This study compares how well different root canal medications reduce pain and bacteria after treatment of lower molar teeth with necrotic pulp. It tests whether adding mesoporous silica nanoparticles-antibacterial particles-to calcium hydroxide makes the treatment more effective. Forty-two adult patients will be randomly assigned to receive either calcium hydroxide alone, nanoparticles alone, or a mix of both for one week during root canal therapy. measure patients' pain levels after 6h,12h,24,48h and 72 hours from treatment and the number of bacteria before and after treatment to see which method gives the best results. The goal is to make root canal treatments more comfortable and successful for future patients.

• Inclusion Criteria:

  1. Patients with an age range between 18 to 40.
  2. No sex predilection.
  3. Patients with necrotic pulp.
  4. Patients able to sign informed consent.
  5. Restorable teeth.
  6. Positive patient's acceptance for participating in the study.
  7. Type III distal and mesial canal of first mandibular molar.

• Exclusion Criteria:

  1. Pregnant females

  2. Medically compromised patients.

  3. Patients having analgesics before the treatment

  4. If antibiotics have been administrated during the past two weeks pre-operatively.

  5. Patients having bruxism or clenching

  6. Patients having sever malocclusion associated with traumatic occlusion.

  7. Teeth that have:

     1. Peri-apical radiolucency
     2. Root resorption.
     3. Pulp stones or calcifications.
     4. Previous endodontic treatment.