Exploring applications of intraoral 3D scanning technology in paleontology

International audience 3D imaging techniques have become an essential part of the investigative toolkit of paleontologists in the study of fossil remains. The 3D models are not only used for research purposes through comparative anatomy or morphometric studies, but also represent relevant resources for teaching or outreach activities, as well as for sharing 3D data and the curation of valuable, unique and often fragile fossil specimens.Through various methods and equipment, highly accurate digital copies can now be generated. 3D models are partly originated from 3D scanning, known as "surface scanning” [1,2]. Techniques like photogrammetry, laser scanning, and structured light scanning capture the outer surface of an object, often including texture. Because of the portable nature of the equipment, these methods are widely used for digitizing fossil specimens in museums or research institutions.However, their usage is predominantly limited to digitizing large objects ranging from centimeters to decimeters in size. Recent advances in scanning techniques, in particular the development of intraoral scanners, offer promising alternatives to overcome these limitations [3-5]. Originally developed in dentistry to digitize dental structures in vivo with high precision, we here demonstrate that intraoral scanners can be successfully used for scanning small fossil skeletal remains, producing 3D models of comparable quality than those generated by traditional 3D scanners. In particular, we compare technical performance of the intraoral scanner (Medit i700) against a benchmark in mobile structured light scanning (Artec Space Spider) and assess their strenghts and advantages and limitations on millimeter to centimeter scale fossil specimens.To account for the effect of size and morphology of fossils in creating 3D models, we selected 10 specimens of various taxa (hominins, cercopithecids, cetartiodactyles, carnivores, rodents) from diverse localities (e.g., Villebramar in France, Toros Menalla in Chad, Shungura in Ethiopia). The specimens, composed of various dental or osseous elements, were digitized with both scanners and reconstructed in 3D using dedicated software (Artec Studio 17, Medit Scan for Clinics). Distance between the two reconstructions were then automatically measured for each specimen with the software Avizo Lite 2020.2 and Geomagic Wrap. The results obtained suggest that both techniques produce 3D models with only small differences of resolution detected (e.g., less than 0.5 mm for the bovid horn-core).Experimentally, the intraoral scanner offers a simpler, more automated workflow than the Artec, which requires multiple steps and manual processing. The Medit, with a resolution of up to 11μm and 70fps capture, significantly outperforms the Artec (100μm, 6fps) in speed and image density. While both produce comparable textures, the Medit performs better on shiny surfaces like enamel. By comparing the morphologies and dimensions of the 3D models, the intraoral scanner accurately captured the surfaces of dental structures ranging from centimeter-sized (anthracothere hemimandible) to 5 mm (teeth of rodent, cainothere or small carnivores). Finally, the Medit has proven its ability to scan elements other than teeth, such ascranial and postcranial bone samples. However, intra-oral scanning is highly automated, particularly during the image alignment phases, which can cause problems of aberrant overlap when the 3D model is reconstructed. Very thin, flat surfaces are particularly prone to this type of error. In addition, automated smoothing, that cannot be disabled, reduces the accuracy of certain small anatomical features.Intraoral scanners have demonstrated their ability to digitize small fossil specimens, despite their limitations. Thanks to their simplicity and practicality, the integration of this technical tool represents an interesting alternative in paleontology for obtaining textured 3D models with high-quality precision.