Thorough medical and dental history for the eligible patients~Thorough intraoral and extraoral diagnosis~Local anesthesia~Isolation and removal of any previous filling or restoration~Removal of old gutta percha and establish patency to the full working length.~1st sample: will be collected using 3 sterile paper points~Chemo-mechanical preparation.~2nd sample collection~• Laser group: The canals will be irradiated with a high-power diode laser, with wavelength of 980 nm, maximum output of 3 watts and coupled with a fiber optic tip of 200 µm diameter.~• Mock laser application (Placebo group): The fiberoptic tip will be inserted inside the root canal, mimicking the laser irradiation, but not activated.~3rd sample collection~A piece of dry cotton will be placed in the access cavity, and then will be sealed with glass ionomer filling material~2nd visit: 1 week later, 4th sample collection then Obturation~Number of visits & follow up period: Two visits
This clinical trial will be conducted to evaluate the amount of Il-8 expression before and after the application of intracanal irradiation with diode laser 980 nm versus placebo in failed endodontic cases with periapical lesions.