This is a case for small claims court. It is a simple breach of contract/warranty case. Do you have the written warranty? If so, bring it small claims and show it to the judge. If you don't have the warranty in writing, you may have a "statute of frauds problem" because the warranty covers a period of time in excess of one year, thus, to be an enforceable obligation, it must be in writing. The only way around the statute of frauds would be to get the dentist to admit in trial that he offers the warranty for these procedures. Go on the small claims court website and it will walk you through the steps to file your lawsuit and prepare for trial.