The purpose is to investigate influence of bioceramic filling of the root canal and photodynamic therapy on periapical healing and development of postoperative pain after endodontic retreatment. Patients are divided into two main groups and each of the group is divided into two subgroups. Main groups are patients receiving photodynamic therapy and patients receiving passive ultrasonic irrigation. Each of the main group is divided by the root canal filling material on the AH+ group and BioRoot group.

Clinical trial will be conducted in Dental clinic Zagreb. Patients will be chosen for this randomized prospective trials from the everyday patients referred by general dentist for endodontic retreatment. In the research will be included only patients with symptoms of chronic apical periodontitis and previous endodontic treatment. It includes teeth sensitive to palpation, percussion or visible sinus tract or swelling and asymptomatic inadequate endodontic filling. Patients that are immunocompromised, pregnant women, teeth with pocket depth bigger then 3mm, teeth with signs of vertical root fracture, teeth that are impossible to restore are excluded from research.

Every patient will be assigned to one group and one subgroup using "wheeldecide" programme. Patients will not be aware what group or subgroup they are assigned. endodontic retreatment will be conducted by one specialist in endodontics. Therapy is single visit retreatment.

Inclusion Criteria:

• Patients with symptoms of periapical disease after endodontic treatment,
• teeth sensitive to percussion and palpation,
• teeth with present sinus tract and
• asymptomatic teeth with radiologically inadequate root canal filling.

Exclusion Criteria:

• Immunocompromised patients,
• pregnancy,
• teeth with signs of vertical root fracture,
• teeth that can't be restored,
• antibiotic usage within last month,
• teeth with acute apical abscess