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 contagious and can be transmitted to other people. They are caused by pathogens that you might also refer to as germs. The most common cause of infectious diseases are pathogens called viruses and bacteria, but they can also be caused by fungi or protozoa. Pathogens can be spread in different ways. Luckily, we can help prevent infectious diseases with good hygiene.