I hope this message finds you well, rpesent circumstances excluded. I am a licensed attorney with over a decade of experience. It is a pleasure to assist you today.
You need to be up front and honest. Tell him that you feel as though the new issues are a direct result of his action on the other tooth. Tell him that you cannot and will not pay for the additional work and that you feel as though his previous work on the crown fell below the applicable standard of care, and actually caused you harm.
He should know, and you should as well, that medical and dental malpractice suits are predicated on not meeting the applicable standard of care. This means that he did you do what a reasonable dentist would have done under the circumstances. It also means he had a duty, he breached that duty, and this breach caused you harm.
You could file a suit against the dentist for his actions. In lieu if filing suit, you should seek to have this issue alleviated free of charge and the charge for the other work should be reduced drastically as well.
So, be up front and honest. Tell him his work was not satisfactory and does not meet the standard of care. Tell him you will not pay for work on the two teeth that fell out due to his poor work and that you feel as though the other bill should be reduced.
If he is unwilling to assist or relent, then you need to explore filing suit.
Let me know if you have any other questions.
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Thanks and Best Wishes!