Observationes quaedam de dentitions tertia – 1786

Practical observations on the human teeth (1783)


Observationes quaedam de dentitions tertia – 1786

Johann Karl
Gehler (1732-1796, supervising professor)

Christian Schenck (defending student)

The title of the work translates to “Some observations about the third dentition” is a dissertation thesis written by Frederick Christian Schenck under the supervision of Professor Johann Karl Gehler. Not much is known about Schenck other than he grew up in Weissensee, Thuringia a small town in Germany with parents who cared deeply for his academic and religious understanding and success. While at the University of Leipzig he was able to take classes in mathematics, anatomy, physiology, general chemistry, pharmacology, and metaphysical sciences. He was one of many students Gehler supervised during his long tenure as both faculty and dean of the University of Leipzig.

Johann Gehler was a German anatomist, physician, and mineralogist. Born in Gorlitz, Germany, at the current border with Poland, between 1751-1758 he studied medicine at the University of Leipzig. Fascinated by the natural sciences he published a mineralogical treatise “De characteribus fossilium externis”, while still in school. He continued his studies in mineralogy as well as medicine with a focus on obstetrics. He began a private medical/midwifery practice while also lecturing on mineralogy at his alma mater. From 1763 to 1789 he was professor of physiology, anatomy, surgery, pathology and therapy. It is during this particular time, Schenck defended his thesis. Subsequently, Gehler was named dean in 1789 and remained at University of Leipzig until his death in 1796, at the age of 64.

Schenck, like most other students during the 18th century, was responsible for completing a project to obtain his doctoral degree. The 14-page study is relatively short even by standard of dissertations of the time and with today’s knowledge we can see that it is based on a misdiagnosis of impacted or supernumerary teeth, presumed to be the “third” dentition. Schenk defended his thesis in May 1786.

The short dissertation thesis starts with a discussion of the way both animals and humans create a balance when it comes to their health. A healthy body is one that is able to change and adapt to its surroundings. He includes examples of how an octopus can regrow tentacles and stags shed their horns every year. In a similar way when humans break their bones in areas of their body, whether it be the skull or elsewhere, the body is able to repair itself. The author goes on to point out examples of witnessing the same phenomenon in teeth. Schenck explains that most people lose their primary teeth by age 7 and have 28 to 32 permanent teeth. Next, the author furnishes three examples that apparently show a “third dentition”. The first an “edentulous elderly man” with a brand new (impacted) canine. The second, a 7-year-old girl with an extra tooth bud appearing above the permanent molar, and the third, a young man, with a molar tooth erupting beneath the maxillary tubercle.

With today’s knowledge it is easy to properly judge this work. It shows the limitations of simple anatomical observations of the time. It makes us wonder if today’s uncertain diagnoses may appear just as preposterous to a reader 250 years from now.

Digital Version

Based on research done by Isabella Biesty (class of 2025), as part of her assignments in Elective in History of Medicine and Dentistry. Edited by Andrew I Spielman.