This site is maintained by a dentist who advocates natural tooth whitening. His book which I just read, covers the topic comprehensively.
I learned some helpful things but his major tooth whitening protocol given at the end of the book, is way too complicated for lazy little moi. On the plus side, it avoids the toxicity of commercial whitening approaches. He mentions oil pulling as a viable approach and says he does it occasionally, but that it didn't get his teeth as white as many say it will.
I guess that is only to be expected if he only does it occasionally! Persistence pays off!
A couple of his tips I've found helpful: rub eggshell powder or the inside peel of a banana on teeth. I saw immediate improvement in one of my front teeth with the eggshell powder,
but lots of swishing helped prepare the way, I'm sure!
I do recommend his site, and the book. His case against veneers made quite an impression on me, for one thing. I no longer feel jealous of movie star smiles!