applied sciences  
A Novel Sol-Gel Bi2-xHfxO3+x/2 Radiopacifier for Mineral Trioxide Aggregates (MTA) as Dental Filling Materials  
[PERSON] 1,1, [PERSON] 2,3,4,4, [PERSON] 5, [PERSON] 2,5, [PERSON] 6, [PERSON] 7, [PERSON] 7, [PERSON] 2,8,9, and [PERSON] 2,10,11,12,*  
Graduate Institute of Biomedical Optomechatronics, Taipei Medical University, Taipei 11031, Taiwan; [EMAIL_ADDRESS] Research Center of Digital Oral Science and Technology, College of Oral Medicine, Taipei Medical University, Taipei 11031, Taiwan; [EMAIL_ADDRESS] (M.-S.C.); [EMAIL_ADDRESS] (C.-Y.C.) Division of Prosthodonics, Department of Dentistry, Taipei Medical University Hospital, Taipei 11031, Taiwan School of Dentistry, College of Oral Medicine, Taipei Medical University, Taipei 11031, Taiwan School of Dentistry, College of Oral Medicine, Taipei Medical University, Taipei 11031, Taiwan Department of Materials Science and Engineering, Feng Chia University, Taichung 40724, Taiwan; [EMAIL_ADDRESS] Department of Pharmaceutical Chemistry, Riga Stradins University, LV-1007 Riga, Latvia; [PERSON] Institute of Chemistry, Vilnius University, Naugarduko 24, LT-03225 Vilnius, Lithuania; [EMAIL_ADDRESS] (A.Z.); [EMAIL_ADDRESS] (A.K.) School of Dental Technology, College of Oral Medicine, Taipei Medical University, Taipei 11031, Taiwan  
Additive Manufacturing Center for Mass Customization Production, National Taipei University of Technology, Taipei 10608, Taiwan Graduate Institute of Nanomedicine and Medical Engineering, College of Biomedical Engineering, Taipei Medical University, Taipei 11052, Taiwan  
International Ph.D. Program in Biomedical Engineering, College of Biomedical Engineering, Taipei Medical University, Taipei 11052, Taiwan Research Center of Biomedical Device, Taipei Medical University, Taipei 11052, Taiwan  
Correspondence: [EMAIL_ADDRESS] (C.-K.L.); [EMAIL_ADDRESS] (J.-C.Y.) The authors contributed equally to the present study. 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 Hafanium 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 \({}^{\circ}\)C). We mixed various precursor mixtures of bismuth nitrate (Bi(NO3)3 5H2O) and Hafanium sulfate (Hf(SO4)2) and controlled the calcination temperatures. The as-prepared Hf-doped Bi2O3 radiogacifier 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-gelted Bi/Hf (90/10) exhibited significantly higher radiopacity (6.36 \(\pm\) 0.34 mmAl), DTS (2.54 \(\pm\) 0.29 MPa), and cell viability (84.0\(\pm\)8.1%) (_p_ < 0.05) when compared to that of Bi/Hf (100/0) powders. It is suggested that the formation of \(\beta\)-Bi7,28H2O12.11 phase with hafnium addition and calcining at 700 \({}^{\circ}\)C can prepare novel bismuth/hafriuum composite powder that can be used as an alternative radiopacifier for root canal filling materials.  
mineral trioxide aggregate; sol-gel; radiopacity, biocompatibility