I'll restate my point.
The dentist is not obligated to treat you. Where are medical circumstances where a doctor has an obligation to treat, those circumstances do not appear to apply here. Because he has no such obligation, you do not have any obvious grounds for a suit.
However, if you believe there is a law or other legal obligation that is being overlooked and which would have forced the dentist to treat you no matter what the circumstances, please state that law.

