I'm not aware of something exactly like what you describe, but it sounds similar to the Body Ritual Among the Nacirema by Horace Miner: a satire of anthropology describing specifically American (spell "Nacirema" backwards) culture in the style of anthropological papers (Miner was an anthropologist himself). The main difference is that it's not about humans in general through alien eyes; it's more about how anything can be described in a way that makes it seem strange or magical, if you don't have the full context of the culture.
One paragraph from the book, specifically about dentists:
In the hierarchy of magical practitioners, and below the medicine men in prestige, are specialists whose designation is best translated as "holy-mouth-men." The Nacirema have an almost pathological horror of and fascination with the mouth, the condition of which is believed to have a supernatural influence on all social relationships. Were it not for the rituals of the mouth, they believe that their teeth would fall out, their gums bleed, their jaws shrink, their friends desert them, and their lovers reject them. They also believe that a strong relationship exists between oral and moral characteristics. For example, there is a ritual ablution of the mouth for children which is supposed to improve their moral fiber.