BackgroundEvidence suggest an inflammatory link between respiratory health and periodontitis. This study aims to evaluate the impact of periodontal therapy on lung function.MethodsSixty-two never-smoking patients with mild periodontitis and without other medical conditions participated in this single-blind, prospective trial. Patients underwent periodontal therapy following an infection control approach. Lung function was measured using forced oscillation technique, assessing airway resistance and reactance, and spirometry evaluating FEV1, FVC, and FEV1/FVC. Lung function and fractional exhaled nitric oxide were assessed at baseline, three and six weeks, and every three months for a year. Periodontal parameters were recorded at baseline, six weeks, six and 12 months. Data were analysed using mixed-effects regression models.ResultsPatients (mean age 36 years, 58% female) showed significant improvements in periodontal parameters (p < 0.001). Oscillometry revealed a significant decrease in airway resistance at 11 Hz and 19 Hz after six weeks, with further significant decreases throughout the study. Resistance at 5 Hz (R5) consistently declined, reaching significance at three months (p = 0.001). By one year, R5, R11, R19, and R5 − 20 showed significant reductions (all p < 0.05). Airway reactance at 5 Hz became less negative at three months (p = 0.002), while the reactance area (AX) decreased significantly at six months (p = 0.008). No significant changes were observed in spirometry or fractional exhaled nitric oxide.ConclusionA decrease in airway resistance was observed after periodontal therapy, underscoring its positive impact on small airway function. These findings suggest that oral infection control is valuable for respiratory health in young adults before chronic conditions establish.Clinical trial registrationThe trial was registered at ClinicalTrials.gov (NCT04781153) on February 19, 2021, prior to participant enrolment.