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.
An infectious disease or communicable disease is caused by a biological agent such as by a virus, bacterium or parasite. The vector does not have to be biological.Many infectious diseases are transmitted by droplets which enter the airway (e.g. common cold and tuberculosis).n immune response against a pathogen, which can include a high fever, inflammation, and other damaging symptoms, can be more devastating than the direct damage caused by the microbe. Infectious disease requires an agent and a mode of transmission (or vector).