An automatic toothbrush having a fluid motor, in particular a water motor, which produces reciprocating movements of a part, such as a piston, coupled to the brush proper, one or more ports being located in the fluid supply passage and/or the fluid discharge passage, which ports can periodically be opened and closed by a member, such as a slide, which is driven by a switching mechanism the position of which is determined by the position of the pistons. Preferably a buckling spring mechanism is used.