The purpose of this randomized clinical trial is to evaluate the incidence of postoperative pain after retreatment after apical enlargement and sonic activation assisted irrigation. The presence of postoperative pain will assess after retreatment cases at 12, 24, 48, 72 hrs and 1 week.

The aim of this clinical study is to evaluate the intensity and duration of postoperative pain after apical enlargement and sonic activation assisted irrigation procedures. Patients who have asymptomatic teeth required retreatment will include in this study and retreatment procedure will be applied to these teeth. One hundreds twenty asymptomatic teeth required retreatment will randomly participate into 4 treatment groups in terms of apical enlargement and sonic activation assisted irrigation procedure applied. The presence of postoperative pain will assess after 12, 24, 48, 72 hrs and 1 week. Postoperative pain will be recorded by each patient by using visual analogue pain scale. Before the treatments, the nature of the study, complications and associated risks will be totally explained and written informed consent will be obtained from all study participants. The local anesthetic will be applied before the treatment start. The routine retreatment procedure will be applied. Different final irrigation solutions will be applied in accordance to the manufacturers' instructions. At the end of treatment, each patient will be given an evaluation sheet, explained the treatment procedure and using of visual analogue pain scales, and informed to be returned during the following one week. After one week the teeth will be examined according to for pain intensity, percussion & palpation sensitivity, swelling, analgesic intake and clinical status.

Inclusion Criteria:

-Patients who were healthy volunteers and who have failed teeth required retreatment with periapical index score 3-5 score requiring root canal treatment for first time.

Patients who were not included the study who;

• were pregnant or breast feeding during the duration of the study,
• have systemic disease, have any pain and/or any facial swelling, abscess,
• were immunocompromised,
• were under 18 yrs. and over 65 yrs. age,
• were taking antibiotics or corticosteroids within previous three days,
• have multiple teeth that required root canal treatment at the same time period; for eliminating pain referral,
• have root canals that could not be well-treated with orthograde retreatment.

Exclusion Criteria:

-The patients who forgot to fill out the form and took antibiotics and/or analgesics right after the first appointment of the therapy were excluded from the study.

Double (Participant and Outcomes Assessor) The patients and outcome assessor were unaware as to which study group they had been allocated.