## 1 Introduction  
Zirconia crowns address the growing esthetic demands in modern pediatric dentistry. These prefabricated crowns provide complete coverage for both anterior and posterior deciduous teeth, with their convenience being especially evident in the anterior dental arch. They come in the form of kits, containing several sizes dedicated to the restoration of specific primary teeth. They are made of crystalline zirconium dioxide, which is a polymorph of three forms--monoclinic, tetragonal, and cubic. Pure zirconia is in the monoclinic phase and stays in that phase up to 1170\({}^{\circ}\)[1]. The indications to use zirconia crowns are the presence of early childhood caries (ECC), severe hard tooth tissue destruction [2; 3; 4; 5; 6; 7; 8; 9], posttraumatic tooth damage [10; 11], developmental tooth disorders [12], and teeth restoration after pulpal therapy [13; 14; 15; 16; 17]. The advantages of zirconia include its good esthetics, high strength, biocompatibility, high wear, and corrosion resistance [13]. It can be used in patients with Ni- Cr allergy or sensitivity. Its disadvantages include its high costs [18]. The use of zirconia crowns involves the necessity for proper tooth preparation, which increases the risk of pulp exposure and requires sufficient cooperation from the pediatric patient [5]. Zirconia crowns cannot be cut and crimped, resulting in the tooth requiring adaptation to the crown, not the other way around [19]. The preparation must be appropriate so that it provides a passive fit [20]. An alternative method of restoration of anterior damaged teeth is the strip crown method or the use of pre-veneered preformed metal crowns (PVPCs) [21]. Based on a study by [PERSON] et al., the retention of zirconia crowns was 100% 6 months after placement, while that of PVPMCs was 95%, and that of the strip crown method was only 78% [22]. Based on [PERSON] et al., the survival rate of zirconia crowns can be found to be 90% in the absence of pulp therapy and 76% for teeth restored with zirconia crowns after pulp therapy. The mean survival time was 39.5 months [23]. In pediatric dentistry, due to the frequent difficulty in guaranteeing cooperation associated with the age of the patient, practitioners strive to use such methods that are associated with a long-term survival rate [22; 23; 24; 25; 26; 27]. Another consideration is the effect of the zirconia crown material on the tissues surrounding the tooth. Studies show no significant inflammation in the surrounding gingival tissues. In comparison to stainless steel crowns (SSCs), the inflammation rate for this material was significantly lower [28; 29]. Gingival health was also better around the zirconia crown compared to that when PVPMCs were used. The study by [PERSON] et al. also showed no increased tissue abrasion of the teeth opposite the zirconia crowns compared to that observed with steel crowns or control enamel tissue. Nevertheless, many experts have drawn attention to the possible risk factors associated with the use of permanent restorations, such as prefabricated zirconia crowns, in the oral environment. The purpose of this study is to evaluate some of the properties of the material from which prefabricated zirconia crowns are made. The first aspect is the physico-chemical composition of the crowns and their potential effect on the surrounding tissues. These effects are not only related to the functional properties of the crown itself; they are also related to the wear products that can be observed in the tissues. The second issue is the microbiological aspect of the zirconia crown material and its possible inflammatory response. Lastly, the cytotoxic aspect of the zirconia biomaterial is evaluated.