Â© 2013 WebMD, LLC. All rights reserved. The teeth are the hardest substances in the human body. Besides being essential for chewing, the teeth play an important role in speech. Parts of the teeth include: â¢ Enamel: The hardest, white outer part of the tooth. Enamel is mostly made of calcium phosphate, a rock-hard mineral. â¢ Dentin: A layer underlying the enamel.
While they are often used synonymously, the terms infectious disease and communicable disease do not have the same meaning. A communicable disease is an infectious disease that is easily spread from one human to another.
Infectious diseases are caused by germs, such as viruses, bacteria, and parasites. Contagious or communicable diseases are those that can be spread from one person to another. Infectious diseases that commonly occur among children are often communicable or contagious and may spread very easily from person to person.