Methods: 10mm x 1mm discs (n=3 each) of the material were exposed to the respective solutions at 37oC for 6 months. Water (pH = 5.6) is the medium used in standard solubility tests for dental cements. PBS (pH = 7.2) is closer to saliva in the oral environment. SEM and EDXA were used to characterize the specimen surfaces before and after solution exposure. Any precipitates formed in any solution during exposure were also examined.
Results: Rely X Unicem reacted differently in the two media. Water exposure led to localized surface erosion and precipitation of a Al-Sr-Ca-Si-F phosphate in the solution. In PBS, the surface was relatively unattacked and was found to be covered with a thin reaction film enriched with calcium and phosphorus. Most notable was the absence of any precipitates in this solution.
Conclusions: Rely X Unicem is less soluble in PBS than in water. The exact nature of the reaction products formed in the two media remains to be identified. Their formation is attributed to a complex dissolution- precipitation reaction in which Sr-Al-F glass, Ca(OH)2, and phosphate ester, all components of the luting cement, strongly participate.
Significance: The ability of Rely X Unicem to form insoluble products enriched with Ca, Sr, and PO4 may be of benefit in reducing marginal leakage and associated clinical consequences.