Abstract
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 °C). We mixed various precursor mixtures of bismuth nitrate (Bi(NO3)3·5H2O) 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 β-Bi7.78Hf0.22O12.11 phase with hafnium addition and calcining at 700 °C can prepare novel bismuth/hafnium composite powder that can be used as an alternative radiopacifier for root canal filling materials.
Highlights
Root canal treatment is an endodontic treatment sequence for removing the infected pulp and protect the fumigated tooth from future bacterial invasion
As revealed by the above radiopacity examination, diametral tensile strength test, and biocompatibility evaluation, we have demonstrated that sol-gelled Bi2-xHfxO3+x/2 composite powder with optimized hafnium addition (x = 0.10, Bi/Hf = 90/10, SGBH100) and calcination temperature (700 °C) exhibited superior performance compared to its pristine bismuth oxide counterpart
The results showed that the SGHB100 (i.e., Bi/Hf (90/10)) powder yields a significant increase of radiopacity over pristine Bi2O3 (i.e., Bi/Hf (100/0)), indicating new dominant βBi7.78Hf0.22O12.11 phase formation as well as possible structure densification by sol-gel procomposite powder with optimized hafnium addition (x = 0.10, Bi/Hf = 90/10, SGBH100)
Summary
Root canal treatment is an endodontic treatment sequence for removing the infected pulp and protect the fumigated tooth from future bacterial invasion. Among the reported radiopacifiers for MTA, bismuth oxide (Bi2 O3 ) exhibited quite a high radiopacity in X-ray photo image contrast for dental clinical uses [11,12]. Radiopacifiers with high atomic number (Z) improve radiopacity by increasing the mass attenuation coefficient (μ) in accordance with the power law of μ ∞ Z3 [22]. It shows almost no scattering radiation and results in a high-quality image. Inspiring by the similar structure in shell electrons but a higher atomic number to zirconium, the study aims to optimize the novel radiopacifier by doping hafnium ions to Bi2 O3 via the sol-gel process for future dental root canal filling materials. The effects of hafnium additions and sol-gel calcination temperatures on the particle morphology, radiopacity, diametral tensile strength, and biocompatibility were investigated to reveal the feasibility of using novel sol-gel Bi2-x Hfx O3+x/2 powder as radiopacifier in MTA
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