A bond between glass ionomer cements (GIC) and resin composites is desirable for the success of the 'sandwich' restoration . Chemically cured glass ionomer cements have been the traditional materials used in this technique since its development, but etching the GIC was necessary to obtain a bond to the composite facing. Producing a very smooth GIC surface has aided in better determining the magnitude of the chemical bond between glass ionomers and resin composites. Shear testing of bonded specimens has revealed that chemical bonding is minimal (0.21 MPa) in conventional glass ionomers, but does exist (4.92 MPa) between GIC and resin composite regardless of the filler content (microfilled vs hybrid) of the composite . Thermal stressing affects the bond to resin-modified glass ionomers, but has no significant effect on selfcured cements. Of all combinations tested, VitremerlScotchbond/Silux Plus showed the highest mean shear bond strength. Based on the clinical need for an adhesive bond between GIC linerlbase and resin composite , the resin-modified glass ionomer would appear to be the material of choice.

Although a 40 per cent solution of silver fluoride would be expected to contain 6 per cent fluoride (60 000 ppm), F‐ levels of 100 000 ppm and 120 000 ppm were found in 14 commercial samples analysed at The University of Western Australia in 1993 and 1994. To determine whether F‐ levels in 40 per cent AgF preparations have remained high, the present investigation was aimed at analysing different batches of commercial preparations obtained more recently. Fluoride ion analysis was carried out on 24 AgF samples using the Ion‐Selective Electrode technique. Independent analyses of the same samples were carried out by a private chemical testing laboratory (Genalysis). Ten samples supplied by Agson Chemical Export were found to contain between 75 000 and 100 000 ppm F‐; Genalysis reported 80 000 to 120 000 ppm. Fourteen samples supplied by Southern Dental Industries were found to contain between 70 000 and 120 000 ppm F‐; Genalysis reported 88 000 to 108 000 ppm F‐. These results confirm significantly higher than expected F‐ levels (ANOVA p<0.05) in commercial preparations of 40 per cent AgF. The solutions tested were found to contain a mixturr of ammonium fluoride, sodium or potassium fluoride, and silver fluoride. The additional presence of silver difluoride and hydrofluoric acid resulting from the manufacturing process has been suggested as an explanation for the much higher than expected levels of fluoride ion. In view of possible toxicity of 40 per cent AgF in young children, it is concluded that such a highly concentrated solution should not be used clinically; instead, lower strength AgF solutions should be investigated for their efficacy in caries treatment.

No abstract