Curasept Proxi T17 Yellow Interdental Brush 5 PCCurasept Proxi Treatment series interdental brushes in the T17 size. This is the ISO size 5 and has a core diameter of 1. 7mm. The brush shape is traditional parallel sided. (see the T17Cone for the cone shaped brush). Our Prevention series of interdental brushes is recommended for larger interdental spaces resulting from gum problems, dental malposition, or dental treatments such as bridges and implants.