This clinical study investigates the effectiveness of antimicrobial photodynamic therapy (aPDT) as an additional disinfection method in root canal treatment of patients with Type 2 Diabetes Mellitus (T2DM) who have apical periodontitis (AP). T2DM is known to negatively impact the healing of periapical tissues due to impaired immune response. In this study, methylene blue is used as a photosensitizer, activated by a specific wavelength of light to eliminate residual bacteria that are difficult to reach with conventional cleaning methods. The bacterial load and changes in the root canal microbiome will be analyzed using next-generation sequencing (NGS) of the 16S rRNA gene. The goal is to assess the microbial elimination and healing of periapical lesions, and to improve treatment outcomes in diabetic patients.

Systemic diseases such as Type 2 Diabetes Mellitus (T2DM) are known to influence both the etiology and healing process of endodontic diseases. T2DM is characterized by chronic hyperglycemia and impaired immune responses, which may negatively affect the resolution of periapical inflammation following root canal treatment. Apical periodontitis (AP) is a common endodontic pathology, often resulting from bacterial infection in the root canal system. The prevalence and severity of AP are higher in diabetic patients, and studies have shown reduced survival rates of endodontically treated teeth in this population.

The primary aim of this study is to evaluate the effectiveness of antimicrobial photodynamic therapy (aPDT) as an adjunctive disinfection method following conventional root canal preparation in T2DM patients with AP. aPDT utilizes a photosensitizer-methylene blue in this study-that, when activated by light of a specific wavelength, generates reactive oxygen species to eliminate residual microorganisms in complex anatomical areas such as isthmuses and lateral canals.

The study will utilize next-generation sequencing (NGS) of the 16S rRNA gene to assess bacterial diversity and quantify microbial elimination before and after aPDT application. The healing response of periapical lesions will also be monitored. The findings aim to contribute to improved treatment strategies and outcomes for endodontic therapy in systemically compromised patients, particularly those with T2DM.

Inclusion Criteria:

• • Individuals aged between 18 and 65 years

  • Voluntarily agree to participate in the study and attend follow-up sessions
  • Systemically healthy individuals (no systemic diseases)
  • Not taking antihypertensive or antidiabetic medications
  • Not pregnant
  • No use of corticosteroids or antibiotics within the last 3 months
  • No history of smoking
  • No acute pain or extraoral swelling
  • No sinus tract or acute apical abscess
  • Presence of a periapical lesion with a Periapical Index (PAI) score ≥ 3
  • Presence of a mature, single-rooted permanent tooth with completed root development

Exclusion Criteria:

• • Severe periodontal disease

  • Internal or external root resorption
  • Open apex (immature root development)
  • Suspected vertical root fracture
  • Non-restorable teeth
  • Teeth with previous root canal treatment
  • Presence of developmental dental anomalies

The impact of gender differences on pain assessment in the study was also evaluated. Additionally, the effect of age on lesion healing was analyzed. Since the study examines the effects of demographic data on lesion healing and post-treatment pain, demographic data will be shared.

The IPD and supporting information will be available for 2 years following the treatment outcomes.