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.
A disease is a condition in the body that disrupts normal functions. Why are some diseases contagious while others aren't? This lesson discusses the difference between communicable and noncommunicable diseases. What Are Diseases. Let's say you're sitting at a gate in a major American airport, waiting to board a flight.