Chicago private equity firm Water Street Healthcare Partners this morning said it has purchased a subsidiary of developer of oral health products for an undisclosed sum.

Water Street said its purchase of OraPharma Inc. from New Jersey health and drug product giant Johnson & Johnson will “expand its group of companies specializing in life sciences, medical devices, distribution and health care services.”

OraPharma’s develops specialized drugs used by dentists such as its flagship antibiotic, Arestin, a treatment for periodontitis, which can lead to loss of teeth.

“Our goal is to build OraPharma into a leading pharmaceutical products company focused exclusively on dental and oral health,” said Al Heller, a Water Street partner who has worked for several Chicago area drug makers over the last two decades.

OraPharma is based in Westminster, Pa., and employs about 175, Water Street said.

Water Street, which invests solely in the health care industry, said it planned to commit more than $100 million toward the growth of OraPharma. Founded in 2005, Water Street said it has more than $1 billion in capital under its management.

bjapsen@tribune.com