The study aims to evaluate and compare the antimicrobial activity of 2% and 5% plum seed extract mouthwash with 0.12% chlorhexidine mouthwash and a control group without mouthwash against Streptococcus mutans and Lactobacillus acidophilus in the dental plaque of patients undergoing fixed orthodontic treatment. Patients aged over 18 years, enrolled for fixed orthodontic treatment without therapeutic extractions, and meeting the inclusion criteria, will be randomly assigned to the four study groups using a computer-generated random chart with allocation concealment through sealed envelopes. Inclusion criteria include patients with a full complement of permanent teeth (excluding third molars), a DMFT score not exceeding 2, a gingival index (Löe) score of less than 1, and those undergoing treatment with 0.022-inch slot MBT prescription stainless steel orthodontic brackets (Mini Diamond, Ormco Corporation, California, USA), with initial archwires tied to the bracket slots using elastomeric ligatures. Participants must also be willing to provide informed consent. Exclusion criteria include smoking habits, current antibiotic therapy, and systemic diseases. Plum seed extract mouthwash will be prepared following established protocols in the literature, while the 0.12% chlorhexidine mouthwash (Perioguard, Colgate Palmolive, India) will be procured without any additional antimicrobial agents. All patients will undergo oral prophylaxis before appliance bonding and will receive uniform oral hygiene and diet instructions. Each patient will be provided with a medium-texture orthodontic toothbrush and non-fluoridated, non-medicated toothpaste, with instructions to brush twice daily for at least three minutes. Group I will use 2% plum seed extract mouthwash, Group II will use 5% plum seed extract mouthwash, Group III will use 0.12% chlorhexidine mouthwash, and Group IV will serve as the control without any mouthwash instructions. A compliance chart will be provided to all patients, who will document mouthwash use, and the chart will be reviewed at each visit. Samples will be collected at 1, 3, and 6 months post-appliance bonding. Supra-gingival plaque samples will be collected from the right lateral incisor using a 4-pass technique during early morning appointments, with patients instructed not to brush their teeth on the day of collection. These samples will be transferred to vials containing appropriate media, transported to the laboratory, and evaluated for Streptococcus mutans and Lactobacillus acidophilus counts. Colony counts will be measured using a colony counter, and the results will be expressed in CFU/mL.