This study aims to evaluate the clinical effectiveness of antimicrobial photodynamic therapy (aPDT) as an adjunct to scaling and root planing (SRP) in the treatment of periodontitis. A split-mouth design will be used, in which one hemiarch receives conventional SRP and the contralateral hemiarch receives SRP combined with aPDT. Clinical periodontal parameters, including probing pocket depth (PPD), clinical attachment level (CAL), bleeding on probing (BOP), plaque index (PI), and gingival index (GI), will be assessed at baseline and 30 days after treatment. The study seeks to determine whether adjunctive aPDT improves periodontal outcomes compared with conventional non-surgical periodontal therapy alone.