If you're going to give your employees free meals, I guess you've got to give them a dentist to take care of the aftermath. I'm not sure if the dental work is free, but via SiliconBeat, you can read more about Google's full-time dentist Dr. Sam Gustard and see pictures of his clinic on his blog, That's The Tooth.
The initial post covers Googlers giving him a "Google Tooth (beta)" logo and why it's cheaper for the company to have a dentist on site than have those employees spending hours going offsite for dental work. Plus, what if you get a toothache during a key product release?
OK, but honestly -- somehow other companies manage to get by with employees making use of personal time to visit a dentist and managing to maintain good enough dental hygiene that an unexpected emergency doesn't stop products from shipping.
Then again, if the money's flowing, who wouldn't want to have a company giving you easy access to a dentist, especially if it's free.
Postscript: Turns out, this is a hoax. More details in Google's Onsite Dentist Is A Hoax!