According to the relevant provisions of the Law of People's Republic of China (PRC) on the Protection of Consumers' Rights and Interests and the Contract Law of People's Republic of China (PRC), consumers have the right to be honest and trustworthy and to choose freely in the process of consumption.

After you have paid all the fees in advance in the individual dentist's office, if you temporarily repent and ask for extra fees, the individual dentist's office should not refuse you to leave. Refusing to release may be suspected of violating your freedom. You can consider calling the police to the relevant authorities or asking for help from consumer protection organizations.

However, please note that the specific operation needs to be judged according to the terms of the contract between the individual dentist office and you, the payment method and the actual situation. If there is a contract or payment voucher as evidence, it will help to solve possible disputes. In addition, try to cooperate with regular dental institutions to ensure that their rights and interests are better protected.

If necessary, it is recommended that you consult relevant local departments or lawyers for more professional legal advice.