Biomedical subjects

G J Pearson

Publications and source records attributed to G J Pearson.

At least 19 recordsLinked to original sources

PubMed2006

Uptake of fluoride ions by the glass component of glass ionomer cement.

OBJECTIVES: The uptake of F(-) ions by glass ionomer cement (GIC) has been extensively studied but the precise location of the F(-) ion in the GIC structure has not been reported. The aim of this study is to use model materials to elucidate the possible locations. GIC consists of residual particles of aluminosilicate glass surrounded by depleted glass in an ionically crosslinked polymeric matrix. This study evaluates uptake by both unreacted glass particles (RAW) and particles acid-treated to produce a depleted glass surface (DEPLETED). METHOD: Three glasses, previously studied as cements, were tested at the particle size used in GICs. LG30 contained Al, Ca, O, P, and Si; LG26 also contained F and AH2 contained Na as well. To produce depleted surfaces they were immersed in acetic acid washed and dried at room temperature. Test samples (N=5) were immersed in KF solution (900ppm F). Control solutions without glass were used. Both were stored at 37C for 48h. F concentrations were measured using ISE with TISAB IV. RESULTS: Uptake was Control-test expressed in micromol/g glass. RAW LG30=56 (16); LG26=35(17); AH2=17(31). DEPLETED LG30=285(41); LG26=431(42); AH2=286(50). The levels of F uptake by DEPLETED were comparable to those found with GICs formed with these glasses. CONCLUSIONS: The glass particles of GIC, and particularly the depleted zones surrounding them, can account for an appreciable amount of the F uptake observed with cements but do not show the same relation between F content and F uptake previously observed with cements.

Fluorides↗

PubMed2006

An alternative regimen for root canal disinfection.

OBJECTIVE: To compare the effect of a combination of 20% citric acid solution and photo-activated disinfection with the use of 20% citric acid and 2.25% sodium hypochlorite solutions on bacterial load on the dentine walls in prepared canals in vivo. SUBJECTS AND METHODS: Sixty-four randomly selected cases were evaluated and allocated to one of two groups. In Group 1, after gaining access to the root canal, bacterial load on the canal walls was sampled using endodontic files. A further sample was taken after apex location and initial widening of the canal had been completed and the photo-activated disinfection process carried out. A final sample was taken after completion of the canal preparation using citric acid and sodium hypochlorite solutions. In Group 2, the initial sample was taken as described previously. A second sample was taken after conventional preparation using 20% citric acid and sodium hypochlorite solutions as co-irrigants. A final sample was then taken after a subsequent PAD treatment. All samples were cultured for facultative anaerobic bacteria. RESULTS: Of the canals treated in Group 1 only two of the 23 canals infected showed culturable bacteria after the use of citric acid and photo-activated disinfection. Of these two canals, one was free of culturable bacteria on completion of conventional treatment but the other still contained culturable bacteria. In Group 2, four canals of the 23 infected initially, remained contaminated after conventional treatment. After subsequent photo-activated disinfection three of these four canals were free of culturable bacteria. CONCLUSION: Results indicate that the use of a chelating agent acting as a cleaner and disrupter of the biofilm and photo-activated disinfection to kill bacteria is an effective alternative to the use of hypochlorite as a root canal cleaning system.

Adolescent↗

PubMed2006

The effects of lubrication on the temperature rise and surface finish of amalgam and composite resin.

UNLABELLED: It was thought that when finishing and polishing direct filling materials lubrication would affect the surface roughness and temperature rise in samples of amalgam and composite. OBJECT: Previous work by the authors has shown that there is an optimum load, speed and time that produced the smoothest surface when finishing amalgam and composite resin using each of four grades of a disc system. This work was undertaken to examine the effects on temperature rise in samples of amalgam and composite resin of finishing dry compared to finishing with different lubricants. The experiments all used these optimum loads, speeds and times. It also compares the surface finish produced using different lubricants. MATERIALS AND METHODS: A high copper amalgam and a hybrid composite resin were finished using the four grades of abrasive discs. Samples produced were 25 mm long by 6 mm wide by 2 mm deep. A thermocouple was inserted 1 mm into the base of the samples. The thermocouple was connected via an electronic thermometer to a computer that permitted the display and recording of temperature against time. After roughening, the samples were finished and polished in a specially constructed jig that mimicked oral finishing. The pre-determined optimum loads, speeds and times were used sequentially for each of the four grades of disc. Five samples were tested for each method of finishing. Firstly, run dry, then in turn lubricated with water, walnut oil and petroleum jelly. After the use of each abrasive disc the surface roughness was measured. One of the five samples was selected at random and prepared for examination in the scanning electron microscope. All results were subjected to non-parametric statistically analyses. RESULTS: With both materials the temperature rise was greatest when run dry, followed by petroleum jelly, walnut oil and the least was when lubricated with water. With these two materials the surface roughness correlates negatively with the temperature rise. The smoothest surface being achieved when finished dry. CONCLUSIONS: To obtain the smoothest surface finish amalgam and composite should be finished dry but further work is needed to assess the effect of the temperature rise found in the materials on the pulp.

Acrylic Resins↗

PubMed2006

Ion processes in glass ionomer cements.

Ion processes are involved in many aspects of glass-ionomer cements. The ions released from the glass take part in the formation of the cement matrix. Although this process has been investigated, particularly using model cement systems, no study provides a complete matrix composition. Combining results from different studies enables an approximate composition to be derived. The importance of Phosphorous in controlling ion release from the glass surface has been identified in a number of studies. The release of ions from the set cement into water (and other aqueous liquids) has been much reported, particularly for fluoride. Over most of the release periods studied (i.e. from >7 days up to 3 years), release of F ion is related to t1/2 indicating a diffusion-controlled process. Other ions, except possibly Na+ also show this relationship. The amount of cumulative F release whilst maintaining this relationship indicates that more F than is in the matrix is involved. Ion chromatography would probably elucidate the precise form of the ionic species released. Glass-ionomer cements take up ions from solutions in which they are immersed. The levels are much higher than required to produce as internal/external equilibrium. Studies using dynamic SIMS and XPS give some information on ion location and elemental association. It is suggested that ToF SIMS would elucidate these further. Re-release of uptaken ions can vary considerably for different cements and ion species. Surface disruption of glass ionomers is caused by both F ion and monofluorophosphate ion and occurs much more readily in F containing cements than in F free ones. The mechanism of this process has not been elucidated. Analysis of the ions released from the cement as disruption occurs should provide an indication of the site of attack.

Aluminum Silicates↗

PubMed2006

Microbiological evaluation of photo-activated disinfection in endodontics (an in vivo study).

OBJECTIVE: To determine the microbiological effect of photoactivated disinfection (PAD) as an adjunct to normal root canal disinfection in vivo. DESIGN: A randomised trial carried out in general dental practice. SUBJECTS AND METHODS: Patients presenting with symptoms of irreversible pulpitis or periradicular periodontitis requiring endodontic therapy were selected at random. A microbiological sample of the canal was taken on accessing the canal, after conventional endodontic therapy, and finally after the PAD process (photosensitiser and light) had been carried out on the prepared canal. All three samples from each canal were plated within 30 minutes of sampling and cultured anaerobically for five days. Growth of viable bacteria was recorded for each sample to determine bacterial load. RESULTS: Thirty of the 32 canals were included in the results. Cultures from the remaining two did not reach the laboratory within the target time during which viability was sustained. Of the remaining 30, 10 canals were negative to culture. These were either one of the canals in multi rooted teeth where the others were infected or where a pre-treatment with a poly-antibiotic paste had been applied to hyperaemic vital tissue. Sixteen of the remainder were negative to culture after conventional endodontic therapy. Three of the four which had remained infected cultured negative after the PAD process. In the one canal where culturable bacteria were still present, a review of the light delivery system showed a fracture in the fibre reducing the effective light output by 90%. CONCLUSIONS: The PAD system offers a means of destroying bacteria remaining after using conventional irrigants in endodontic therapy.

Adolescent↗

PubMed2006

Interaction between GIC and S. sanguis biofilms: antibacterial properties and changes of surface hardness.

OBJECTIVE: The aim of this study was to investigate the interaction of Streptococcus sanguis with two glass-ionomer formulations (GIC:A containing fluoride and GIC:B without fluoride) with particular reference to bacterial growth and changes in hardness of the cement with respect to time. MATERIALS AND METHODS: Discs of two water activated glass-ionomer cements were prepared according to the manufacturer's instruction. Hydroxyapatite discs (HA) were used as controls. 3D laser scanning technique was used to characterize surface roughness and area of the substrate prior to growing biofilms. Surface hardness was evaluated before and after biofilm growth. A constant depth film fermenter system (CDFF) was used to grow S. sanguis biofilms on the specimens in a similar manner to that described previously by Wilson et al. in 1995. For susceptibility measurement, specimens were removed from CDFF aseptically over periods up to 14d after the first colonization with bacteria. Counts of viable bacterial in the accumulating biofilm layer on each surface were measured and converted to colony forming units per unit surface area. To determine the effect of storage media, hardness discs were exposed to distilled water, lactic acid pH 4, lactic acid pH 5, citric acid pH 5, artificial saliva and S. sanguis biofilms. Twenty-four hours after preparing and subsequent autoclaving, specimens were transferred to a vessel containing 40 ml storage medium. The specimens were investigated for periods up to 7d. RESULTS: The viable counts of S. sanguis per mm2 on GIC:A were significantly less than those on HA and GIC:B during the first 5d (p<0.05). The viable counts of bacteria on the surface of GIC:B were lower during the initial 5d when compared to HA. Exposure of GIC:A and GIC:B to different medium produced softening to the surface of cement. It is apparent that the effects of the biofilms are significantly greater than storage in water but similar to storage in lactic acid pH 5. CONCLUSIONS: This investigation showed that the growth of S. sanguis biofilms were significantly affected by both glass-ionomer formulations, the greater reduction being noted on the surface of the fluoride containing GIC. S. sanguis biofilms produced reduction on the surface hardness of the cement equivalent to that seen after immersion in lactic acid at pH 5. This indicates that while S. sanguis biofilm is affected by the GIC, there is also a decrease in hardness of the cement indicating some cement degradation.

Analysis of Variance↗

PubMed2006

The effects of lubrication on the temperature rise and surface finish of glass-ionomer cements.

OBJECT: Previous work [Jones CS. Factors influencing the finishing of direct filling materials. PhD Thesis, University of London; 2002] has shown that there is an optimum load, speed and time that produced the smoothest surface when finishing glass-ionomer cement using each of four grades of a disc system. This study looks at the effects of lubrication on the temperature produced in samples of GIC when finished dry and with different lubricants using these optimal loads, speeds and times. It also compares the surface finish produced using different lubricants. MATERIALS AND METHODS: A thermocouple connected so that it permitted the display and recording of temperature against time was inserted 1mm into the base of samples of a glass-ionomer cement. The samples were finished and polished using each of the grades of a disc system in a specially constructed jig that mimicked oral finishing. After roughening, the pre-determined optimum loads, speeds and times were used sequentially for each of the four grades of disc. Five samples were tested for each method of finishing. Firstly run dry, then in turn lubricated with water, walnut oil and petroleum jelly. After the use of each abrasive disc the surface roughness was measured using a profilometer. One of the five samples was selected at random and prepared for examination in the scanning electron microscope. All results were subjected to non-parametric statistically analyses. RESULTS: Walnut oil and petroleum jelly produced significant temperature increases compared to both dry and with water finishing. Lubricated with water significantly reduced the temperature rise compared to dry. The Ra values of 0.5 microm was obtained for the coarse and a value of 0.3 microm for the medium discs run without lubrication. With lubrication the Ra increased although there was little difference between the lubricants. However the photomicrographs showed that walnut oil and petroleum jelly caused gross morphological changes indicating major surface destruction. CONCLUSIONS: The practice of finishing GICs using petroleum jelly or similar lubricant appears to be detrimental. Further experimental work needs to be done to advise practitioners on finishing GICs to produce the smoothest surface possible.

Dental Polishing↗

PubMed2006

Characterisation of some experimental silicones.

Release of antimicrobials/antibacterials like chlorhexidine diacetate (CHD) has proved successful in inhibiting Candidal colonisation of silicone-based biomaterials. However, their addition will increase water uptake and may compromise the mechanical integrity. Two experimental silicones (S1 and S2) differing only in the surface treatment of the filler, were investigated. Ultimate tensile strength (UTS), % elongation at break (Eb), Shore A hardness and, when doped with 1% CHD, water uptake and CHD release were measured. Elastic modulus (E) was calculated from the hardness measurements. There was no significant difference in UTS and Eb between the two materials. However S1 had a higher hardness (30.6 +/- 0.97) and thus E (0.76 MPa) than S2 (hardness = 23.8 +/- 0.48, E = 0.45 MPa). Water uptake for S2 (0.6%) was higher than for S2 (0.1) and addition of CHD dramatically increased the uptake of both (S1 = 3.1%, S2 = 4.0%). Release of CHD was higher for S2 (30%) than S1 (27%). Equating osmotic pressure within the droplets with elastic restraining force gave an extension ratio of 1.95 for S1 and 5.39 for S2. Thus, addition of a hydrophilic agent can compromise the mechanical integrity of low modulus silicones.

Biocompatible Materials↗

PubMed2005

Laboratory study of the loads, speeds and times to finish and polish direct restorative materials.

This study investigated the loads, speeds and times required to achieve the smoothest surface on samples of amalgam, composite resin and glass-ionomer cement using the four grades of a disc polishing system. The tests were conducted on a specially constructed jig. The restorations were abraded with the appropriate disc using a range of loads, speeds and times based on a previous practitioner study. The surface roughness of each material was measured before and after abrading. The load was varied first, followed by speed and finally time. Photomicrographs were taken of a sample finished at the optimum load, speed and time and of loads above and below the optimum that produced the smoothest surface finish. In addition the fractured edge of a sample finished at the optimum values was examined. There was an optimum load, speed and time that produced the smoothest surface for each restorative material. For amalgam and composite the surface roughness value decreased as the discs became finer. There was a reduction in the roughness value for glass-ionomer cement using the two roughest discs. The values obtained were substantially in contrast from the earlier practitioner study. There were specific values for load, speed and time that produced a smoother surface for each material.

Composite Resins↗

PubMed2004

The advantages and disadvantages of running a clinical trial in general practices.

This paper reviews the experiences encountered in running a clinical trial on the use of a metal reinforced glass-ionomer cement in general dental practices. The practitioners were asked to place both the test material and amalgam in the same patient and to take impressions both at placement and at three recall intervals. Subsequently plaster casts were produced from these impressions. These were then assessed by three independent observers to provide evaluation of the relative wear of the two restoratives under evaluation. A commercial laboratory manufactured the models on which the three independent observers carried out the assessment of wear. Although the practitioners indicated they would be able to provide the number of restorations required in a relatively short period these expected numbers were never achieved. Despite recruitment of additional participants the trial never did achieve the number of restorations required. The performance of the metal reinforced glass ionomer appeared to vary dependent on the practitioner placing the filling. Questioning of the participants found that some participants were finishing the material using a method specifically contraindicated in the protocol for the trial, the directions supplied with the product, and in briefing sessions held prior to the trial. This implies that there can be major problems in undertaking clinical trials of this nature in the general dental service and has serious clinical implications for those contemplating this type of evaluation and for manufacturers introducing new products.

Dental Amalgam↗

PubMed2004

The in vivo perception of roughness of restorations.

OBJECTIVE: To determine a threshold of detection value for surface roughness of restorations by patients using their tongue. METHOD: Samples of composite resin were finished with differing grades of abrasive. The surface roughness (Ra) was measured and representative scanning electro-micrographs taken. These were compared with labial enamel. Twenty-five volunteers were asked to rank them in order of perceived roughness using the tip of their tongue. RESULTS: These showed that the 60% of volunteers were able to rank the specimens correctly, and were able to distinguish differences in roughness values from between 0.25 and 0.50 microm. This range encompasses that of natural enamel. CONCLUSIONS: The subjects were able to distinguish lower roughness values than have previously been reported. It is concluded that when finishing restorations the surface should have a maximum roughness 0.50 microm if it is not to be detected by the patient.

Adult↗

PubMed2004

Glass ionomer cement: evidence pointing to fluorine release in the form of monofluorophosphate in addition to fluoride ion.

The fluoride ion released from glass ionomer cements into water is reportedly, in part, complexed with other elements present in the cement. When measured using ion selective electrode potentiometry (ISE) a decomplexant TISAB IV (T) is used to convert all fluoride to F- ion which the ISE can detect. In this study, an additional decomplexing procedure (H) designed to hydrolyse fluorine covalently bonded to phosphorus in the monofluorophosphate (MFP) ion into F- was also used. The soluble products from three glass ionomers were analysed by both techniques (H & T). Five 1 x 10 mm discs were each immersed in 10 ml of de-ionised water. This was changed and 4 ml analysed by T and 4 ml by H at 1, 2, 3, 6, 10, 13, 17, 21, 24, 28, and 31 days. H was greater than T for 161 of the 165 pairs ( chi2=74.7, p=<0.001 ). The total cumulative F release H (in micromol/g cement) at 31 days for AH2 was 122.3, s.d. 30.8; LG26 44.0, s.d. 1.55; LG30 10.0, s.d. 3.15 as compared T results of 100.1, s.d. 31.1; 30.3, s.d. 1.92; 3.7, s.d. 1.36, respectively. In all three cases the H was significantly greater than T (matched pair 't' test with p=0.01 or less). H-T was show to have a very strong associative relationship with t1/2 (R2=0.98 or greater p<0.001 ). Evaluating the ratio of P:F in the cements in comparison with the ratio of additional F measured by H to that measured by T produced a relationship log[(H-T)/T]=0.28 x log[P/F]-0.45 with R2=0.999. It is concluded that glass ionomers release more fluorine than is detected by ISE using TISAB IV. If this F is in the form of MFP this may be released more completely into saliva than F as F-, release of which is substantially reduced by Ca2+, since calcium monofluorophosphate is more soluble than CaF2.

Electrochemistry↗

PubMed2004

Chlorhexidine release from an experimental glass ionomer cement.

Glass ionomer cements (GIC) can potentially be used as matrices for the slow release of active species, as has been shown previously for fluoride ions. This study investigated the use of an experimental GIC as a carrier for the release of chlorhexidine acetate (CHA) at included concentrations ranging from 0.5% to 13.0% of CHA by weight. Release into water was examined using high-performance liquid chromatography. All measurable chlorhexidine was released within 22 h1/2, however this was less than 10% of the total mass incorporated in the specimens. An increased percentage of CHA incorporated into the powder gave an increased release into the surrounding water. The bulk of the CHA was retained within the cement. For comparison, the surface chemistry of a CHA-containing GIC was examined using X-ray photoelectron spectroscopy before and after prolonged immersion in water. This confirmed retention of a large amount of CHA. Spectra after leaching appeared very similar to those from a CHA-free GIC after immersion in a CHA solution. In order to explore the effect of CHA-inclusion on the cement properties, compressive strengths, working and setting times were also measured. In general, compressive strengths were found to be decreased in direct proportion to the quantity of CHA added, while working and setting times increased.

Anti-Infective Agents, Local↗

PubMed2004

Effects of variation in particle size on biaxial flexural strength of two conventional glass-ionomer cements.

Conventional glass-ionomer cements (GICs) have a slow maturation time. Reduction in time of maturation may be achieved by acceleration of the setting reaction. One factor that assists this is the reduction in glass particle size producing a larger surface area for reaction. The resulting rapid set and more rapid maturation should potentially lead to less long-term degradation. Biaxial strength measurements were made with respect to time for two GICs of similar compositions but with differing particle size distributions at different time intervals after immersion in both water and artificial saliva. There was little difference between the strength of the two materials over periods up to 12 weeks. A theoretical estimation of the relative surface areas of glasses showed that, despite there being twice the surface area available for reaction for one glass, there was little difference in strengths values between the two materials at any of the times tested here. The similarity in strength values despite this substantial difference suggests that the larger particles may have a greater influence in the cement forming process.

Dental Stress Analysis↗

PubMed2003

Fluoride uptake by glass ionomer cements: a surface analysis approach.

Despite extensive research, the mechanism by which glass ionomer cements take up fluoride ions from solution remains unclear. To date, the majority of studies have concentrated on measuring the removal of ions from solution. In this study, we demonstrate the application of X-ray photoemission spectroscopy and secondary ion mass spectrometry to the surface analysis of the cements, after the introduction of fluoride either by doping or by immersion. Fluoride ion uptake from potassium fluoride solution is correlated with the formation of a surface layer which is rich in calcium as well as fluoride.

Fluorides↗

PubMed2003

The effects of adding fluoride compounds to a fluoride-free glass ionomer cement on subsequent fluoride and sodium release.

Studies have shown that ions in a glass ionomer matrix are 1-10% of the amounts present in the original glass. To measure more precisely the release from a cement matrix, known amounts of ions were added to LG30 glass which was fluoride and sodium-free. Cement without additions acted as the control. 1.4-1.6% of each of sodium, calcium and aluminum fluorides were added to three portions of control blend. The sodium and fluoride release into deionised water from five discs of each cements blend was measured for 8 months. This represented complete release for sodium but not for fluoride. Traces of fluoride and sodium in the glass produced low but measurable amounts indicating about a third of the fluoride and substantially all sodium present in LG30 was released. The addition of calcium fluoride had no significant effect on sodium or fluoride release and aluminium fluoride minimal effects. Adding sodium fluoride significantly enhanced release of both ions although fluoride release was less than from a glass containing 5% fluoride. Only small proportions of the additions, 2-5% of the fluoride and 13% of sodium, were released. Sodium and fluoride appeared to be released independently. For LG30 cements additives were poor at supplying extra ions.

Acrylic Resins↗

PubMed2003

Is oral azithromycin effective for the treatment of cyclosporine-induced gingival hyperplasia in cardiac transplant recipients?

Anecdotal evidence suggests that azithromycin is effective for the treatment of cyclosporine-induced gingival hyperplasia in solid-organ transplant recipients. We present the cases of two heart transplant patients who insidiously developed gingival hyperplasia, likely because of immunosuppression with cyclosporine, which was treated with azithromycin. Evidence supporting the efficacy of azithromycin in the treatment of cyclosporine-induced gingival hyperplasia in solid organ transplant recipients was searched for, identified, and then critically assessed. While no data were found specifically evaluating azithromycin in cardiac transplant patients, there were nine pertinent papers identified that evaluated the clinical question of interest in the renal transplant population [Wahlstrom et al. (1995) The New England Journal of Medicine 332, 753; Boran et al. (1996) Transplantation Proceedings 28, 2316; Gomez et al. (1997) Nephrology Dialysis Transplantation 12, 2694; Ljutic (1997) Dialysis & Transplantation 26, 787; Puig et al. (1997) Transplantation Proceedings 29, 2379; Nash et al. (1998) Transplantation 65, 1611; Nowicki et al. (1998) Annals of Transplantation 3, 25; Wirnsberger et al. (1998) Transplantation Proceedings 30, 2117; Citterio et al. (2001) Transplantation Proceedings 33, 2134]. These studies and case reports are summarized. While more evidence is required to support routine use of azithromycin for the treatment of cyclosporine-induced gingival hyperplasia in cardiac transplant recipients, preliminary published evidence from renal transplant patients is certainly favourable.

Administration, Oral↗

PubMed2003

The role of lasers in dentistry: present and future.

Lasers have been used for hard tissue cutting in dentistry for a number of years. The quality of the cavity preparation and the surface finish achievable is variable and is dependent on operating wavelength. The collateral damage, which may be produced at differing wavelengths, is quite marked. Lasers in current form are now able to remove tissue in bulk at a similar rate to conventional methods such as bur and turbine handpiece. Some lasers may, however, provide precision cutting, which may be developed further in the future. Alternative uses of laser light are potentially more beneficial in the shorter term. The use of diode lasers as a means of activating a photosensitizer to carry out photo-activated disinfection appears to be beneficial.

Bacteria↗