A system for determining the orientation of a toothbrush (4), the system comprising an orientation sensor (27) configured for attachment to a toothbrush (4) and one or more processors (29) configured to receive orientation information from the orientation sensor (27). The one or more processors (29) are further configured to determine whether the sensor (27) is in a first orientation (41) or a second orientation (33). The first orientation (41) corresponds to use of the toothbrush (4) on a surface of teeth on the left (42) of a user's mouth. The second orientation (33) corresponds to use of the toothbrush (4) on a surface of teeth on the right (40) of a user's mouth.