Abstract
Among the various phases of bismuth oxide, the high temperature metastable face-centered cubic δ phase attracts great attention due to its unique properties. It can be used as an ionic conductor or an endodontic radiopacifying material. However, no reports concerning tantalum and bismuth binary oxide prepared by high energy ball milling and serving as a dental radiopacifier can be found. In the present study, Ta2O5-added Bi2O3 composite powders were mechanically milled to investigate the formation of these metastable phases. The as-milled powders were examined by X-ray diffraction and scanning electron microscopy to reveal the structural evolution. The as-milled composite powders then served as the radiopacifier within mineral trioxide aggregates (i.e., MTA). Radiopacity performance, diametral tensile strength, setting times, and biocompatibility of MTA-like cements solidified by deionized water, saline, or 10% calcium chloride solution were investigated. The experimental results showed that subsequent formation of high temperature metastable β-Bi7.8Ta0.2O12.2, δ-Bi2O3, and δ-Bi3TaO7 phases can be observed after mechanical milling of (Bi2O3)95(Ta2O5)5 or (Bi2O3)80(Ta2O5)20 powder mixtures. Compared to its pristine Bi2O3 counterpart with a radiopacity of 4.42 mmAl, long setting times (60 and 120 min for initial and final setting times) and 84% MG-63 cell viability, MTA-like cement prepared from (Bi2O3)95(Ta2O5)5 powder exhibited superior performance with a radiopacity of 5.92 mmAl (the highest in the present work), accelerated setting times (the initial and final setting time can be shortened to 25 and 40 min, respectively), and biocompatibility (94% cell viability).
Highlights
If brittle and ductile powders are used together, fractured brittle powder will be embedded within ductile materials, refined continuously, and mechanically alloyed or forming a homogeneous composite at the end of process [5,6], whereas brittle materials alone will crack into pieces, entangle with each other, and be progressively refined
Alternative processes based on high energy ball milling include mechanical milling [7,8] and mechanochemical synthesis [9,10]
A suitable amount of the as-milled powder was extracted for structural characterization by X-ray diffraction (XRD) and scanning electron microscopy (SEM)
Summary
Ever since Benjamin first synthesized oxide dispersion strengthened superalloys by mechanical alloying (MA) [1], the high energy ball milling process presented in his work has been widely used to prepare materials that are difficult to synthesize by conventional. When using a ductile metallic powder mixture, a lamellar structure can be observed, refined continuously, and results in a homogeneous phase or phases. If brittle and ductile powders are used together, fractured brittle powder will be embedded within ductile materials, refined continuously, and mechanically alloyed or forming a homogeneous composite at the end of process [5,6], whereas brittle materials alone will crack into pieces, entangle with each other, and be progressively refined. Alternative processes based on high energy ball milling include mechanical milling [7,8] and mechanochemical synthesis [9,10]
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