The most often cause of discilorite is the material used in tooth canal treatment. Even when their quality is great, sometimes teeth change their colour and become dark-yellow, brownish or even blackish.
Meanwhile, in Soviet Union dentists used the resorcinol-formalin paste, the worst idea when we talk about aesthetics of the smile. Unfortunately, in some places they still use this material today, while in western countries, it has been forgotten for already half a century. That's why in professional slang we call the resorcinol-formalin paste «Red Russian» — tell us what materials you have in your teeth and we'll tell you what country you originate from!