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The authors have hitherto reported a series of basic studies on visible light

Various improvements have been introduced in dental cement recently, and its physical properties have been developed to a great degree. But still there remains room for improvement as to after-settled dimensional changes and solubilities. Especially, the solubilities of cement has been considered to be one of the causes of secondary caries[1]. That is, the solubility of cement, the smaller the better, should be further examined. Many reports have been published regarding the solubility of dental cement, and the general conception is that the solubility varies to a great degree in accordance with the kinds of solutions in which cement is soaked[2]. That is, as to the solubility in the oral cavity, zinc phosphate cement is larger than silicate cement, while in the distilled water silicate cement is larger. Again, according to SKINNER, et al.[1] and NORMAN et al.[3], the solubility of cement in the organic acid solutions is very large compared with in the water. again, the solubility increases proportionally to the soaking time. KOHATA et al[4] say that the solubility of zinc phosphate cement soaked in the distilled water for a day is 0.08-0.12%), and 0.14-0.18% for 7 days. Carboxylate cement shows the minimum 0.04% and the maximum 0.17% in a day soaking, and the solubility of silicate cement is very large[5-8]. Generally the soluble amount of cement is determined by soaking the set products of cement in solutions to measure the whole dissolved amount by the gravimetric method. But in case the soluble amount is very small, the gravimetric method becomes uncertain, the balance reaching its measuring limit. Again, these methods cannot make the soluble elements determined. Now, from the above-mentioned viewpoints, the authors try to make out the main soluble elements of cement and their amounts, and from the results obtained , perform the present studies to establish the basis for developing the cement with small solubilities. * Studies on the Dental Cement 25 School of Dentistry, Tokyo.

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