Ubrush! Refill Interdental Brush Size- 0.9mm with tapered brush shape One unit contains- 11 pcs Choose the correct brush size. (You may need 2 or even 3 sizes). Replace the brush when it is worn out and insert a new one in the handpiece. Feed carefully into the interdental area. It becomes easier when you get used to it. Increase the effect by inserting the brush 3-4 times in each interdental space and move back and forth.