN: There were three phases. In phase 1, a retrospective chart analysis of 35 post-CABG AF patients over three consecutive months was conducted to assess current practice patterns. All published studies on this subject were also collected and analysed. A survey of pharmacological treatment preferences was distributed to local stakeholders during phase 2. The third phase involved the development and implementation of treatment guidelines. RESULTS: This study identified a highly variable approach to the treatment of post-CABG AF. The mean number of agents used to treat AF post-CABG was two (range 1-4); all patients (100%) were prescribed rate-controlling agents and 37% were prescribed an antiarrhythmic drug. There was also a mismatch between practice pattern beliefs and actual practice. CONCLUSIONS: This reinforced the need for a consistent treatment approach that was facilitated with the development and implementation of local guidelines.

Aged↗

PubMed2001

Kinetics of fluoride release from zinc oxide-based cements.

Considerable attention has been given to the release of the cariostatic fluoride ion from glass-based dental cements (dental silicate and glass ionomer). In these, the total available fluoride content is not precisely known since fluorine is distributed between the cross-linked aqueous salt matrix, partially dissolved glass, and undissolved glass. In analogous cements based on zinc oxide the fluoride is added as highly soluble SnF2. The object of this study is to compare the F- ion release profiles of commercial zinc polycarboxylate and zinc phosphate containing 4.4 and 3.6% SnF2, respectively. Mixed cements were clamped in split ring moulds to produce discs of 10 mm x 1 mm after storage at 37 degrees C for 1 h. Each was weighed and immersed in 10 ml of deionised water. When this changed, at 13 time intervals up to 98 days, the fluoride content was measured using an ion selective electrode. The mean (N = 3) values obtained were expressed cumulatively [F] in micromol F ion/g cement. The total [F] released was 111 for the zinc polycarboxylate and 286 for zinc phosphate compared with total F in the cements of 561 and 464, respectively. When the cumulative [F] was plotted versus t(1/2) close associations were found for both cements. For the polycarboxylate the regression line [F] = 10.6t(1/2) + 9.9 fitted well over the whole 98 days (R = 0.997). For the phosphate a better fit regression line was obtained using results up to 32 days only; [F] = 36.8t(1/2) - 8.4 (R = 0.999). For t > 32 days results increasingly deviated from this line. These results fitted a regression line of the form [F] = 81.7log(e) t - 87.3 (R = 0.9997). Comparisons are made with data from previous authors both for zinc phosphate cement and glass-based cements and with diffusion theory of F ion release. It is concluded that zinc-based cements provide some indications of how glass-based cements may behave over long periods of release and that zinc phosphate is the material of clinical choice for orthodontic cementation if maximal fluoride release is the prime criterion.

Cariostatic Agents↗

PubMed2001

Interactions between glass ionomer cement and alkali metal fluoride solutions: the effect of different cations.

This study examines the effect of different cations in equimolar alkali metal fluoride solutions on their interactions with glass ionomer cements. Uptake of both fluoride and cation were measured together with change in solution pH and morphological changes in the cement surface. Two cements were used; AH2, a dental restorative cement containing both fluorine and alkali metal (Na) as glass components and LG30, which contained neither. Discs of cement 1 x 10 mm were set in moulds at 37 degrees C for 1 h then, stored in water for 3 days at 37 degrees C. Discs in each test group (N = 5) were immersed in 10 ml of solutions of either NaF, KF, or RbF, all containing 900ppm F, control discs were stored in water, all at 37 degrees C for 24h. Solutions were analysed for F- by ISE potentiometry, Na+ by the same technique and K+ and Rb+ were analysed by atomic absorption spectrometry. Uptake was obtained by difference between solution used for immersion and the control solution. Solution pH was measured potentiometrically. The surface roughness of the discs was measured by linear stylus profilometry. Fluoride ion uptakes for AH2 were 451 micromol/g NaF, 378 KF, and 318 RbF. The comparable figures for LG30 were 202, 161, and 159. Differences between cements were all statistically significant and also between solutions pairings except for the KF/LG30 vs. RbF/LG30. Uptake of cations was equimolar for AH2/ NaF, AH2/RbF and LG30/KF but M+:F- ratios were significantly above unity for AH2/KF and LG30/NaF and significantly below unity for LG30/RbF. The pH changes were all positive and were significantly higher for AH2 than LG30 and for RbF compared to the other fluoride solutions for each cement (probably because of its lower initial pH). The final pH of all solutions were less than I pH unit from neutral (pH7). The AH2 cement test discs all showed significant increase in roughness (Ra) compared to control discs stored in water whereas the LG30 discs showed no such difference. Regression analysis showed a significant positive correlation between fluoride uptake and Ra. It was concluded that changing the alkali metal cation influenced all four variables examined (F- uptake, M+ uptake, pH change and extent of cement surface roughening).

Cations↗

PubMed2001

Evaluation of the use of evidence-based angiotensin-converting enzyme inhibitor criteria for the treatment of congestive heart failure: opportunities for pharmacists to improve patient outcomes.

BACKGROUND: The under-utilization and under-dosing of angiotensin-converting enzyme inhibitors (ACEIs) in patients with congestive heart failure (CHF) continues to be a problem observed in clinical practice. OBJECTIVE: To develop and implement drug use evaluation (DUE) criteria for the use of ACEIs in patients with CHF which could be used by pharmacists to ensure that all eligible patients receive an ACEI at an appropriate dose. METHODS: A retrospective chart review of all patients discharged from the study institution with a diagnosis of CHF during the period of March 1 to July 31, 1998 was conducted using the DUE criteria developed. RESULTS: Of the 138 patients evaluated, only 68.6% were discharged on ACEI therapy. Additionally, only 40% of those discharged on an ACEI achieved target dose. Multiple regression analysis revealed that males were 2.43 times more likely to be discharged on an ACEI than females, while those on concomitant diuretics or digoxin were less likely to be discharged on an ACEI (25% and 18%, respectively). CONCLUSIONS: The application of these DUE criteria by pharmacists in hospital and community practice has the potential to improve utilization and dosing of this important class of medications for the management of the symptoms and progression of CHF.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2001

A long term study of fluoride release from metal-containing conventional and resin-modified glass-ionomer cements.

The objective of this study was to determine long term release of fluoride from a resin-modified glass-ionomer cement (RMGIC) (Fuji II LC (FLC)) compared with that from two conventional acid-base setting cements (HiDense (HD) and KetacSilver (KS)) marketed for similar restorative purposes. Fluoride release from discs of cement immersed in water or artificial saliva was measured for 2.7 years using an ion selective electrode technique. The RMGIC was affected by water if immersed immediately after setting. This is similar to conventional acid-base cements and the experimental method was designed to allow for this. Over the 2.7-year period, the RMGIC and HD released similar amounts of fluoride into both water and artificial saliva. In water, the RMGIC released the most fluoride, while in artificial saliva the highest release was from HD. KS released the least amount of fluoride in both immersing liquids. In artificial saliva, release was reduced to 17-25% of that found in water, with the RMGIC showing the greatest reduction. Both acid-base cured cements showed changes in colour over the 2.7-year span, while the colour of the RMGIC was stable. It was concluded that the RMGIC released equivalent or greater amounts of fluoride than the two acid-base cure glass-ionomers over a period of 2.7 years.

Acids↗

PubMed2001

An ex vivo investigation into the fluoride release and absorption profiles of three orthodontic adhesives.

Prevention of peri-bracket decalcification is essentially mediated by effective oral hygiene, which is patient dependent. The potential to compensate for poor oral hygiene may be through the release of free fluoride ions from direct bonding agents. It is well established that glass ionomer cements (GICs) release free fluoride ions which may be replenished by exposure to fluoride containing solutions. The aim of this ex vivo study was to compare the fluoride release and absorption profiles of a recently developed low fusion, monophase GIC, Limerick glass, with two materials in common clinical use, namely, Fuji-Ortho L.C. and Concise. Ten test specimens of each material were fabricated and stored in deionized water at 37 degrees C. The concentration of fluoride release was measured daily for the first 7 days after immersion and then weekly for 5 weeks. On day 42 the test specimens were recharged in 2 per cent sodium fluoride solution and fluoride release was measured initially after 24 hours and then every 48 hours. The recharge regimen was repeated for 3 weeks. Both Limerick glass and Fuji-Ortho L.C. demonstrated the characteristic fluoride release pattern of GIC with a rapid elution of fluoride after the first 24 hours followed by a more gradual release profile over the following 2 weeks. Fuji-Ortho L.C. released the greatest quantity of fluoride but the release profile of Limerick glass was more sustained. Concise released negligible amounts of fluoride. Limerick glass and Fuji-Ortho L.C. showed an increase (P < 0.01) in fluoride release following exposure to 2 per cent sodium fluoride that decreased both with time and subsequent exposures to fluoride supplement.

Absorption↗

PubMed2000

Effect of Nd:YAG radiation at millisecond pulse duration on dentine crater depth.

BACKGROUND AND OBJECTIVE: The effect of laser parameters on laser-dentine interaction has not been explored fully. This in vitro study investigated the effect on dentine crater depth of Nd:YAG laser radiation with varying repetition rates, total delivered energy, and dentine site either dyed or undyed. STUDY DESIGN/MATERIALS AND METHODS: One hundred forty-four caries-free third molars were sectioned transversely to provide 288 upper and lower cut surfaces. The upper surfaces were dyed (IR5). These upper and lower cut surfaces were exposed to an Nd:YAG laser with a 7 millisecond (msec) pulse duration, pulse repetition rates (RR) of 2. 5, 5.4, and 10.5 Hz, and four total energies (2.28, 2.64, 3.6, 4.2 joules). Dentine crater depth was measured by using a Reflex microscope. Results were statistically analysed with analysis of variance. RESULTS: Crater depth increased with increase in total delivered energy and in dyed and inner dentine sites (P<0.0001) but decreased with increasing repetition rate (P< 0.0001). CONCLUSIONS: Increasing energy, dyed, and inner dentine sites produced deeper craters.

Analysis of Variance↗

PubMed2000

Effect of monovalent ions in glass ionomer cements on their interaction with sodium fluoride solution.

The effects on surface morphology of glass ionomer cements following exposure to 0.2% NaF solution were studied. The effect of cement on the solution was also evaluated. The four cements were chosen to contain Na and F, Na alone, F alone and neither Na nor F to show any interactions produced by having the same ion in both the cement and solution. Four glass ionomer cements were formulated so that they differed only in respect of the glass component. AH2 (a glass used in dental restorative cement) contained both Na and F, MP4 (a glass used in orthopaedic cement) contained Na only, LG26 (a glass used in surgical cement) contained F only and LG30 (an experimental control glass) contained neither F nor Na. Discs of cement were set in moulds at 37 degrees C for 1 h, then matured in water for 3 d. Each test disc was then immersed in 10 ml 0.2% NaF for 24 h at 37 degrees C whereas control discs remained in water. The test and control disc surfaces were assessed qualitatively using electron microscopy and quantitatively by linear profilometry generating roughness values (Ra). Test solution pH was measured before and after cement immersion. Inspection of the electron micrographs showed considerable disruption of AH2 and LG26 test surfaces compared to their controls whereas MP4 and LG30 showed similar surfaces for test and control. Statistical analysis of the Ra values showed that AH2 and LG26 test surfaces were significantly rougher than their controls as well as LG30 and MP4 test surfaces, which were not significantly different from their controls. All NaF solutions show pH increases; those for AH2 and MP4 were significantly higher than those for LG26 and LG30. The F-containing cements were subject to surface disruption whereas F-free cements were not. The Ra values of test surfaces correlated strongly (r = 0.998) with the F uptake of the cements (data from a previous study) but it was not possible to ascribe the causality to this association. The pH changes appear to be influenced by whether or not Na is present in the cement. The resultant pH values are too near to neutral for pH alone to explain the surface disruption observed. In addition, it is concluded that the changes in OH ion concentration are too low to permit F-/OH- interchange as a possible explanation for F uptake by these cements.

Anions↗

PubMed2000

Effects of adding sodium and fluoride ions to glass ionomer on its interactions with sodium fluoride solution.

This investigates the effects of the addition of Na and F ions to a glass ionomer cement in which those ions are not inherently present on its interactions with dilute (0.2%) NaF solution. Both the effect of the solution on the cement's surface morphology and the effect of the cement on the solution in terms of take up of Na+ and F- and of change in pH are to be investigated. These results are to be compared to previous results obtained with glasses which contained both, one, or neither of the ions as components of their glasses. NaF (1.3% by weight in the mixed cement) was added to the powder components of a glass ionomer based on LG30 glass (which contains Al, Si, Ca, P, and O only). Discs of cement were set in moulds at 37 degrees C for 1 h then stored in water at 37 degrees C for 3 days. Each test disc was then immersed in 10 ml 0.2% NaF solution whereas controls remained immersed in water (N = 3 for test and control). Test and control disc surfaces were assessed both qualitatively by electron microscopy and quantitatively by linear profilometry (Ra values). Potentiometry was used to measure solution pH and Na and F concentrations using a pH electrode and suitable ion selective electrodes both before and after cement immersion. The surface of test specimens was subject considerable disruption with the polysalt cement matrix being removed and residual glass particles being disclosed. The controls showed no such disruption. This effect was reflected in a significant difference of Ra. Such an effect was not shown by test and control surfaces of LG30 but a similar effect was to that shown by LG26 (which contains F as a glass component). Solution pH changed by 1 unit which was much more than the change shown by LG30 or LG26 but is similar to that of AH2 and MP4 cements which both contain Na. The Na and F uptake was much lower than for LG30 whereas that of LG26 was higher than LG30. The Na:F ratio was 0.29:1 compared to 1.26:1 for LG30 (LG26 = 1.01:1, AH2 = 1.02:1, MP4 = 1.04:1). Fluoride addition to a F-free glass ionomer renders it vulnerable to surface disruption by NaF solution showing that fluoride complexes produced in glass dissolution are not necessarily involved in this process. Sodium addition to a Na-free glass ionomer confirms the role of this cement in enhancing pH change in NaF solution. The level of uptake of F- from a NaF solution in much lower than that for the F-free glass ionomer which shows there is no direct relationship between F- uptake and surface disruption. The ratio of Na:F uptake is below 0.3:1, but the pH change is similar to cements where the ratio is close to unity which indicates that F-/OH- interchange is not a significant mechanism even when anion/cation uptake is not balanced.

Anions↗

PubMed1999

Comparison of ion release from a glass ionomer cement as a function of the method of incorporation of added ions.

The addition of potassium and fluoride ions to a water-admixed glass ionomer cement initially free from either ion was accomplished either by addition via the mixing water or by immersing mixed set cement in a solution of the ions in water. In both cases the aqueous concentration of ions was the same. The release of both potassium and fluoride was measured for 500 days. Ion release from immersed specimens was some 20-fold higher than from the other method indicating enhanced concentration of ions inside the cement. This calculation assumes that the ions resided in the aqueous phase. Ions added by mixing appeared to follow the release pattern shown by glass ionomers containing intrinsic fluoride; ions added by immersion did not. As specimens matured the amount which could be taken up by immersion was reduced. Potassium release was still continuing at 500 days whereas fluoride release was complete.

Aluminum Oxide↗

PubMed1999

Effect of monovalent ions in glass ionomer on their uptake and re-release.

AIMS: The study aims to directly measure uptake of Na and F ions by glass ionomer cement from dilute NaF solution and compare this with the subsequent re-release of these ions into water. In addition, the effect of the presence or absence of Na and/or F as a component of the glass is evaluated. MATERIALS AND METHODS: The four glass ionomers used differed only in glass composition; AH2 contained both Na and F, LG26 contained F, MP4 contained Na and LG30 contained neither Na nor F. Discs of cement were set in moulds at 37 degrees C for 1 h and matured in water at 37 degrees C for 3 days. Test discs were immersed in 0.2% NaF solution for 24 h, control discs in water. Discs were subsequently immersed in water which was changed regularly. Ion-selective electrode measurements (F and Na) and atomic absorption spectrometry (Na) were used to determine uptake (change in immersion solution concentration) and re-release into water. RESULTS: All cements took up large quantities of Na and F ions (range 95-336 mumol g-1). This resulted in internal ion concentrations from 16 to 56 times higher than the immersing solution. All re-release was complete within 97 days. No cement re-released more ion than taken up. Glass ionomers containing fluoride took up more Na and F than fluoride-free ones and then re-released a lower percentage of these ions. The cements all took up Na and F ions in equimolar proportions, but initially re-released more F than Na with F-free cement results tending to unity by 97 days. CONCLUSIONS: Glass ionomer cements take up Na and F ions from NaF solution in large quantities and in equimolar proportion. This is re-released either wholly or in part in 97 days by which time the release does not differ from the controls. The presence or absence of F in the cement composition markedly influences both uptake and re-release. Fluoride/hydroxyl interchange does not appear to play an important role in uptake.

Acrylic Resins↗

PubMed1999

The influence of sample dimensions on fluoride ion release from a glass ionomer restorative cement.

The fluoride release from a commercial, restorative glass ionomer cement was found to be strongly dependent on sample surface area rather than volume. This was noted for disc, cylindrical- and bar-shaped specimens over periods ranging from 1 day to 3 yr. Release from all shapes of specimen followed the established pattern of an initial non-linear region followed by one where release was proportional to the square root of time. If fluoride levels in the cement matrix of specimens were artificially increased by incorporation during the mixing then the release pattern during the first few months was altered. The initial release increased for some specimen sizes and decreased for others. The dependency on surface area was greatly reduced for several months. By the time a year had elapsed the correlation between fluoride ion release and surface area had been re-established. The influence of additional fluoride during setting can therefore act to perturb the normal release pattern and may in some instances reduce the initial fluoride release. Release should be quoted in terms of, or with measurements of, the surface area of specimens under investigation.

Drug Stability↗

PubMed1999

Flexural and thermal cycling of resins for veneering removable overlay dentures.

OBJECTIVES: This investigation compared the effect of flexural and thermal cycling upon resins, bonded via adhesive primers to cobalt-chromium alloy to identify appropriate materials for veneering overlay dentures which may flex in function. METHODS: The resins investigated were an acrylic resin, a crown and bridge resin, a urethane dimethacrylate and a hybrid composite resin systems. The first three were bonded via an adhesive primer/opaque system based upon 4-methacryloxyethyl trimellitate anhydride (4-META) and the last via one based on 10-methacryloxyldecyl dihydrogen phosphate (MDP). Cast alloy beams 30 x 4 x 0.8 mm with 2 mm resin veneers were stored in H2O for three days or three months, and subjected to 1000 thermo-cycles between 4 and 60 degrees C, and/or 5000 flexural cycles to a displacement of 0.1 mm. Three-point bend testing was carried out in an Instron 4505 UTM. The increase in the flexural moduli of the cast beams, due to the addition of the resin spines, together with the displacements and loads at yield were recorded. RESULTS: The adhesive resin systems varied in their abilities to withstand conditioning stresses, this appeared to reflect the rigidity of the resin component as well as the performance of the adhesive bond. CONCLUSIONS: While the composite/MDP system maintained the highest bond strength throughout the conditioning, its low displacement at yield indicates that it may be more suitable for rigid areas of a removable partial denture. Acrylic resin, with its high load and displacement at yield, make it the material of choice for veneering the more flexible saddle areas of partial dentures.

Acrylic Resins↗

PubMed1999

The effect of curing regime on the release of hydroxyethyl methacrylate (HEMA) from resin-modified glass-ionomer cements.

This study investigated the effects of degree of cure and specimen maturation on the release of HEMA from four resin-modified glass-ionomer cements. Disc specimens were light-cured for either the manufacturers' recommended time (MRT) for that material, or were under-cured (irradiated for 0.5 MRT), over-cured (1.5 MRT) or allowed to dark-cure (0 MRT). Specimens were matured in the mould at 37 degrees C until set or for 10 min, 40 min or 24 h prior to immersion in distilled water (at 37 degrees C) for 4 h. The HEMA release was determined by measuring the HEMA concentration in the storage water by HPLC. Vitremer, Fuji II LC and Fuji Lining LC set without light-curing (0 MRT) in less than 6 min and these specimens released low levels of HEMA (approximately 1, 7 and 4% of the included HEMA, respectively). Dark-cured Vitrebond took 15 min to set and the HEMA release was high (approximately 50% of the included HEMA) indicating that the material had only set by the acid-base reaction. HEMA release from light-cured Vitremer or Vitrebond was not affected by under- or over-curing but release from Fuji II LC was reduced by over-curing (1.5 MRT). Under-curing Fuji Lining LC caused a significant increase in HEMA release. Specimen maturation times of 10 min, or longer, had little effect on the measured HEMA release. All the materials released HEMA into their storage solutions. In order to minimise HEMA release, resin-modified glass-ionomers should always be cured for at least the manufacturers' recommended time at thicknesses no greater than the maximum recommended.

Chromatography, High Pressure Liquid↗

PubMed1999

An in vitro investigation of a poly(vinyl phosphonic acid) based cement with four conventional glass-ionomer cements. Part 1: Flexural strength and fluoride release.

OBJECTIVE: To investigate the flexural strength and fluoride release of four conventional glass-ionomer cements: Ketac-Molar (KM), HiFi (HF), Vivaglass Fil (VF), Ketac-Fil (KF) and a newly developed glass polyphosphonate cement, Diamond Carve (DC). METHOD: Disc specimens (10 mm diameter, 1 mm thick) were prepared and mould stored at 37 degrees C. After one hour, the specimens were removed from their mould and immersed in 20 ml of deionised water until required for testing. Biaxial flexural strength was determined at 1 hour and at 1, 7, 30 and 90 days after the start of mixing. Measurements of fluoride release from the specimens were carried out at 2 hours and at 1, 3, 7, 14, 30, 60 and 90 days after the start of mixing using a fluoride ion selective electrode. The results were analysed using ANOVA and student 't' tests. RESULTS: All the materials displayed different flexural strength patterns. KM and DC became stronger whilst KF and VF plateaued in strength with time. HF peaked in strength and then became weaker. At 90 days, the mean flexural strengths in decreasing order was as follows: KM > or = VF > or = DC > or = HF > KF. An initial fast rate of fluoride release followed by a slower but steady release of fluoride was observed in each of the materials. The mean cumulative fluoride release in decreasing order was as follows: VF > KF > or = HF > DC > KM. VF released significantly higher level and KM significantly lower level of fluoride than the other materials. CONCLUSIONS: The acid used to form the cement could not be used to predict changes in cement strength behaviour with respect to time. DC increased in strength with time and its flexural strength at 90 days was comparable to that of HF and VF. The cumulative and rate of fluoride release varied for the materials. DC had a low fluoride release consistent with a fast setting material with good early resistance to water.

Analysis of Variance↗

PubMed1999

An in vitro investigation of a poly (vinyl phosphonic acid) based cement with four conventional glass-ionomer cements Part 2: Maturation in relation to surface hardness.

OBJECTIVE: To investigate the surface hardness of four conventional glass-ionomer cements: Ketac-Molar (KM), HiFi (HF), Vivaglass Fil (VF), Ketac-Fil (KF) and a newly developed glass polyphosphonate based cement, Diamond Carve (DC) at different maturation times in water and to investigate the effects of early water exposure on their surface hardness. METHOD: Disc specimens (10 mm diameter, 1 mm thick) were prepared and mould stored at 37 degrees C. The effect of different maturation times (15, 30 and 60 min) and storage in water over 24 h after those maturation times on surface hardness was determined using a microindentor with a Vickers diamond indentor. The results of the surface hardness tests were analysed using Mann-Whitney non-parameteric statistics (p < or = 0.05). The working (WT) and setting (ST) times of the cements were also measured using a modified Wilson oscillating rheometer. RESULTS: All the materials became harder after 24 h immersion in water. HF, VF and DC showed initial sensitivity to a short maturation time, but only HF was adversely affected by early moisture exposure. KF and KM were least sensitive to short maturation time or early water exposure. DC had the shortest and HF the longest WT and ST. HF and VF had a high WT:ST ratio of 1:7 and 1:9, respectively. CONCLUSIONS: A short maturation time (of 15 min) and early exposure to water did not adversely affect the surface hardness of KF, KM, VF and DC. DC, based on poly(vinyl phosphonic acid), had the shortest WT and ST. Poly(acrylic acid) based HF and VF had a long ST in relation to their WT.

Composite Resins↗

PubMed1998

Fluoride ion release from two methacrylate polymer systems.

The release of fluoride ions from two room-temperature polymerising systems containing sodium and potassium fluoride, respectively, has been studied. The polymer systems comprised poly(ethyl methacrylate) powder (PEM), with tetrahydrofurfuryl methacrylate (THFM), and n-butyl methacrylate (nBM), respectively. The water uptake of these systems was drastically increased by the presence of fluorides, the increase being much higher with the PEM/THFM system. In both cases, uptake was a monotonic function of the molarity of the fluoride added. The uptake process was in general non-Fickian. However, for all systems, the fluoride release process was Fickian, and diffusion coefficients could be calculated. The amount of fluoride released, and the diffusion coefficients obtained, appeared unrelated to the extent of water uptake of the parent polymers.

Absorption↗