I havn’t used Max in several years now but regardless - for something of this sort - you are going to have to setup the bristals with some bones. For example drawing several simple bones or chains (1-3 bones) which will controll the bristals. You will prolly want to have several specific “hero” ones towards the outside of the brush… the ones which we be seen the most. The bristals towards the center can be group together so you don’t have to animate EACH and EVERY one.
To be honest… if your setup is sloppy then your animation is going to look sloppy. You need to spend some time setting up the tooth brush if you want it to deform, bend, and react like a real legit tooth brush. -D