## 1 Introduction  
Root canal sealers are used during endodontic obturation to achieve a hermetic seal throughout the root canal system including minor discrepancies and canal irregularities [1]. Therefore, ideal endodontic sealers should prevent leakage, minimize the risk of bacterial invasion from the periapical tissues, and resolve the periapical lesion [1, 2]. In addition, root canal sealer should be biocompatible, dimensionally stable, set slowly to ensure sufficient working time, provide an excellent seal when set and provide an adequate adhesion to the canal walls. It also should be insoluble to tissue fluids [3].  
Solubility is defined as material mass loss during certain immersion time in aqueous environment [4]. It is an undesirable physical property for root canal sealers. It can induce sealer degradation; creating gaps at sealer/dentin or sealer/gutta-percha interface which compromise the apical seal of the obturation system [5] and enhance bacterial leakage [5]. Solubility behavior is influenced by the setting time and pH of the sealer [6]. In fact, the degraded byproducts and the released particles induce changes in pH of the media and in the sealer surface morphology which may affect the biological property of the sealer [7, 8].  
Nowadays, various endodontic sealers are available in the market, including sealers based on glass ionomer, calcium hydroxide, resin, zinc oxide eugenol, silicone, and bioceramic (BC)-based root canal sealers. BC-Endoequence sealer (Brasseler USA, Savannah, GA, USA) was the first bioceramic-based root canal sealer introduced in 2009 [9]. It is a premixed paste sealer composed of calcium, phosphate, and silicate. It is categorized as hydraulic calcium silicate cement as it sets in the presence of a moist environment [10]. It has the ability to form calcium hydroxide as a byproduct of hydration reaction [11], and is responsible for its alkaline pH inducing antibacterial properties [12]. It is a biocompatible, bioactive sealer and enhances the osteogenic potential [10; 13; 14]. Its nanoparticle size allows an excellent flow to the dentin wall and improve the sealing ability [9]. In addition, it is available in injectable syringe enhances easy method of delivery and application. Previous studies reported high solubility of EndoSequence sealer [4; 6; 8] that exceeds the acceptable level of ISO [15].  
Recently, a new BC- HiFlow sealer (Brasseler USA, Savannah, GA, USA) launched in the market, and it is compatible with heat generated during warm vertical compaction technique. Few studies were recently published on the effect of heat on its physico-chemical properties [16; 17; 18]. It claimed to be less soluble due to its fast setting [16]. More information about chemical changes of BC- HiFlow sealer when immersed in aqueous media are required. The purpose of this study was to evaluate the effect of water solubility on the chemical properties (setting time, pH and released calcium (Ca\({}^{2+}\)), phosphate (PO\({}_{4}\)\({}^{3-}\)) and silicon (Si\({}^{4+}\)) ions) and surface structure of recent generation BC-HiFlow versus old generation BC-EndoSeqence biocearamic-based root canal sealers. The null hypothesis was that there was no significant difference between both sealers.