Abstract
Mineral trioxide aggregate (MTA) typically consists of Portland cement (75 wt.%), bismuth oxide (20 wt.%), and gypsum (5 wt.%) and is commonly used as endodontic cement. Bismuth oxide serving as the radiopacifying material reveals the canal filling effect after clinical treatment. In the present study, bismuth/zirconium oxide composite powder was prepared by high energy ball milling of (Bi2O3)100−x (ZrO2)x (x = 5, 10, 15, and 20 wt.%) powder mixture and used as the radiopacifiers within MTA. The crystalline phases of the as-milled powders were examined by the X-ray diffraction technique. The radiopacities of MTA-like cements prepared by using as-milled composite powders (at various milling stages or different amount of zirconia addition) were examined. In addition, the stability of the as-milled powders stored in an ambient environment, an electronic dry box, or a glove box was investigated. The experimental results show that the as-milled powder exhibited the starting powder phases of Bi2O3 and ZrO2 and the newly formed δ-Bi7.38Zr0.62O2.31 phase. The longer the milling time or the larger the amount of the zirconia addition, the higher the percentage of the δ-Bi7.38Zr0.62O2.31 phase in the composite powder. All the MTA-like cements prepared by the as-milled powder exhibited a radiopacity higher than 4 mmAl that is better than the 3 mmAl ISO standard requirement. The 30 min as-milled (Bi2O3)95(ZrO2)5 composite powder exhibited a radiopacity of 5.82 ± 0.33 mmAl and degraded significantly in the ambient environment. However, storing under an oxygen- and humidity-controlled glove box can prolong a high radiopacity performance. The radiopacity was 5.76 ± 0.08 mmAl after 28 days in a glove box that was statistically the same as the original composite powder.
Highlights
Mineral trioxide aggregates (MTAs) are widely used as lateral perforation sealing and root canal filling materials in dentistry [1,2]
The high energy ball milling process was used to prepare the (Bi2 O3 )100−x (ZrO2 )x composite powder that served as the radiopacifier within MTA
Though the radiopacity of a material mainly depends on the atomic number and its density, the variation of the crystalline phase and grain size during the milling process of composite powders may affect the solidification process and the density of MTA-like cements
Summary
Mineral trioxide aggregates (MTAs) are widely used as lateral perforation sealing and root canal filling materials in dentistry [1,2]. Various oxides, including TiO2 [31], SnO2 [32], ZrO2 [33], HfO2 [33], Ta2 O5 [30,34,35,36], Nb2 O5 [26,36], MoO3 [36], and WO3 [31,36], have been investigated to prepare the metastable bismuth oxide phases. Among these oxides, zirconia is widely used in dentistry due to its high compatibility, mechanical strength, good abrasion resistance, and chemical stability. The reliability of MTA powder stored at various conditions for different durations was investigated
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