N.H. Rev. Stat. Ann. § 317-A:27-a

Dentists and dental hygienists shall make a record of all examinations and treatments performed or recommended. The record shall be in such a manner and in sufficient detail that it may be used for identification purposes. A dentist shall maintain patients' paper or electronic, and radiographic records, for at least 7 years from the time the dentist or dental hygienist last treated the patient. In the case of a minor patient, a dentist shall maintain a patient's paper or electronic, and radiographic dental records for at least 7 years past the age of majority.