Three dental offices in Philadelphia have been closed because of unsafe practices that could lead to HIV, hepatitis B and C infections, officials said Monday.

Trieu Family Dental Clinics at 437 W. Chew Ave., 5427 N. Fifth St, and 6536 Woodland Ave. were closed in early December after investigators from the city Department of Public Health found evidence of improper safety practices. Patients were notified by letter that they should be tested for HIV, hepatitis B and C as a precaution.

The Health Department said in a statement Monday that it believes “the risk of infection to be low, and is not aware of any infections as a result of these unsafe practice.”

The clinics were closed in coordination with the Pennsylvania Department of State, which also has been investigating. The clinics can be reopened after health and licensing authorities are satisfied they are safe, officials said.