Mandibular molar root morphology in Neanderthals and Late Pleistocene and recent Homo sapiens.

Neanderthals have a distinctive suite of dental features, including large anterior crown and root dimensions and molars with enlarged pulp cavities. Yet, there is little known about variation in molar root morphology in Neanderthals and other recent and fossil members of Homo. Here, we provide the first comprehensive metric analysis of permanent mandibular molar root morphology in Middle and Late Pleistocene Homo neanderthalensis, and Late Pleistocene (Aterian) and recent Homo sapiens. We specifically address the question of whether root form can be used to distinguish between these groups and assess whether any variation in root form can be related to differences in tooth function. We apply a microtomographic imaging approach to visualise and quantify the external and internal dental morphologies of both isolated molars and molars embedded in the mandible (n=127). Univariate and multivariate analyses reveal both similarities (root length and pulp volume) and differences (occurrence of pyramidal roots and dental tissue volume proportion) in molar root morphology among penecontemporaneous Neanderthals and Aterian H. sapiens. In contrast, the molars of recent H. sapiens are markedly smaller than both Pleistocene H. sapiens and Neanderthals, but share with the former the dentine volume reduction and a smaller root-to-crown volume compared with Neanderthals. Furthermore, we found the first molar to have the largest average root surface area in recent H. sapiens and Neanderthals, although in the latter the difference between M(1) and M(2) is small. In contrast, Aterian H. sapiens root surface areas peak at M(2). Since root surface area is linked to masticatory function, this suggests a distinct occlusal loading regime in Neanderthals compared with both recent and Pleistocene H. sapiens.

Kupczik K ，Hublin JJ 《-》

A comparison of tooth structure in Neanderthals and early Homo sapiens sapiens: a radiographic study.

Zilberman U ，Smith P 《-》

Mandibular molar root and pulp cavity morphology in Homo naledi and other Plio-Pleistocene hominins.

The craniomandibular morphology of Homo naledi shows variable resemblances with species across Homo, which confounds an easy assessment of its phylogenetic position. In terms of skull shape, H. naledi has its closest affinities with Homo erectus, while mandibular shape places it closer to early Homo. From a tooth crown perspective, the smaller molars of H. naledi make it distinct from early Homo and H. erectus. Here, we compare the mandibular molar root morphology of six H. naledi individuals from the Dinaledi Chamber to those of African and Eurasian Plio-Pleistocene fossil hominins (totalling 183 mandibular first, second and third molars). The analysis of five root metric variables (cervical plane area, root length, root cervix volume, root branch volume, and root surface area) derived from microCT reconstructions reveals that the molar roots of H. naledi are smaller than those of Homo habilis, Homo rudolfensis, and H. erectus, but that they resemble those of three Homo sp. specimens from Swartkrans and Koobi Fora in size and overall appearance. Moreover, though H. naledi molar roots are similar in absolute size to Pleistocene Homo sapiens, they differ from H. sapiens in having a larger root volume for a given cervical plane area and less taurodont roots; the root cervix-to-branch proportions of H. naledi are comparable to those of Australopithecus africanus and species of Paranthropus. H. naledi also shares a metameric root volume pattern (M2 > M3 > M1) with Australopithecus and Paranthropus but not with any of the other Homo species (M2 > M1 > M3). Our findings therefore concur with previous studies that found that H. naledi shares plesiomorphic features with early Homo, Australopithecus, and Paranthropus. While absolute molar root size aligns H. naledi with Homo from North and South Africa, it is distinguishable from these in terms of root volumetric proportions.

Kupczik K ，Delezene LK ，Skinner MM 《-》

Root canal morphology of permanent three-rooted mandibular first molars--part I: pulp floor and root canal system.

Racial variations in root form and canal anatomy present endodontic challenges for clinicians. This study examined root canal morphology of three-rooted mandibular first molars by micro-computed tomography scans. A total of 122 extracted mandibular first molars were collected from a native Chinese population. After calculating the frequency of occurrence, 20 three-rooted (experimental group) and 25 two-rooted first molars (control group) were scanned and reconstructed three-dimensionally. The frequency of three-rooted mandibular first molars was 31.97% (39/122). The mean interorifice distances from the distolingual (DL) canal to the distobuccal (DB) and mesiolingual canal were 2.93 mm and 2.86 mm, respectively. The mesial root predominately contained a type 2-2 root canal, with an incidence of 65% in the experimental group and 64% in the control group. Type 1-1 canals were seen more frequently in the DL and DB roots of the three-rooted first molars as well as in the distal roots of the two-rooted first molars. The incidences were 100% (20/20), 95% (19/20), and 72% (18/25), respectively. Accessory and lateral canals rarely occurred in the extra DL roots. The incidence was only 10% (2/20). A furcation canal extending from the floor to the furcation region was not observed. Three-rooted mandibular first molars commonly have 4 separate canals with high incidences of accessory canals in the mesial and DB root. The geometric data of pulp floors are useful for locating the extra DL canal.

Gu Y ，Lu Q ，Wang H ，Ding Y ，Wang P ，Ni L ... -  《-》

Taxonomic differences in deciduous upper second molar crown outlines of Homo sapiens, Homo neanderthalensis and Homo erectus.

A significant number of Middle to Late Pleistocene sites contain primarily (and sometimes only) deciduous teeth (e.g., Grotta del Cavallo, Mezmaiskaya, Blombos). Not surprisingly, there has been a recent renewed interest in deciduous dental variation, especially in the context of distinguishing Homo neanderthalensis and Homo sapiens. Most studies of the deciduous dentition of fossil hominins have focused on standard metrical variation but morphological (non-metric and morphometric) variation also promises to shed light on long standing taxonomic questions. This study examines the taxonomic significance of the crown outline of the deciduous upper second molar through principal components analysis and linear discriminant analysis. We examine whether or not the crown shape of the upper deciduous second molar separates H. neanderthalensis from H. sapiens and explore whether it can be used to correctly assign individuals to taxa. It builds on previous studies by focusing on crown rather than cervical outline and by including a large sample of geographically diverse recent human populations. Our samples include 17 H. neanderthalensis, five early H. sapiens, and 12 Upper Paleolithic H. sapiens. In addition, we include two Homo erectus specimens in order to evaluate the polarity of crown shape differences observed between H. neanderthalensis and H. sapiens. Our results show that crown outline shape discriminates H. sapiens and H. neanderthalensis quite well, but does not do well at distinguishing H. erectus from H. sapiens. We conclude that the crown outline shape observed in H. sapiens is a primitive retention and that the skewed shape observed in H. neanderthalensis is a derived condition. Finally, we explore the phylogenetic implications of the results for the H. erectus molars.

Bailey SE ，Benazzi S ，Souday C ，Astorino C ，Paul K ，Hublin JJ ... -  《-》