A Novel Sol-Gel Bi(2-X)Hfxo(3+X/2) Radiopacifier For Mineral Trioxide Aggregates (Mta) As Dental Filling Materials

Mineral trioxide aggregate (MTA) is well known as an effective root canal filling material for endodontics therapy. Within MTA, bismuth oxide (Bi2O3) serving as the radiopacifier still has biocompatibility concerns due to its mild cytotoxicity. In the present study, we tried to modify the Bi2O3 radiopacifier by doping hafnium ions via the sol-gel process and investigated the effects of different doping ratios (Bi2-xHfxO3+x/2, x = 0-0.3) and calcination temperatures (400-800 degrees C). We mixed various precursor mixtures of bismuth nitrate (Bi(NO3)(3)center dot 5H(2)O) and hafnium sulfate (Hf(SO4)(2)) and controlled the calcination temperatures. The as-prepared Hf-doped Bi2O3 radiopacifier powders were investigated by thermogravimetric analysis (TGA), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). Portland cement/radiopacifier/calcium sulfate (75/20/5) were mixed and set by deionized water (powder to water ratio = 3:1). Changes in radiopacity, diametral tensile strength (DTS), and in vitro cell viability of the hydrated MTA-like cement were carried out. The experimental results showed that the group containing radiopacifier from sol-gelled Bi/Hf (90/10) exhibited significantly higher radiopacity (6.36 +/- 0.34 mmAl), DTS (2.54 +/- 0.29 MPa), and cell viability (84.0 +/- 8.1%) (p < 0.05) when compared to that of Bi/Hf (100/0) powders. It is suggested that the formation of beta-Bi7.78Hf0.22O12.11 phase with hafnium addition and calcining at 700 degrees C can prepare novel bismuth/hafnium composite powder that can be used as an alternative radiopacifier for root canal filling materials.