A methacrylate-based cement used as a root canal sealer.

In this study, a methacrylate-based orthopaedic bone cement was modified for use as a root canal sealer by changing the monomer from n-butyl methacrylate to tetrahydrofurfuryl methacrylate. The sealing and bonding capabilities, solubility and handling properties of the resin were evaluated. Seventy-three extracted mature human teeth with single canals were used. The teeth were randomly divided into two experimental groups each of 30 teeth; three control teeth were set aside for the leakage tests. Ten teeth were reserved for the scanning electron microscope studies. All the experimental teeth were root filled with gutta-percha and the resin sealer. The particle size of the polymer was limited in Group 1 to 75 microns or less and in Group 2 to 45 microns or less. The controls were filled with gutta-percha only. Silver nitrate solution was used as the leakage indicator. In Group 1 the mean linear penetration of the indicator was 1.10 mm +/- 1.04; four roots showed no leakage. In Group 2 the mean linear penetration of the indicator was 0.57 mm +/- 0.65; 12 roots showed no leakage. The test bodies showed no weight change after 1 and 3 months' storage in saline at 37 degrees C. The scanning electron microscope examination revealed a bond both between the resin and the dentine and between the resin and the gutta-percha. The working time of the new resin composition was normally about 50 min, and handling was found to be easy.

An update on glass-ionomer cements.

It has been claimed that glass-ionomer cements possess properties that could make them the "ideal' restorative material. In the light of current disquiet about the safety of dental amalgam, are glass-ionomer cements likely to become the replacement materials of choice?

A comparison of the apical dye penetration patterns shown by methylene blue and india ink in root-filled teeth.

This study compared the linear leakage patterns shown by 5% aqueous solution of methylene blue (MB) and India ink (II). One-hundred and twenty-five roots with single canals from extracted human teeth were used. The canals were cleaned and shaped using the step-back technique under copious irrigation. Three groups were arranged to receive root fillings of gutta-percha and one of three proprietary sealers using standard lateral condensation techniques: Sealapex (40 roots), Tubli-Seal (40 roots) and Ketac-Endo (20 roots). The remaining roots were used as controls: positive with gutta-percha and no sealer and negative with the apices sealed with nail varnish. The roots were randomly selected for 7-day immersion in either MB or II, then sectioned longitudinally; dye penetration was assessed using a Wild Leitz stereomicroscope. In all groups MB showed more penetration than II. The results were statistically significant at the P = 0.01 level, with the exception of the positive control groups. Negative controls showed no penetration. It is concluded that MB, which has a low molecular weight penetrated more deeply along root canal fillings than II, which has a large particle size.

Shear bond of resin cement to post-cured hybrid composites.

Various surface treatments affected the shear bond strength of a dual-cured resin cement to a post-cured composite. Disks of post-cured composite inlay 2.0 mm thick by 10.0 mm in diameter, were mounted in acrylic cylinders. Various surface treatments were tested including: 1) smooth material; 2) treated by sandblasting (air abrasion); 3) sandblasting and etching with hydrofluoric acid (HF); 4) sandblasting and silane priming; 5) sandblasting, HF etching and silane priming; 6) HF etching alone; 7) HF etching and silane priming; and 8) silane priming alone. Specimens of dual-cured cement, 4.0 mm in diameter, were light-cured onto the prepared surfaces. The samples were stored in water at 37 degrees C for 7d before shear bond testing. The highest mean shear bond strengths were achieved for specimens with the following surface treatments: 1) by a combination of sandblasting, HF etching and silane priming; 2) sandblasting and HF etching; and 3) sandblasting and silane priming. Most bond failures in these groups were cohesive within the post-cured composite inlay disks. The bond strengths of the specimen in other groups were significantly lower and bond failures were mainly adhesive at the interface between the disk of post-cured composite and dual-cured resin cement.

Load deformation behaviour during a diametral test.

The deformation of a cylinder in the diametral mode proved to be a linear function of the applied load for silicate cements, glass ionomer cements and glass. Two theoretical analyses were investigated, namely, Hertzian indenter theory and integration of the Hondros diametral theory. Whilst both theories predicted the experimentally observed linear behaviour, neither were quantitatively correct. Furthermore, the Hondros theory contained an experimentally inaccessible parameter, the angle subtended by the contact width at the centre.

Glass-ionomer cements--clinical usage and experience: 2.

Glass-ionomer cements have unique and varied properties: they are tough, translucent, biologically inert, resistant to degradation in the mouth, adhesive to tooth structure and they inhibit caries. In a number of ways they are probably the one substance available today that most approaches the ideal restorative material. In Part 1 of this two-part article the authors reviewed the physical and clinical properties of glass-ionomer cements, here they go on to describe their use in practical and sometimes novel restorative procedures.

Glass-ionomer (Polyalkenoate) cements. Part 1. Development, setting reaction, structure and types.

The unique properties of the glass-ionomer (or polyalkenoate) cement have widened the compass of restorative and preventive dentistry and changed traditional practice methods. Glass-ionomer cements are the reaction product of an aluminosilicate glass and a polyacid, for example poly (acrylic acid).

Fluoride ion diffusion from polyalkenoate (glass-ionomer) cements.

Long-term elution of fluoride ions has been studied for one silicate and six glass-ionomer cements over a period of some two and-a-half years. Because equilibrium was not reached, classical diffusion theory could not be applied to the process. It was postulated that two elution processes were taking place, one short-term and rapid, the other more gradual and prolonged. It was possible only to estimate the maximum value for the diffusion coefficients.

Thermal diffusivity of glass-ionomer cements.

Thermal diffusivity, a property related to the thermal insulative efficiency of a material, was measured in nine glass-ionomer cements and compared with results from a silicate and a polycarboxylate cement. Each cement was mixed at various powder-liquid ratios (P/L) and moulded into a rectangular prism of approximate dimensions 2 cm cube with a thermocouple embedded in it. The prism was immersed in a constant-temperature bath at 1 degree C, and the fall in temperature was observed over a period of three min. Except for the initial and later stages, the plot of the logarithmic difference between external and internal temperatures of each block of cement against time showed a straight line in accord with theoretical prediction. From the slope, the thermal diffusivity of the material was calculated. The values for the silicate, polycarboxylate, and glass-ionomer-metal (cermet) showed a marked rise with increasing P/L, whereas at higher P/L, glass ionomer cements showed gradual change, with values being only slightly higher than the thermal diffusivity of dentin. Glass-ionomer cements are good thermal insulators over a wide range of P/L, and close agreement between experimental and theoretical data shows that glass-ionomer cements are homogenous isotropic materials.

Dielectric properties of glass ionomer cements--further studies.

Two recent proprietary glass ionomer cements showed that in the early stages of set the changes in relative permittivity (dielectric constant) and resistivity were rapid. However, when set, measurements indicated that the cements were highly ionic and polar and behaved similarly to the glass ionomer cements previously reported.