A wisdom tooth, in humans, is any of the usually four third molars. Wisdom teeth usually appear between the ages of 16 and 25. Most adults have four wisdom teeth, but it is possible to have more, in which case they are called supernumerary teeth. Wisdom teeth commonly affect other teeth as they develop, becoming impacted or “coming in sideways.” They are often extracted when this occurs. About 35% of the population do not develop wisdom teeth at all. Wisdom teeth present potential problems when they are misaligned – they can position themselves horizontally, be angled toward or away from the second molars or be angled inward or outward. Poor alignment of wisdom teeth can crowd or damage adjacent teeth, the jawbone, or nerves. Wisdom teeth that lean toward the second molars make those teeth more vulnerable to decay by entrapping plaque and debris. In addition, wisdom teeth can be entrapped completely within the soft tissue and/or the jawbone or only partially break through or erupt through the gum. Teeth that remain partially or completely entrapped within the soft tissue and /or the jawbone are termed “impacted.” Wisdom teeth that only partially erupt allows for an opening for bacteria to enter around the tooth and cause an infection, which results in pain, swelling, jaw stiffness, and general illness. Partially erupted teeth are also more prone to tooth decay and gum disease because their hard-to-reach location and awkward positioning makes brushing and flossing difficult.