Until yesterday I had one wisdom tooth (third molar) left, and on my last cleaning the dentist recommended extraction since it was crowding the second molar. It was a completely painless procedure including the two injections, the extraction, and post-extraction recovery (there was virtually no pain, and I didn’t take painkillers or antibiotics). At the end I had this souvenir:
After it was out, the dentist peered into the bloody socket and said, “Holy cow, there’s a small abscess in there.” Peering more closely, he said, “Nope, that’s a BIG abscess!” I was a bit unnerved, of course, but he just reached in with some tweezers and, with judicious manipulation, pulled out the abscess as a whole. It was a perfectly spherical capsule, about a centimeter across, filled with fluid, white blood cells (aka “pus”) and granular material. I much regret not having photographed it, but you can understand that the last thing I was thinking of at the time was my camera. I won’t make that mistake again.
The dentist told me that the abscess wasn’t visible on the X-ray, and asked me if I had had any sinus problems (the tooth was on the upper right side). I said, yes, for a couple of years, and had had an expensive and futile operation to correct them. It turns out that although they’ve abated, they could have been caused by this undetected abscess blowing bacteria up into my sinuses.
Apart from my personal medical woes, there are two evolutionary lessons here. The first is that the wisdom teeth are vestigial organs: they are a remnant of the time when our ancestors had larger jaws and needed the full set of 32 teeth to process a diet consisting largely of vegetation. Our jaws are smaller now and can’t fit those four back teeth, with the result that they are often impacted—that is, they don’t erupt properly. This can cause a whole host of problems, including infections, cysts, and even tumors. As Christopher Hitchens used to argue, many of our ancestors probably died from infected teeth, particularly before there was extraction. As the link above notes, “the American Association of Oral and Maxillofacial Surgeons estimates that about 85 percent of wisdom teeth will eventually need to be removed.” Others take issue with this figure.
Here’s a Wikipedia photo of a severely impacted wisdom tooth (CT scan); I’ve added the arrow:
Finally, like many vestigial traits, wisdom teeth are variable in both expression and numbers. One paper shows tremendous variability both within and among populations:
This study contains information on the occurrence of agenesis of one to four third molars among the population and ethnic groups of Europe, North America, Africa and Asia (Japan), based on the results of investigations carried out by dozens of authors. Recent discoveries have been supplemented with corresponding data concerning the skeletal remains of the jaws of individuals living from the ice age to the middle ages. The results show unbelievably large diversities as regards the frequency of agenesis [non-appearance] of third molars in different populations from practically zero (Tasmania) to nearly 100% (Mexican Indians).
Finally, the abscess. I was amazed that the whole mess was enclosed in a spherical membrane. This was new to me, as I haven’t really paid much attention to abscesses. It turns out that the abscess is a capsule formed by normal tissue to try to prevent an infection from spreading to other parts of the body. This is almost certainly a result of natural selection. My periapical (root) abscess was completely painless, which is why, combined with its invisibility to X-rays, it was not detected. Here’s a more severe abscess, again from Wikipedia: