Objective: The aim was to characterize the chemical interaction of MTA (Dentsply, Tulsa Dental) with a synthetic tissue fluid. The information is relevant to understand the reported osteogenic characteristic of this root end filling material.

Methods: Slurry samples of MTA with water were exposed to a synthetic tissue fluid composed of a phosphated buffer saline (PBS) solution (pH=7.2) at 37^oC for either 3 d or 2 w. Within 1-2 h of exposure, white precipitates were seen growing on the sample and in the solution. The solutions (n=3) with precipitates from 3 d exposure were analyzed for cations by inductively coupled plasma atomic emission spectroscopy (ICP-AE). The filtered precipitates (n=2) from 2 w exposure were characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA), and X-ray diffraction (XRD).

Results: The amounts (ppm; Mean ± St. Dev.) of various elements observed in the solution were: Ca - 176.67 ± 3.30, Si - 13.43 ± 0.58, Bi - 6.10 ± 0.45, Fe - 2.47 ± 0.40, Al - 2.27 ± 0.15, and Mg - 1.00 ± 0.10. SEM and EDXA revealed the precipitate to be of globular morphology containing mainly Ca, P, and O which is consistent with the composition of hydroxyapatite (HA). The XRD confirmed the precipitate to be HA.

Conclusion: MTA is not an inert material as it is believed. In contact with tissue fluid, it releases an abundance of Ca ions which react with (PO₄)^-3 leading to the formation of HA. The osteogenic activity of MTA is attributed to this dissolution-precipitation reaction.

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