There is no evidence to support the claim that dentists can tell if someone has performed oral sex. This claim is likely based on the misconception that dentists can see evidence of oral sex on a person's teeth or gums. However, there is no scientific evidence to support this claim. In fact, a study published in the Journal of the American Dental Association found that dentists were unable to distinguish between people who had performed oral sex and those who had not.
Even if dentists could tell if someone had performed oral sex, it would not be considered a breach of patient confidentiality. Dentists are required to maintain the confidentiality of all patient information, including information about a patient's sexual history.