I didn't know much about teeth whitening until a few weekends ago when I took a friend with me to my dentist on the border. My friend is 70 years old and had even gone as far as taking a course to explore all of the possibilities. My dentist told him he would not treat him because his enamel is too thin from ware and too porous. He said your teeth color comes mainly from your dentine color, because your enamel is transparent. My friend was very happy that he told him the truth and even more happy that he didn't charge him a penny. Check out the dentist in Nuevo Progreso at http://www.painlessdentalwork.com