You just need oven bake clay!
We used what we had leftover from our sonic screwdrivers and lightsabers!
And we even used GLOW in the DARK clay too!
So clay and an oven...and your toothbrush.
Okay, we just rolled out a ball.
Squished our toothbrush in it gently so it didn't poke through the bottom.
The kids have little kid sized brushes, so they didn't need
to be big monsters to hold them.
If you are using a tall adulty type toothbrush, use a bigger wad of clay.