By far, one of the most common retouching tasks you will undertake is whitening someone's teeth. Luckily, unlike some other editing requests, whitening teeth is a fairly straightforward and quick process. This excellent video tutorial will show you how to do it in Photoshop.
Coming to you from Aaron Nace with Phlearn, this great video tutorial will show you how to whiten teeth in Photoshop. The majority of people do not have perfectly white teeth, as such, you will commonly be asked to touch them up in post. As you will see, it is a fairly straightforward Hue/Saturation and Curves adjustment. Because of its ease, however, it can be rather easy to go overboard. Taking the adjustment too far can end up making your subject's teeth appear overly bright and white, making them look rather artificial and turning them into a distraction. One of the easiest ways to avoid this is to zoom out a bit when you are done, then step away from the computer for a minute or two. When you come back with a fresh set of eyes, any major issues will likely jump out more obviously. Check out the video above for the full rundown from Nace.
Phlearn is such a good channel....
I think using the raw camera filter and tweaking the color balance is easier.