Disclosed is an interdental tooth cleaning appliance for use in cleaning a space formed between adjacent teeth. In order to clean more effectively as compared with a known appliance, the cross-sectional shape of the bristles as seen in a plane perpendicular to the longitudinal axis of the brush is such as to provide three circumferentially spaced groups of bristles which are longer than the remaining bristles. The interdental tooth cleaning appliance of this invention is provided with a guide which makes it a more convenient one. It also has a device for injecting a liquid medicine.