[Dissolution and radio-opacity of apatite cement]

Dissolution and remineralization behaviors of self-setting apatite cement is organic acids and synthetic saliva and the effect of barium apatite (BaAp)on physicochemical and mechanical properties of the apatite cement were investigated. One-week solubility of several types of apatite cement was considerably smaller than that of commercially available dental cements in 1 mM of acetic, lactic and citric acids (pH4.0 at 37 degrees C). For example, the one-week solubility in citric acids was less than 4.5%. To investigate the dissolution behavior of the apatite cement in detail, two types of 45Ca labeled apatite cement were prepared. In one, the seed apatite was labeled with 45Ca(45Ca-HAp cement) and in the other the matrix apatite was labeled with 45Ca through use of 45Ca-DCPD (45Ca-DCPD cement). Solubility, estimated from the concentration of 45Ca released in 1mM of the organic acid was approximately zero for 45Ca-HAp cement, whereas the solubility of 45Ca-DCPD cement was similar to that of unlabeled cements. This suggests cat dissolution of the matrix apatite governs dissolution of the set cement. In synthetic saliva, the solution phosphate decreased with time once the set cement was introduced to the solution, whereas the solution calcium increased. The former finding suggests that some phosphate compounds precipitated in the synthetic saliva and the latter finding indicates that some portion of the set cement dissolved. The thermodynamic analysis of the solution compositions strongly suggests that remineralization is a major process and dissolution a minor one. In fact, in systhetic saliva labeled with 45Ca having a degree of supersaturation with respect to apatite comparable to rest saliva, 45Ca concentration in solution decreased once the cement pellet was introduced. This finding clearly suggests that the set apatite cement has the ability to remineralize but not to dissolve in synthetic saliva even if the degree of supersaturation with respect to apatite is relatively low. Addition of barium hydroxyapatite (BaAp) successfully bestowed clinically acceptable radio-opacity to the apatite cement. To accelerate the setting reaction which was retarded by Ba2+ released from BaAp at a lower pH during the first stage of spatulation, calcium hydroxyapatite (CaAp) was added to the cement mixture. At 20wt% of BaAp and 20wt% CaAp, the setting reaction proceeded at a neutral or weak alkaline pH, which is one of the most promising aspects of the apatite cement. The cement spaturated at L/P = 0.4 set within 10 minutes and its radio-opacity was comparable to or more than that of tooth enamel.(ABSTRACT TRUNCATED AT 400 WORDS)