Biomedical subjects

G M Knight

Publications and source records attributed to G M Knight.

16 recordsLinked to original sources

PubMed2006

The effect of silver fluoride and potassium iodide on the bond strength of auto cure glass ionomer cement to dentine.

BACKGROUND: Diamine silver fluoride (Ag(NH3)2F), referred to as AgF, has been shown to reduce the incidence of caries in primary dentitions. The clinical application of this material has been limited by staining associated with both teeth and restorative materials. The application of potassium iodide (KI) after AgF eliminates stain formation. There is a lack of information as to how the addition of AgF followed by KI may affect the bond strength to dentine. The purpose of this study was to compare the bond strengths of auto cure glass ionomer cement to dentine surfaces that had been treated with AgF and KI and without treatment. METHODS: Ten recently extracted human third molars were embedded into methyl methacrylate resin and sliced to form a square block of exposed dentine surfaces. Each of the four surfaces were treated by one of the following procedures: (a) etching with 37 per cent phosphoric acid; (b) applying GC dentine conditioner; (c) etching, followed by application of AgF/KI then washing off the precipitate and air drying; and (d) etching, applying AgF/KI and air drying the reaction products on the surface. Fuji VII auto cure glass ionomer cement was bonded onto each sample and fracture tested. RESULTS: The dentine samples treated with AgF/KI followed by washing away the precipitate and air drying had bond strengths (2.83 MPa) not significantly different from samples that had been conditioned (2.40 MPa). Samples where the AgF/KI precipitate had been air dried onto the dentine surface had significantly lower bond strengths (1.49 MPa) than the washed samples. Samples that were etched had significantly lower bond strengths (1.91MPa) than the conditioned samples. CONCLUSIONS: This study found that the application of AgF/KI to etched dentine samples followed by washing off the precipitate, created bond strengths that were not significantly different to conditioned samples. Leaving the AgF/KI precipitate on the dentine surface significantly reduced the bond strength of auto cured glass ionomer cement to dentine. Washing away the reaction products and air drying is recommended as the clinical protocol for using AgF and KI on dentine surfaces prior to application of an auto cure glass ionomer cement.

Acid Etching, Dental↗

PubMed2006

Bond strengths between composite resin and auto cure glass ionomer cement using the co-cure technique.

BACKGROUND: The clinical technique for sandwich restorations prescribes etching initially set auto cure glass ionomer cement (GIC) prior to placing a layer of resin bond to develop a weak mechanical bond between composite resin and GIC. Co-curing a resin modified glass ionomer cement (RMGIC) bond and composite resin to GIC may create a chemical bond and improve the bond strengths between these two materials. METHODS: A total of 48 specimens were prepared, 12 in each of four categories. Capsulated GIC was placed into a mould and allowed to set for four minutes, etched for five seconds followed by placement of a resin bond and photo cured for five seconds over which a composite resin was puddled onto the resin bond and photo cured for 10 seconds. Capsulated GIC was placed into a mould and allowed to set for four minutes after which a sample of RMGIC (Riva LC) was prepared using twice the liquid powder ratio and painted over the surface of the set GIC using a micro brush. An increment of composite resin was added over the RMGIC and both materials were photo co-cured for 10 seconds. Capsulated GIC was placed into a mould and RMGIC (Riva LC) that had been prepared using twice the liquid powder was brushed over the GIC (prior to initial set) followed by the placement of a layer of composite resin and photo co-cured for 10 seconds. Capsulated GIC was placed into a mould and RMGIC (Fuji II LC) that had been prepared using twice the liquid powder was brushed over the GIC (prior to initial set) followed by the placement of a layer of composite resin and photo co-cured for 10 seconds. Shear testing of each of the samples was carried out and specimens were examined to determine the nature of the fracture. Selected samples were prepared for SEM investigation to observe the interfaces between the GIC and composite resin. RESULTS: There were significantly lower bond strengths (P < 0.05) amongst samples that had been etched and bonded (2.42MPa) compared to the other samples that had been co-cure bonded with RMGIC (6.48-7.05MPa). There were no significant differences amongst the bond strengths of the samples co-cure bonded with RMGIC. Specimens prepared by the 'etch and bond' technique failed adhesively and co-cured specimens failed cohesively within the GIC. SEM investigation showed chemical bonds between RMGIC bond and GIC and composite resin. CONCLUSIONS: The co-cured RMGIC bonding system eliminates several placement steps and produces a significantly stronger chemical bond between GIC and composite resin than the 'etch and bond' technique. RMGIC bond and composite resin may be co-cured to GIC either before or after initial set has occurred.

Acrylic Resins↗

PubMed2006

Ion uptake into demineralized dentine from glass ionomer cement following pretreatment with silver fluoride and potassium iodide.

BACKGROUND: Diamine silver fluoride (Ag(NH3)2F), referred to as AgF, has been shown to provide a pronounced antimicrobial action against caries. The clinical application of this material has been limited by the staining associated with both teeth and tooth coloured restorative materials. The application of potassium iodide (KI) after AgF eliminates stain formation. The purpose of this study was to determine if a prior application of silver fluoride and potassium iodine to demineralized dentine affected the uptake of strontium and fluoride from a glass ionomer cement restoration. METHOD: Three cavities were prepared in each of five recently extracted human third molars. The cavities were demineralized and treated as follows. In each tooth, one cavity was left as a control, one cavity was restored with glass ionomer cement and one cavity was treated with 1.8M AgF and a saturated KI solution and then restored with glass ionomer cement. The penetration of the various elements into demineralized dentine was measured by their relative percentage weights using electron probe microanalysis (EPMA). RESULTS: Fluoride uptake was significantly higher in the AgF and KI treated samples compared to the other two samples and significantly higher in the glass ionomer restored sample compared to the control. The application of AgF and KI did not significantly interfere with the transfer of strontium from glass ionomer cement into dentine. Silver and iodine deposits were present in the demineralized dentine treated with AgF and KI. CONCLUSIONS: The application of AgF and KI onto dentine prior to the placement of glass ionomer cement did not significantly affect the strontium uptake into the subjacent demineralized dentine and the fluoride levels in this zone were significantly increased.

Anti-Infective Agents↗

PubMed2005

An in vitro model to measure the effect of a silver fluoride and potassium iodide treatment on the permeability of demineralized dentine to Streptococcus mutans.

BACKGROUND: Diamine silver fluoride (Ag(NH3)2F), referred to as AgF, has been used to reduce the incidence of caries in primary dentitions but has been limited by the associated staining of both teeth and restorative materials. The application of potassium iodide (KI), following AgF prevents staining but its effects on the ability of AgF to reduce caries are not known. The aim of this study was to develop an in vitro model that would provide an indication of the permeability of demineralized dentine to Streptococcus mutans after treatment of the dentine with AgF followed by KI. METHODS: Forty dentine discs were bonded to the base of forty 5mL polycarbonate screw top vials (that had had their bases removed), filled with nutrient medium, sterilized and placed into a continuous culture of S. mutans. Samples were divided into four groups as follows: 10 samples of demineralized dentine as a control, 10 samples of demineralized dentine treated with AgF/KI, 10 samples of demineralized dentine treated with KI and 10 samples of demineralized dentine treated with AgF. After two weeks the optical density of the growth medium chambers was measured to determine bacterial penetration and growth. Cultures were plated out to determine migration through the discs by S. mutans. RESULTS: S. mutans migrated through all dentine discs. However, the samples treated with AgF and AgF/KI had significantly lower optical densities than the corresponding controls. The range of optical densities was least amongst demineralized samples treated with AgF/KI. CONCLUSIONS: Under the conditions of this study, treatment of demineralized dentine discs with AgF followed by KI allowed the penetration of S. mutans. Based on optical density measurements, the treatment resulted in significantly fewer microorganisms being present subjacent to the discs treated with AgF and KI than the control discs at the end of the experimental period.

Bacteriological Techniques↗

PubMed1994

The co-cured, light-activated glass-ionomer cement-composite resin restoration.

The simultaneous curing of unpolymerized composite resin and inactivated light-curing glass-ionomer cement appears to offer a number of clinical improvements to the laminated glass-ionomer cement-composite resin restoration. The observation that composite resin cures before the glass-ionomer cement suggests that the polymerization shrinkage of the resin may be taken up by the uncured glass-ionomer cement, reducing the internal stress of the restoration. A procedure is described for the placement of this type of laminate restoration that reduces both technique sensitivity and placement time, by eliminating a number of the steps required for a conventional "sandwich" restoration. The apparent clinical success of this technique indicates the need for laboratory testing to evaluate the potential of this procedure.

Composite Resins↗

PubMed1994

The fractured cusp.

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Composite Resins↗

PubMed1992

The tunnel restoration--nine years of clinical experience using capsulated glass ionomer cements. Case report.

The clinical potential of the tunnel restoration is restrained by perceived difficulties of access to proximal caries and lack of long-term clinical data. This paper describes a technique that affords proximal access similar to that of a standard Class II cavity preparation and provides an evaluation of a technique, using capsulated glass ionomer cements. It is supported by more than nine years of clinical experience that confirms the viability of this procedure as an alternative to conventional Class II cavity restorations for initial proximal lesions.

Acid Etching, Dental↗

PubMed1984

Changes in the DNA content of amoebae of Dictyostelium discoideum during growth and development.

A fluorimetric assay has been used to determine the DNA content of amoebae of Dictyostelium discoideum during growth and development. Amoebae grown in axenic culture tended to be multinucleate and had a greater DNA content than amoebae grown with a bacterial substrate, which were mononucleate. During the first 10 h of development there was little change in the DNA content of amoebae grown with a bacterial substrate, but the average DNA content per cell in amoebae grown axenically decreased as the amoebae became virtually mononucleate. Amoebae at 10 h development that had been harvested during exponential axenic growth were divided into two populations by countercurrent distribution in a polymer two-phase system. DNA content indicated that one population was largely in the G2-phase of the cell cycle, whereas the other population was largely in the G1-phase. Similar results were obtained at 10 h development with amoebae harvested during the stationary phase of axenic growth, although these amoebae start development all in the G2-phase of the cell cycle. Spores had a low DNA content, indicating that they were in G1-phase. It is proposed that all amoebae in G2-phase after early development differentiate, after mitosis, into spores and that stalk cells are formed from amoebae that remain in G1-phase after 10 h development.

Cell Nucleus↗

PubMed1984