Lateral force can not brush back and forth otherwise they will damage gums.

Big diameter pipe can be composed of several round steel brush together, at both ends with wire tightly, within the lumen pull brush back and forth, until the metal color, reoccupy cotton brush clean.

Brush on the origin of different in history, said the most recorded in history is the story of Penpower brush making, but modern scholars believe that there is a brush back in Penpower existed before.