An evolutionary perspective on craniomandibular dysfunctions

Craniomandibular dysfunctions (CMDs) are a set of clinical disorders primarily affecting the masticatory muscles and the temporomandibular joints manifesting as pain syndrome, functional limitations and hard and soft tissues degeneration. CMDs have a high impact on the patients’ quality of life as they limit important functions like chewing and deglutition, respiration, speech and social interaction, stress management and postural control. In industrialized societies, the incidence of adult CMD patients needing treatment is estimated to be about 5%, with females showing at least twice the prevalence of males. A review of the anthropological, clinical and biological evidence was carried out to elucidate adaptive aspects of the evolutionary origin of CMDs. The effects of modern lifestyle on the health and function of the stomatognathic system was evaluated and the hypothesis that CMDs should be considered diseases of civilization was tested within a theoretical framework. To prove this assumption, it must be shown that cultural and technological changes have affected the orofacial structures and that these changes have had negative functional effects that are causal to CMDs. Compared to pre-industrial populations, contemporary modern humans are characterized by smaller, retrognathic mandibles, with narrower dental arches and deeper palates and the presence of malocclusion. Anthropological and experimental animal research has shown that such changes are associated with a highly refined diet, typical of industrialized societies. The functional implications of these morphological changes can be derived from experimental and clinical studies. In the medical setting, CMDs’ etiological factors have long been discussed however, occlusion\u27s role in the onset and maintenance of these disorders remains controversial. Yet, the interrelationship between the morphology of the masticatory structures and CMDs can be clarified by close examination and deductive reasoning applied to the available anthropological, clinical and biological evidence

An evolutionary perspective on craniomandibular dysfunctions

Craniomandibular dysfunctions (CMDs) are a set of clinical disorders primarily affecting the masticatory muscles and the temporomandibular joints manifesting as pain syndrome, functional limitations and hard and soft tissues degeneration. CMDs have a high impact on the patients’ quality of life as they limit important functions like chewing and deglutition, respiration, speech and social interaction, stress management and postural control. In industrialized societies, the incidence of adult CMD patients needing treatment is estimated to be about 5%, with females showing at least twice the prevalence of males. A review of the anthropological, clinical and biological evidence was carried out to elucidate adaptive aspects of the evolutionary origin of CMDs. The effects of modern lifestyle on the health and function of the stomatognathic system was evaluated and the hypothesis that CMDs should be considered diseases of civilization was tested within a theoretical framework. To prove this assumption, it must be shown that cultural and technological changes have affected the orofacial structures and that these changes have had negative functional effects that are causal to CMDs. Compared to pre-industrial populations, contemporary modern humans are characterized by smaller, retrognathic mandibles, with narrower dental arches and deeper palates and the presence of malocclusion. Anthropological and experimental animal research has shown that such changes are associated with a highly refined diet, typical of industrialized societies. The functional implications of these morphological changes can be derived from experimental and clinical studies. In the medical setting, CMDs’ etiological factors have long been discussed however, occlusion\u27s role in the onset and maintenance of these disorders remains controversial. Yet, the interrelationship between the morphology of the masticatory structures and CMDs can be clarified by close examination and deductive reasoning applied to the available anthropological, clinical and biological evidence

Testing the second Australopithecine species hypothesis for the South African site of Sterkfontein: geometric morphometric analysis of maxillary molar teeth

The morphological variability of the australopithecine fossil record from Sterkfontein Member 4, generally regarded as Australopithecus africanus, has been interpreted in various ways by different authors. However, R. J. Clarke originally put forward the hypothesis that such variability can be explained with the occurrence of a distinct and new Australopithecus species showing notable affinities with Paranthropus. Focusing on the study of maxillary molar morphology, through the geometric morphometric analysis of data gathered from three-dimensional virtual images from CT-scanning, the aim of this project was to establish a new methodology for the study of hominid dentition, with the particular goal of contributing to the issue of Clarke’s “second australopithecine species hypothesis” for Sterkfontein Member 4 site. The methods applied have been demonstrated to be statistically valid. Likewise, the procedure for landmark collection has been shown to be repeatable. The results obtained have provided further information with regard to the variability of the South African Plio-Pleistocene hominids attributed to the genera Australopithecus, Paranthropus and Homo, as shown by their maxillary molars. Most importantly the research supports, with new evidence, the hypothesis of the occurrence of a second australopithecine species in Sterkfontein Member 4

Premolar Extraction Affects Mandibular Kinematics

Objectives: The practice of premolar extraction in orthodontics is controversial for its potential detrimental effects on the stomatognathic system. However, the ways in which premolar extraction affects mandibular function are still poorly understood. The purpose of this study was to assess the influence of premolar extraction on mandibular kinematics by evaluating axiographic tracings. Materials and methods: Forty-five orthodontically treated patients with premolar teeth extraction were compared with 45 paired untreated controls, selected for the absence of malocclusions. Systematic three-dimensional axiographic recordings of the mandibular movements were performed for protrusive-retrusive movements and speech. The transversal deviations and length of the movements were recorded for both sides along with the rotation angle during speech. Statistical analysis: Differences between the axiographic variables were analyzed via the permutation test and Wilcoxon rank-sum test. Linear regression was performed to test whether axiographic parameters were predictive of group affiliation. Dot plots were used to explore the distribution of each of the axiographic outcomes, and isometric principal component analysis to assess the differences between the cumulative effects of premolar extraction on jaw motion. Results: The mandibular lateral translation in protrusion-retrusion and speech, the amount of rotation as well as the length of mandibular movements during speech were significantly higher in the treated subjects than in the controls, while retral stability did not differ. The linear regression yielded significant results for the mandibular lateral translation in protrusion-retrusion. The isometric principal component analysis showed higher values of the axiographic variables for 11 out of 45 individuals in the study sample compared with the control group. Conclusions: Premolar extraction altered mandibular kinematics in at least 25% of the cases within our sample, and the transversal discrepancy between protrusive and retrusive tracings was even predictive of group affiliation. These results support the notion that the routine practice of premolar extraction as part of the orthodontic treatment should be discouraged. It is compelling to perform further studies to assess whether a disrupted kinematics of the mandible is associated to temporomandibular disorders

Sex classification using the human sacrum: Geometric morphometrics versus conventional approaches

The human pelvis shows marked sexual dimorphism that stems from the conflicting selective pressures of bipedal locomotion and parturition. The sacrum is thought to reflect this dimorphism as it makes up a significant portion of the pelvic girdle. However, reported sexual classification accuracies vary considerably depending on the method and reference sample (54%-98%). We aim to explore this inconsistency by quantifying sexual dimorphism and sex classification accuracies in a geographically heterogeneous sample by comparing 3D geometric morphometrics with the more commonly employed linear metric and qualitative assessments. Our sample included 164 modern humans from Africa, Europe, Asia, and America. The geometric morphometric analysis was based on 44 landmarks and 56 semilandmarks. Linear dimensions included sacral width, corpus depth and width, and the corresponding indices. The qualitative inspection relied on traditional macroscopic features such as proportions between the corpus of the first sacral vertebrae and the alae, and sagittal and coronal curvature of the sacrum. Classification accuracy was determined using linear discriminant function analysis for the entire sample and for the largest subsamples (i.e., Europeans and Africans). Male and female sacral shapes extensively overlapped in the geometric morphometric investigation, leading to a classification accuracy of 72%. Anteroposterior corpus depth was the most powerful discriminating linear parameter (83%), followed by the corpus-area index (78%). Qualitative inspection yielded lower accuracies (64–76%). Classification accuracy was higher for the Central European subsample and diminished with increasing geographical heterogeneity of the subgroups. Although the sacrum forms an integral part of the birth canal, our results suggest that its sex-related variation is surprisingly low. Morphological variation thus seems to be driven also by other factors, including body size, and sacrum shape is therefore likely under stronger biomechanical rather than obstetric selection

Centric relation : a matter of form and substance

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.The recent review article by Zonnenberg, Türp and Greene ‘Centric relation critically revisited – What are the clinical implications’? opens an important debate by addressing topics of central relevance in Dentistry, namely the relationship between occlusion and the condyle-to-glenoid-fossa position, and the need for diagnostic assessment and therapeutic alteration of the condylar position in orthodontic patients. Zonnenberg, Türp and Greene concluded that the mandibular condyle is correctly situated in most orthodontic patients. Thus, in their view, orthodontists can disregard this aspect during treatment, and rely on the plastic properties of the masticatory supporting structures, while aiming at finishing the cases in a good occlusal relationship. We think that this approach fails to consider that biological variation of the stomatognathic structures can also be pathological and that, as dental occlusion determines condylar relative position within the glenoid fossa, changes in the occlusion are likely to alter the original condylar-to-glenoid-fossa relation. Hence, we claim that whenever the occlusal relationship must be changed, the clinician should carefully monitor the condyle position and the mandibular function to prevent possible iatrogenic effects. To advance the discourse on the topic, we invite Zonnenberg, Türp and Greene to clarify their definition of ‘average patient’ and their interpretation of ‘full-mouth orthodontic and orthognathic treatment’, their understanding of ‘biologically acceptable condylar relationship’, their justification of maximum intercuspation as reference position, the extent to which they think it is safe to rely on the TMJ resilience, and finally their alternative to centric relation in the treatment of patients needing condylar repositioning.info:eu-repo/semantics/publishedVersio

Centric relation: A matter of form and substance

The recent review article by Zonnenberg, Türp and Greene ‘Centric relation critically revisited – What are the clinical implications’? opens an important debate by addressing topics of central relevance in Dentistry, namely the relationship between occlusion and the condyle-to-glenoid-fossa position, and the need for diagnostic assessment and therapeutic alteration of the condylar position in orthodontic patients. Zonnenberg, Türp and Greene concluded that the mandibular condyle is correctly situated in most orthodontic patients. Thus, in their view, orthodontists can disregard this aspect during treatment, and rely on the plastic properties of the masticatory supporting structures, while aiming at finishing the cases in a good occlusal relationship. We think that this approach fails to consider that biological variation of the stomatognathic structures can also be pathological and that, as dental occlusion determines condylar relative position within the glenoid fossa, changes in the occlusion are likely to alter the original condylar-to-glenoid-fossa relation. Hence, we claim that whenever the occlusal relationship must be changed, the clinician should carefully monitor the condyle position and the mandibular function to prevent possible iatrogenic effects. To advance the discourse on the topic, we invite Zonnenberg, Türp and Greene to clarify their definition of ‘average patient’ and their interpretation of ‘full-mouth orthodontic and orthognathic treatment’, their understanding of ‘biologically acceptable condylar relationship’, their justification of maximum intercuspation as reference position, the extent to which they think it is safe to rely on the TMJ resilience, and finally their alternative to centric relation in the treatment of patients needing condylar repositioning

Lithium limits trimethyltin-induced cytotoxicity and proinflammatory response in microglia without affecting the concurrent autophagy impairment

Trimethyltin (TMT) is a highly toxic molecule present as an environmental contaminant causing neurodegeneration particularly of the limbic system both in humans and in rodents. We recently described the occurrence of impairment in the late stages of autophagy in TMT-intoxicated astrocytes. Here we show that similarly to astrocytes also in microglia, TMT induces the precocious block of autophagy indicated by the accumulation of the autophagosome marker, microtubule associated protein light chain 3. Consistent with autophagy impairment we observe in TMT-treated microglia the accumulation of p62/SQSTM1, a protein specifically degraded through this pathway. Lithium has been proved effective in limiting neurodegenerations and, in particular, in ameliorating symptoms of TMT intoxication in rodents. In our in vitro model, lithium displays a pro-survival and anti-inflammatory action reducing both cell death and the proinflammatory response of TMT-treated microglia. In particular, lithium exerts these activities without reducing TMT-induced accumulation of light chain 3 protein. In fact, the autophagic block imposed by TMT is unaffected by lithium administration. These results are of interest as defects in the execution of autophagy are frequently observed in neurodegenerative diseases and lithium is considered a promising therapeutic agent for these pathologies. Thus, it is relevant that this cation can still maintain its pro-survival and anti-inflammatory role in conditions of autophagy bloc

Autophagy is differently regulated in astrocytes and microglia exposed to environmental toxic molecules

Autophagy is generally considered a degradation pathway involved in many neurodegenerative processes. It can be observed in different stress conditions such as starvation generally improving cell survival. Our previous results described the occurrence of autophagy in neuronal cultures exposed to the toxic compound trimethyltin (TMT) (1). TMT belongs to a family of organotin compounds with wide industrial and agricultural applications, especially as heat stabilizers in PVC production and as biocides. In the nervous system TMT determines the selective destruction of neurons in specific brain regions such as the olfactory bulb and the hippocampus. When this toxic molecule was administered to glial cells we observed in astrocytes a rapid block of the autophagic flux and a consequent increased expression of LC3 and p62 which can be observed both in cultured astrocytes and in the brain of intoxicated animals. Conversely, in microglia autophagy was not impaired in the same conditions and p62 accumulation was not observed neither in vitro primary cultures, nor in brain sections of TMT-treated rats. The protein p62 (also known as SQTM1) is known to be selectively degraded through autophagy and its accumulation activates the transcription factor Nrf2 by sequestering Keap1 (2). To note the block of autophagy has been reported to exert an immunosopressive effect in macrophages (3). Thus, the impairment of autophagy in astrocytes could be related to their limited production of pro-inflammatory cytokines and nitric oxide respect to microglia observed after TMT treatment. This work was supported by grant from Ricerca Scientifica 2013 to L.F

Author Correction: Dynamic finite-element simulations reveal early origin of complex human birth pattern

Human infants are born neurologically immature, potentially owing to conflicting selection pressures between bipedal locomotion and encephalization as suggested by the obstetrical dilemma hypothesis. Australopithecines are ideal for investigating this trade-off, having a bipedally adapted pelvis, yet relatively small brains. Our finite-element birth simulations indicate that rotational birth cannot be inferred from bony morphology alone. Based on a range of pelvic reconstructions and fetal head sizes, our simulations further imply that australopithecines, like humans, gave birth to immature, secondary altricial newborns with head sizes smaller than those predicted for non-human primates of the same body size especially when soft tissue thickness is adequately approximated. We conclude that australopithecines required cooperative breeding to care for their secondary altricial infants. These prerequisites for advanced cognitive development therefore seem to have been corollary to skeletal adaptations for bipedal locomotion that preceded the appearance of the genus Homo and the increase in encephalization