The toothbrush includes a handle portion and a brushhead assembly which comprises a head portion and a stem portion. The head portion includes a bellows-like acoustic action member for creating acoustic wave action as it moves in and out in response to an acoustic driving force. A drive system is located in the handle and includes an audio speaker-type assembly to create acoustic waves which are transmitted through a transmission line to the acoustic action member. The acoustic action member is driven toward and away from the teeth when the toothbrush is operatively positioned within the mouth. The action of the acoustic member is directly or indirectly coupled to the fluid in the mouth, producing a foam which couples shear forces between the acoustic action member and the teeth/gums to produce a desired cleaning/therapeutic effect.