Tomographic imaging of unique objects: annual layers in tooth cementum of Anna Catharina Bischoff born 1719

The famous Swiss mummy, the "Lady of the Franciscan Church", is located in Basel. Subsequent to discovery in 1975, many investigations of her origin were performed without success. Four decades later, however, the mummy's origin has been identified: Anna Catharina Gernler-Bischoff (1719-1787), who was a direct ancestor of Boris Johnson, the former Prime Minister of the United Kingdom. Further details about her life have been collected. For this purpose, teeth were removed and physically sliced for imaging using optical microscopy. One single tooth remained and became available for this cementochronology study. We have applied microtomography to visualize the annual deposits in tooth cementum, termed incremental layers, without the need of physical slicing. The applicability of synchrotron radiation-based tomography to cementochronology has previously been investigated and showed promise. It is, however, unclear how far tomography will work for the mummy tooth. Laboratory-based microtomography enabled us to discriminate between enamel, dentin, and cementum, but the annual layers remained invisible. The improved density and spatial resolution of the tomography setup at the beamline ANATOMIX, Synchrotron SOLEIL, France, however, brought the incremental layers to light. We have counted 30 layers on average. Their thickness corresponds to (4.6 +/- 1.4) mu m. The available tomography data of the entire tooth should be further analyzed to correlate the life history of Anna Catharina Gernler-Bischoff with thickness and contrast of the incremental layers. The pipeline developed and the gained knowledge will be beneficial for cementochronology of humans dead and alive.