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This study examined the activity and ability of materials to mineralize teeth in gaps, simulating microleakage between the materials and teeth. Three restorative materials (two glass ionomer cements and a compomer) were used in this study. Cured disks of restoratives were placed over flat human tooth surfaces (enamel and dentin), separated by a standardized 20-μm interfacial space, and stored in water for 24 h or 1 yr. After the water-storage period, the materials were detached from the teeth and the opposing surfaces were examined by scanning electron microscopy (SEM) and electron probe micro analysis (EPMA).Hemispherical-shaped precipitations, composed of minute semicircle plate-like crystals, were observed by SEM on the enamel surface after 1 yr of water storage for glass ionomer cement. The amount of crystal growth with the chemical-cured type of glass ionomer cement was greater than with the dual-cured type of glass ionomer cement. However, there was no crystal formation in the compomer. Moreover, no structural changes were observed on dentin surfaces for any material in water after 1 yr. The elements detected in the crystals by EPMA were calcium (Ca), phosphorus (P), and aluminum (Al). The two glass ionomer cements tested have the ability to induce crystals whose composition might be derived from cured glass ionomers.

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Abstract:The monthly changes in the counts of anaerobic bacteria, streptococci, and mutans streptococci in plaque of caries-susceptible rats (SDC) and control rats (CSC) were examined at 1, 2, 3, and 4 months. Carious lesions were also evaluated at each change by Keyes' method .No changes in the bacterial counts were observed but there was a transient increase at 3 months , especially in mutans streptococci counts. Also, no significant difference in bacterial counts was found between SDC and CSC rats. However, SDC rats had significantly higher caries scores than CSC rats after 3 months (p<0.01). The monthly age of SDC rats when their caries scores were increased was consistent with the age when their bacterial counts were significantly increased.These results suggested that the number of mutans streptococci contributed to dental caries in SDC rats, but that it was only a necessary conditions, but not a sufficient condition, for the occurrence of caries.