## 4 Discussion
studied 21 children aged 4 to 7 years with bilateral decayed molars, who were divided into two groups: one group had zirconia crowns and the other had SSCs. After 1 and 3 months, plaque samples were taken from the gingival fissures, buccal mucosa, and cuspid surfaces of the teeth. To assess gingival health, the gingival index (GI) and plaque index (PI) were measured. Adherence of bacteria (S. mutans) to zirconia crowns was lower compared to that with SSCs, as demonstrated by their better gingival health and oral hygiene [61]  
The team of [PERSON] et al. compared zirconia crowns with strip crowns in terms of gingival health, plaque accumulation, recurrent caries, failure of fillings, and abrasion of opposing teeth at 3, 6, and 12 months in 120 patients. They observed that teeth covered with zirconium crowns exhibited better gingival health, less bleeding, and reduced plaque accumulation. None of the teeth with zirconia crowns developed recurrent caries throughout the follow-up period. In contrast, 6.7% of teeth covered with composite resin strip crowns developed secondary caries during the 12-month observation period [60,61]. [PERSON] et al. sampled 129 anterior primary teeth, comparing resin composite strip crowns and pre-veneered stainless steel crowns to zirconia crowns. The conclusion of their 6-month observations suggest that zirconia crowns used in anterior teeth show the lowest gingival inflammation rate compared to other restoration methods and show the lowest retention failure [60,62]. Ideally, dental prosthetic materials should closely mimic natural tooth structures [48]. The main advantage of zirconia crowns is their esthetics [13]. Zirconia crowns made of zirconium oxide are durable and color-matched to tooth tissue [38]. Thanks to these properties, they are rated as an alternative to SSCs [55]. In the studies published in the literature, the range of crown surface roughness values is characterized by a large spread in the results obtained, in (0.02-1.9) \(\upmu\)m [63, 64, 65, 66], mainly due to the different measurement ranges. The larger the surface area, the more varied and higher the values of the roughness parameters. The use of recent measurement techniques, such as confocal microscopy or AFM [63], makes it possible to obtain values that characterize a very small area, making the roughness results independent of the waviness of the surface. The results of the surface roughness (Sa) values (Table 2) are 29.18 nm for the anterior side and 66.05 nm for the posterior side, and the Ra parameters (measured for the test section) are 40 nm and 50 nm, respectively. These values characterize materials of roughness class N2, i.e., materials with very low roughness values. These results are also confirmed by microscopic observations (Figure 3) in which the material is homogeneous; only at a magnification of \(\times\)4500 is porosity visible, with pores no larger than a single nanometer. Surface properties can significantly influence bacterial adhesion. Materials with high surface roughness and low hydrophobicity are more prone to plaque accumulation compared to those with low surface roughness and high hydrophobicity [43]. Bacteria tend to adhere most effectively to slightly hydrophobic or hydrophilic surfaces. The hydrophobicity or hydrophilicity of a surface correlates with the wettability of the surface, often expressed as the wetting angle (\(\theta\)) of a water droplet on the substrate. In addition, bacteria tend to adhere best to surfaces with moderate wettability. The studies carried out show that, despite the differences in the structure and topography of the crown surface, the wetting angle values for each side are less than 90\({}^{\circ}\), and are 66.57 \(\pm\) 2.6\({}^{\circ}\) for the anterior surface and 75.95 \(\pm\) 3.6\({}^{\circ}\) for the posterior surface. Ceramic is therefore a material characterized by high wettability, which increases its water adsorption capacity and the adhesion of different types of cells.