The goal of this clinical trial is to learn if Neodymium-Doped Yttrium Aluminum Garnet（Nd: YAG） Laser-assisted non-surgical periodontal treatment is effective in treating stage II/III periodontitis. It will also evaluate the safety and impact of the laser treatment. The main questions it aims to answer are:

1. Does Nd: YAG Laser treatment reduce probing depth, gingival inflammation, and clinical attachment loss more effectively than standard Scaling and root planing(SRP) therapy alone?
2. What changes in inflammatory markers and oxidative stress levels occur when patients receive laser-assisted therapy? Researchers will compare Nd: YAG Laser treatment to standard periodontal therapy alone to determine the effectiveness of the laser treatment.

Participants will:

1. Receive Nd: YAG Laser assisted therapy on one side of their mouth and standard therapy on the other side.
2. Visit the clinic at baseline, 6 weeks, and 3 months for follow-up assessments and tests.
3. Provide samples and have measurements taken of periodontal health and biomarkers of inflammation and oxidative stress.

To investigate the clinical effect of Nd: YAG laser assisted non-surgical periodontal treatment on the patients with stage II / III periodontitis. This study included patients with stage II/III periodontitis who visited the Second Affiliated Hospital of Zhejiang University School of Medicine. Using a split-mouth design, the random number method was used to determine whether the left or right half of the subjects were in the laser group, and the remaining half were in the control group. All subjects underwent periodontal initial therapy, and the laser group received extra periodontal irradiation treatment using Nd: YAG laser. Before treatment, 6 weeks after treatment, and 3 months after treatment, the probing depth (PD), gingival index (GI), and clinical attachment loss (CAL) of all subjects were recorded. At the same time, the gingival crevicular fluid samples of thesubjects were collected using absorbent paper tips. The levels of Interleukin-6 (IL-6), Tumor necrosis factor-alpha (TNF-α), and Malondialdehyde (MDA) were measured using assay kits. Analyze and compare the changes in data before and after each group.

Inclusion Criteria:

• Age between 18 and 65 years, with no gender restrictions.
• Diagnosed with stage II or III periodontitis according to the 2018 Classification of Periodontal and Peri-Implant Diseases and Conditions.
• In each of the four quadrants of the oral cavity, at least one tooth must have at least one site with a probing depth ≥5 mm, clinical attachment loss ≥2 mm, and bleeding on probing.
• Participants must provide informed consent and sign the informed consent form.

Exclusion Criteria:

• Fewer than 20 remaining teeth (10 pairs of opposing teeth) or a significant discrepancy in the number of remaining teeth between the left and right sides of the mouth.
• Patients who have undergone periodontal treatment within the past six months or are currently undergoing orthodontic treatment, which may affect periodontal health.
• Patients with systemic diseases that could influence the outcomes of periodontal treatment.
• Patients with severe infections, malignancies, or other major diseases affecting overall health.
• Pregnant or breastfeeding women.
• Individuals with a history of smoking.
• Patients who are unable to comply with or complete periodontal treatment.