The dentist can choose not to disclose an information, if he thinks it can harm sound medical or dental judgement, which is known as:

A therapeutic privilege (or therapeutic exception) refers to an uncommon situation whereby a physician may be excused from revealing information to a patient when disclosing it would pose a serious psychological threat, so serious a threat as to be medically contraindicated.The therapeutic privilege is an exception to the general rule of informed consent, and only applies when disclosure of the information itself could pose serious and immediate harm to the patient, such as prompting suicidal behavior. The exception of therapeutic privilege does not apply when disclosure will merely lead to refusal of care that the physician thinks beneficial.