Smile Brands Group Inc. in Irvine has been acquired by private equity firm Grpyhon Investors in San Francisco on undisclosed terms.

Smile Brands provides services to dental offices.

Gryphon backed a predecessor firm to Smile Brands—Bright Now! Dental Inc.—between 1998 and 2005. Bright Now! Dental Inc. was cofounded by Steven Bilt and Bradley Schmidt, who later parted ways with the company.

Gryphon, Bilt and Schmidt last year formed a company, OneSmile LLC, to buy dental practices.

Bilt and Schmidt will return as chief executive and chief financial officer, respectively, of Smile Brands.

Smile Brands was No. 41 on the Business Journal’s 2016 list of OC-based private companies; it has an estimated $450 million in revenue and 425 local employees, and some 4,500 workers companywide and 350 practices under three brands—Bright Now! Dental, Monarch Dental, and Castle Dental—in 17 states in its network.

Bilt won a Business Journal ‘Excellence in Entrepreneurship’ award in 2011.

Gryphon has committed more than $2 billion of equity in companies. Individual investments range from $35 million to $150 million in companies with annual revenue between $50 million and $500 million.