You just haven't got the technique of dentist-management sorted out yet.
What you do is you lay down in the chair, and when he is ready to start work, you grab hold of him, firmly, by the goolies, and assure him in your best straight-faced voice, that it
IS going to hurt him more than it hurts you.
Works wonders ..... I'm told.
PS. There is a technical flaw in this method if you have a lady dentist. I'll leave the adaptation to the technique as an exercise for the student.
PPS. If you get arrested, or end up with no teeth at all .... don't blame me.