Effect of Irrigation With Antibiotic-containing Solutions Versus Sodium Hypochlorite on Postoperative Pain and Intra-canal Bacteria in Teeth With Necrotic Pulps (a Randomized Double-blind Clinical Trial)

• After confirming the diagnosis and making sure that the patient conforms to all eligibility criteria, the principal investigator will enroll the patient in the study.
• The operator will complete treatment of all cases in two visits as follows:

1. Anesthesia will be achieved using inferior alveolar nerve block for mandibular premolar teeth and infiltration technique for maxillary anterior teeth with local anesthesic solution of 1.8 mL of 2% Mepivacaine HCl with 1:100,000 epinephrine.
2. Caries and/or coronal restorations will be completely removed with sterile bur and rubber dam will then be applied.
3. The operative field, including the tooth, the clamp and rubber dam sheet will be cleaned with 30% hydrogen peroxide for 30 seconds, followed by a sterile cotton swab with 5.25% NaOCl for the same period of time and then inactivated with 5% sodium thiosulphate.
4. Access cavity will be prepared using a sterile round carbide bur size 3 and a sterile Endo-Z bur.
5. The operative field and the pulp chamber will be cleaned and disinfected once again in the same way mentioned above.
6. Patency of the root canals will be achieved using #10 or #15 size stainless steel hand K-files. Working length (WL) will be determined using an electronic apex locator then confirmed radiographically to be 1 mm shorter than radiographic apex.
7. Debridement and mechanical preparation will be performed with the initial file along with 2 mL of 0.9% sterile saline solution and then a pre-instrumentation sample will be collected from the root canal.
8. The pre-instrumentation sample (S1) will be collected as follows: a sterile paper point will be placed inside the root canal to soak up the fluid in the canal to a level approximately 1 mm short of the tooth apex. The paper point will be left in the canal for 60 seconds. This will be repeated using three sterile paper points. Paper points will then be transferred aseptically to tubes containing 20 mL of sterile thioglycolate broth.

Microbiological analysis To test for the presence of cultivable bacteria, cultures will be inoculated in thioglycolate broth. For the identification of main anaerobic taxa, the root canal samples will be plated on 5% sheep blood agar, neomycin blood agar and phenyl ethyl alcohol agar with metronidazole (5μg, Oxoid, Basingstoke, UK) disc. Cultures will be incubated at 37°C for 72 hours in an anaerobic chamber . In addition, specimens will also be cultured aerobically on 5% sheep blood agar and MacConkey's agar. 9. Mechanical preparation will be completed in a crown down technique with Protaper Next rotary files set on an endodontic motor adjusted at a speed of 300 rpm and torque of 2 Ncm. In-and-out motions will be applied with stroke lengths not exceeding 3 mm in the cervical, middle, and apical thirds until attaining the established WL. All root canals will be enlarged to size X4 (40.06). The canal will be irrigated and recapitulated after the use of each instrument according to the allocated group as follows:

Group 1: Alternate irrigation with 1 mL antibiotic-containing solution followed by 4 mL 2.5% sodium hypochlorite solution between each size instrument and the consequent one. The antibiotic-containing solution will be prepared by mixing equal quantities of 1.2 gm Co-amoxiclav solution and 600 mg Clindamycin solution at a ratio of 1:1 by volume.

Group 2: Irrigation with 5 mL MTAD irrigating solution for 5 minutes between each size instrument and the consequent one.