Most humans have three molars, but many — especially in America — have their third molars (called wisdom teeth) extracted. Some people do not develop third molars at all, or they never erupt into occlusion.
Humans are not alone. Some other kinds of primates have entirely lost their third molars and normally erupt only two in each quadrant. The South American monkeys called callitrichids (marmosets and tamarins) are small-bodied monkeys who normally have only two molars in each quadrant of the jaw.
Many people begin to develop third molars within their jaws, but the teeth never erupt. Others don't have any development of the third molars at all. We may not know about this unless we learn it from X-ray images. Sometimes teeth are extracted before they emerge from the jaw, or erupt, but typically any problems become apparent at or after eruption.
We are interested in showing whether third molar eruption or extraction can be correlated with any of the measurements you took earlier in the semester. In the spreadsheet, for each of your third molars, indicate whether you have it in the tooth row now, whether it has been extracted, or whether it never erupted at all.
The two incisors, one canine, two premolars and three molars on both top and bottom are called the human dental formula. We write a dental formula as follows:
2 1 2 3
What is the dental formula of a human who has never erupted her upper wisdom teeth, but who has the lower ones?