N-Acetyl Cysteine Protects Pulpal Stem Cells in Endodontic Revascularization

We will recruit 14-18 patients under the age of 18 by means of advertising at UCLA. Two groups will be formed, one with NAC treatment during endodontic revascularization and one without. Each patient will have an adult tooth where the following criteria are met: * Tooth with necrotic pulp and immature apex(apices) * Pulp space is not needed for post/core, final restoration * Compliant patient who is willing to come for at least 2-3 treatment appointments and 2-3 follow-up recall appointments. * Patients are not allergic to calcium hydroxide intra-canal medicament Appropriate consent forms will be obtained by the patient and the patient's parent or legal guardian. If we recruit 18 patient, 9 patients will be under regenerative endodontic therapy/re-vascularization with NAC and 9 patients without NAC. The following procedures will be applied to the patients. First Appointment: * Local anesthesia administration, dental dam isolation and access * Copious, gentle irrigation with 20mL NaOCL (sodium hypochlorite) using an irrigation system that minimizes the possibility of extrusion of irrigants into the periapical spaces. The concentration of NaOCL will be low (1.5%, 20mL/canal for 5 minutes). Afterwards, irrigation with 17% EDTA (20mL/canal for 5 minutes) will be done. Irrigating needle position should be about 1mm from root end, to minimize cytotoxicity to stem cells in the apical tissues. * Dry canals with paper points * Place calcium hydroxide into canal(s) delivered via syringe * Seal access with 3-4mm of a temporary restorative material such as CavitTM, IRMTM or glass ionomer. Dismiss patient for 2-4 weeks. Second Appointment: * Assess response to initial treatment. If there are signs/symptoms of persistent infection, consider repeating the procedures of the First appointment. * Anesthesia with 3% mepivacaine without vasoconstrictor, dental dam isolation * Copious gentle irrigation with 20mL of 17% EDTA * Take a radiograph to ensure previous calcium hydroxide has been fully removed form the canal system * Dry with paper points * For study patients only: Irrigate canal system with NAC (20mM NAC, 30mL/canal) gently for 10 minutes and then dry canal(s) with paper points * Create bleeding into the canal system by over-instrumenting (endo file, endo explorer). Induce bleeding by rotating a pre-curved (approximately 45 degrees at the apical 1-2mm of file) K-file at 2mm past the apical foramen with the goal of having the entire canal filled with blood to the level of the cemento-enamel junction. * Stop the bleeding at a level that allows for 3-4mm of restorative material. Place a resorbable matrix (CollaPlugTM, CollacoteTM, CollatTapeTM) over the blood clot if necessary to achieve a better stop for mineral trioxide aggregate (MTA) or Bioceramic fast set putty (BC). Place white MTA as capping material on top of the resorbable matrix. * The access is closed with 3-4mm layer of glass ionomer (Fuji IXTM, GC America, Alsip, IL), composite or alloy over the capping material. For resin modified glass ionomers and composite, 40 seconds of light curer will be done. Follow-up recall appointments: Clinical and Radiographic exam * Extra-oral examination: No pain, extra-oral swelling nor extra-oral sinus tract * Intra-oral examination: No pain, intra-oral swelling of mucosa nor intra-oral sinus tract * Take 1 straight on periapical radiograph and 1 angled periapical radiograph. Resolution of apical radiolucency (often observed within 6-12months). * Record any increased width of root walls (this is generally observed before apparent increase in root length and often occurs 12-24 months after treatment) * Record any increase in root length (in mm) * Test vitality of pulp with Endo-Ice and Electric pulp tester (EPT). * Record which goals have been attained (primary, secondary and/or tertiary) The degree of success of RET is measured by the extent to which it is possible to attain primary, secondary and tertiary goals: * Primary goal: The elimination of symptoms and the evidence of bony healing * Secondary goal: Increased root wall thickness and/or increased root length * Tertiary goal: Positive response to vitality testing