Functional links between canine height and jaw gape in catarrhines with special reference to early hominins

This study tests the hypothesis that decreased canine crown height in catarrhines is linked to (and arguably caused by) decreased jaw gape. Associations are characterized within and between variables such as upper and lower canine height beyond the occlusal plane (canine overlap), maximum jaw gape, and jaw length for 27 adult catarrhine species, including 539 living subjects and 316 museum specimens. The data demonstrate that most adult male catarrhines have relatively larger canine overlap dimensions and gapes than do conspecific females. For example, whereas male baboons open their jaws maximally more than 110% of jaw length, females open about 90%. Humans and hylobatids are the exceptions in that canine overlap is nearly the same in both the sexes and so is relative gape (ca. 65% for humans and 110% for hylobatids). A correlation analysis demonstrates that a large portion of relative gape (maximum gape/projected jaw length) is predicted by relative canine overlap (canine overlap/jaw length). Relative gape is mainly a function of jaw muscle position and/or jaw muscle‐fiber length. All things equal, more rostrally positioned jaw muscles and/or shorter muscle fibers decrease gape and increase bite force during the power stroke of mastication, and the net benefit is to increase the mechanical efficiency during chewing. Similarly, more caudally positioned muscles and/or longer muscle fibers increase the amount of gape and decrease bite force. Overall, the data support the hypothesis that canine reduction in early hominins is functionally linked to decreased gape and increased mechanical efficiency of the jaws. Am J Phys Anthropol, 2013. © 2012 Wiley Periodicals, Inc.     

Protective effect of nebivolol on reserpine-induced neurobehavioral and biochemical alterations in rats

Reserpine-induced orofacial dyskinesia is a model that shares some mechanists’ aspects with tardive dyskinesia whose pathophysiology has been related to oxidative stress. The present study was aimed to explore neuroprotective effects of nebivolol, an antihypertensive agent, on reserpine-induced neurobehavioral and biochemical alterations in rats. Reserpine (1 mg/kg, s.c.) was used to induce neurotoxicity. Administration of reserpine for 3 days every other day significantly increased the vacuous chewing movements (VCMs), tongue protrusions (TPs) and reduced the locomotor activity in rats. Pre-treatment with nebivolol (5 and 10 mg/kg, p.o. for 5 days) showed dose dependant decrease in VCMs and TP induced by reserpine. Nebivolol also showed significant improvement in locomotor activity. Reserpine significantly increased lipid peroxidation and reduced the levels of defensive antioxidant enzymes like catalase (CAT), superoxide dismutase (SOD) and reduced glutathione (GSH) in rat brain. Nebivolol reversed these effects of reserpine on oxidative stress indices; indicating amelioration of oxidative stress in rat brains. The results of the present study indicated that nebivolol has a protective role against reserpine-induced orofacial dyskinesia. Thus, the use of nebivolol as a therapeutic agent for the treatment of tardive dyskinesia may be considered.     

Masseter electromyography during chewing in ring-tailed lemurs (Lemur catta)

We examined masseter recruitment and firing patterns during chewing in four adult ring-tailed lemurs (Lemur catta), using electromyography (EMG). During chewing of tougher foods, the working-side superficial masseter tends to show, on average, 1.7 times more scaled EMG activity than the balancing-side superficial masseter. The working-side deep masseter exhibits, on average, 2.4 times the scaled EMG activity of the balancing-side deep masseter. The relatively larger activity in the working-side muscles suggests that ring-tailed lemurs recruit relatively less force from their balancing-side muscles during chewing. The superficial masseter working-to-balancing-side (W/B) ratio for lemurs overlaps with W/B ratios from anthropoid primates. In contrast, the lemur W/B ratio for the deep masseter is more similar to that of greater galagos, while both are significantly larger than W/B ratios of anthropoids. Because ring-tailed lemurs have unfused and hence presumably weaker symphyses, these data are consistent with the symphyseal fusion-muscle recruitment hypothesis stating that symphyseal fusion in anthropoids provides increased strength for resisting forces created by the balancing-side jaw muscles during chewing. Among the masseter muscles of ring-tailed lemurs, the working-side deep masseter peaks first on average, followed in succession by the balancing-side deep masseter, balancing-side superficial masseter, and finally the working-side superficial masseter. Ring-tailed lemurs are similar to greater galagos in that their balancing-side deep masseter peaks well before their working-side superficial masseter. We see the opposite pattern in anthropoids, where the balancing-side deep masseter peaks, on average, after the working-side superficial masseter. This late activity of the balancing-side deep masseter in anthropoids is linked to lateral-transverse bending, or wishboning, of their mandibular symphyses. Subsequently, the stresses incurred during wishboning are hypothesized to be a proximate reason for strengthening, and hence fusion, of the anthropoid symphysis. Thus, the absence of this muscle-firing pattern in ring-tailed lemurs with their weaker, unfused symphyses provides further correlational support for the symphyseal fusion late-acting balancing-side deep masseter hypothesis linking wishboning and symphyseal strengthening in anthropoids. The early peak activity of the working-side deep masseter in ring-tailed lemurs is unlike galagos and most similar to the pattern seen in macaques and baboons. We hypothesize that this early activity of the working-side deep masseter moves the lower jaw both laterally toward the working side and vertically upward, to position it for the upcoming power stroke. From an evolutionary perspective, the differences in peak firing times for the working-side deep masseter between ring-tailed lemurs and greater galagos indicate that deep masseter firing patterns are not conserved among strepsirrhines.     

Jaw-muscle electromyography during chewing in Belanger's treeshrews (Tupaia belangeri)

We examined masseter and temporalis recruitment and firing patterns during chewing in five male Belanger's treeshrews (Tupaia belangeri), using electromyography (EMG). During chewing, the working-side masseters tend to show almost three times more scaled EMG activity than the balancing-side masseters. Similarly, the working-side temporalis muscles have more than twice the scaled EMG activity of the balancing-side temporalis. The relatively higher activity in the working-side muscles suggests that treeshrews recruit less force from their balancing-side muscles during chewing. Most of the jaw-closing muscles in treeshrews can be sorted into an early-firing or late-firing group, based on occurrence of peak activity during the chewing cycle. Specifically, the first group of jaw-closing muscles to reach peak activity consists of the working-side anterior and posterior temporalis and the balancing-side superficial masseter. The balancing-side anterior and posterior temporalis and the working-side superficial masseter peak later in the power stroke. The working-side deep masseter peaks, on average, slightly before the working-side superficial masseter. The balancing-side deep masseter typically peaks early, at about the same time as the balancing-side superficial masseter. Thus, treeshrews are unlike nonhuman anthropoids that peak their working-side deep masseters early and their balancing-side deep masseters late in the power stroke. Because in anthropoids the late firing of the balancing-side deep masseter contributes to wishboning of the symphysis, the treeshrew EMG data suggest that treeshrews do not routinely wishbone their symphyses during chewing. Based on the treeshrew EMG data, we speculate that during chewing, primitive euprimates 1) recruited more force from the working-side jaw-closing muscles as compared to the balancing-side muscles, 2) fired an early group of jaw-closing muscles followed by a second group of muscles that peaked later in the power stroke, 3) did not fire their working-side deep masseter significantly earlier than their working-side superficial masseter, and 4) did not routinely fire their balancing-side deep masseter after the working-side superficial masseter.     

Association of occlusal wear facets in patients with temporomandibular disorders

Occlusal changes were important factors in temporomandibular disorder (TMD). It is of interest to evaluate the association of occlusal wear facets in TMD patients. We used a dataset of 49 patients with and without TMD for this study. Occlusal wear facets were evaluated using Smith and Knight tooth wear index. Data shows that teeth wear was present more in patients with TMD (55%). The age group 26-40 years showed high prevalence of teeth wear (grade1) in TMD patients (P value = 0.034). TMD was present more in females than males. Female (54%) patients with TMD showed more teeth wear compared to males. Most patients with TMD showed posterior teeth wear (61%) than generalized teeth wear. Thus, association was present between occlusal teeth wear and TMD patients especially in the age group of 26-40 years. Hence, proper evaluation of occlusal factors will aid in early diagnosis of TMDs.     

Postural stability and occlusal status among Japanese elderly

doi: 10.1111/j.1741‐2358.2011.00596.x
Postural stability and occlusal status among Japanese elderly Background: There are still no data available on the relationship between postural stability and occlusal status among the elderly. Objectives: To examine relationships between postural stability and occlusal status through a cohort study among elderly Japanese. Method: Oral examination, occlusal status, postural stability and a questionnaire were conducted and given to 87 community‐dwelling Japanese at enrolment. Results: The average occlusal pressure of the female group was statistically higher than the male group while average occlusal pressure and postural stability length were lesser in the group with more remaining teeth. Postural stability area and number of remaining teeth showed statistically significant correlations. Postural stability length was lesser in the group with strong occlusal force. Furthermore, the number of decayed teeth was fewer in the good hygiene group. Conclusions: This study identified a close relationship between occlusal status and postural stability of Japanese older individuals. Occlusal hypofunction was observed more in those with occlusal problems, and a decrease in their occlusal functions resulted in postural instability.     

The natural history of the helicoidal occlusal plane and its evolution in early Homo

In modern man the pitch of the occlusal plane may vary along the tooth-row. When anterior cheek-teeth show a plane sloping upward palatally, whilst that on posterior cheek-teeth slopes upward buccally, there results a twisted or helicoidal occlusal plane (Ackermann). Several hypotheses have been proposed for the structural basis of the helicoidal occlusal plane. Campbell's proposal ('25) has gained widest acceptance, namely that the helicoid results from anteroposterior differences in upper and lower alveolar arch width. In the early 1960s, while studying the Olduvai hominids assigned to Homo habilis, the author noted changing occlusal slopes along the tooth-row and a slight helicoid, although these featues had not been noted in other early hominids. Subsequently, Wallace showed a total absence of the helicoid from South African australopithecines, and its presence in Swartkrans Homo, SK 45 and SK 80. Recent studies confirm the presence of the helicoid in all available specimens of H. habilis, including Stw 53 found at Sterkfontein in 1976. Hence, this trait may distinguish between Australopithecus and early Homo. Measurements of the maxillary arch widths have shown that, whereas in Australopithecus arch widths increase to a maximum at M3, in early Homo maxillary arch widths are greatest at M2. The decline in posterior maxillary arch width is part of a general reduction of that region. Thus despite striking elongation of premolars and M1 in early Homo, M2 and M3 are mesiodistally abbreviated. It is hypothesized that the onset of posterior arch reduction, with the appearance of a helicoid, was a structural and functional concomitant of the transition from the presumed australopithecine ancestor to H. habilis.     

There is no general model for occlusal kinematics in conodonts

Knowledge of conodont element function is based largely on analysis of morphologically similar P₁ elements of few comparatively closely related species known from abundant articulated remains. From these, a stereotypical pattern of rotational occlusion has been inferred, leading to the suggestion that this may represent a general model for ozarkodinin P₁ elements at the very least. We test the generality of this occlusal model through functional analysis of Pseudofurnishius murcianus P₁ elements which, though superficially similar to homologous elements in gnathodids, evolved their platform morphology independently, through a different mode of morphogenesis, and in a different topological position within the element. Our integrated functional analysis of several articulated clusters of P₁ elements encompassed physical and virtual occlusal analyses, constrained by microwear and sharpness analyses. All of the evidence supports an occlusal model in which the Pseudofurnishius P₁ elements occluded with the dextral blade located between the rostral face of the sinistral blade and the first cusp of the rostral primary process. In achieving this, the dorsal and ventral blades guided the opposing elements, and the rostral processes of both elements guided the final stages of precise occlusion. Spalling and microwear on the non‐occlusal side of the element evidence malocclusion, requiring the complete separation of elements within the occlusal cycle. This occlusal cycle is entirely linear, orthogonal to the plane of attachment of the elements. Evidently, the rotational occlusal model is not general for P₁ elements, even for ozarkodinins, and it is likely that among conodonts occlusal kinematics are as disparate as element morphologies. Attempts to elucidate the diversity of occlusal kinematics and, therefore, feeding ecologies of conodonts will be repaid by an understanding of the role of this important abundant and diverse clade in Palaeozoic and Mesozoic marine ecosystems.     

Transverse masticatory movements, occlusal orientation, and symphyseal fusion in selenodont artiodactyls

Based on extensive experimental work on primates, two masticatory loading regimes have emerged as the likely determinants of mandibular symphyseal fusion-dorsoventral shear and lateral transverse bending (wishboning) (Ravosa and Hylander, 1994; Hylander et al., 1998, 2000). Recently, however, it has been argued that, rather than functioning to strengthen the symphysis during mastication, fusion serves to stiffen the symphyseal joint so as to facilitate increased transverse jaw movements during occlusion (Lieberman and Crompton, 2000). As part of this transverse stiffness model, it has been suggested that taxa with fused symphyses should also exhibit more horizontally oriented occlusal wear facets. Using a series of univariate and bivariate analyses, we test predictions of these three models in a sample of 44 species of selenodont artiodactyls. Consistent with the wishboning and transverse stiffness models, taxa with fused symphyses (camelids) have more horizontally oriented M(2) and M(2) occlusal wear facets, anteroposteriorly (AP) elongate symphyses, and relatively wider corpora. Contrary to the dorsoventral shear model, camelids do not have relatively deeper corpora (due to greater parasagittal bending). While taxa with ossified symphyses have relatively larger symphysis cross-sectional areas, this appears to be the byproduct of an increase in AP symphysis length due to greater lateral transverse bending of the mandible. Theoretical consideration of the biomechanics of mastication further suggests that strength, not stiffness, is the critical factor in determining symphyseal ossification. Thus, like anthropoid primates, fusion in selenodont artiodactyls appears to function in resisting increased wishboning stresses arising from an emphasis on transverse occlusal/mandibular movements and loads.     

Reliability and comparison of two facial measurements to detect changes of occlusal vertical dimension in complete denture wearers

Gerodontology 2010; doi: 10.1111/j.1741‐2358.2009.00353.x
Reliability and comparison of two facial measurements to detect changes of occlusal vertical dimension in complete denture wearers Background: Facial measurements are frequently used to determine OVD. However, the reliability of neither the method nor the chosen landmarks has been cleared yet. Objective: This study compares the reliability of two facial measurements, subnasal (SN) to chin (C) and tip of the nose (TN) to C, for determining occlusal vertical dimension (OVD). Materials and methods: Thirty edentulous subjects with adequate neuromuscular co‐ordination, without signs and symptoms of temporomandibular disorders and who had been wearing complete dentures for at least 5 years were enrolled. A modified central bearing device was used to alter the OVD and facial measurements were made with a digital caliper. Student’s t‐test was used to compare the two measurements. Interobserver and intraobserver reliability were evaluated with Spearman’s rho correlation test. Results: TN–C distance had an improved correlation with the changes in intraoral alterations than SN–C distance. While the means of the changes in facial measurements were in good agreement with the intraoral alterations, the ranges were wide. Both interobserver and intraobserver reliability of the measurements were high. Conclusion: While facial measurement is not a good predictor of OVD, TN–C distance appears to be more reliable than SN–C distance.     

A novel computational method to determine subject-specific bite force and occlusal loading during mastication

The evaluation of three-dimensional occlusal loading during biting and chewing may assist in development of new dental materials, in designing effective and long-lasting restorations such as crowns and bridges, and for evaluating functional performance of prosthodontic components such as dental and/or maxillofacial implants. At present, little is known about the dynamic force and pressure distributions at the occlusal surface during mastication, as these quantities cannot be measured directly. The aim of this study was to evaluate subject-specific occlusal loading forces during mastication using accurate jaw motion measurements. Motion data was obtained from experiments in which an individual performed maximal effort dynamic chewing cycles on a rubber sample with known mechanical properties. A finite element model simulation of one recorded chewing cycle was then performed to evaluate the deformation of the rubber. This was achieved by imposing the measured jaw motions on a three-dimensional geometric surface model of the subject’s dental impressions. Based on the rubber’s deformation and its material behaviour, the simulation was used to compute the resulting stresses within the rubber as well as the contact pressures and forces on the occlusal surfaces. An advantage of this novel modelling approach is that dynamic occlusal pressure maps and biting forces may be predicted with high accuracy and resolution at each time step throughout the chewing cycle. Depending on the motion capture technique and the speed of simulation, the methodology may be automated in such a way that it can be performed chair-side. The present study demonstrates a novel modelling methodology for evaluating dynamic occlusal loading during biting or chewing.     

Methodological analysis of finite helical axis behavior in cervical kinematics

Although a far more stable approach compared to the six degrees of freedom analysis, the finite helical axis (FHA) struggles with interpretational difficulties among health professionals. The analysis of the 3D-motion axis has been used in clinical studies, but mostly limited to qualitative analysis. The aim of this study is to introduce a novel approach for the quantification of the FHA behavior and to investigate the effect of noise and angle intervals on the estimation of FHA parameters. A simulation of body movement has been performed introducing Gaussian noise on position and orientation of a virtual sensor showing linear relation between the simulated noise and the error in the corresponding parameter.FHA axis behavior was determined by calculating the intersection points of the FHA with a number of planes perpendicular to the FHA using the Convex Hull (CH) technique. The angle between the FHA and each of the IHA was also computed and its distribution was also analyzed.Input noise has an inversely proportional relationship with the angle steps of FHA estimation. The proposed FHA quantification approach can be useful to provide new approaches to researchers and to improve insight for the clinician in order to better understand joint kinematics.     

Jaw movement kinematics and jaw muscle (EMG) activity during drinking in the pigeon (Columba livia)

Summary Movements of the maxilla and mandible were recorded during drinking in the head-fixed pigeon and correlated with electromyographic activity in representative jaw muscle groups. During drinking, each jaw exhibits opening and closing movements along both the dorso-ventral and rostro-caudal axes which may be linked with or independent of each other. All subjects showed small but systematic increases in cycle duration over the course of individual drinking bouts. Cyclic jaw movements during drinking were correlated with nearly synchronous activity in the protractor (levator) of the upper jaw and in several jaw closer muscles, as well as with alternating activity in tongue protractor and retractor muscles. No EMG activity was ever recorded in the lower jaw opener muscle, suggesting that lower jaw opening in this preparation is produced, indirectly, by the contraction of other muscles. The results clarify the contribution of the individual jaws to the generation of gape variations during drinking in this species.Abbreviations AMEM adductor mandibulae externus muscle - DM depressor mandibulae muscle - EMG electromyographic - GENIO geniohyoideus muscle - LB lower beak - LED light-emitting diode - PQP protractor quadrati et pterygoidei muscle - PVL pterygoideus ventralis muscle, pars lateralis - SeH/StH serpihyoideus or stylohyoideus muscle - UB upper beak     

Virtual human hand: model and kinematics

The human hand plays an important role in daily life. It is the interface between the human and the exterior world by positioning, orienting, touching and grasping objects. The human hand has multiple degrees of freedom (DOFs) to enable mobility and dexterity. A virtual human hand model can be inserted into CAD (Computer Aided Design) models to assess the manipulation capabilities in the early design stage to reduce design time and cost. Joystick assessment is one of the important design cases. This study is a first step towards a comprehensive hand simulation tool to simulate the manipulation and grasping of objects. This paper presents a novel 25 DOFs' hand skeletal model based on hand anatomy and hand kinematics: (1) joint range of motion, (2) Denavit–Hartenberg method to define the joint relationship and (3) finger workspace determination. Novelty for this hand model includes arching the palm with the four DOFs added in the carpometacarpal and wrist joints for the ring and small fingers.