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The disintegration of glass ionomer cements was evaluated with referred to the amounts of component elements of powders dissolved into solutions at various starting times of immersion. Glass ionomer cement products, three for luting and three for filling, were used. The starting times of immersion in solutions were; setting time and 10, 30 and 60 minutes and 24 hours after start of mixing. After the immersion in 30 ml of distilled water and physiological saline solution for 1 week, these solutions were analyzed by an atomic absorption spectrophotometer to determine the amounts of Ca, Al and Si. The amount of each element dissolved was highest when immersion in the solutions was started at the setting time except for Ca dissolved in physiological saline solution, and it tended to decrease as the start of immersion in the solutions was delayed. Some products contained Sr instead of Ca. The results indicated that glass ionomer cement should be protected from exposure to oral fluids for about 30 minutes in clinical use.

The authors have been developing an improved method that an alginate mix is applied to gelled agar to obtain precise impressions. In the present study, the bond strength of the improved method was investigated. Thirty-one agar impression materials and thirteen alginate impression materials were used. The tensile-bond strength between an alginate (VAd) and various agars (exp. 1), and between an agar (DBRS) and various alginates (exp. 2), was measured by means of the Instron Testing Machine (model 1123) operated at a cross-head speed of 500 mm/min. The bond strength varied with the combinations of the products of agar and alginate. The bond strength of some combinations was higher than the stress in removing impressions from the mouth. Comparing the products of the same manufacture, the bond strength varied with the different colors (composition) of agar, but didn't vary with the different types of cartridge++ or syringe. The result suggested that the bond strength between agar and alginate depended, not only on the agar, but also on the alginate.