(Backordered) Philips Sonicare 3100 Series Electric Toothbrush HX3671/33 (White)Sonic Water Flow: High speed vibrations of approximately 31,000 strokes per minute loosen plaque, and the wide range of the brush head's oscillations removes it. At the same time, these movements generate a "sonic water flow" that stimulates saliva flow in the mouth, gently and effectively removing plaque. Overpressure Prevention Sensor (notifies you when you're brushing too hard): If the overpressure prevention sensor detects that you're brushing too