Abstract: A power driven dental toothbrush mechanism is provided having a suitable power source such as a water turbine motor or an electric motor operating through a drive shaft and gear train assembly to accomplish controlled rotation of a plurality of gear driven bristle tufts. A brush head assembly is releasably connected to a motor housing structure and defines an internal gear chamber within which is located a plurality of bristle tuft gears and drive gears therefor. The toothbrush mechanism incorporates a flushing water supply passage in communication with a water inlet source and which transitions the joint between the brush head and housing structure and opens into the internal gear chamber. The brush head and housing structure also define a flushing water exhaust passage in communication with the internal gear chamber of the brush head opposite the flushing water inlet.