Your teeth are constructed of three layers: The enamel, dentin and roots of the tooth. The enamel is the hard outer surface of the teeth that covers the dentin. The dentin covers the roots. When the enamel of your teeth is worn away and the dentin is exposed, your teeth become sensitive to hot, cold, sweet or sour foods. There are several factors that cause the dentin on your teeth to be exposed and they are all preventable or treatable!