Dentinal sensitivity describes the exposure of the dentin; the middle layer of the tooth that is usually covered by enamel. Dentin may be exposed by acids in food and other things eroding the enamel, causing the dentin to show. The more frequent reason is that the dentin on the roots of the teeth become exposed with increasing age. Within the dentin are tubules that carry nerves. These nerves are branches from the nerve in the pulp at the very center of the tooth. So when dentin is exposed, the nerve branches are stimulated.
Pulpal sensitivity occurs at the center of the tooth in the pulp, where vessels and nerves supply the tooth with nourishment and sensation. Pulpal sensitivity can be caused by infection, fillings, cracks in the crown of the tooth, or pressure from grinding.
Initially some amalgam fillings may make your tooth sensitive to cold, but this may fade in time.