## Materials and Methods
### Bacteriological Tests  
* Study group  
A prospective study was conducted in Constanta, on 60 adults, who required endodontic therapy, in the Endodontics Department of Dentistry Faculty, \"Ovidius\" University of Constanta. Ethical approval for the study was obtained from the Bioethic's committee of Ovidius University 15547/09.11.2018. The study was conducted following the Helsinki declaration that was revised in 2013. Evaluation took place for two years, started on December 2018 and finished on November 2020. All patients with posterior teeth diagnosed with pulp necrosis (i.e., negative response to pulp sensitivity test with cold stimulus, confirmed by absence of bleeding during access cavity preparation), asymptomatic or symptomatic apical periodontitis were considered eligible and included in the study group after providing signed informed consent for the research. All personal data collected from the subject were blinded and stored with the given unique registration number. The inclusion criteria in the study were: participants had to be over 18 years of age without allergic reactions with posterior teeth diagnosed with pulp necrosis. Moreover, the included teeth also had either symptomatic apical periodontitis, asymptomatic apical periodontitis or chronic apical abscess associated with a periapical radiolucency; absence of root fracture of the involved tooth, absence of periodontal pocket. The exclusion criteria from the study were: patients who are unable to appear for periodic check-ups, teeth with simple decay, teeth with hyperemia, poor oral hygiene, absence of enough tooth structure for rubber dam isolation, patients with the contributory medical history, patients who received antibiotic therapy during the previous 6 months. At the beginning of the study, 60 patients with asymptomatic or symptomatic apical periodontitis were examined; only 40 of them were accepted for inclusion in the study based on acceptance criteria. * Harvesting pathological products  
The pathological product, infected dentin, was harvested using a sterile Kerr file (20 ISO, Dentsply Sirona), which was then placed in a container with culture medium (Bio-Merieux, France) and transported to the Microbiology Laboratory of the Faculty of Dentistry of the \"Ovidius\" University of Constanta. The products were seeded on culture medium (Columbia agar +5% sheep blood, Bio-Merieux, Craponne, France) which were then thermostated at 37 \({}^{\circ}\)C for 24 h (Figure 1a,b). * Bacteriological identification technique  
After seeding on culture media and thermostating, bacterial identification was made using the API (Bio-Merieux, Craponne, France) method (Figure 2a,b). Figure 1: (a,b)—Bacterial cultures developed from pathological products after thermostating at 37 \({}^{\circ}\)C for 24 h.  
Among the bacterial species, identified from the pathological products taken, are: White _Staphylococcus_, _Streptococcus mitis_, _Streptococcus sanguis_, _Enterococcus faecalis_ and _Escherichia coli_ (Figures 3 and 4). The Kirby-Bauer test for antibiotic susceptibility, known as the disc diffusion test, is a standard that has been used for years. This test determines the sensitivity or resistance of bacterial strains to antibiotics. The principle of the method relies on the direct proportionality relationship between the level of sensitivity and the size of the inhibition area of germs colonies developed around the tested substance. Bacterial sensitivity test was realized by adapting the Kirby-Bauer diffusion method in accordance with the protocol described by Romanian Microbiology Society in the Clinical microbiology guide (2017) [31; 32]. The method's adaptation consisted of replacing the antibiotic discs with sterile filter paper discs, with the same size as those used in antibiograms; the discs were saturated with 50 \(\upmu\)L of the test solution.