Anatomy and Anthropology

The Levant is characterized by changes in human economic behavior and subsistence strategies, following the transition from a hunting and gathering society in terminal Pleistocene to a settled, agricultural society in the Holocene. Using an advanced approach previously recognized to be associated to some extent with masticatory system function, we aimed to examine the morphological changes in the mandible during these periods and determine whether they were associated with reduced demands of mastication force. Three major prehistoric populations of the Levant were studied: Natufian hunter-gatherers (n = 41), early farmers Pre-pottery Neolithic (n = 28), and Chalcolithic farmers (n = 13), samples of which are housed in the Anthropological collection at the Sackler Faculty of Medicine, TAU. A modern population was included as a control group (n = 61). Two types of measurements were carried out using CT scans of the mandibles: size measurements: 14 linear and cross-sectional area (CSA) measurements; and orientation measurements: four angular measurements. One Way ANOVA or Kruskal-Wallis tests were carried out to examine differences in measurements between the studied groups. Our results show a reduction in mandibular size during the last 15 thousand years, although some reduction occurred only after the Chalcolithic period. In addition, the mandibular body became positioned more upright and the mandibular angle increased. Some of the changes observed can be associated with mastication loadings. We therefore concluded that the ongoing reduced demand on the masticatory system during the Holocene was probably due to a softer diet, resulting in dramatic changes in the mandibular size and orientation. Moreover, we offer a set of measurement parameters that can be reliably used for the analyses of archaeological populations when studying dietary habits.

Dentition is considered a dynamic system with forces that directly affect dental treatment stability and success. Understanding the biomechanical forces that influence tooth alignment is essential for both planning and performing dental treatments, as well as for anthropological and evolutionary studies. While there is currently an abundance of research on the mechanics of dental wear at the occlusal surface, the mechanics
of interproximal dental wear is largely unexplored. The fretting mechanism, a wear process resulting from small-amplitude cyclic motion of
2 solid contacting surfaces, was refuted as a possible mechanism for occlusal wear but has never been considered for interproximal wear.
Therefore, the aim of the current study was to reveal the biomechanical process of the interproximal wear and to explore whether the fretting
mechanism could be associated with this process. Premolar teeth with interproximal wear facets were examined by 3-dimensional surface
texture analysis using a high-resolution confocal disc-scanning measuring system. The unique texture topography of 3 areas in the proximal surface of each tooth was analyzed by applying 3D dental surface texture analysis. Each area showed unique texture characteristics, presenting statistically significant differences between the inner area of the facet and its margins or the surface outside the facets borders. Based on these results, we concluded that fretting is a key mechanism involved in interproximal wear.

Understanding how and to what extent forces applied to the mandible by the masticatory muscles influence its form, is of considerable importance from clinical, anthropological and evolutionary perspectives. This study investigates these questions. Head CT scans of 382 adults were utilized to measure masseter and temporalis muscle cross-sectional areas (CSA) as a surrogate for muscle force, and 17 mandibular anthropometric measurements. Sixty-two mandibles of young individuals (20–40 years) whose scans were without artefacts (e.g., due to tooth filling) were segmented and landmarked for geometric morphometric analysis. The association between shape and muscle CSA (controlled for size) was assessed using two-block partial least squares analysis. Correlations were computed between mandibular variables and muscle CSAs (all controlled for size). A significant association was found between mandibular shape and muscle CSAs, i.e. larger CSAs are associated with a wider more trapezoidal ramus, more massive coronoid, more rectangular body and a more curved basal arch. Linear measurements yielded low correlations with muscle CSAs. In conclusion, this study demonstrates an association between mandibular muscle force and mandibular shape, which is not as readily identified from linear measurements. Retrodiction of masticatory muscle force and so of mandibular loading is therefore best based on overall mandibular shape. The influence of masticatory muscle action on the development of craniofacial morphology has received considerable attention in the dental literature (see review article by Pepicelli et al. 1). Since bone adapts to loads by remodeling to reach the optimal form to withstand them (Wollf 's law) 2 , it has been hypothesized that craniofacial skeletal form is largely determined by mechanical loading (e.g. 3–6). This has been supported by many clinical and experimental studies. Thus, an association exists between muscle cross-sectional areas, which are approximately proportional (excluding pinnate muscles) to force generation, and craniofacial morphology, as found by studies using a range of methodological approaches (e.g., finite elements, CT models, strain gauges) 7–12. Accordingly, it was established that facial types are associated with bite force, i.e. brachycephalic pattern with strong bite force and dolichocephalic with weak bite force 7,13,14. Experimental studies show that the decreased functional demands on mandibles of animals fed a soft diet results in structural changes in the masticatory muscles 15 , as well as morphological alterations of the mandible, such as reduced size of the alveolar bone 16–18. Mandibular form and development have been extensively studied (e.g. 19,20). Yet, how common measurements of human mandibular morphology and size covary with masticatory muscle forces has not been investigated in detail. This is a significant shortcoming for clinicians and anthropologists alike, since knowledge of how mas-ticatory muscle force and mandibular form covary could enable the latter to be used to reconstruct diet and food preparation techniques in ancient populations. Although several studies have shown associations between craniofacial and mandibular shape and different feeding strategies 21–24 , efforts to reveal dietary habits and food preparation techniques from the oral apparatus have focused mainly on the study of oral pathologies such as caries, periodontal diseases, ante-mortem tooth loss, and attrition 25,26. Published: xx xx xxxx OPEN

Your selection(s) could not be saved due to an internal error. Please try again. ... Received 4 May 2010. Revised 31 January 2011. Accepted 12 February 2011. Available online 5 April 2011. ... Few studies have directly evaluated the association of lumbar lordosis and segmental wedging of the vertebral bodies and intervertebral discs with the prevalence of spinal degenerative features. ... To evaluate the association of computed tomography (CT)–evaluated lumbar lordosis as well as segmental wedging of the vertebral bodies and that of the intervertebral discs ...

Reconstructing the lordotic curvature of the lumbar spine in humans is essential for understanding their posture and locomotion. To date there is still no reliable method for predicting the lordotic curvature of disarticulated spines (in the absence of intervertebral disks). This article examines two possible methods for predicting the lordotic curvature of the lumbar spine. The first--the traditional method--is based on the degree of wedging of the vertebral bodies, and the second--the suggested new method--is based on a lateral view of the orientation of the inferior articular processes. We propose a linear regression model for predicting the lordotic curvature of the lumbar spine (lordosis angle) in disarticulated human spines. This model, derived directly from our new method, is a more reliable predictor of the lumbar lordosis angle in disarticulated spines.

Recently, interest has peaked regarding the posture of extinct hominins. Here, we present a new method of reconstructing lordosis angles of extinct hominin specimens based on pelvic morphology, more specifically the orientation of the sacrum in relation to the acetabulum (pelvic incidence). Two regression models based on the correlation between pelvic incidence and lordosis angle in living hominoids have been developed. The mean values of the calculated lordosis angles based on these models are 36°-45° for australopithecines, 45°-47° for Homo erectus, 27°-34° for the Neandertals and the Sima de los Huesos hominins, and 49°-51° for fossil H. sapiens. The newly calculated lordosis values are consistent with previously published values of extinct hominins (Been et al.: Am J Phys Anthropol 147 (2012) 64-77). If the mean values of the present nonhuman hominoids are representative of the pelvic and lumbar morphology of the last common ancestor between humans and nonhuman hominoids, then both pelvic incidence and lordosis angle dramatically increased during hominin evolution from 27° ± 5 to 22° ± 3 (respectively) in nonhuman hominoids to 54° ± 10 and 51° ± 11 in modern humans. This change to a more human-like configuration appeared early in the hominin evolution as the pelvis and spines of both australopithecines and H. erectus show a higher pelvic incidence and lordosis angle than nonhuman hominoids. The Sima de los Huesos hominins and Neandertals show a derived configuration with a low pelvic incidence and lordosis angle.