I've noticed that electric toothbrushes these days typically come in one of two shapes, or a combination of the two.
The first shape is a circular shape, where the bristles spin in a circle.
The second shape is the more traditional oblong shape that we recognize from manual toothbrushes. Electric toothbrushes of this kind tend to vibrate up and down or front to back.
The third shape is a circular shape in the front, with an additional oblong shape behind it. The circular shape spins, and the oblong shape vibrates.
Is there any medical evidence that one of these shapes is better for cleaning the teeth? What about for cleaning the gums?