Background: Immunosuppressive therapy in organ transplantation reduces immunity, making patients vulnerable to infections. Pretransplant dental care is vital to minimize posttransplant infection risks and improve transplant success. Regular dental check-ups and maintenance are crucial due to the infection risk from immunosuppressive drug use. This study investigates the efficacy of telemonitoring oral care using a smart toothbrush in liver or kidney transplant patients. Methods: The study included patients scheduled for liver or kidney transplant patients with at least 16 teeth, including implants and bridges, were divided into three subgroups: smart toothbrush without telemonitoring (Oral-B iO9; OB), smart toothbrush with telemonitoring and expert advice (Mombrush; MB), and manual toothbrush (Benco; MTB). Evaluations were conducted at baseline (V1), immunosuppressive drug cessation day (V2), and 3 months after V2 (V3). Relative plaque removal efficacy, halitosis, and oral and gut microbiome were assessed. Results: The MB group showed the most significant improvement in plaque control based on QHI changes, with all groups returning to baseline levels at V3. Halitosis levels were similar between groups and visits. Oral microbiome analysis revealed no significant differences in high-risk periodontal bacteria among groups at different time points. In caries-related bacteria, caries-risk bacteria decreased and anticaries bacteria increased over time in the MB group compared to the MTB and OB groups. Similarly, in the gut microbiome, it was found that enterobacterales with potential pathogenicity were relatively reduced in the MB, OB group compared to the MTB group. Conclusions: Interest in oral care declined after immunosuppressive drug cessation, but telemonitoring with Mombrush facilitated continuous oral hygiene maintenance. However, patient interest in smart toothbrushes decreased after 3 months. Oral hygiene management is critical for liver or kidney transplant patients, considering the correlation between oral and gut microbiome. Adequate monitoring and follow-up notifications are essential to keep users engaged.