# Characterization and Crystallinity of Two Bioactive Sealers: Qualitative and Quantitative Analysis
## 1 Introduction  
To ensure successful endodontic treatment, the root canal sealer used with a guttaptercha core should form an adhesive mass and fill all gaps between the obturating material and radicular dentin to eliminate bacterial microleakage [1; 2; 3; 4; 5]. According to [PERSON]'s recommendation, the sealer should be bactericidal or at least bacteriostatic, biocompatible, provide a fluid-tight seal, and be insoluble when in contact with tissue fluid [1; 2; 3; 4; 5]. AH-26 is an epoxy resin-based root canal sealer. It was found to meet most of the requirements of an ideal root canal sealer [6]. It is composed of methanamine, bismuth oxide, silver or titanium, and calcium tungsten [7]. Although epoxy resin-based root canal sealers have a low rate of solubility [8] and a high possibility of dentin adhesion [9], they have a degree of toxicity with no bioactive properties [10]. Calcium silicate-based materials are widely used owing to their biological and bioactive behaviors [11; 12]. Bioceramic-based sealers, including Endosequence, are hydraulic calcium silicate materials composed mainly of tri- and dicalcium silicate, calcium phosphate, zirconium oxide, tantalum oxide, and fillers [13; 14]. According to the manufacturer's instructions, Endosequence does not shrink during the setting reaction and has an ability to form hydroxyapatite when exposed to tissue fluid that provides a chemical bond with radicular dentin and improves its sealing ability [15]. It was proven that all calcium silicate-based root canal sealers, including bioceramic sealers, possess a high solubility percentage that exceeds the acceptable limit [6; 8; 16; 17] that could be reduced by their bioactivity [11]. Bioceramic materials are characterized by their bioactive property, which is defined as the bio-mineralization ability of the material to induce the formation of hydroxyapatite-like crystals on their surface when exposed to tissue fluid. This fact is a result of the reaction between the calcium content of the sealer and the phosphate content of the surrounding solution [18]. This can improve the sealing ability of these materials to the root canal system [19]. Furthermore, hydroxyapatite can reinforce the material and improve its mechanical as well as biological properties [20]. During the last few years, there have been much competition between manufacturers to produce the best sealer types with the maximum adherence to the specifications required. Numerous bioceramic brands have been launched on the market, including Cerafil root canal sealers. According to the manufacturer's brochure, Cerafil is composed of calcium silicate, calcium phosphate, calcium sulfate, calcium oxide, zirconium oxide, bioactive glass, fillers, and accelerator agents [21]. In endodontics, it is of great interest to use sealers with apatite-forming ability. Recently, it was proven that both Endosequence and Cerafil sealers have bioactive properties associated with hydroxyapatite formation that enable them to resist the tendency toward solubility [11]. The formation of hydroxyapatite has attracted much attention because it chemically bonds to the radicular dentin and enhances the sealing of fillings [22]. In a previous study, the influence of bioactivity on the solubility of both Cerafil and Endosequence was evaluated [11]. It proved that both sealers gained weight and resisted solubility, as hydroxyapatite crystals were formed after immersion in phosphate buffer solution (PBS) to a variable degree. The varied degree of crystalline hydroxyapatite for both sealers may depend on their variable crystallinity degree and mineral maturity. Crystallinity refers to the degree of crystalline mineral structure (crystal lattice) within a solid material and may influence the material's hardness and density. In turn, this may affect and reduce its solubility [23]. The crystallinity and mineralization of hydroxyapatite may differ from one material to another depending on their composition, particularly their calcium and phosphate contents.