Wisdom teeth, or third molars, are the last teeth to develop and appear in your mouth. They come in between the ages of 17 and 25.
When a tooth is unable to fully enter the mouth, it is said to be “impacted.” In general, impacted teeth are unable to break through the gums because there is insufficient space. Nine in ten people have at least one impacted wisdom tooth.
If left in the mouth, impacted wisdom teeth may damage neighboring teeth, or become infected. Because the third molar area of the mouth is difficult to clean, it is a site that invites the bacteria that leads to gum disease. Furthermore oral bacteria may travel from your mouth through the bloodstream, where it may lead to possible systemic infections and illnesses that affect the heart, kidneys and other organs.   
Research has shown that once periodontal disease is established in the third molar areas, the problem is persistent and progressive, but may improve following extraction of the teeth.   
Many people believe that as long as they are not in pain, they do not have to worry about their wisdom teeth. However, pain free does not mean disease or problem free. In fact, wisdom teeth that come in normally may still be prone to disease, according to a study by the American Association of Oral and Maxillofacial Surgeons and the Oral and Maxillofacial Surgery Foundation.
In general, dental and medical professionals agree that wisdom teeth should be removed in the following instances:
Wisdom teeth that are completely erupted and functional, painless, cavity-free, in a hygienic environment with healthy gum tissue, and are disease-free may not require extraction. They do, however, require regular, professional cleaning, annual check-ups and periodic radiographs to monitor for any changes.
Wisdom teeth are easier to remove when the patient is younger, since their roots are not completely formed, the surrounding bone is softer, and there is less chance of damaging nearby nerves or other structures. Removal of wisdom teeth at a later age becomes more complicated as the roots have fully developed (may involve the nerve), and the jawbone is denser.
In some cases a fluid-filled cyst or tumor may form around the base of the untreated wisdom tooth. As the cyst grows it may lead to more serious problems as it hollows out the jaw and damages surrounding nerves, teeth and other structures.
Any surgical or invasive procedure carries risks. Before proceeding, you should seek a second opinion from an appropriately qualified health practitioner. Ash M. Costich ER, Hayward JR: A study of periodontal hazards of third molars. Journal of Periodontology 1962;33:209  Elter JR, Coumo CJ, Offenbacher S, et.al. Third molars associated with periodontal pathology in NHANES III. Journal of Oral and Maxillofacial Surgery, 2004; 62:440  Elter JR, Offenbacher S, White RP, et.al. Third molars associated with periodontal pathology in older Americans. Journal of Oral and Maxillofacial Surgery, 2005; 63:179  Stewart PS, Costerton JW: Antibiotic resistance of bacteria in biofilms. Lancet 2001;358:135  Stewart PS, Costerton JW: Antibiotic resistance of bacteria in biofilms. Lancet 2001;358:135  Sedghizadeh pp, Kumar SKS, Gorur A, et.al. : Identification of microbial biofilms in osteonecrosis of the jaws