The most common reason for dark spots between your teeth is tartar buildup. The tartar is porous and sensitive to staining and discoloration. Some specific foods and beverages will turn the tartar into a brown color.  It often happens when you don't brush and floss regularly. People who maintain a strict and consistent dental hygienic routine will not encounter problems related to tartar buildup. However, dark spots can also alert you about some specific gum diseases. Tartar can occur even if you practice good dental hygiene. That is why you should seek the help of a professional and schedule a cleaning with them as soon as possible. They will take care of it and advise you on prevention and maintaining an effective oral hygienic routine.