A tooth is one of your teeth. Teeth are in your mouth and are used for biting and chewing.
Frazzle is brushing his teeth. He has one toothbrush for each tooth.
A brush is a tool made of bristles fastened to a handle.
Ernie wants to paint the hallway. He has a can of paint. Which brush is better for him?
Bert wants to clean his teeth. He has some toothpaste. Which brush is better for him?