Dental Tissue Proportions Research Articles

Dental maturational sequence and dental tissue proportions in the early Upper Paleolithic child from Abrigo do Lagar Velho, Portugal

Neandertals differ from recent and terminal Pleistocene human populations in their patterns of dental development, endostructural (internal structure) organization, and relative tissue proportions. Although significant changes in craniofacial and postcranial morphology have been found between the Middle Paleolithic and earlier Upper Paleolithic modern humans of western Eurasia and the terminal Pleistocene and Holocene inhabitants of the same region, most studies of dental maturation and structural morphology have compared Neandertals only to later Holocene humans. To assess whether earlier modern humans contrasted with later modern populations and possibly approached the Neandertal pattern, we used high-resolution microtomography to analyze the remarkably complete mixed dentition of the early Upper Paleolithic (Gravettian) child from Abrigo do Lagar Velho, Portugal, and compared it to a Neandertal sample, the late Upper Paleolithic (Magdalenian) child of La Madeleine, and a worldwide extant human sample. Some aspects of the dental maturational pattern and tooth endostructural organization of Lagar Velho 1 are absent from extant populations and the Magdalenian specimen and are currently documented only among Neandertals. Therefore, a simple Neandertal versus modern human dichotomy is inadequate to accommodate the morphostructural and developmental variation represented by Middle Paleolithic and earlier Upper Paleolithic populations. These data reinforce the complex nature of Neandertal-modern human similarities and differences, and document ongoing human evolution after the global establishment of modern human morphology.

Brief communication: High‐resolution assessment of the dental developmental pattern and characterization of tooth tissue proportions in the late Upper Paleolithic child from La Madeleine, France

Affinities and differences in dental maturational patterns between modern humans and Neanderthals remain a matter of discussion. In particular, deciduous teeth are rare for Late Pleistocene humans, and few entire sequences have been detailed for their developmental status. Here, we report the results from the 3D virtual reconstruction and structural analysis of the deciduous lower dentition (nine teeth in situ) of the child from La Madeleine (LM4), France, the first Upper Paleolithic specimen detailed so far by means of high-resolution microtomography (microCT). With respect to the modern dental developmental standards, age at death of this individual is now more likely estimated within the interval 3-4 years. LM4 lacks the slight discrepancy between a proportionally advanced stage of mineralization of the deciduous first molar and a relatively delayed maturational level of the incisors, which is found in Neanderthals (Bayle et al.: J Hum Evol 56 [2009] 66-75). By using a Bayesian approach, we calculated the probability that its maturational sequence is found within the extant human variation as represented by a tomographic (CT) reference sample of 45 children scored according to the same protocol (Liversidge and Molleson: Am J Phys Anthropol 123 [2004] 172-180). Results show that the specific sequence of this Magdalenian individual is found three times in the comparative sample included in this study. LM4 absolute tooth size and relative dental tissue proportions are close to the modern human figures (characterized by proportionally reduced dentine volumes) and lie systematically below the values shown by the Neanderthal child from Roc de Marsal, France (OIS 5a).

Dental developmental pattern of the Neanderthal child from Roc de Marsal: a high-resolution 3D analysis

The assessment of the degree of similarity or difference between Neanderthals and modern humans in their patterns of dental development remains a controversial matter. Here we report results from the microtomographic-based (SR-μCT) high-resolution structural investigation of the maxilla and mandible of the Neanderthal child from Roc de Marsal, Dordogne, France (likely from OIS 5a). Following their virtual extraction and 3D rendering, we assessed the maturational stage of each of the 41 dental elements (20 deciduous and 21 permanent) forming its mixed dentition. By using a Bayesian approach, we calculated the probability that its deciduous and permanent mandibular sequences are found within the extant human variation as illustrated by a tomographic CT-based sub-sample of 32 children (deciduous dentition) and a panoramic radiographic- and CT-based whole sample of 343 living children (permanent dentition). Results show that neither the deciduous nor the permanent mandibular sequences displayed by Roc de Marsal are precisely found within our modern comparative files. In both sequences, the most influential factor is represented by a slight discrepancy in the Neanderthal child between the stage of mineralization of the first molar, which is proportionally advanced, and the maturational level reached by its incisors, which are proportionally delayed. Following a quantitative volumetric analysis of the deciduous teeth, we suggest that this characteristic may be related to differences between Neanderthals and modern humans in absolute dental size and relative size proportions between front and cheek teeth, as well as to structural differences in dental tissue proportions.

Dental tissue proportions and enamel thickness in Neandertal and modern human molars

The thickness of dental enamel is often discussed in paleoanthropological literature, particularly with regard to differences in growth, health, and diet between Neandertals and modern humans. Paleoanthropologists employ enamel thickness in paleodietary and taxonomic studies regarding earlier hominins, but variation in enamel thickness within the genus Homo has not been thoroughly explored despite its potential to discriminate species and its relevance to studies of growth and development. Radiographic two-dimensional studies indicate that Neandertal molar enamel is thin relative to the thick enamel of modern humans, although such methods have limited accuracy. Here we show that, measured via accurate high-resolution microtomographic imaging, Neandertal molar enamel is absolutely and relatively thinner than modern human enamel at most molar positions. However, this difference relates to the ratio of coronal dentine volume to total crown volume, rather than the quantity of enamel per se. The absolute volume of Neandertal molar enamel is similar to that of modern humans, but Neandertal enamel is deposited over a larger volume of coronal dentine, resulting in lower average (and relative) enamel thickness values. Sample sizes do not permit rigorous intragroup comparisons, but Neandertal molar tissue proportions evince less variation than the modern human sample. Differences in three- and two-dimensional enamel thickness data describing Neandertal molars may be explained by dimensional reduction. Although molar tissue proportions distinguish Neanderthals from recent Homo sapiens, additional study is necessary to assess trends in tissue proportions in the genus Homo throughout the Pleistocene.