Apical Size and Root Canal Treatment Success Trial (AS-RCT Trial)

We will perform a randomized, blinded clinical trial with clinical, microbiological and volumetric outcomes. The study population will be selected from adult patients in need of endodontic treatment on mandibular molars diagnosed with pulp necrosis and presenting with a visible radiographic lesion associated with at least the mesial root. Patients will be randomized into one of the two arms (group S: apical size#25; group L: apical size#35) and followed for 2 years post-treatment. Treatment sequence Endodontic residents under the direct supervision of a study investigator will perform all treatments; all providers will be trained and calibrated for root canal treatment protocol and microbial sample collection. The calibration session will be repeated annually until completion of the study. Treatment protocol First Appointment 1. Pre-operative CBCT will be obtained and baseline clinical signs and symptoms will be recorded. Pain level will be recorded on a 0-10 visual analog scale (VAS). 2. After ascertaining adequate local anesthesia, rubber dam isolation will be obtained and the field will be disinfected with 3% hydrogen peroxide and 2.5% sodium hypochlorite (NaOCl) solution as previously described (37). 3. Access will be performed and the operative field will be again disinfected with 2.5% NaOCl followed by 5% sodium thiosulphate. A microbiological sample (S0) of the field will be obtained with paper points. S0 will be used as a negative control (i.e. sterility sample). 4. The mesial canal walls will then be touched lightly with hand files to disrupt bacterial biofilms and a microbiological specimen (S1) will be obtained (described in detail below). 5. Orifice will be enlarged with a Protaper Universal SX rotary file (Dentsply, Tulsa, OK) Apical patency will be determined with a size #10 hand file and working length will be obtained with the use of Root ZX apex locator (J Morita USA, Irving, CA) and verified with a PA radiograph. 6. Coronal 2/3 of mesial canal WL will be instrumented with Vortex Blue rotary file 25/06 (Dentsply). First apical binding file (FABF) will be recorded at this stage to serve as a covariable in the analyses. 7. Apical 1/3 instrumentation of mesial canals will be carried out according to assigned group as follows: 1\. Group S: Instrumentation technique to working length (WL) using the sequence 15/04 →20/04 →25/04 →25/06 Vortex Blue rotary file system (Dentsply). 2\. Group L: Instrumentation technique to WL using the sequence 15/04 →20/04 →25/04 →25/06 → 30/04 →35/04 Vortex Blue rotary file system (Dentsply). 8\. Distal(s) canal instrumentation will be standardized for both groups as follows: 1\. Coronal 2/3 of distal canal will be instrumented with Vortex Blue rotary file 25/06 2. Apical instrumentation to WL using the sequence 15/04 →20/04 →25/04 →25/06 → 30/04 →35/04→40/04 Vortex Blue rotary file system (Dentsply) 9. The canals will be irrigated using a 30-gauge side-vented needle with 6% NaOCl (10ml/canal) followed by 17% ethylenediaminetetraacetic acid (EDTA; 5ml/canal) followed by a final rinse of 6% NaOCl (10ml/canal) and 5% sodium thiosulfate (2ml/canal). 10\. A microbiological specimen (S2) will be obtained from mesial canals, and then the canals will be dried with paper points. 11\. Calcium hydroxide \[Ca(OH)2\] will be placed as an interim intracanal medicament and a temporary restoration consisted of Fuji II LC (GC Corp, Tokyo, Japan) will be placed in the access. A post-op radiograph will be made. Second appointment (within 10-14 days) 1. Clinical signs and symptoms will be recorded. Pain level will be recorded on a VAS. 2. After ascertaining adequate local anesthesia, rubber dam isolation will be obtained and the field will be disinfected as described above. 3. Root canal system will be accessed and a second sterility microbiological sample will be obtained (S00). 4. Ca(OH)2 will be removed by irrigating with 6% NaOCl (10ml/canal) followed by 17% EDTA (5ml/canal) and a final rinse of 6% NaOCl (10ml/canal). This will be followed by irrigation with 5% sodium thiosulfate (2ml/canal). 5. A microbiological specimen (S3) will be obtained from mesial canals, and then the canals will be dried with paper points. 6. Final obturation will be performed with gutta-percha and AH+ sealer utilizing the continuous wave condensation technique. 7. Access will be restored permanently and patient will be referred to their dentist for full coverage restoration. Adequate existing full coverage restorations will remain in place. A post-op radiograph will be made.