Your teeth will lighten, but more than likely not "whiten." Teeth have a variety of colors within them like blues, grays, reddish/orange within the dentin layer just under the enamel layer. Anything that will stain a white shirt will also stain your teeth. Using a good electric toothbrush will help eliminate extrinsic stain. I recommend using the chairside bleaching (aka laser whitening) because your teeth will get as light as you want them to be in the one session and touch up with trays once a month there after. Otherwise, the entire time you are using trays for two weeks minimum, you will not be able to eat or drink anything g that will stain a white shirt. The napkin test advertised on tv is not ideal. Not one human should have teeth that white! Your tooth shade should match the whites of your eyes for the ideal "whiteness." Anything lighter than the whites of your eyes looks like a neon sign or Ross from "Friends."