## 3 Discussion  
There are two main limitations to this work. The first one--due to the authors' interests--is the focus on the use of nanoparticles in endodontics, whereas these materials are used in the whole spectrum of dentistry. The second limitation, resulting from the attempt to systematize the latest achievements, was the inclusion in the review mainly of articles published in the last five years. In this case, however, a few exceptions were made, because several of the cited works are considered milestones in the discussed subject. In the field of dentistry, modern nanomaterials play an increasingly important role. Thanks to their nanometric structure, they provide a high durability, aesthetics and an abrasion resistance higher than traditional materials, which is why they are used as fillers in modern dental composites. Due to their fine-particle structure, these substances contribute to the better penetration and sealing of root canals, which is crucial for the success of endodontic treatment [185]. Moreover, dynamic research on the use of nanomaterials for tissue regeneration in dentistry has resulted in the development of new antibacterial coatings on dental implants and prosthetic tools, which significantly minimizes the risk of infection. What is worth emphasizing is the fact that a broad spectrum of antibacterial activity and an increased ability to induce the processes of differentiation and mineralization of pulp cells have been proven [186; 187]. Nanoparticles can also be used for the controlled release of growth factors, which accelerates the process of wound healing and tissue regeneration [188; 189]. The nanoparticles described in this work are intended for use in endodontics, but they do not exhaust the catalog of materials and solutions that may be implemented in dental procedures in the near future. An example is very sensitive and precise sensors made of quantum dots, which can be used to diagnose caries and periodontal diseases [190]. Another solution, still in the experimental phase, is nanorobots programmed to precisely perform minor surgical operations in the oral cavity, thereby minimizing the risk of tissue damage and shortening the recovery time. Nanoparticles are designed to combine different functions, such as drug delivery and imaging. Thanks to this, synergistic therapeutic and diagnostic effects can be achieved. These particles can be modified in such a way as to respond to various stimuli, such as changes in pH, temperature, or the presence of biomolecules. This allows for the controlled release of drugs in response to biological environmental conditions [191; 192; 193]. However, remaining in the circle of considerations regarding materials used in the treatment and reconstruction of dental pulp and roots, it is necessary to emphasize once again their high bactericidal potential and the need to limit the development of biofilm, which causes superinfection and forces repeated cleaning procedures of infected tissue structures [25; 27]. Bacteria often penetrate so deeply that tissue resection is necessary, the reconstruction of which requires more serious treatments and complex medical procedures. Therefore, a very important aspect of endodontic treatment is to thoroughly clean the canals and protect them so that they are not colonized by microorganisms [49; 50]. And nanoparticles fulfill this task in an unquestionable way, which has been proven by many researchers. Moreover, the remineralization potential of some of these nanomaterials and the inhibition of demineralization should be emphasized. The results indicating the reconstruction of the hydroxyapatite layer became the basis for further research analyzing the molecular phenomena occurring at the tissue-biomaterial interface [52; 194; 195; 196; 197]. An important application of nanocomposites from the point of view of endodontics is their inclusion in the composition of sealing and restorative materials.