## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & \multicolumn{2}{c}{**FT (K\({}_{\text{IC}}\)) 2 h**} & & & \\ \hline
**Authors** & **Ceramics/Manufacturer** & \begin{tabular}{c} **Heat Teatent/Furnace** \\ **Manufacturer** \\ \end{tabular} & **Time** & \
\begin{tabular}{c} **FT** \\ **(K\({}_{\text{IC}}\))** \\ \end{tabular} &
\begin{tabular}{c} **FT** \\ **(K\({}_{\text{IC}}\))** \\ \end{tabular} \\ \hline [PERSON] et al. & Razor Zirconia/U\&C & 1230 \({}^{\circ}\)C & Zircon Plus, & 4.99 & 0.14 \\
2023 [42] & International & KDF/Denken High Dental & 2 h & 6.28 & 0.27 \\ \hline [PERSON] et al. & Razor Zirconia/U\&C & 1430 \({}^{\circ}\)C & Zircon Plus, & 4.88 & 0.31 \\
2023 [42] & International & KDF/Denken High Dental & 2 h & 6.09 & 0.20 \\ \hline \hline \end{tabular} SD: Standard deviation; FT: Fracture toughness.  
\end{table} 
Table 12: FT results in the group of silicate ceramics in a period of 2 h.  
These results are at variance with those found by [PERSON] et al. [37], who conducted a study on Vita Suprinity, stating that the crystallization process, using the Ivoclar Vivadent Programat 310 Furnace at a temperature of 840 \({}^{\circ}\)C for 8 min, achieves an FS of 267.15 \(\pm\) 32.7 MPa. Likewise, another investigation [45] opted for a prolonged heat treatment approach, 25 min at 850 \({}^{\circ}\)C, obtaining significantly lower FS results of 134.7 \(\pm\) 29.5 MPa. This discrepancy highlights the importance of material sensitivity to variations in the thermal protocol, suggesting that indiscriminate increases in time and temperature do not necessarily guarantee improvements in desired mechanical properties. This was demonstrated by [PERSON] et al. who analyzed and compared in a recent study the FS of four CAD/CAM glass ceramics, showing that the AHT of CEREC Tessera at 760 \({}^{\circ}\)C for 2 min obtained the best results of 437,462 \(\pm\) 69.17 MPa [58]. Celtra Duo (Dentsply Sirona, Germany), according to the manufacturer, presents an initial flexural strength of 210 MPa. Once subjected to an AHT of 840 \({}^{\circ}\)C for 8 to 10 min, its FS can increase to 379 MPa [53]. The results presented by [PERSON] et al. [38] reported that by using Dentsply Sirona's Multimat furnace at a temperature of 830 \({}^{\circ}\)C for 10 min, an FS of 251 \(\pm\) 0.59 MPa was obtained. In a similar vein, a study conducted by [PERSON] et al. [36] indicates that using a different furnace (DEKEMA, Austromat 624i) at a temperature of 820 \({}^{\circ}\)C for 7 min yields similar results of 252 \(\pm\) 53.78 MPa. The variability in results could be attributed to differences in heat treatment protocols, including temperature and exposure time. It is evident that factors such as the choice of furnace and the specific conditions of the thermal process can significantly influence the mechanical properties of the ceramic. These findings underscore the importance of precise control of thermal parameters to achieve the desired properties in ceramic restorations. In relation to MH and FT, several researchers opted for different heat treatment protocols [38; 39; 40] with different furnaces. However, the most outstanding results were observed when using the Programat Ep 510 furnace (Ivoclar Vivadent) with MH values of 7.6 GPa and FT of 2.8 KIC, as observed in 5 and 6. [PERSON] et al. (2022) reinforce the findings presented by evaluating the mechanical properties of three varieties of ceramics. They conclude that, within a temperature range of 810 to 840 \({}^{\circ}\)C for 8 to 10 min, the Vita Suprinity ceramic exhibited specific values of 7.6 GPa for MH and 4.7 Pa m\({}^{1/2}\) for FT [27]. On the other hand, [PERSON] et al. determined and compared the FT between e.max CAD and Press using a furnace of the same commercial house (Programat P500; Ivoclar Vivadent AG) at 840 \({}^{\circ}\)C, following the manufacturer's instructions. Their results were significantly lower for e.max CAD at 1.79 KIC than those presented in our SR [59].