The effect of Coca-Cola and fruit juices on the surface hardness of glass-ionomers and 'compomers'.

The interaction of tooth-coloured dental restorative materials (a conventional glass-ionomer, two resin-modified glass-ionomers and two compomers) with acidic beverages has been studied with the aim of investigating how long-term contact affects solution pH and specimen surface hardness. For each material (ChemFil Superior, ChemFlex, Vitremer Core Build-Up/Restorative, Fuji II LC, Dyract AP and F2000) disc-shaped specimens were prepared and stored in sets of six in the following storage media: 0.9% NaCl (control), Coca-Cola, apple juice and orange juice. After time intervals of 1 day, 1 week, 1 month, 3 months, 4 months, 6 months and 1 year, solution pH and Vickers Hardness Number were determined for each individual specimen. Differences were analysed by anova followed by Student-Newman-Keuls post hoc analysis. All materials were found to reduce the pH of the 0.9% NaCl, but to increase the pH of the acidic beverages. The conventional glass-ionomers dissolved completely in apple juice and orange juice, but survived in Coca-Cola, albeit with a significantly reduced hardness after 1 year. The other materials survived in apple juice and orange juice, but showed greater reductions in surface hardness in these beverages than in Coca-Cola. Fruit juices were thus shown to pose a greater erosive threat to tooth coloured materials than Coca-Cola, a finding which is similar to those concerning dentine and enamel towards these drinks.

The effect of saliva on surface hardness and water sorption of glass-ionomers and "compomers".

A study is reported in which commercial dental materials (glass-ionomers, resin-modified glass-ionomer and polyacid-modified composite resins) in the form of discs of dimensions 6 mm diameter x 1 mm thickness were prepared and exposed to natural salivas (parotid and unstimulated whole), artificial saliva and water for up to 1 year. Surface hardness was measured at various time intervals, and water sorption characteristics were determined. For all types of material, storage in artificial saliva gave specimens of lowest surface hardness by amounts that were generally significant to p<0.05, whereas no differences were found between specimens stored in water or either of the natural salivas. Water sorption characteristics were found to be unaffected by the nature of the storage medium. These results contrast with some previous findings and were not expected, given the known surface reactions between salivas and glass-ionomers, or the known enzymic degradation of composite resins. They demonstrate, however, that the current widespread practise of employing pure water for storage of specimens in laboratory studies is acceptable.