An electric toothbrush like your sonic toothbrush has been designed to vibrate at more than 30,000 brush strokes per minute. Turbulent fluid dynamics are created near the tips of the bristles due to the high speed brushing action. Consequently, a creation of waves of pressure and shear forces in liquids like salvia that surround your teeth, create the minute bubbles that are propelled forcefully against the surfaces where plaque resides. The combination of these various fluid dynamics results in forces that are capable of getting rid of dental plaque in hard to reach areas like between teeth and below the gum line. The cleaning effect of these fluid forces has been measured to occur at distances of up to 4 millimeters beyond where the bristles of your sonic toothbrush can actually reach.