insert 2 objects - both sprites - one teeth one round cube.
add pin behavior to teeth. add solid to both.
open teeth / circle image editor - go to collision box right click em and select "guess collision polygon"
after that in events - on start of layout pin teeth to circle. if you want a special position to pin, set their position to image-point.
- do your stuff to move /whatever and enable collisions on your sprites - then you should collide nicely.