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Thick molar enamel is among the few diagnostic characters of hominins which are measurable in fossil specimens. Despite a long history of study and characterization of Paranthropus molars as relatively 'hyper-thick', only a few tooth fragments and controlled planes of section (designed to be proxies of whole-crown thickness) have been measured. Here, we measure molar enamel thickness in Australopithecus africanus and Paranthropus robustus using accurate microtomographic methods, recording the whole-crown distribution of enamel. Both taxa have relatively thick enamel, but are thinner than previously characterized based on twodimensional measurements. Three-dimensional measurements show that P. robustus enamel is not hyper-thick, and A. africanus enamel is relatively thinner than that of recent humans. Interspecific differences in the whole-crown distribution of enamel thickness influence crosssectional measurements such that enamel thickness is exaggerated in two-dimensional sections of A. africanus and P. robustus molars. As such, two-dimensional enamel thickness measurements in australopiths are not reliable proxies for the three-dimensional data they are meant to represent. The three-dimensional distribution of enamel thickness shows different patterns among species, and is more useful for the interpretation of functional adaptations than single summary measures of enamel thickness.

Dental enamel thickness continues to feature prominently in anthropological studies of ape and human evolution, as well as studies of preventative oral care and treatment. Traditional studies of enamel thickness require physical sectioning of teeth for linear and scaled measurements. Recent applications of microtomographic imaging allow scientists to employ larger and more diverse samples, including global samples of recent humans as well as fossil hominin teeth. Unfortunately, little is known about the degree of enamel thickness variation among human populations, particularly across the dentition. This study employed microtomography to virtually image, section, and quantify the average enamel thickness of a sample of clinically extracted Indonesian canine and premolar teeth. This virtual sample was compared to physically sectioned African and European teeth. The results demonstrate that average enamel thickness is similar among human dentitions; no significant differences were detected within tooth positions, which is surprising given developmental differences between European and African canines and premolars. When populations were combined, differences were found in average enamel thickness between maxillary and mandibular premolars, and between canines and premolars within both dental arcades. This finding is potentially due to differences in premolar morphology and a trend of increasing enamel thickness distally throughout the dentition. The finding of limited population variation within tooth positions and significant variation between tooth positions is consistent with previous two-dimensional and three-dimensional studies of human molar enamel thickness. Average enamel thickness in canines and premolars does not differ between the sexes in our sample, although male teeth tend to have larger enamel and dentine cross-sectional areas, enamel-dentine junction lengths, and bi-cervical diameters. Males have significantly greater dentine area and enamel-dentine junction length than females for maxillary canines and premolars. The results of this study suggest that enamel thickness values in mixed-populations of humans are appropriate for comparisons with fossil hominins.

For centuries, cadaveric dissection has been the touchstone of anatomy education. It offers a medical student intimate access to his or her first patient. In contrast to idealized artisan anatomical models, it presents the natural variation of anatomy in fine detail. However, a new teaching construct has appeared recently in which artificial cadavers are manufactured through three-dimensional (3D) printing of patient specific radiological data sets. In this article, a simple powder based printer is made more versatile to manufacture hard bones, silicone muscles and perfusable blood vessels. The approach involves blending modern approaches (3D printing) with more ancient ones (casting and lost-wax techniques). These anatomically accurate models can augment the approach to anatomy teaching from dissection to synthesis of 3D-printed parts held together with embedded rare earth magnets. Vascular simulation is possible through application of pumps and artificial blood. The resulting arteries and veins can be cannulated and imaged with Doppler ultrasound. In some respects, 3D-printed anatomy is superior to older teaching methods because the parts are cheap, scalable, they can cover the entire age span, they can be both dissected and reassembled and the data files can be printed anywhere in the world and mass produced. Anatomical diversity can be collated as a digital repository and reprinted rather than waiting for the rare variant to appear in the dissection room. It is predicted that 3D printing will revolutionize anatomy when poly-material printing is perfected in the early 21st century.