Dental Education Lecture: Lower Wisdom Teeth
In last lecture, we discussed upper wisdom teeth. Today we are going to discuss lower wisdom teeth. Fig.1 illustrates lower 1st, 2nd and 3rd molars. The thick line attached to the back surface of the 3rd molar (wisdom tooth) is representing the gums. Normal alignment makes it easy to clean in the back of the mouth (Fig.1). The lower wisdom tooth often cannot come into the mouth normally. This condition is called impaction. The 3rd molar is tilted against 2nd molar (Fig.2). It is difficult to clean the dead corner between the last 2 molars. Food and germs accumulate underneath the gums surrounding 3rd molar (arrows, Fig.3), causing the gum to become swollen (thicker) and inflamed (red, Fig.3). If the infection is so severe, we have to take out the wisdom teeth early.
If kids brush the dead corner very well, gum infection around the wisdom tooth may go unnoticed. However, food and germs can be trapped between 2nd and 3rd molars (arrow, Fig.4). In due time, cavities can develop in the biting surface of the 3rd molar and in the root area of the 2nd molar (black spots in Fig.5). To save the 2nd molar, we need to do 2 things. First we need to extract the 3rd molar (Fig.6, arrow) by sectioning the impacted tooth to reduce extraction resistance. Second, we need to sacrifice a lot of sound tooth structure in order to get rid of cavity. The shaded area in Fig. 6 is filling we need to do after removing cavity. Therefore, it is beneficial to extract impacted/mal-positioned wisdom tooth before it causes problems. The worst scenario is that the patient ignores the small cavity in the root area of the 2nd molar, waiting and waiting. One day the cavity gets into the nerve of the 2nd molar. He or she has to spend a lot of money and time to finish root canal, build-up (filling after root canal) and crown to save the 2nd molar.
Scientific studies have demonstrated that early extraction of wisdom teeth helps maintain health of the 2nd molar. To keep our teeth in the mouth, we need bone. The amount of bone surrounding the teeth depends upon local oral hygiene. Bone between 2nd molar and impacted 3rd molar is lower than that between the 1st and 2nd molars (Fig.7 gray areas). This is due to accumulation of food and germs as mentioned above (arrow). Research has shown that if we remove the 3rd molar before the age of 25, there is a chance for the bone to grow into normal height as indicated by arrow in Fig.8. If we procrastinate and have the wisdom teeth extracted after the age of 25, the chance of bone re-growth is much less (arrow in Fig.9), Some of unlucky guys will lose the 2nd molar as well in the future due to severe gum disease.
Xin Wei, DDS, PhD, MS 1st edition 01/17/2009, last revision 03/20/2010