## 4 Discussion
Thus, the longer the time elapsed since the application of FDP is, the higher the average values of periodontal clinical parameters are, as a result of the evolution of the periodontal inflammatory process. Performing a comparison of IP values, probing depth, and sulcus bleeding index, between ceramic crowns on zirconia support obtained by CAD/CAM and metal-ceramic restorations with Ni-Cr-based metal substructure 12 months after application, they showed higher values in the case of the second category. Thus, ceramic crowns on a zirconium support promote the health of the marginal periodontium, due to the biocompatibility of the material [21]. Another study confirming the reduction in the inflammation process and the maintenance of the health of oral tissues by fixed prosthetic restorations on zirconium support obtained by the CAD/CAM technique, compared to those whose substructures are made of metal alloys, is that of SrimaneepongV. [22]. FDP with zirconium support manufactured by CAD/CAM technique shows better results on the health of periodontal tissues compared to a metal-ceramic prosthetic with Co-Cr-based metal substructure obtained either by conventional technique or by CAD/CAM technique [10] so, our patients are more exposed to a worsening of their periodontal status. In the present study, the CRP value from the GCF content, a pro-inflammatory marker, was evaluated. There is a statistically significant difference between the average CRP values obtained in teeth with metal-ceramic crowns compared to those from intact teeth. Moreover, a strong and statistically significant correlation resulted between CRP and GI, and CRP and PPD. These results confirm/emphasize the idea that the presence of FDP causes inflammation in the periodontal tissues (translated by higher average GI values in the T group). As a result of the initiation and evolution of this inflammation, there is also an increase in CRP levels within the GCF, the more significant, the more advanced being the state of inflammation (translated by higher average values of GI and PPD). Furthermore, the older the MC, the more pronounced the degree of periodontal tissue inflammation is (highly significant correlation between L and CRP within the T group). Periodontal diseases are correlated with elevated CRP values, both in serum and in GCF, the patients with high values of IL-1B (locally) or CRP (systemically) have a high probability of being affected by periodontal disease [23; 24]. CRP values in GCF and serum increased proportionally with the severity of periodontal diseases. It also showed positive correlations with periodontal clinical parameters [25]. In the case of chronic periodontal diseases, as well as in the case of aggressive periodontal diseases, at the level of untreated sites, the IL-6, TNF-\(\alpha\), CRP and ALP values from the analysis of the collected GCF showed higher values compared to the sites at the level of marginal periodontitis with intact status [26]. In severe chronic gingivitis, CRP and TNF-alpha levels may be reduced in GCF following treatment [27]. Referring to the longevity of FDP, in our group of periodontal-affected patients, the mean age was 6.5 years with a maximum longevity of 11 years. There are noteworthy studies that evaluate the clinical performance over time in the presence of MC crowns in comparison with crowns made of other types of materials, related or not to topography at the level of the dental arch by analyzing the survival rate of the prosthetic construction according to the occurrence of clinical complications represented by diseases of the teeth, or damage to the integrity of the FDP, requiring its removal. The survival rate after 8 years since the application of the MC crown is 94.3% \(\pm\) 1.8% [28], and after >8 years it varies between 92.3% and 95.9% [9]. The study by [PERSON] et al. finds a survival rate after 3 years of 94.9% of ceramic crowns with titanium metal substructure obtained by CAD/CAM technology, due to mechanical complications but without the presence of biological ones [29].