Synthesis and Characterization of Ion Permeable Microcapsules for Remineralization

Purpose: The objective of this study was to synthesize novel fillers for dental materials containing biologically available ions for use in remineralization formulations.  Methods: A heterogeneous polymerization technique was utilized to prepare microcapsules containing either an aqueous solution of potassium phosphate dibasic or an aqueous solution of calcium nitrate or an aqueous solution of sodium fluoride. Microcapsules containing only nanopure water were also synthesized.  These microcapsules were charged with the different ions by soaking the microcapsules in the aforementioned salt solutions. Six different polyurethane based microcapsule shells were prepared and characterized based on ethylene glycol, butanediol, hexanediol, octanediol, triethylene gylcol and bisphenol A structural units.  The microcapsules were characterized by diffential scanning calorimetry, thermogravimetric analysis and optical microscopy.

Results:

Optical microscopy provided support for the successful synthesis of microcapsules containing the aqueous solutions with biologically available ions.  The mixing conditions played an important role on the size of the microcapsule produced.  Thermogravimetric analysis was a useful technique for determining the relative amounts of aqueous solution encapsulated to the shell material.  The technique was also useful for supporting the encapsulation of the salt and the quantity present.  Differential scanning calorimetry was used to determine the glass transition temperature of the microcapsule shell material.  This property is important in understanding the release of ions from these microcapsules. Conclusions: It was possible to prepare microencapsulated aqueous solutions that contained biologically available ions useful in remineralization.  In separate experiments, microcapsules that contained nanopure water were successfully charged with calcium, phosphate and fluoride ions.  This work is funded in part by Premier Dental Products Incorporated.