Compositional Changes of Mineral Trioxide Aggregate Subcutaneously Implanted in Rats

Objectives: Mineral trioxide aggregate (MTA) is a bioactive endodontic material currently used in a wide range of applications. The setting reaction of MTA involves hydration of anhydrous mineral oxide compounds to produce calcium silicate hydrate and calcium hydroxide phases. Dissolution of calcium hydroxide and formation of precipitates on MTA have been suggested to contribute to the bioactivity of MTA. The purpose of this study was to analyze compositional changes of MTA when implanted in rat subcutaneous tissue. Methods: Teflon tubes of approximately 5 mm in length and an inner diameter of 2 mm were filled with a mixture of white MTA (ProRoot MTA, Dentsply Tulsa Dental Products) and distilled water, and then implanted into the subcutaneous tissue of 4-week-old male Wistar rats. After 1, 2 and 4 weeks, the implants were removed, fixed in 70% ethanol for 24 h, and then immersed in 5% sodium hypochlorite to remove the connective tissue. The specimens were dehydrated with ethanol and embedded in resin. The distribution of Ca, P, Si, and Al were analyzed with a wavelength-dispersive X-ray spectroscopy electron probe microanalyzer (EPMA) along the cross-section of the specimens. SEM observation and chemical composition analysis of MTA surface were also conducted in selected specimens. Results: A layer of low Ca concentration (Ca-leached layer) formed in the periphery of MTA. This layer increased in thickness with time. The most superficial layer showed high concentration of Ca and P. Si and Al formed a zone of increased concentration within the Ca-leached layer. SEM observation on the surface of MTA revealed the formation of cubic-like or slate-like crystalline structures containing Ca and P. Conclusion: Implantation of MTA in rat subcutaneous tissue resulted in the formation of a Ca-leached layer and surface precipitation of crystalline-like structures containing Ca and P at the MTA-connective tissue interface.