## 4 Discussion
In our study, irreversibly inflamed pulp samples showed higher levels (1.853 \(\pm\) 0.59 ng/mg protein) of MMP-7 than healthy pulp samples (2.3 \(\pm\) 0.85 ng/mg protein), but differences were not statistically significant (\(p>0.05\)). During the inflammatory process, MMP-9, or gelatinase, or type IV collagenase, is mainly secreted by PMNs. We found slightly higher levels of MMP-9 in the control group (1.568 \(\pm\) 0.44 ng/mg protein) than in irreversibly inflamed dental pulp samples (1.496 \(\pm\) 0.5 ng/mg protein), but the results did not differ significantly (\(p\) = 0.625). In contrast with these findings, previous studies using various methodologies (ELISA, RT-PCR, Western blot, Zymography assay), reported elevated levels of MMP-9 in irreversibly inflamed dental pulp samples, as compared to healthy pulp samples [51; 52; 53; 54]. A possible explanation for our findings regarding MMPs levels, could be that a symptomatic pulpal condition may not always be associated with microabscesses, or severe tissue degradation [51; 55]. Another possible explanation is that some dental pulps were less inflamed than they appeared clinically (children may tend to overreact to painful stimuli, or a child could fail to understand the tests used for diagnosis); moreover, for similar clinical symptoms, the amount, or intensity, of the trigger that determines MMPs production may differ [54]. Dental pulp collection, either by pulpectomy, for the irreversibly inflamed dental pulp tissues, or by removing the pulp tissue after extraction of the teeth, was conducted carefully. We tried to remove the pulp tissue gently, in a single piece, to prevent its destruction. All dental treatments (the removal of caries and pulp chambers and the splitting of the extracted teeth) were performed under continuous cooling water, avoiding excessive heat in the pulp chamber and the possibility of protein denaturation, which could affect the results of the study. Furthermore, all dental pulp samples were collected in aseptic conditions, while infected dentine, from the teeth with irreversible inflammation, was thoroughly removed before pulp extraction to avoid further bacteria contamination. The ability of the dental pulp to respond to an injury depends on the severity of the impact. Dental pulp can respond by initiating an inflammatory reaction, which, at the beginning, is limited to an area. At the same time, reactionary, or reparative, dentin is secreted for reparation. If the impact is mild and the odontoblasts survive, deposition of reactionary dentin occurs [45]. On the other hand, when the intensity of the injury is higher, this results in odontoblast death, and new odontoblast-like cells are required to produce dentine (reparative dentinogenesis). In irreversible inflammation, vital inflamed pulp is unable to heal and total pulpal necrosis may occur, triggering the periapical pathology with local bone involvement [56]. Less severe cases of pulp inflammation are represented by reversible pulpitis, clinically accompanied by hypersensitivity, or short-term pain [57]. In reversible pulpitis, once the inflammation resolves, the dental pulp has the potential to return to normal [56]. Vital pulp treatment should be the golden standard in case of reversible pulpitis, mainly in children with immature permanent teeth. This kind of treatment should promote pulpal healing of the remaining dental pulp, leading to apexogenesis with root development and apical closure. On the other hand, treatment of an irreversible pulp inflammation should aim to eliminate pulp infection and to induce the formation of a hard tissue barrier in the apical portion of the root of immature permanent teeth by apexification procedures. This study's hypothesis was to determine if there are any differences in the levels of various biomarkers of inflammation, oxidative stress, and ECM degradation in irreversibly inflamed, compared to healthy, dental pulp samples, collected from young permanent teeth.