Dental records used to ID five members of a New Jersey family killed in a tragic fire also exposed fraud by the victims’ dentist, The Post has learned.

Investigators trying to identify the four children and one adult killed in the Feb. 23 blaze in South Plainfield found that their dental work didn’t match what was claimed in family and insurer bills, said law-enforcement sources who declined to ID the dentist.

“It’s an active and ongoing investigation,” said Jim O’Neill, a spokesman for the Middlesex County Prosecutor’s Office.

Ann Jefferson, 62, died in the blaze, along with four of her grandchildren — Alize, 12, Tyler, 7, Christopher, 3, and Elijah, 2.