San Francisco-based Delta Dental of California remains the largest dental insurer in Los Angeles County with 4.2 million subscribers. The company saw its subscriber base increase by about 25 percent due to a merger with its PMI Dental Health Plan subsidiary.

Delta Dental reported an increase of approximately 500,000 subscribers statewide in 2008.

“We’ve seen healthy activity from midsized accounts,” said Elizabeth Risberg, Delta spokeswoman. Midsized groups are companies with 1,000 employees or more.

It has also added several large accounts of 10,000 or more from a diverse industry sector including school districts, engineering firms and software developers.

In June, the company announced a donation of $340,000 to Louisiana State University’s dental school for reconstruction of an auditorium destroyed by Hurricane Katrina. The company made a $380,000 donation to the school immediately after the disaster three years ago.

Delta Dental of California and its affiliates reported $5.1 billion in consolidated revenues for 2007. The company provides coverage for 17.6 million people.

It is part of a larger network of dental providers, Delta Dental Plans Association, which jointly covers 50 million people, nearly 30 percent of all those who have dental coverage nationwide.