The aim of this study is to measure and compare the effectiveness of nanosilver combined calcium hydroxide and conventional calcium hydroxide intracanal medications in reducing postoperative pain in patients with Symptomatic Root Canal treatment Failure .

• 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. First session:

     • Patients will be asked to rate their pain level on NRS before treatment is started.

     • Patient will be anesthetized by using nerve block local anesthesia or infiltration local anesthesia according to the tooth location in mandibular or maxillary arch respectively.

     • Previous coronal restoration will be removed:

       • If the access will be cut through metal (amalgam alloy or cast metal) or composite resin, carbide fissure bur will be used.
       • In case of porcelain fused to metal (PFM) crown a round diamond is used to cut through the porcelain layer, then Transmetal bur is used to cut through and remove the core material.

     • Teeth will be isolated with rubber dam.

     • Gutta percha removal will be done using protaper rotary retreatment files in the following manner D1 has a cutting tip to facilitate initial penetration into the filling material (coronal third). D2 and D3 both have non-cutting tips and are used to remove material from the middle and apical thirds, respectively using gutta percha solvent

     • Working length will be determined using an electronic apex locator then confirmed with intraoral periapical radiograph, to be 0.5-1 mm, shorter than radiographic apex.

     • Cleaning and shaping will be done using crown down preparation technique with the use of protaper rotary files in an endodontic motor according to the manufacturer instructions, the canals will be thoroughly irrigated using 3ml of 2.5% Sodium hypochlorite between every subsequent instruments.

     • MD-Chelcream will be used as lubricant during mechanical preparation.

     • After instrumentation of the canals paper points (Protaper Paper Points) will be used for drying.

     • Using Lentulo Spiral Filler, medicaments will be placed under aseptic conditions into the canals according to each group, Experimental group Ca (OH) 2 ( Ca (OH) 2with nanosilver suspension and comparison group Ca (OH) 2 with sterile water then access cavity will be closed with a temporary filling

     • Patient will be instructed to call in case of severe pain in between visits, an emergency analgesics are to be prescribed to the patient (Brufen 400mg)

  2. Second session:

     • After 7 days, rubber dam will be placed , the temporary fillings will be removed and master apical file will be introduced in each root canal to loosen medicament and to create a space for subsequent irrigant, then each root canal will be washed with 5 mL of sterile saline, irrigated with 1 mL of 20% citric acid and again irrigated with 5 mL sterile saline.
     • Dryness of the canals by paper points (Protaper Paper Points).
     • Obturation will be carried out using the cold lateral condensation technique with protaper gutta percha cones and resin sealer with spreader size according to master cone size , its depth short 2 mm of the working length, and auxiliary cones size 25.
     • After obturation a cotton pellet will be placed in the pulp chamber and the access cavity will be closed with a temporary filling to avoid coronal leakage.
     • The patient is given a NRS and asked to rate his pain level at 6, 12, 24 & 48 hours after root canal retreatment .

Inclusion Criteria:

• Medically free patients.
• Patient's age between 25-50 years.
• Anterior or premolar teeth diagnosed clinically and radio graphically as symptomatic root canal treatment failure.
• Positive patient's acceptance for participation in the study.
• Sex include both male and female.
• Patients who can understand Numerical Rating Scale (NRS)
• Patients able to sign informed consent.

Exclusion Criteria:

• Pregnancy or lactation.
• Medically compromised patients.
• Patient with multiple teeth that required retreatment to eliminate the possibility of pain referral.

Bottles of nanosilver solution & distalled water will be covered and coded either A or B by assistant supervisor, and then given to the operator.

Participants will be blinded as regard to either intervention or control Participant and operator who is also the outcome assessor are blinded.