## 2 \(C\)
### Introduction  
The current concept among clinicians is that after debridement, disinfection and preparation, complete obturuation of the root canal space with a biocompatible/bioactive material constitutes the key for successful endodontic therapy [1]. For this purpose, different materials and techniques have been advocated for filling root canals, while gutta-percha and a sealer cement are still the most widely used [2; 3]. In this respect, the warm vertical compaction of gutta-percha technique (WVCT) has been used to obtain a three dimensional root canal obturuation [4]. Among a large variety of endodontic sealers, the epoxy resin-based sealer AH Plus (AHPS; Dentsply Sirona, Konstanz, Germany) is widely used in conjunction with gutta-percha and is considered the gold standard. AH Plus is a paste/paste epoxy resin-based material showing excellent physicochemical properties [5; 6] and is well tolerated by living tissues [1; 7]. More recently, calcium silicate-based sealers have gained popularity among clinicians and are being used for root canal obturuation [8; 9; 10; 11; 12; 13]. Previous reports have shown that these sealers showed promise for in vivo human clinical trials [14]. Among a variety of calcium silicate-based sealers, EndoSequence BC sealer (ESBC; Brasseler, Savannah, GA, USA), which is also known as iRoot SP (Innovative Bioceramis Inc., Vancouver, BC, Canada), has been an attractive alternative for clinicians due to its favorable properties [15]. ESBC is an injectable pre-mixed and ready-to-use sealer containing calcium silicate, calcium phosphate, zirconium oxide, calcium hydroxide, additional fillers and thickening agents [16]. The sealer is dimensionally stable and possesses high flowability and excellent sealing properties [17]. Previous studies demonstrated that ESBC possesses biocompatibility and has bioactive osteo-inducing properties [18; 19; 20]. For root canal obturuation ESBC is indicated for use with a single cone (SCT) [21] or the warm vertical compaction technique (WVCT) [22]. [PERSON] et al. [22] reported that the WVCT with ESBC is more effective than the SCT for in vitro obturuation in an artificial root canal system. However, [PERSON] et al. [23] cautioned that the increase in temperature during the WVCT may alter the physical properties of ESBC and could negatively affect the quality of the obturuation.  
To overcome this problem, a new hydraulic high-temperature-resistant silicate-based sealer named EndoSequence BC Hi Flow (ESHF; Brasseler) has recently been introduced. According to the manufacturer, the chemistry of the sealer is like ESBC, but it flows better due to its lower viscosity. [PERSON] et al. [24] reported that this sealer exhibited excellent results in oval-shaped preemolars when used in combination with the WVCT. Previous in vitro [25] and recent in vivo implantation studies in subcutaneous connective tissue in rats [26] showed that ESHF demonstrated biocompatibility and bioactive properties through forming apatite crystals while promoting macrophage polarization. To the best of our knowledge, little is known about the above-mentioned properties of ESHF or AHPS in bone after having been exposed to high temperatures. It is conceivable that due to exposure to high temperatures the chemical composition of the sealers is negatively affected causing them to be less clinically effective. The aim of the present study was to evaluate the effect of high temperatures on the biocompatibility and osteogenic capacity of ESHF and AHPS when implanted in the tibas of rats. The null hypothesis was that there are no statistically significant differences in biocompatibility between ESHF and AHPS after exposure to high temperatures and that the bioactivity of ESHF is not affected, regardless of the period of observation.