The goal of this clinical trial is to learn whether two different irrigation activation methods - passive ultrasonic irrigation (PUI) and sonic activation - help periapical healing in root canal treatments of single-rooted teeth with apical periodontitis.

Researchers will also compare these methods with the traditional needle irrigation technique.

The main questions this study aims to answer are

Do sonic irrigation activation or PUI activation methods lead to faster or better early periapical healing compared with traditional needle irrigation?

Is there any difference in healing volume measured by cone-beam computed tomography (CBCT) after 6 months?

Participants in this study will:

Adults with single-rooted teeth showing apical periodontitis (PAI ≥ 3),

Receive root canal treatment using either PUI, sonic activation, or traditional needle irrigation (assigned randomly).

Participants will have CBCT scans before treatment and again at 6 months to measure changes in lesion volume.

Researchers will analyze the 3D images using specialized software to calculate periapical lesion volumes before and after treatment. The study will evaluate how much the lesion size decreases in each group and whether any activation method improves healing compared with standard irrigation.

Apical periodontitis (AP) develops as a consequence of pulpal infection and the subsequent host inflammatory response. The success of root canal treatment depends greatly on eliminating intraradicular biofilm and preventing reinfection. Adjunctive activation of irrigants-such as sonic or passive ultrasonic irrigation-has been proposed to enhance irrigant penetration, debris removal, and overall microbial disruption compared with conventional needle irrigation. This randomized, three-armed, parallel clinical trial evaluates whether sonic or ultrasonic activation of irrigating solutions leads to superior early periapical healing in single-rooted teeth diagnosed with AP. The study is based on the biological premise that activation improves irrigant replacement dynamics, acoustic streaming, and penetration into anatomically complex spaces that standard needle irrigation may not adequately reach. All participants received standardized root canal treatment using contemporary instrumentation, irrigation solutions, and obturation materials. The three intervention groups differed only in the method used to activate irrigants during the final cleaning phase. This uniformity ensured that any differences in healing outcomes reflect the effect of activation rather than variations in clinical technique. Early healing was assessed volumetrically using cone-beam computed tomography (CBCT), which enables three-dimensional visualization of periapical tissues and provides a sensitive measure of lesion change over time. Volumetric analysis was performed with a predefined workflow to ensure reproducibility, including blinded assessment to minimize bias. The study focuses on quantifying the reduction in periapical lesion volume at 6 months and exploring whether sonic or ultrasonic activation offers measurable advantages in early tissue healing compared with conventional irrigation. The findings aim to contribute to evidence-based endodontic protocols, particularly regarding the role of adjunctive activation techniques in improving periapical healing following root canal treatment.

Inclusion Criteria:• American Society of Anesthesiologists physical status classification system (ASA) class I and II

• Individuals between 13 and 65 years of age
• Good oral hygiene

Tooth-related:

• Single-rooted teeth
• Sufficient amount of coronal tooth structure
• Probing depth of ≤ 4 mm
• Presence of Apical periodontitis (AP) on radiographs
• Asymptomatic teeth
• Periapical Index (PAI) score ≥ 3
• Negative response to pulp vitality tests
• Mature teeth

Exclusion Criteria:• ASA class III or higher

• Pregnancy or lactation
• Individuals with mental retardation
• Allergy to Sodium hypochlorite (NaOCl), Chlorhexidine (CHX), or latex

Tooth-related:

• Extensive structural loss that cannot be restored with a filling
• Presence of subgingival caries
• Teeth previously treated with root canal therapy
• Fractured or cracked teeth due to trauma
• Non-vital teeth without radiographic evidence of AP
• Immature teeth
• Positive response to pulp vitality tests
• Presence of internal or external root resorption detected on radiographs
• Increased mobility due to insufficient bone support