# Hydration Characterization of Two Generations of MTA-Based Root Canal Sealers
## 4 Discussion  
The initial setting time indicates the beginning of sealer solidification that was associated with a decrease in the penetration depth of the Vicat needle [40], while the final setting time indicates the complete hardness of the sealer without obvious indentation at the sealer surface [12]. According to the favorable requirements described by [PERSON], the root canal sealer must have a slow initial setting time to promote sufficient working  
Figure 2: X-ray diffraction pattern (XRD) with phases identification of MTA-Bioseal (**A**), MTA-Fillapex (**B**), and Adseal (**C**) root canal sealers. time [2]; however, a prolonged final setting time directly correlates with the degree of cytotoxic reaction [12]. The present study evaluated the setting characterization of the first (MTA-Fillapex) versus recent (MTA-Bioseal) generations of MTA-based sealers and compared them with an epoxy resin (Adesal) sealer. The current result revealed that the three tested sealers had different setting characterizations; therefore, the null hypothesis was rejected. This study revealed a significant prolonged initial setting time exhibited by MTA-Fillapex (29 \(\pm\) 0.74 h) with no significant difference between MTA-Bioseal and Adseal (\(\approx\)1.3 \(\pm\) 0.12 h at \(p\) = 0.99). Finally, Adseal exhibited significantly fast setting (4.7 \(\pm\) 0.46 h). MTA-Bioseal showed no indentation after 11.4 \(\pm\) 1.34 h, but remained fragile until 72 h. The samples of MTA-Fillapex were not completely set for three months. The current study is the first publication to evaluate the setting characterization of MTA-Bioseal. It recorded a setting time that exceeded that claimed by the manufacturer with a 23-min working time and a setting time within two hours. This finding may be attributed to the nature of MTA-based materials, as they take a prolonged time for setting [5,6]. According to ISO 6876 for testing the root canal sealers, it did not exceed 10% longer than that claimed by the manufacturer [16]. Sealers that exhibit a prolonged setting time may promote periapical irritation and inflammatory reaction if exposed to periapical tissues [12]. MTA-Fillapex and Adseal have been extensively investigated [13,41,42, 43]. The fast setting of Adseal (\(\leq\)2 h) was consistent with previous studies [13,44], but there was a conflict with the previous results related to MTA-Fillapex. Some studies recorded a short setting time similar to that of Adseal [41,42] or faster than AH plus [43]; however, it failed to completely set in other studies [11,13]. Although [PERSON] et al. [43] determined a final setting time of MTA-Fillapex (\(\approx\)4.55 h), similar to that described by the manufacturer (130 \(\pm\) 10 min) [10], other studies by [PERSON] et al., 2017 [13] and [PERSON] et al., 2017 [11] suggested that it did not set indefinitely. The setting times of the sealer are proposed to depend on their composition, temperature, and humidity [45]; it was suggested that calcium silicate sealers could not set when stored dry [46]. The MTA-Fillapex is a premixed injectable paste of hydraulic calcium silicate sealer, containing a water-free thickening vehicle [12]. For its hydration reaction, it needs water to permit final setting and maximum hardness. According to [PERSON] et al., 2017 [13], a humid incubator condition is not sufficient for a complete setting of such hydraulic sealers (MTA-Fillapex). However, in a clinical situation, when such a sealer is inserted in the root canal, the dental tubules are filled with fluid that enhances its hydration reaction and complete setting. This fact can explain the failure of MTA-Fillapex setting during the environment of the current study. The constituents of the sealer affect and regulate its setting time and the hydration reaction. Salicylate resin was recently added to a root canal sealer to enhance its antibacterial properties [47]. All three tested sealers contain calcium particles and salicate resin to promote a favorable biological response [42] and allow their polymerization.