The lawsuit, filed in December in Santa Clara Superior Court, alleges that dentist Yvonne Wong was defamed by comments made on Yelp by parents Tai Jing and Jia Ma. The couple complained that Wong filled their four-year-old son's cavity with mercury and made him "light-headed" from laughing gas. Wong's attorney says the couple signed a consent form that informed them of the mercury.

Currently Yelp lists only , two that are one-star ratings and two five-star reviews. One negative review alludes to the lawsuit.

This not the first lawsuit involving a Yelp review. Another suit brought by a San Francisco chiropractor against a patient who complained about a bill on Yelp was settled in January. At the time, Yelp CEO Jeremy Stoppleman was quoted as saying that no Yelp poster has ever been successfully sued.

Yelp itself is protected from lawsuits by a that does not allow Web sites to be sued over third-party content posted by readers. Given the growing chorus of angry businesses who claim Yelp unfairly manipulates reviews, that's probably a good thing for the site. In recent months, Stoppelman and Yelp staff have been forced to respond to charges from business owners that Yelp's ad salespeople are practicing extortion, offering to bury negative reviews in return for doing business with Yelp. At first Stoppelman denied the charges, but his response to the latest negative piece in the shows a different PR tactic. Now he's going on the offensive, condescendingly suggesting via a that most small businesses are simply not Web savvy enough to understand how Yelp's sophisticated review algorithm works.

Stoppelman continued this theme in a .