## 4 Contemporary Sealers with Indications for the Treatment of Teeth with Periapical Lesions
### Nanomaterials of Hydroxyapatite as Root Canal Filling Materials  
Nanostructured materials composed of hydroxyapatite (HA) are biocompatible, more reactive, and capable of adhering to dental tubules. Nano-HA is identical to the structure of dentine and/or enamel, and the nanometer-sized particles have been shown to increase osteoblast adhesion, proliferation, and mineralization and speed up bone repair processes [63; 64]. Tooth #21 was prepared for endodontic treatment with preoperative radiographic observation--two- and three-dimensional images. The patient's informed consent was provided before performing the endodontic therapy. The preoperative radiographs on tooth #21 present extensive resorption, both intraforeminal and internal radicular. The CBCT images confirmed this radiographic analysis. The apical zone is obturated with nanometer-sized bioceramics (\(\beta\)-TCP) as a barrier, and the root canal space is sealed with a bioceramic sealer (iRoot SP, Innovative Bioceramix, Vancouver, BC, Canada) and injected with thermoplastic gutta-percha (Bee Fill, VDW, Munich, Germany) after the completed preparation. The control radiographs were obtained during the 1 st and 4 th years of treatment. A successful result of the treatment was represented by enlarged apical areas (Figure 1A-H) [64].  
Nano-HA is biocompatible, dynamic, and capable of adhering to the tubules of the dentin. In addition, it stimulates apical healing and is capable of producing an apical hermetic seal. Various filling procedures based on heated or preheated gutta-percha have been developed to improve the root canal's three-dimensional filling. Little is known about the apical sealing capabilities of the novel experimental nano-HA sealer when used in conjunction with various occlusion procedures [65]. In the field of nano-calcium phosphate-based sealers, we synthesized a biphasic filling material characterized using X-ray diffraction, tests for biotoxicity and microbiologic studies [64; 66], which can be applied for the treatment of apical root resorption in long-standing periapical diseases. It is widely known that the apices of teeth with necrotic pulps exhibit moderate to severe resorption of the apical foramen and peri-apical bone zone. We used an orthograde filling method to seal these zones with nano-biphasic material containing a physiological solution or 0.1% hyaluronen [67]. Water and hydroxyapatite are natural molecular ingredients in the life of biomineralized structures and represent a great biomimetic challenge in root canal-filling materials.  
Figure 1: (**A**) Preoperative radiograph on tooth #21 with extensive resorption; (**B,C**) CBCT images; (**D–F**) the apical zone is obturated with nanometer-sized bioceramics (\(\beta\)-TCP) as a barrier, and the root canal space is sealed with a bioceramic sealer (iRoot SP) and injected with thermoplastic gutta-percha (Bee Fill, VDW, Germany). The control radiographs are obtained during the 1 st and 4 th years of treatment; (**G,H**) the result of the treatment is shown in the enlarged apical areas (With permission of [PERSON]).