Lindsay Lohan finished up her teeth-whitening treatments on Saturday -- just in time to go out for Halloween!

The actress Tweeted the above pic of herself with the message, "Thanks Dr. Dorfman for the zoom... My gums are so sore though!"

The Zoom whitening system involves using a gel on the teeth and a bright light that works with the gel. It's applied in three fifteen-minute sessions.

Dr. Dorfman is a dentist to the stars -- he's been featured on Extreme Makeover and boasts a client list that also includes Jessica Simpson, Anne Hathaway, Usher, Eva Longoria, Debra Messing and Ozzy Osbourne.

His website boasts in bold: " ... we also understand that your privacy is of paramount importance ... " -- that's so true for celebs! Although, seems like Lindsay doesn't mind!

Lindsay got criticism for her yellow teeth a few weeks ago, and was even more embarrassed when dad Michael Lohan went on HLN and said Lindsay's teeth were from her smoking crack or meth.