INTRODUCTION: Probiotics are living micro-organisms that are likely to influence oral health by modulating the oral microbiota and offer a promising preventive approach to gum and dental disease. This approach is particularly relevant for orthodontic patients, who are more susceptible to gingival inflammation and plaque accumulation. The aim of this randomized controlled study was to compare the effects of a probiotic toothpaste versus a regular toothpaste on gingival health and plaque levels in orthodontic patients. METHODS: Participants were recruited between 4 June 2024 and 15 July 2024, and were aged between 18 and 50years. They did not suffer from mental/physical disabilities, craniofacial disorders, enamel/tooth dysplasia and were not taking medication affecting plaque build-up. Participants were randomized in two groups using a computer programme and sealed envelopes: the group A (control) used an ordinary toothpaste (Colgate) twice a day for four weeks, the group B used a probiotic toothpaste containing Lactobacillus paracasei twice a day for four weeks. Standard oral hygiene instructions were given to all participants. The primary outcome was the mean change in gingival bleeding index (GBI) and plaque index (PI) over four weeks. This was an open-label trial. Only the evaluator was blinded and the evaluation criteria were objective. RESULTS: Forty-four participants, 22 in each group, were finally included and analysed. After the intervention, the probiotic group had a significantly lower median gingival score [0.12 (IQR 0.09, 0.16)] than the control group [0.15 (IQR 0.10, 0.18)], with a p-value of 0.041 (95% CI: 0.009-0.18). However, there was no significant difference in plaque scores between the two groups [Probiotic: 20.0 (IQR 18.0, 21.0) vs. control: 21.0 (IQR 19.0, 22.0), P=0.15]. No significant adverse events or side effects were reported. CONCLUSION: Under the conditions of this trial, the probiotic toothpaste only significantly improved the gingival bleeding index in orthodontic patients compared to regular toothpaste. TRIAL REGISTRATION: ClinicalTrial.gov (NCT06473792).