27 subjects on SPT, each with at least two residual pockets ≥5mm, were recruited for this randomised, split-mouth controlled trial, providing a total of 72 sites. At baseline, probing pocket depth (PPD), recession, clinical attachment level (CAL), plaque and bleeding on probing (BOP) of all sites were examined. Gingival crevicular fluid (GCF) were collected to determine level of cytokines IL-1β, -6, -8, TNF-α and MMP-8 via ELISA. Control sites received subgingival instrumentation and rubber cup polishing with pumice. In addition test sites received a single application of PDT using Fotosan® and photosensitizer consisting of toludine blue O solution. The subjects were recalled three and six months later and re-examined. Site level analysis was performed.

Inclusion Criteria:

1. Good general health with no systemic diseases causing manifestation of periodontal diseases
2. Age ≥ 21 years
3. History of chronic periodontitis
4. At least two residual PPD ≥ 5 mm with or without bleeding on probing
5. Compliant with recalls, i.e. last SPT visit at most 6 months before start of trial
6. Able to give written informed consent

Exclusion Criteria:

1. Pregnant or lactating females
2. Local or systemic antibiotics intake in the past 3 months
3. Systemic conditions which could affect progression of periodontitis
4. Long term use of NSAIDs or immunosuppressive medications
5. Participation in other clinical trials