Tooth bounces off of invisible object

I want his teeth to fall out but they are not respecting the mesh. You can see the tooth in front of his chest (The blue one). it straight falls down and at this position bounces off and falls forward to the ground. But there is nothing there. He is posed and has Mesh as collision source. The tooth isn’t reacting to the lips and falls through and then bounces off of that position. Split Impulse is on, Steps per second is on 300, solver iterations is on 100, Collision form for the tooth is cube (other forms make it jiggle around), friction is on 0,5 and bounciness on 0. The question is what causes this collision? I know that there is nothing there.