The toothbrush includes a handle portion (12 or 55) and a brushhead portion (14 or 57) with a bristle set (20 or 53) at one end of the brushhead. At least one sensor (16 or 56 is located either on the handle of the toothbrush or on the bristle set back plate (54) of the toothbrush. When the sensor is located on the handle of the toothbrush, the position of the brushhead is determined by a processor (44 or 58) relative to the inside or outside surfaces of the teeth on the basis of the temperature detected by the sensor, either the outside environmental temperature or the skin temperature of the user. When the sensor is located on the bristle set back plate, the determination is made on the basis of the position of the bristle set relative to the cheek of the user.