Discoloration Improvement by Mechanically-Milled Binary Oxides as Radiopacifier for Mineral Trioxide Aggregates

Mineral trioxide aggregates (MTA) have been widely used in endodontic treatments, but after some time, patients suffer tooth discoloration due to the use of bismuth oxide (Bi(2)O(3)) as a radiopacifier. Replacement of Bi(2)O(3) with high energy ball-milled single (zirconia ZrO(2); hafnia, HfO(2); or tantalum pentoxide, Ta(2)O(5)) or binary oxide powder was attempted, and corresponding discoloration improvement was investigated in the present study. Bi(2)O(3)-free MTA is expected to exhibit superior discoloration. The radiopacity, diametral tensile strength, and discoloration of MTA-like cements prepared from the as-milled powder were investigated. Experimental results showed that MTA-like cements prepared using Ta(2)O(5) exhibited a slightly higher radiopacity than that of HfO(2) but had a much higher radiopacity than ZrO(2). Milling treatment (30 min to 3 h) did not affect the radiopacities significantly. These MTA-like cements exhibited superior color stability (all measured ΔE(00) < 1.0) without any perceptible differences after UV irradiation. MTA-like cements prepared using ZrO(2) exhibited the best color stability but the lowest radiopacity, which can be improved by introducing binary oxide. Among the investigated samples, MTA-like cement using (ZrO(2))(50)(Ta(2)O(5))(50) exhibited excellent color stability and the best overall performance with a radiopacity of 3.25 mmAl and a diametral tensile strength of 4.39 MPa.