Chapter 31 Three-Dimensional Assessment of Crown Size and Eruption Space for Developing Third Molars: Data Collection Techniques Based on Cone-Beam Computed Tomography (CBCT) D. F. Marchiori, G. V. Packota, and J. C. Boughner Abstract Third molar development and eruption are two related areas of major interest in dental research into the etiology of “wisdom tooth” impaction. Third molars are not only an excellent model for studying dental development but also of fundamental clinical importance because they are very frequently impacted. Because the third molar is located in the distal-most region of the oral cavity, clinical access is relatively challenging. With the increasingly widespread use of cone-beam computed tomography (CBCT) in dentistry, studies and measurements of the third molar and its eruption area have become considerably easier to do. Here we present a novel CBCT-based measurement methodology we developed for our recent investigations that we hope will also be useful for the broader dental research community. Key words Third molar, 3D imaging, Measurement techniques, Tooth development, Research methods, Wisdom tooth impaction 1 Introduction The third molar (M3) is an optimal model for studying dental development because this distal-most molar is the only human tooth that can be observed radiographically from initiation to root completion [1]. Because the M3 is located in the distal and less accessible regions of the oral cavity, its actual spatial position relative to adjacent structures—such as the first (M1) and/or sec- ond (M2) permanent molars—is not always accurately depicted by conventional radiographic methods [2–4]. Simultaneously, the technical limitations [5] of these conventional radiographic meth- ods (e.g., elongation, distortion, superposition) traditionally used in dental research also pose challenges for designing measurement- based studies of M3 mineralization and eruption [6]. As a result, 3D imaging methods such as cone-beam computed tomography Petros Papagerakis (ed.), Odontogenesis: Methods and Protocols, Methods in Molecular Biology, vol. 1922, https://doi.org/10.1007/978-1-4939-9012-2_31, © Springer Science+Business Media, LLC, part of Springer Nature 2019 341