Objective: This study aimed to improve the health of peri-implant tissues through continuous intake of Lactobacillus salivarius WB21 (LSWB21) tablets. Methods: A double-blind, randomized controlled trial was conducted with 23 maintenance patients who had generally healthy oral peri-implant tissues. Participants were divided into a test group (n = 12) receiving LSWB21 tablets and a control group (n = 11) receiving placebos. All patients took one tablet three times daily for 2 months. Evaluation measures included modified Gingival Index (mGI), modified Plaque Index (mPI), modified Bleeding Index (mBI), salivary secretory IgA, and oral symptoms assessed at baseline, 1 month, and 2 months. Results: After 2 months, significant improvements in the mGI, mPI, and mBI were observed in the test group; significant improvement in the mPI was observed in the control group. Changes in the mGI over 2 months significantly differed between the groups (p = 0.038), and multiple regression analysis confirmed the effectiveness of LSWB21 in reducing the mGI (p = 0.034). Subjective symptoms such as bad breath in the test group and tongue symptoms in the control group also significantly improved. Conclusion: Continuous intake of LSWB21 may be beneficial for stabilizing peri-implant tissue. Trial registration: UMIN000039392 (UMIN-CTR).
