assessment of bacterial reduction and post-operative pain following Laser activated irrigation using sodium hypochlorite and a 980 nm diode laser device as an adjunct to conventional root canal treatment, and comparing it with passive ultrasonic irrigation using sodium hypochlorite and an ultrasonic device in patients with single rooted asymptomatic necrotic teeth.

After thorough diagnosis and recording of the patient's perceived preoperative pain using the numeric rating scale (NRS), which should be zero. Patients with single rooted necrotic teeth will be randomly divided into two groups for endodontic treatment in a single visit:

Group LAI (in which laser activated irrigation will be done) and group PUI (in which passive ultrasonic irrigation will be done).

The teeth are anesthetized and isolation is done. the clamp, tooth crown and rubber dam are disinfected using 2.5% sodium hypochlorite and 30% hydrogen peroxide then sodium thiosulphate to neutralize their effects.

Removal of caries and defective restorations is done, followed by access cavity preparation using round burs and fine tapered stones. then the first microbiological sample is taken using paper points. Afterwards root canal preparation is done using Protaper Next files and irrigation is done using 2.5% sodium hypochlorite and a 30 -gauge side vented needle.

After chemomechanical preparation of the canal, the second microbiological sample is taken, afterwards the canals are filled with sodium hypochlorite and according to the group, the following is done:

In group LAI: the 200 micrometer fibre of the diode laser device enters the root canal and the device is activated at a setting of 980 nm and 1.5 Watts for 5 seconds, repeated 4 times with a 10 seconds gap in between.

In group PUI: the ultrasonic device is activated inside the canal using a passive non cutting tip and kept activated for 1 minute.

Then, irrigation with saline solution is done then the third microbiological sample is taken, afterwards obturation is done and temporization. the patient is referred to the restorative dentistry clinic to complete the restoration of his tooth.

The patient is instructed to record his pain at 6,12,24 and 48 hours postoperatively and the microbiological samples are analyzed

Inclusion Criteria:

• Medically free patients.

• Patients with necrotic pulp in single rooted teeth with:

  • Closed apex.
  • Associated with or without periapical radiolucency.
  • No response of vital pulp with the electric pulp tester.

• Healthy dental and periodontal status.

• Positive patients' acceptance for participation in the study.

Exclusion Criteria i. Patients on medication for chronic pain. ii. Patients with pre-operative pain. iii. Patients having significant systemic disorders. iv. Patients with two or more adjacent teeth requiring root canal therapy. v. Patients who had received antibiotics in the last month. vi. Teeth that have:

• Vital pulp tissues.
• Association with swelling or fistulous tract.
• Acute peri-apical abscess.
• Greater than grade I mobility.
• Pocket depth greater than 5mm.
• No possible restorability.
• Previous endodontic treatment.
• Open apex.
• Extra coronal restorations.