The influence of alveolar structures on the torsional strain field in a gorilla corporeal cross-section

Anthropologists have often used mandibular torsional properties to make inferences about primate dietary adaptations. Most of the methods employed are based on assumptions related to periodontal and alveolar properties. This study uses the finite element method to evaluate some of these assumptions with a cross-section through the third molar of a gorilla. Results indicate that the properties of alveolar bone play an important role in determining the strain field. In comparison, the exact stiffness values of the periodontal ligaments seem to have a much smaller impact. Replacing the dental roots and periodontal ligaments with alveolar bone, however, has a significant influence on the strain field. It underestimates the maximum shear strain by about 28% along its periosteal aspect when alveoli are modeled as cortical bone. It overestimates the strain by a smaller amount when alveoli are modeled as trabecular bone.This study supports the assumption that primate mandibles behave like a closed-section under torsion under the limiting condition that the alveolar bone stiffness is more than half of the value of cortical bone; alveolar bone can then be modeled as cortical bone with a minimal loss of accuracy. In addition, this study suggests that the minimum cortical thickness should be considered for torsional strength. Finally, modeling accuracy can be significantly increased if both dental and periodontal structures can be realistically incorporated into mandibular biomechanical models. However, this may not be always feasible in studies of fossil mandibles. This is due mainly to the difficulties involved in estimating alveolar bone densities and in distinguishing boundaries between cortical bone, alveolar bone, periodontal ligaments, and dental roots in fossil specimens.     

Population variation in tooth, jaw, and root size: a radiographic study of two populations in a high-attrition environment

Radiographs were taken of the jaws of skeletal remains of two populations of different-phenotype Prehistoric Australians from Roonka and Early New Zealanders (Maoris). On these radiographs crown, root, and corpus size were measured. Corpus height was subdivided into alveolar bone height, defined as the bone superior to the mandibular canal, and basal bone height, defined as that inferior to the mandibular canal. Both between and within the two populations there was a significant and negative correlation between crown size and corpus height. The differences between the two populations in corpus height were associated with differences in alveolar bone height rather than basal bone height and support hypotheses associating continued eruption of adult teeth with growth of the alveolar bone. The findings also support previous studies that have shown only a low correlation between crown size, root size, and corpus height.     

New facial measurement used in the determination of palatine index and thickness of the mandibular body index

Measurements of the height of the mandibular body and the length of the palate rest on the assumption that the alveolar parts of the mandible and maxilla are not altered. Unfortunately, in the skeletal remains of the past population most of the molar teeth are often antemortem lost and this tooth loss is followed by resorption of the alveolar ridge. A new method of taking mandibular and palate measurements, which could be used in these cases is proposed in the study.     

Biomechanical scaling of mandibular dimensions in New World Monkeys

Previous studies show that folivorous Old World monkeys have shorter, deeper mandibles and shorter, wider condyles than frugivorous ones. These morphologies have been related to leaf mastication in colobines and ingestion of large, tough fruits in cercopithecines. This study examines New World monkeys in order to determine whether they exhibit similar adaptations to diet. New World monkeys have relatively long, transversely thin mandibles and somewhat deep mandibles and narrow condyles. Except for their deep mandibles, folivorous New World monkeys (i.e., Alouatta) do not exhibit the mandibular and condylar specializations typical of cercopithecid folivores. Reliance on comparatively nonfibrous foods plus alterations in masticatory muscle ratios among New World monkeys partially accounts for observed differences between folivorous New and Old World monkeys. In addition, adaptations for howling in Alouatta appear to have a significant effect on mandibular morphology. A biomechanical interpretation of craniofacial scaling patterns suggests that the mandibles of New World monkeys are subjected to lower condylar loads and considerably less twisting of the mandibular corpus than those of comparable Old World monkeys.     

Occlusal forces and mandibular bone strain: Is the primate jaw “overdesigned”?

Finite element modelling of the function of the periodontium and surrounding alveolar bone suggests these tissues are subjected to unusually large strains in comparison with the bone of the basal mandibular corpus. These studies, in addition to certain experimental investigations, have led to the suggestion that the strains experienced in the basal mandibular corpus are not functionally important. Under this view, size and shape of the basal corpus are not functionally linked to masticatory forces. Since previous comparative investigations have been premised on the assumption that masticatory strains in the basal corpus are functionally important, the assertion that masticatory stresses are concentrated primarily in the alveolar process undermines the credibility of this body of work. The hypothesis that the biomechanical effects of masticatory forces are localized in the alveolar process can be evaluated by reference to a number of bone strain investigations, as well as through consideration of current understanding of bone biology and behavior. Experimental studies indicate that the effects of occlusal forces during mastication are quite apparent in alveolar bone, although relatively large strains are also observed in regions well-removed from a loaded alveolus. It is also apparent that both alveolar and basal mandibular bone are subject to bending and twisting strains associated not only with occlusal forces, but also with muscular and condylar reaction forces. The result is that strain levels in alveolarvs.basal bone may be roughly similar, in contradiction to some published theoretical models. Based on empirical evidence and theoretical considerations, it is premature to conclude that mandibular corpus size and shape are not functionally linked to the biomechanics of chewing and biting.     

A biomechanical analysis of mandibular scaling in old world monkeys

Scaling of mandibular dimensions in male Old World monkeys was investigated. Mandibular condyle length, width, and area were regressed separately against body mass and mandibular length for a total of 14 species of Cercopithecoids. Scaling of mandibular depth and width against both body mass and mandibular length were also investigated. When results of regression analysis using the two different independent variables (body mass and mandibular length) were compared, there were significant pattern differences in scaling of cercopithecines versus colobines. Compared to body mass, male cercopithecines had relatively large mandibles (length, width, and depth) and also relatively large condyles (length, width, and area). However, compared to mandibular length, cercopithecines had relatively transversely thin and shallow mandibles and relatively narrow condyles. It is shown that a “biomechanical” interpretation of mandibular scaling patterns against body mass in Old World monkeys demonstrates only that cercopithecines have prognathic faces, an already well-known and well-documented condition. When the biomechanical effects of prognathic faces are controlled for (by scaling against mandibular length), it is shown that cercopithecines possess special adaptations in condyle length while colobines possess special adaptations in condyle width and mandibular depth and width. These results clearly demonstrate the importance of selecting a relevant reference variable in scaling studies where biomechanical interpretations are attempted.     

Mandibular condylar growth alterations after unilateral partial facial paralysis: an experimental study in the rabbit.

In a previous study in the rabbit, the authors defined the macroscopic growth alterations after unilateral partial facial paralysis. Dry skull measurements revealed a reduced premaxillary, maxillary, mandibular, and anterior corpus length with a simultaneous increase in mandibular ramal height on the paralyzed side. The authors hypothesize that these mandibular growth alterations are, among others, caused by alterations in condylar growth activity and that an altered occlusal relationship may be involved in the adaptive condylar growth response after facial paralysis.A total of 84 New Zealand White rabbits were used for this study. The animals were randomly assigned to either a control group that was not operated on (n = 28), a group that underwent a sham-operation (n = 28), or an experimental group (n = 28). In the sham-operation group, the facial nerve was dissected as in the experimental group but was left intact. In the experimental group, a left-side partial facial paralysis involving the midfacial muscles was induced by an operation at the age of 12 days. After different follow-up time intervals of 3.5, 7, 14, 21, 28, 42, and 56 days, four control, four sham-operation, and four experimental animals (all randomly selected) were killed for histomorphometric measurements of the left control and sham condyles and the left-side and right-side experimental condyles.No significant differences between the control and sham-operation groups were found. The other results revealed that shortly after the paralysis in the experimental group, as compared with the controls, a decrease in condylar growth activity was seen before a catch-up increase in activity, as expressed by the time-sequenced decrease and increase in the height of the functional and hypertrophic chondroblast layer. The response on the right side was analogous, though less intense.It is suggested that the mandibular ramal growth alterations might be the result of a chain of adaptations involving the lateral pterygoid muscle and the condylar growth activity. The unilaterally restricted length increment of the maxillary snout, as a result of the loss of tensile forces caused by paralysis of the midfacial musculature, necessitated an adaptation in the position of the mandible to maintain a normal occlusal relationship. Subsequently, the function of muscles involved or influenced by an altered mandibular position, such as the lateral pterygoid muscle, were changed. These altered muscle activities induced condylar growth adaptations, which in turn explained the alterations in mandibular ramal growth.     

Morphometric estimation of torsional stiffness and strength in primate mandibles

In comparative studies of masticatory function and mandibular biomechanics, the mediolateral dimension of the postcanine corpus (corpus breadth) is commonly utilized as a measure of torsional stiffness from which relative torsional strength is inferred. The use of this dimension entails certain assumptions about corpus shape and cortical bone distribution that are invalid. When corpus breadth is related to an appropriate, empirically supported measure of torsional strength, it is revealed that this dimension has limited utility for inference of biomechanical competence under torsion. The use of linear dimensions to infer structural adaptations to specific loading regimes is problematic given that bone tissue is not optimally deployed to minimize strain levels arising from isolated loads. For the inference of the masticatory biomechanical environment, the more reasonable approach is to consider overall size of the corpus (i.e., cross-sectional area) for inference of intra- and inter-specific differences in masticatory forces.     

Detection of FOXO1 break-apart status by fluorescence in situ hybridization in atypical alveolar rhabdomyosarcoma

The morphologies of alveolar rhabdomyosarcoma(ARMS) are various. Some cases entirely lack an alveolar pattern and instead display a histological pattern that overlaps with embryonal rhabdomyosarcoma(ERMS). The method of pathological diagnosis of ARMS and ERMS has been updated in the 4th edition of the World Health Organization's guidelines for classification of skeletal muscle tumors. Under the new guidelines, there is still no molecular test to distinguish between these two subtypes of rhabdomyosarcoma(RMS). In the present study, we applied fluorescent in situ hybridization(FISH) and found that the Forkhead box O1(FOXO1) gene broke apart, amplified, and displayed an aneuploid signal that was related to the RMS pathological subtype.Aside from the fact that FOXO1 break-apart and its amplification were correlated with atypical ARMS, aneuploidies were usually found in atypical ERMS. In conclusion, our results detail a potential biomarker to improve the accuracy of pathological diagnosis by discriminating between atypical ARMS and atypical ERMS.     

下颌种植覆盖义齿的生物力学研究进展

口腔生物力学是用生物力学的概念和方法,研究口腔医学中的有关基础性科学问题、解决口腔医学中的临床实际问题、发展口腔临床技术的一门学科。在口腔正畸学、修复学、种植学及口腔颌面外科学等领域存在着大量的生物力学问题,生物力学已成为口腔医学的基础科学之一。传统全口义齿修复常常会出现固位稳定差、咀嚼效率低、患者有疼痛感、适应时间长等情况,很大程度上不能满足患者的修复要求。种植覆盖义齿对于下颌牙槽嵴严重吸收的患者,效果尤为明显。种植覆盖义齿是义齿与种植体之间以不同的附着体作为连接,形成患者可以自行摘戴的种植体支持的覆盖义齿修复。下颌种植覆盖义齿因其能有效地提高下半口义齿的固位性和稳定性、显著提高了患者的咀嚼效率,目前已成为修复下颌牙槽骨严重吸收的无牙颌患者的有效修复方法。本文针对下颌种植覆盖义齿的生物力学研究进展作一综述。     

Resorption of mandibular alveolar bone following loss of molar teeth and its relationship to age at death in a human skeletal population

Estimating adult age at death in skeletal remains is problematic, particularly in older adults. Molar wear is arguably the most reliable ageing technique for palaeopopulations, but many older adult skeletons have lost their molar teeth ante mortem, precluding its application. Resorption of the alveolar process occurs following tooth loss, and this appears to continue for a prolonged period. The current work investigates the relationship of this process to individual age in a nineteenth century AD European archaeological skeletal series of known age at death (N = 92 individuals), and discusses its potential as an age indicator. Mandibular corpus height was measured at the different molar positions. In females, reduction of corpus height with age was found at molar positions showing ante mortem loss. In both sexes, a relationship was found between age and a simple composite measure of corpus height in the molar region in those showing ante mortem loss of one or more mandibular molars. The correlation was stronger in females (r = ?0.74) than in males (r = ?0.49), appeared approximately linear, and continued into the ninth decade, the oldest age group in the study material. The results suggest that investigation of height of the posterior part of the mandibular corpus as a skeletal age indicator for individuals that have lost one or more molar teeth is merited in other palaeopopulations. Am J Phys Anthropol 153:643–652, 2014. © 2014 Wiley Periodicals, Inc.     

拔除下颌第三磨牙对下颌角区形态影响的CBCT 研究

目的:探讨下颌第三磨牙的拔除会否造成下颌角区骨骼形态的变化以及这种变化对面型的影响。方法:30例因矫治需要拔除下颌第三磨牙的成人正畸患者,在拔牙前和拔牙后6个月拍摄CBCT片,采用三维测量软件mimics10.01测量下颌第三磨牙所在的下颌角区牙槽骨骨质的宽度、高度和长度,利用SPSS18.0统计软件分析前后数值有无差异。结果:下颌第三磨牙拔除前后下颌角区骨质宽度和高度减小,差异有统计学意义(P<0.05),下颌角区骨质前后向长度未见明显差异。结论:拔除下颌第三磨牙能从一定程度上减小下颌角区骨质高度和宽度,但是前后向长度度基本没有变化。     

MORPHOLOGICAL INTEGRATION IN MAMMALIAN LIMB PROPORTIONS: DISSOCIATION BETWEEN FUNCTION AND DEVELOPMENT

During mammalian evolution, fore- and hindlimbs underwent a fundamental reorganization in the transformation from the sprawled to the parasagittal condition. This caused a dissociation between serial and functional homologues. The mobilized scapula functions as the new proximal forelimb element and is functionally analogous to the femur of the hindlimb. Tarsus and metatarsus built a new functional hindlimb element that is functionally analogous to the forearm of the forelimb. Morphological covariation between serially homologous fore- and hindlimb elements can conflict with biomechanical demands when certain intralimb proportions are required for the postural stability of motion. The limb proportions of 189 mammalian species were examined to test whether intralimb proportions are governed by a general principle that corresponds to biomechanical predictions. Morphological covariation between functionally analogous and serially homologous fore- and hindlimb elements was tested by a correlation analysis. A clear relationship exists between the proportions of the first and the third elements of each limb, while the middle element is less involved in alterations of intralimb proportions. Hindlimb proportions are largely uniform across mammals and correspond to biomechanical predictions regarding postural stability. The greater variability in forelimb proportion is likely be the expression of various adaptations but might results also from constraints due to the shared developmental programs with the hindlimb.     

Experimental observation, theoretical models, and biomechanical inference in the study of mandibular form

Experimental studies and mathematical models are disparate approaches for inferring the stress and strain environment in mammalian jaws. Experimental designs offer accurate, although limited, characterization of biomechanical behavior, while mathematical approaches (finite element modeling in particular) offer unparalleled precision in depiction of strain magnitudes, directions, and gradients throughout the mandible. Because the empirical (experimental) and theoretical (mathematical) perspectives differ in their initial assumptions and their proximate goals, the two methods can yield divergent conclusions about how masticatory stresses are distributed in the dentary. These different sources of inference may, therefore, tangibly influence subsequent biological interpretation. In vitro observation of bone strain in primate mandibles under controlled loading conditions offers a test of finite element model predictions. Two issues which have been addressed by both finite element models and experimental approaches are: (1) the distribution of torsional shear strains in anthropoid jaws and (2) the dissipation of bite forces in the human alveolar process. Not surprisingly, the experimental data and mathematical models agree on some issues, but on others exhibit discordance. Achieving congruence between these methods is critical if the nature of the relationship of masticatory stress to mandibular form is to be intelligently assessed. A case study of functional/mechanical significance of gnathic morphology in the hominid genus Paranthropus offers insight into the potential benefit of combining theoretical and experimental approaches. Certain finite element analyses claim to have identified a biomechanical problem unrecognized in previous comparative work, which, in essence, is that the enlarged transverse dimensions of the postcanine corpus may have a less important role in resisting torsional stresses than previously thought. Experimental data have identified subperiosteal cortical thinning as a culprit in diminishing the role of cross-sectional geometry in conditioning the strain environment. These observations raise questions concerning the biomechanical significance of mandibular form in early hominids, fueling persistent arguments over whether gnathic morphology can be related to dietary specialization in the "robust" australopithecines. Nonmechanical explanations (e.g., tooth size or body size) for Paranthropus mandibular dimensions, however, are not compelling as competing hypotheses. Both theoretical and experimental models are in need of refinement before it is possible to conclude that the jaws of the "robust" australopithecines are not functionally linked to elevated masticatory loads.     

Proximal gait adaptations in individuals with knee osteoarthritis: A systematic review and meta-analysis

Clarifying proximal gait adaptations as a strategy to reduce knee joint loading and pain for individuals with knee osteoarthritis (OA) contributes to understanding the pathogenesis of multi-articular OA changes and musculoskeletal pain in other joints. We aimed to determine whether biomechanical alterations in knee OA patients during level walking is increased upper trunk lean in the frontal and sagittal planes, and subsequent alteration in external hip adduction moment (EHAM) and external hip flexion moment (EHFM). A literature search was conducted in PubMed, PEDro, CINAHL, and Cochrane CENTRAL through May 2018. Where possible, data were combined into a meta-analysis; pooled standardized mean differences (SMD) of between knee OA patients and healthy adults were calculated using a random-effect model. In total, 32 articles (2037 participants, mean age, 63.0 years) met inclusion criteria. Individuals with knee OA had significantly increased lateral trunk lean toward the ipsilateral limb (pooled SMD: 1.18; 95% CI: 0.59, 1.77) along with significantly decreased EHAM. These subjects also displayed a non-significantly increased trunk/pelvic flexion angle and EHFM. The GRADE approach judged all measures as “very low.” These results may indicate that biomechanical alterations accompanying knee OA are associated with increased lateral trunk lean and ensuing alterations in EHAM. Biomechanical alterations in the sagittal plane were not evident. Biomechanical adaptations might have negative sequelae, such as secondary hip abductor muscle weakness and low back pain. Thus, investigations of negative sequelae due to proximal gait adaptations are warranted.     

Autophagy is not required to sustain exercise and PRKAA1/AMPK activity but is important to prevent mitochondrial damage during physical activity

Physical activity has been recently documented to play a fundamental physiological role in the regulation of autophagy in several tissues. It has also been reported that autophagy is required for exercise itself and for training-induced adaptations in glucose homeostasis. These autophagy-mediated metabolic improvements are thought to be largely dependent on the activation of the metabolic sensor PRKAA1/AMPK. However, it is unknown whether these important benefits stem from systemic adaptations or are due solely to alterations in skeletal muscle metabolism. To address this we utilized inducible, muscle-specific, atg7 knockout mice that we have recently generated. Our findings indicate that acute inhibition of autophagy in skeletal muscle just prior to exercise does not have an impact on physical performance, PRKAA1 activation, or glucose homeostasis. However, we reveal that autophagy is critical for the preservation of mitochondrial function during damaging muscle contraction. This effect appears to be gender specific affecting primarily females. We also establish that basal oxidative stress plays a crucial role in mitochondrial maintenance during normal physical activity. Therefore, autophagy is an adaptive response to exercise that ensures effective mitochondrial quality control during damaging physical activity.     

Autophagy is not required to sustain exercise and PRKAA1/AMPK activity but is important to prevent mitochondrial damage during physical activity

Physical activity has been recently documented to play a fundamental physiological role in the regulation of autophagy in several tissues. It has also been reported that autophagy is required for exercise itself and for training-induced adaptations in glucose homeostasis. These autophagy-mediated metabolic improvements are thought to be largely dependent on the activation of the metabolic sensor PRKAA1/AMPK. However, it is unknown whether these important benefits stem from systemic adaptations or are due solely to alterations in skeletal muscle metabolism. To address this we utilized inducible, muscle-specific, atg7 knockout mice that we have recently generated. Our findings indicate that acute inhibition of autophagy in skeletal muscle just prior to exercise does not have an impact on physical performance, PRKAA1 activation, or glucose homeostasis. However, we reveal that autophagy is critical for the preservation of mitochondrial function during damaging muscle contraction. This effect appears to be gender specific affecting primarily females. We also establish that basal oxidative stress plays a crucial role in mitochondrial maintenance during normal physical activity. Therefore, autophagy is an adaptive response to exercise that ensures effective mitochondrial quality control during damaging physical activity.     

钛镍记忆合金牵张器复合脱细胞真皮基质增高犬牙槽嵴的初步研究

目的用成年杂种犬建立钛镍记忆合金牵张器复合脱细胞真皮基质增高犬牙槽嵴动物模型,为下一步利用钛镍记忆合金牵张器行下颌后牙牙槽嵴增高术奠定基础。方法健康成年雄性杂种犬4只。全麻下拔除双侧下颌4个前磨牙和第一磨牙,1个月后拍摄双侧后牙区X线光片,观察拔牙窝愈合情况。采用4种类型的牵张器随机在4只犬的下颌两侧行牵张手术并观察牵张后1周和1月牙槽嵴增高的情况。结果拔牙后1个月,牙槽嵴黏膜愈合良好。X线片示下颌神经管清晰可见,其上方牙槽窝内有较低密度骨质存在。放置4种牵张器牵张术后1周、1月后牙槽嵴增高的高度分别为3.24 mm、3.76 mm、4.58 mm、5.09 mm;3.15 mm、3.67 mm、4.64 mm、5.01mm,术后一周X线可见后有明显的牵张间隙,1月时牵张区有新骨形成,骨密度增高。结论犬耐受力强,后牙区下颌骨体积大,手术易操作,是理想的牙槽嵴萎缩动物模型。拔牙后1个月,拔牙创愈合良好,可以进行牵张手术。D组＂S＂形牵张器牵张后的高度比较理想,能满足后期种植体的植入。     

Functional morphology of the mangabey mandibular corpus: relationship to dental specializations and feeding behavior

Recent molecular and morphological surveys suggest that mangabeys do not represent a monophyletic group. Specifically, Cercocebus is the sister taxon of Mandrillus, whereas Lophocebus forms an unresolved trichotomy with Papio and Theropithecus. The Cercocebus-Mandrillus clade is characterized by skeletal and dental adaptations related to acquisition and processing of hard-object foods that resist decomposition for months on the forest floor. Although species of both mangabey genera can be described as frugivorous seed predators with a strong reliance on hard-object foods, a growing body of evidence indicates that Cercocebus (terrestrial) and Lophocebus (arboreal) mangabeys differ in the hardness of the seeds they consume and the manner in which seeds are processed. The taxa are also distinguished on the basis of dental morphology. Given the purported differences in feeding behaviors of the two mangabey genera, we consider whether there are predictable biomechanical consequences of these behaviors that are reflected in mandibular corpus dimensions. In addition, we present metric data summarizing functional aspects of mangabey mandibular corpus morphology. Mangabey genera are generally not distinguished by differences in relative corpus size, either in postcanine or symphyseal regions. Distinct symphyseal scaling patterns characterize the Papio-Lophocebus clade and the Mandrillus-Cercocebus clade, while the postcanine corpus scales similarly between them. The hypothesis that preferential use of the incisors vs. premolars to initially process these foods results in distinct stress environments is weakly supported, given circumstantial evidence that the relative importance of bending vs. torsion may differ between Cercocebus and Lophocebus.