The goal of this clinical trial is to learn whether regenerative endodontic treatment (RET) should be performed in one visit or two visits in people with mature permanent teeth with chronic apical periodontitis.

RET is a dental treatment used for teeth with necrotic pulp and infection around the root. The procedure disinfects the root canal and promotes the formation of new tissue inside the canal space, which may support healing of the tissues around the tooth root.

The main questions this study aims to answer are:

Does single-visit RET cause different levels of postoperative pain compared with two-visit RET? Do teeth treated with single-visit or two-visit RET show different levels of healing around the root? Participants will receive RET using either a single-visit or two-visit treatment protocol. Participants will record their pain levels during the first week after treatment using a visual analog scale (VAS). Participants will return for follow-up visits at six months and one year, when dental radiographs will be taken to evaluate healing around the tooth root.

Inclusion Criteria The inclusion criteria for this study were defined as follows: individuals aged between 18 and 40 years who were classified as ASA I (systemically healthy) according to the American Society of Anesthesiologists (ASA) classification; mature permanent teeth with completed root development (closed apex); single-rooted and single-canal maxillary central or lateral incisors; teeth that had not received previous endodontic treatment; teeth diagnosed with chronic apical periodontitis and presenting with a lesion with a periapical index (PAI) score ≥3 according to the classification; teeth that were asymptomatic in the preoperative clinical evaluation; teeth that were restorable and did not require post or core placement for permanent restoration; and patients who signed the informed consent form to participate in the study.

Exclusion Criteria The exclusion criteria were as follows: individuals younger than 18 years or older than 40 years; patients with systemic diseases classified as ASA II or higher according to the ASA classification; pregnant or breastfeeding women; teeth with root fractures or internal or external root resorption; and teeth presenting with advanced periodontal destruction, pathological periodontal pocket depth ≥3 mm, or mobility greater than Grade 1.