## 3 Results and Discussion
### Preparation and Characterization of Sol-Gel Bi\({}_{2x}\)Hf\({}_{x}\)O\({}_{3+x/2}\) Powders
This test method of the diametral tensile strength (DTS), also known as the splitting tensile strength, is commonly used when conventional tensile testing is difficult to carry out due to the brittle nature of the test specimens. Figure 6 showed DTS values of the MTA-like cement and Portland cement (PC, control group) hydrated using the DDW. After the hydration of 24 h, the MTA-like cement containing sol-gel Bi/Hf (90/10) powders had a DTS value of 2.54 \(\pm\) 0.29 MPa, which was significantly higher than that of Bi/Hf (100/0) powders (1.78 \(\pm\) 0.42 MPa) but not significantly different from the control group of PC (\(p<\) 0.05). As to the commercial WMTA (ProRoot MTA, Dentsply/Tulsa Dental, Tulsa, OK) set by DDW, the DTS value of 4.4 \(\pm\) 0.1 MPa was reported by [PERSON] et al. [37]. It is known that particle sizes play a major role in the mechanical properties of cement mortar [38]. All the DTS differences among the experimental groups and commercial MTA might be attributed to the particle fineness and size distribution difference due to agglomeration. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Calcination**} & \multicolumn{4}{c}{**Means and Standard Deviations of Radiopacity (mmAl)**} \\ \cline{2-6}  & **SGB** & **SGBH075** & **SGBH100** & **SGBH125** & **SGBH150** \\ \hline
400 & 4.67 \(\pm\) 0.25 & 5.45 \(\pm\) 0.33 & 5.35 \(\pm\) 0.22 & 5.19 \(\pm\) 0.25 & 4.88 \(\pm\) 0.12 \\
500 & 4.59 \(\pm\) 0.19 & 5.53 \(\pm\) 0.26 & 5.51 \(\pm\) 0.19 & 5.39 \(\pm\) 0.19 & 5.03 \(\pm\) 0.13 \\
600 & 4.68 \(\pm\) 0.12 & 5.56 \(\pm\) 0.21 & 5.87 \(\pm\) 0.14 & 5.45 \(\pm\) 0.28 & 5.16 \(\pm\) 0.17 \\
700 & 4.82 \(\pm\) 0.21 & 5.92 \(\pm\) 0.26 & 6.26 \(\pm\) 0.34 & 5.78 \(\pm\) 0.28 & 5.31 \(\pm\) 0.25 \\
800 & 4.75 \(\pm\) 0.16 & 5.76 \(\pm\) 0.25 & 5.89 \(\pm\) 0.29 & 5.55 \(\pm\) 0.22 & 5.19 \(\pm\) 0.18 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Radiopacities of MTA-like cement prepared by sol-gelled powders. Radiopacities of Portland cement (PC) and PC with commercially available Bi\({}_{2}\)O\({}_{3}\) are 0.90 \(\pm\) 0.15 and 4.56 \(\pm\) 0.13 mmAl, respectively. Figure 5: The radiopacity for MTA-like cements comprising various radiopacifiers of Bi/Hf (100/0) Bi/Hf (92.5/7.5) Bi/Hf (90/10) Bi/Hf (87.5/12.5) Bi/Hf (85/15) prepared from calcination temperature from 400 \({}^{\circ}\)C to 800 \({}^{\circ}\)C for 1 h.  
A biocompatibility test is important to investigate the potential adverse tissue responses to biomaterials when applied as intended. Figure 7 presents the cell viability of MC3T3-E1 cells seeded on hydrated MTA-like cement containing sol-gel Bi/Hf (100/0) and (90/10) powders where Portland cement (PC) and polyethylene (PE) are control groups. The cell survival rate for MTA-like cement prepared by Bi/Hf (90/10) powder was 84.0 \(\pm\) 8.1% that is statistically higher than that prepared by its counterpart Bi/Hf (100/0) (75.3 \(\pm\) 6.3%) (\(p\) < 0.05), but did not significantly different from both of the control groups (\(p\) > 0.05). As revealed by the above radiopacity examination, diametral tensile strength test, and biocompatibility evaluation, we have demonstrated that sol-gelled Bi\({}_{2\times}\)Hf\({}_{x}\)O\({}_{34\times/2}\)  
Figure 6: The DTS (diametral tensile strength) of MTA-like cement containing radiopacifier of Bi/Hf (100/0) and (90/10), where Portland cement (PC) is the control group. * indicated that these Table 95. confidence interval. Figure 7: Cell viability of MTA-like cement containing different Bi/Hf radiopacifiers where Portland cement (PC) and polyethylene (PE) are control groups. * indicated that these two sets of samples were statistically different at a 95% confidence interval. composite powder with optimized hafnium addition (x = 0.10, Bi/Hf = 90/10, SGBH100) and calcination temperature (700 \({}^{\circ}\)C) exhibited superior performance compared to its pristine bismuth oxide counterpart. Investigations concerning tooth discoloration and in vivo animal tests can proceed in future work.