Respiratory infectious diseases (RIDs) are generally spread through person-to-person contact. The human oral cavity, in particular, is a significant source of particles that can cause RIDs. Electric toothbrushes, popular for oral cleaning in recent years, work via high-frequency vibration, which can theoretically spread droplets or small-size aerosols containing viruses. However, the particle emission rates and the potential to spread RIDs using electric toothbrushes are still unclear. In this paper, we investigated the particle emissions from using electric tooth-brushes by designing a three-step approach, i.e., a preference survey on toothpaste and toothbrush selections, a behavior test on toothpaste usage, and a standardized particle emission test. The results showed that, first, the toothpaste would be rapidly decomposed into foams, and the emission rates quickly increased to a peak within approximately 10s. Then, the particle emissions decreased slightly and entered a steady phase until the 2-min brushing period stopped. Second, more than half of the detected particles were PM1, and almost all were PM5, which can be considered aerosols, and the emissions can reach up to 5433 counts/s. Third, the emissions heavily depended on toothbrush and toothpaste selections, the brushing post, i.e., the teeth. This study suggests that using electric toothbrushes can pose risks of spreading RIDs in enclosed indoor environments such as private homes or, more significantly, public washrooms in school dormitories, airports, train stations, etc. Limited usage of electric toothbrushes and better designs of public washrooms in the context of a global pandemic may be advised.