Mechanical compensation in the evolution of the early hominin feeding apparatus.

Australopiths, a group of hominins from the Plio-Pleistocene of Africa, are characterized by derived traits in their crania hypothesized to strengthen the facial skeleton against feeding loads and increase the efficiency of bite force production. The crania of robust australopiths are further thought to be stronger and more efficient than those of gracile australopiths. Results of prior mechanical analyses have been broadly consistent with this hypothesis, but here we show that the predictions of the hypothesis with respect to mechanical strength are not met: some gracile australopith crania are as strong as that of a robust australopith, and the strength of gracile australopith crania overlaps substantially with that of chimpanzee crania.

Biomechanics of the mandible of Macaca mulatta during the power stroke of mastication: Loading, deformation, and strain regimes and the impact of food type.

Mandible morphology has yet to yield definitive information on primate diet, probably because of poor understanding of mandibular loading and strain regimes, and overreliance on simple beam models of mandibular mechanics. We used a finite element model of a macaque mandible to test hypotheses about mandibular loading and strain regimes and relate variation in muscle activity during chewing on different foods to variation in strain regimes. The balancing-side corpus is loaded primarily by sagittal shear forces and sagittal bending moments.

Masticatory properties in pre-modern Holocene populations from Northern China.

Recent studies indicate that evolution of the craniofacial skeleton is influenced by dietary behavior, which in turn alters masticatory efficacy and temporomandibular joint (TMJ) stability. In this study the mechanical properties of the masticatory system and the integrity of the TMJ in human populations from Northern China, dated to between 3800 BCE and 100 CE, were assessed. The results demonstrate that the mechanical efficiency is comparable to other modern human populations, though variations are present across different populations.

Two distalization methods compared in a novel patient-specific finite element analysis.

Introduction: Orthodontic mini-implants aid in the correction of distocclusions via direct anchorage (pull from mini-implant to teeth) and indirect anchorage (teeth pulled against other teeth anchored by the mini-implant). The aim of this study was to compare stress levels on the periodontal ligament (PDL) of maxillary buccal teeth in direct and indirect distalization against orthodontic mini-implants and accounting for individual variation in maxillary anatomy and biomechanical characteristics of the compact bone.

Methods: A 3D model of the maxilla containing the different components (teeth, PDL, trabecular and cortical bones) was generated from a computed tomographic scan.

Divided zygoma in Holocene human populations from Northern China.

Objectives: Divided zygoma (DZ) occurs in contemporaneous human populations, with the highest incidences in people from East Asia and Southern Africa. The present study examines the prevalence and variation of this condition in the Holocene populations of Northern China for the first time.

Methods: In this study, 1145 skulls from various human populations living in Northern China from the Neolithic Age to recent dynasties (5000-300 years BP) were examined.

Odontogenic abscesses in rhesus macaques (Macaca mulatta) of Cayo Santiago.

Objectives: Odontogenic abscesses are one of the most common dental diseases causing maxillofacial skeletal lesions. They affect the individual's ability to maintain the dental structures necessary to obtain adequate nutrition for survival and reproduction. In this study, the prevalence and pattern of odontogenic abscesses in relation to age, sex, matriline, and living periods were investigated in adult rhesus macaque skeletons of the free-ranging colony on Cayo Santiago, Puerto Rico.

VEGF-C promotes the development of lymphatics in bone and bone loss.

Patients with Gorham-Stout disease (GSD) have lymphatic vessels in their bones and their bones gradually disappear. Here, we report that mice that overexpress VEGF-C in bone exhibit a phenotype that resembles GSD. To drive VEGF-C expression in bone, we generated double-transgenic mice.

In vivo bone strain and finite element modeling of a rhesus macaque mandible during mastication.

Finite element analysis (FEA) is a commonly used tool in musculoskeletal biomechanics and vertebrate paleontology. The accuracy and precision of finite element models (FEMs) are reliant on accurate data on bone geometry, muscle forces, boundary conditions and tissue material properties. Simplified modeling assumptions, due to lack of in vivo experimental data on material properties and muscle activation patterns, may introduce analytical errors in analyses where quantitative accuracy is critical for obtaining rigorous results.

Biomechanical implications of cortical elastic properties of the macaque mandible.

Knowledge of the variation in the elastic properties of mandibular cortical bone is essential for modeling bone function. Our aim was to characterize the elastic properties of rhesus macaque mandibular cortical bone and compare these to the elastic properties from mandibles of dentate humans and baboons. Thirty cylindrical samples were harvested from each of six adult female rhesus monkey mandibles.

Elevation of a full-thickness mucoperiosteal flap alone accelerates orthodontic tooth movement.

Introduction: Our objective was to determine whether the elevation of a full-thickness mucoperiosteal flap alone, without cortical cuts, decreases the amount of bone around teeth and accelerates mesial tooth movements.

Methods: The mandibular second premolars of 7 beagle dogs were extracted, and on a randomly selected side, a full-thickness mucoperiosteal buccal flap extending from the distal aspect of the third premolar to the mesial aspect of the first premolar was elevated. The other side did not receive flap surgery.

Evolution of the Jugal/Zygomatic Bones.

This issue of the Anatomical Record is the second of a two-volume set on the zygoma (also called the cheek bone, the zygomatic bone, the malar, or the jugal, the latter term being used in vertebrates other than mammals). The zygoma is an important component of the craniofacial skeleton, in which the zygoma is a connection between the midfacial and the cranial skeletons; has a functional role as the origin of one of the masticatory muscles, the masseter muscle, and several facial muscles; has been considered as an essential buttress of the facial skeleton for resisting masticatory forces; and has importance for determining phylogenetic relationships. In humans, the zygoma is also of aesthetic significance for facial appearance, and its restoration following trauma has resulted in a large clinical literature.

The Biomechanics of Bony Facial "Buttresses" in South African Australopiths: An Experimental Study Using Finite Element Analysis.

Australopiths exhibit a number of derived facial features that are thought to strengthen the face against high and/or repetitive loads associated with a diet that included mechanically challenging foods. Here, we use finite element analysis (FEA) to test hypotheses related to the purported strengthening role of the zygomatic root and "anterior pillar" in australopiths. We modified our previously constructed models of Sts 5 (Australopithecus africanus) and MH1 (A.

Review of In Vivo Bone Strain Studies and Finite Element Models of the Zygomatic Complex in Humans and Nonhuman Primates: Implications for Clinical Research and Practice.

The craniofacial skeleton is often described in the clinical literature as being comprised of vertical bony pillars, which transmit forces from the toothrow to the neurocranium as axial compressive stresses, reinforced transversely by buttresses. Here, we review the literature on bony microarchitecture, in vivo bone strain, and finite-element modeling of the facial skeleton of humans and nonhuman primates to address questions regarding the structural and functional existence of facial pillars and buttresses. Available bone material properties data do not support the existence of pillars and buttresses in humans or Sapajus apella.

Internal Bone Architecture in the Zygoma of Human and Pan.

The internal and external anatomy of the primate zygoma is central to orofacial function, health, and disease. The importance of variation in its gross morphology across extinct and extant primate forms has been established using finite element analysis, but its internal structure has yet to be explored. In this study, µCT is used to characterize trabecular bone morphometry in two separate regions of the zygoma of humans and Pan.

Divided Zygomatic Bone in Primates With Implications of Skull Morphology and Biomechanics.

Typically the zygoma is a single bone in the facial skeleton whose shape uniquely copes with loads associated with mastication. Rarely but naturally, the zygoma is divided into two or more parts by supernumerary sutures. These extra intrazygomatic sutures are located at an area of critical morphological and biomechanical importance, yet their impacts have not been studied.

Elastic Properties of Chimpanzee Craniofacial Cortical Bone.

Relatively few assessments of cranial biomechanics formally take into account variation in the material properties of cranial cortical bone. Our aim was to characterize the elastic properties of chimpanzee craniofacial cortical bone and compare these to the elastic properties of dentate human craniofacial cortical bone. From seven cranial regions, 27 cylindrical samples were harvested from each of five chimpanzee crania.

Development, Structure, and Function of the Zygomatic Bones: What is New and Why Do We Care?

This issue of The Anatomical Record is the first of a two-volume set on the zygoma (also called the cheek bone, the zygomatic bone, the malar, or the jugal, the latter term being used in vertebrates other than mammals). The zygoma is an important component of the craniofacial skeleton, in which the zygoma is a connection between the midfacial and the cranial skeletons; has a functional role as the origin of one of the masticatory muscles, the masseter muscle, and several facial muscles; has been considered as an essential buttress of the facial skeleton for resisting masticatory forces; and has importance for determining phylogenetic relationships. In humans, the zygoma is also of aesthetic significance for facial appearance, and its restoration following trauma has resulted in a large clinical literature.

Human feeding biomechanics: performance, variation, and functional constraints.

The evolution of the modern human (Homo sapiens) cranium is characterized by a reduction in the size of the feeding system, including reductions in the size of the facial skeleton, postcanine teeth, and the muscles involved in biting and chewing. The conventional view hypothesizes that gracilization of the human feeding system is related to a shift toward eating foods that were less mechanically challenging to consume and/or foods that were processed using tools before being ingested. This hypothesis predicts that human feeding systems should not be well-configured to produce forceful bites and that the cranium should be structurally weak.

Mechanical evidence that Australopithecus sediba was limited in its ability to eat hard foods.

Australopithecus sediba has been hypothesized to be a close relative of the genus Homo. Here we show that MH1, the type specimen of A. sediba, was not optimized to produce high molar bite force and appears to have been limited in its ability to consume foods that were mechanically challenging to eat.

Twist1 Is Essential for Tooth Morphogenesis and Odontoblast Differentiation.

Twist1 is a basic helix-loop-helix-containing transcription factor that is expressed in the dental mesenchyme during the early stages of tooth development. To better delineate its roles in tooth development, we generated Twist1 conditional knockout embryos (Twist2(Cre) (/+);Twist1(fl/fl)) by breeding Twist1 floxed mice (Twist1(fl/fl)) with Twist2-Cre recombinase knockin mice (Twist2(Cre) (/+)). The Twist2(Cre) (/+);Twist1(fl/fl) embryos formed smaller tooth germs and abnormal cusps during early tooth morphogenesis.

The mandibles of castrated male rhesus macaques (Macaca mulatta): The effects of orchidectomy on bone and teeth.

Objectives: The objectives of this study were to evaluate the long-term effects of orchidectomy and low testosterone on the craniofaciodental development and maintenance of skeletal and oral health in rhesus macaques.

Materials And Methods: Mandibles of four castrated and intact age-matched male rhesus monkeys (Macaca mulatta) from Cayo Santiago were compared for mandibular morphology and teeth, abnormalities, pathology, and cortical bone thickness and density using a digital sliding caliper and analysis of three-dimensional X-ray images.

Results: Although all four castrates were generally comparable to intact males in overall mandible and teeth size, there were some significant differences.

The winds of change revisited: progress towards building a culture of evidence-based dentistry.

In 2008, Texas A&M University Baylor College of Dentistry launched a comprehensive four-year curriculum in evidence-based dentistry (EBD) along with a series of faculty development initiatives to create an EBD culture. The aim of this study was to determine the institution's success in achieving this goal. The assessment tool used was the PEAK instrument, which measures respondents' EBD Practices, Experience, Attitudes, and Knowledge.

Dentate transport discs can be used to reconstruct large segmental mandibular defects.

Purpose: This study tested the use of a dentate transport segment for the reconstruction of a large U-shaped defect in the anterior segment of the canine mandible using a novel curved reconstruction plate. The quality and quantity of bone regenerate formed by dentate versus edentulous transport segments were compared.

Materials And Methods: In 5 adult foxhound dogs, a defect of 70 to 75 mm was created in the canine mandible by excising the mandible anterior to the right and left fourth premolars.

The feeding biomechanics and dietary ecology of Paranthropus boisei.

The African Plio-Pleistocene hominins known as australopiths evolved derived craniodental features frequently interpreted as adaptations for feeding on either hard, or compliant/tough foods. Among australopiths, Paranthropus boisei is the most robust form, exhibiting traits traditionally hypothesized to produce high bite forces efficiently and strengthen the face against feeding stresses. However, recent mechanical analyses imply that P.