No, you are not obligated to continue receiving treatment from the same dentist. If you are unsatisfied, find another dentist.
Whether you are legally entitled to recover the cost of services rendered by the dentist depends on whether his treatment was so poor as to constitute a material breach of contract or medical malpractice (negligence). That determination would require an intensive fact investigation and the engagement of an expert witness (who could testify that "the industry standard is "X" and the services rendered were "not X"). Without the assistance of an attorney, that avenue can be very complicated.
I suggest you address your concerns with your dentist directly before you result to legal recourse. But if you do decide to sue him/her, I strongly recommend consulting with an attorney first.
you are not obligated to stay with the dentist, nor should anyone ever stay with a medical/dental care provider in whom trust and confidence has been lost. As for a refund, you would likely not be able to get a refund for the work already done, unless you can establish that what was done was incorrect or improper (would require another dentist to prove), but if you are paying in installments, you should not have to pay for the work that was not yet done; and should get a refund for that portion if it was paid in advance.
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