A. It's a familiar story to general dentists and orthodontists alike. An adult patient points to his lower incisors (front teeth) and complains that his once-straight teeth have become "cooked" in recent years. He suggests that the crowding was caused by his "wisdom teeth," which are still present in spite of advice from a previous dentist to have them removed. He wants to know more about why the crowding developed, and whether extracting the third molars (wisdom teeth) would have prevented it. More importantly, he is concerned that the crowding will worsen with time, and is interested in having it corrected.

Late crowding of lower incisors is so common, it is sometimes considered a normal part of the aging process. Research suggests that, without orthodontic treatment, approximately two-thirds of adolescents with good tooth alignment and normal occlusion (bite), will develop incisor irregularity by early adulthood. As might be expected, orthodontic treatment and retention in adolescence do not protect against later crowding. Fortunately, although incisor irregularity may continue to increase as a person ages, the rate of change appears to slow with time.

So what differentiates the one-third of adolescents whose tooth alignment doesn't appear to worsen with age? Unfortunately, the risk of late lower incisor crowding is unpredictable on an individual basis, and it is undoubtedly caused by many factors. One of the reasons most commonly given for late lower incisor crowding is the third molars. This theory proposes that the erupting third molars push against the other lower teeth forcing the back teeth forward and crowding the lower incisors. Although this idea seems to make sense, research has shown that the problem is not that simple. Many studies have found no clinically significant reduction in the incidence of incisor crowding following third molar extractions. In fact, patients who are congenitally (from birth) missing third molars are still affected by late crowding. A recent publication by the American Association of Orthodontists stated, "Although there are valid reasons for extracting the third molars, preventing lower incisor crowding does not appear to be one of them."

Even though it may not be a good idea to extract third molars solely to prevent crowding of incisors, there are many good reasons these teeth may need to be extracted. By far, one of the most common findings is that there is simply not enough room for these teeth to erupt normally into the dental arches. This can lead to several situations. One is that the teeth remain completely buried in the jaw in which they developed. This condition is known as impaction. In the case of the fully impacted tooth, it may continue to sit in the bone, surrounded by the normal cyst in which all teeth develop. However, this normal cyst may enlarge later in life and even develop changes in the cells that line the cyst. In the case where the third molar erupts only partially, it can make cleaning the adjacent second molar more difficult. Also, the gum tissue that covers the erupting tooth can create a warm, moist environment where bacteria may flourish and form an infection known as pericoronitis. It is generally agreed that, in cases where third molars do require extraction, having them removed while the patient is relatively young (typically late teens and early twenties) may be easier and less traumatic than later in life.

In summary, current research does not seem to support the widely held belief that third molars cause crowding of lower front teeth. However, there may be many other valid reasons for having third molars removed. Patients would be well advised to check with their dentist or an oral surgeon for more information.