Patterns of dental wear and the role of the canine in Cercopithecinae.

The importance of dental wear patterns in understanding masticatory functions in primates has long been appreciated. However, studies of wear patterns among populations of nonhuman primates are few. The purpose of this investigation is to establish the developmental aspects of dental wear in the Cercopithecinae and to describe certain relevant morphological traits. Studies were made of dental casts from 200 primate specimens of Macaca nemestrina, Macaca mulatta, and Papio cynocephalus. These casts were taken at four-month intervals, beginning at two years of age and continuing over a period of six to seven years. The wear pattern starts with the rounding and eventual flattening of the protoconid and protocone of the erupted first molars. Once this stage is reached, the hypoconid and metaconid of the mandibular, and the hypocone and paracone of the maxillary molars are rounded and eventually flattened. This pattern is maintained until the cusp tips are removed and the dentin exposed, however, the entoconid and metacone are not subjected to significant wear at this stage. Analysis of these dental casts and museum specimens has provided data on the development of dental wear during the maturation of these primates. The distribution of forces acting upon the teeth produce diagnostic patterns of wear, which provide evidence of the force location and magnitude. In examining the data, the hypothesis of canine guidance and its limitation of mandibular motion was evaluated. Specimens whose canines were removed demonstrate that the canines play no significant role in the development or maintenance of dental wear planes.     

Dental arch shape and tooth wear variability

The rapid rate of tooth wear frequently reported among certain contemporary aboriginal populations has often been attributed to dietary form and abrasives. Several investigators have reported a close correlation between food bulk and the wear planes formed over the dental arches, i.e., steep oblique wear vs. flat horizontal planes. In this investigation we demonstrate that arch shape is an additional and a significant factor influencing the distribution of wear facets and exposed dentin over occlusal surfaces. We examined 64 dental stone casts of Aboriginals from Yuendumu, Central Australia, born between 1900 and 1940. These casts offer a record of the variety of tooth wear and arch forms and their interrelationships. This group of individuals, some subsisting on abrasive and some on soft diets, have dentition which exhibit various wear rates and wear patterns probably due to the diversity of arch shape, size, and occlusal relationships. Hypsiloid or U-shaped maxillas had a more buccally directed wear in contrast to the parabolic or hyperbolic forms, which exhibit a heavier lingual loading. Varying occlusal conditions also contribute to differing wear patterns over the arches. Individuals with alternate intercuspation, for example, have a more horizontally directed wear. These and other conditions of shape, size, and occlusion emphasize the importance of morphological factors in the production of tooth wear rates and patterns in addition to dietary abrasives.     

Measurements of tooth wear among Australian Aborigines: I. Serial loss of the enamel crown

The dental casts made from Aboriginal children during the course of a longitudinal growth study in Central Australia provided material for analyzing tooth wear under known environmental conditions. The wear facets produced on the occlusal surfaces were clearly preserved on the dental stone casts and recorded the progress of enamel attrition from ages 6 to 18. These casts were photographed and traced by electronic planimetric methods that automatically recorded the location and size of wear facets on the first and second permanent molars. These areas of worn tooth surface were compared to the total tooth surface. The worn surface was regressed on age to calculate wear rates of each tooth. Discriminant analyses were also performed to determine the significance of dental attrition differences between the sexes at each age group. The total wear on each tooth was highly correlated with age as expected but females wore their teeth at a significantly higher rate than males. The mandibular molars wore more rapidly than maxillary teeth in both sexes. The discriminant analysis successfully grouped 91% of the cases according to age and sex. Pattern of wear, the location, and size of wear facets also differed between age groups and sex. The questions of why there is a difference between male and female wear or why there is greater wear on one arch or arch region have no ready answers. The differing rates and pattern of dental wear do suggest that arch shape and growth rates may be the answer though it has yet to be tested. However, the occlusal surface wear is useful for age estimation in a population and provides a record of shifting masticatory forces during growth.     

The remapping of space in motor learning and human–machine interfaces

Studies of motor adaptation to patterns of deterministic forces have revealed the ability of the motor control system to form and use predictive representations of the environment. One of the most fundamental elements of our environment is space itself. This article focuses on the notion of Euclidean space as it applies to common sensory motor experiences. Starting from the assumption that we interact with the world through a system of neural signals, we observe that these signals are not inherently endowed with metric properties of the ordinary Euclidean space. The ability of the nervous system to represent these properties depends on adaptive mechanisms that reconstruct the Euclidean metric from signals that are not Euclidean. Gaining access to these mechanisms will reveal the process by which the nervous system handles novel sophisticated coordinate transformation tasks, thus highlighting possible avenues to create functional human–machine interfaces that can make that task much easier. A set of experiments is presented that demonstrate the ability of the sensory-motor system to reorganize coordination in novel geometrical environments. In these environments multiple degrees of freedom of body motions are used to control the coordinates of a point in a two-dimensional Euclidean space. We discuss how practice leads to the acquisition of the metric properties of the controlled space. Methods of machine learning based on the reduction of reaching errors are tested as a means to facilitate learning by adaptively changing he map from body motions to controlled device. We discuss the relevance of the results to the development of adaptive human–machine interfaces and optimal control.     

Intrapopulation variation in macro tooth wear patterns—a case study from Igloolik,Canada

The pattern of human tooth wear—the way it varies between teeth in the mouth—is crucial to our understanding of important questions in archeology and paleoanthropology, such as the contrasts in diet and behavior between Neanderthals and early modern humans in Europe and Asia, or with the adoption of agriculture in the Americas. Little is known, however, about the way in which wear patterns develop with increasing age or the way in which they differ between males and females. One explanation is that few living people show the high rates of tooth wear seen worldwide throughout the preindustrial archaeological record. The study described here investigates the macroscopic pattern of tooth wear in a unique group of known age and sex dental casts from living Canadian Inuit from Igloolik. The results show that the Igloolik people possessed a pattern of extremely heavy anterior tooth wear, relative to the first molar and the other posterior teeth, which is attributed to the use of the anterior teeth in cultural practices as well as the extreme and marginal environments in which they lived. Heavy anterior tooth wear was established at an early age and maintained throughout life; statistically significant differences were found between the wear patterns of males and females and are explained in terms of sexual division of labor within the community. This study highlights the need to understand both intra‐ and interpopulation variation in tooth wear patterns when interpreting patterns in past human groups. Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc.     

Experimental studies in human tooth wear: I

The construction of a machine called CANIBAL which is capable of simulating the actions of the human mandible during chewing is reported. Powered by an electric motor, a cam activated rocker arm assembly transmits force by means of wires to each point on the mandible where muscles would be attached. A separately adjustable cam, rocker arm, directional pulley and wire represents each muscle. Models of dental arches cast in dental stone or other materials can be mounted and subjected to extended wear. With different cam settings, wear patterns can be produced which resemble those seen on various fossil and living human dental arches.     

Murray James Barrett, dental anthropologist: Yuendumu and beyond

Murray James Barrett (1916-1975) graduated from the University of Adelaide's Bachelor of Dental Surgery programme in 1939 and subsequently became a colleague of Professor Thomas Draper Campbell (1893-1967). Campbell's passion for dental anthropology and his special interest in food habits and dental disease inspired Barrett to commence a longitudinal growth study in the 1960s of Aboriginal Australians living at Yuendumu in the Northern Territory of Australia. This study, referred to as the Dentgro project, involved the collection of dental records, growth data and cultural information about the Wailbri people.Murray Barrett's application of computer technology enabled him to automate the entry of data derived from the Dentgro study and to develop programmes to analyse those data. The collection of dental casts (over 1700 serial casts for more than 450 individuals) and other records have provided a unique resource for research and teaching purposes. The casts have been in constant use for over 40 years providing insights into many aspects of dental development, including: the timing and sequence of tooth emergence; the nature and extent of variation in dental crown size and morphology in human populations; the patterns of growth in the dental arches over time; the range of occlusal variation between individuals; and the effects of wear on the dentition. The Yuendumu cast collection, representing a population with limited exposure to European customs and dietary habits, continues to attract the Adelaide School of Dentistry many interstate and overseas researchers interested in genetic and environmental influences on human dental development.     

Origin of bipedalism

Human and chimpanzee locomotor behaviors are described and compared using field patterns derived from measurements of the motions at the joints. Field patterns of human and ape bipedalism are so different that it is doubted whether the nonhuman type could ever have been a precursor of the human type. Chimpanzee quadrupedal vertical climbing and human bipedalism are, on the other hand, similar and a particular variety of this kind of climbing probably was the precursor of human bipedalism. Animals adapted to this variation would have had some brachiation-like morphological traits in their pectoral limbs and some hominid-like morphological traits in their pelvic limbs, traits anticipating the human condition. The australopithecines possessed these traits and must have been adapted to arboreal quadrupedal vertical climbing, having the capacity, at the same time, to perform facultative terrestrial bipedalism, moving on the ground in a manner visually identical to that of humans.     

Improved single- and multi-contact life-time testing of dental restorative materials using key characteristics of the human masticatory system and a force/position-controlled robotic dental wear simulator

This paper presents a new in vitro wear simulator based on spatial parallel kinematics and a biologically inspired implicit force/position hybrid controller to replicate chewing movements and dental wear formations on dental components, such as crowns, bridges or a full set of teeth. The human mandible, guided by passive structures such as posterior teeth and the two temporomandibular joints, moves with up to 6 degrees of freedom (DOF) in Cartesian space. The currently available wear simulators lack the ability to perform these chewing movements. In many cases, their lack of sufficient DOF enables them only to replicate the sliding motion of a single occlusal contact point by neglecting rotational movements and the motion along one Cartesian axis. The motion and forces of more than one occlusal contact points cannot accurately be replicated by these instruments. Furthermore, the majority of wear simulators are unable to control simultaneously the main wear-affecting parameters, considering abrasive mechanical wear, which are the occlusal sliding motion and bite forces in the constraint contact phase of the human chewing cycle. It has been shown that such discrepancies between the true in vivo and the simulated in vitro condition influence the outcome and the quality of wear studies. This can be improved by implementing biological features of the human masticatory system such as tooth compliance realized through the passive action of the periodontal ligament and active bite force control realized though the central nervous system using feedback from periodontal preceptors. The simulator described in this paper can be used for single- and multi-occlusal contact testing due to its kinematics and ability to exactly replicate human translational and rotational mandibular movements with up to 6 DOF without neglecting movements along or around the three Cartesian axes. Recorded human mandibular motion and occlusal force data are the reference inputs of the simulator. Experimental studies of wear using this simulator demonstrate that integrating the biological feature of combined force/position hybrid control in dental material testing improves the linearity and reduces the variability of results. In addition, it has been shown that present biaxially operated dental wear simulators are likely to provide misleading results in comparative in vitro/in vivo one-contact studies due to neglecting the occlusal sliding motion in one plane which could introduce an error of up to 49% since occlusal sliding motion D and volumetric wear loss V(loss) are proportional.     

Use of biorobotic models of highly deformable fins for studying the mechanics and control of fin forces in fishes

Bony fish swim with a level of agility that is unmatched in human-developed systems. This is due, in part, to the ability of the fish to carefully control hydrodynamic forces through the active modulation of the fins' kinematics and mechanical properties. To better understand how fish produce and control forces, biorobotic models of the bluegill sunfish's (Lepomis macrochirus) caudal fin and pectoral fins were developed. The designs of these systems were based on detailed analyses of the anatomy, kinematics, and hydrodynamics of the biological fins. The fin models have been used to investigate how fin kinematics and the mechanical properties of the fin-rays influence propulsive forces and to explore kinematic patterns that were inspired by biological motions but that were not explicitly performed by the fish. Results from studies conducted with the fin models indicate that subtle changes to the kinematics and mechanical properties of fin rays can significantly impact the magnitude, direction, and time course of the 3D forces used for propulsion and maneuvers. The magnitude of the force tends to scale with the fin's stiffness, but the direction of the force is not invariant, and this causes disproportional changes in the magnitude of the thrust, lift, and lateral components of force. Results from these studies shed light on the multiple strategies that are available to the fish to modulate fin forces.     

Slide track analysis of the relative motion between femoral head and acetabular cup in walking and in hip simulators

Joint simulators are important tools in wear studies of prosthetic joint materials. The type of motion in a joint simulator is crucial with respect to the wear produced. It is widely accepted that only multidirectional motion yields realistic wear for polyethylene acetabular cups. Multidirectionality, however, is a wide concept. The type of multidirectional motion varies considerably between simulators, which may explain the large differences in observed wear rates. At present, little is known about the relationship between the type of multidirectional motion and wear. One illustrative way to compare the motions of various hip simulators is to compute tracks made on the counterface by selected points of the surface of the femoral head and acetabular cup due to the cyclic relative motion. A new computation method, based on Euler angles, was developed, and used to compute slide tracks for the three-axis motion of the hip joint in walking, and for two hip simulators, the HUT-3 and the biaxial rocking motion. The slide track patterns resulting from the gait waveforms were found to be similar to those produced by the HUT-3 simulator. This paper is the first to include a verification of the computed simulator tracks. The tracks were verified in the two simulators using sharp pins, embedded in acetabular cups, engraving distinct grooves onto the femoral heads. The engravings were identical to the computed tracks. The results clearly differed from earlier computations by another research group. This study is intended to start a thorough investigation of the relationship between the type of multidirectional motion and wear.     

In situ stems: preservation states and growth habits of the Pennsylvanian (Carboniferous) calamitaleans based upon new studies of Calamites Sternberg, 1820 in the Duckmantian at Brymbo,North Wales,UK

Calamitalean stems that are preserved in growth position in Carboniferous sedimentary deposits have been described many times in the literature as either pith casts or stem casts. Many of these in situ stems show branching, which gives some information on their patterns of growth. Their manner of preservation is discussed in the light of a new stand of well‐preserved in situ stem and branch pith casts of Calamites discovered in mid to upper Duckmantian sandstone at Brymbo in the Wrexham Coalfield of North Wales. Analysis of a brown mineralized layer surrounding the casts and below the black compression remains of the stem tissues has shown the presence of goethite, muscovite, quartz and kaolin. Deposition of these minerals around the inside of the central stem cavity would have provided rigidity and sufficient support, while the pith cavity filled with sediments. The outer tissues would then have been compressed to form a thin coal layer around the mineralized infill of the pith cavity. Cross sections of stems were found clustered together in relatively small areas, and kernel density map and nearest neighbour analysis suggest that each small patch of these pith casts represents an individual plant spread by rhizomatous growth. Stems found in ironstone nodules are external casts of leafy stems preserved by the deposition of siderite on their surfaces. A length of rhizome found at Brymbo was similarly preserved as a cast in ironstone.     

True grit: A microwear experiment

Recently we noted the effects of experimental diets on microscopic dental wear in the American opossum and concluded that it might prove difficult to distinguish the microwear produced by an insectivorous diet from that produced by some kinds of herbivorous ones. We also noted that wear caused by gritty diets and those containing plant opal, although they might be confused with one another, are easily distinguished from other sorts of dietary wear. Our conclusions have been challenged on the basis that possibly we did not allow sufficient time in the experiments for diagnostic wear patterns to emerge. Additional data reported here show that this is not so. Even in our n “control” animals, fed a relatively soft unabrasive diet, enough time elapsed to produce significant dental wear. A new technique is described which for the first time allows the study of changing patterns of microscopic wear in a living animal over a period of time, thus allowing each animal to serve as its own control. A solution containing a broad-spectrum proteolytic enzyme when applied to the teeth of an anesthetized animal removes the proteinaceous coat (pellicle) which will otherwise obscure wear scratches. Precision dental impressions can then be made which reveal the details of the pattern of microwear on the teeth.     

Dental topography and molar wear in Alouatta palliata from Costa Rica

Paleoprimatologists depend on relationships between form and function of teeth to reconstruct the diets of fossil species. Most of this work has been limited to studies of unworn teeth. A new approach, dental topographic analysis, allows the characterization and comparison of worn primate teeth. Variably worn museum specimens have been used to construct species-specific wear sequences so that measurements can be compared by wear stage among taxa with known differences in diet. This assumes that individuals in a species tend to wear their molar teeth in similar ways, a supposition that has yet to be tested. Here we evaluate this assumption with a longitudinal study of changes in tooth form over time in primates. Fourteen individual mantled howling monkeys (Alouatta palliata) were captured and then recaptured after 2, 4, and 7 years when possible at Hacienda La Pacifica in Costa Rica between 1989-1999. Dental impressions were taken each time, and molar casts were produced and analyzed using dental topographic analysis. Results showed consistent decreases in crown slope and occlusal relief. In contrast, crown angularity, a measure of surface jaggedness, remained fairly constant except with extreme wear. There were no evident differences between specimens collected in different microhabitats. These results suggest that different individual mantled howling monkeys wear their teeth down in similar ways, evidently following a species-specific wear sequence. Dental topographic analysis may therefore be used to compare morphology among similarly worn individuals from different species.     

Evolutionarily accelerated invasions: the rate of dispersal evolves upwards during the range advance of cane toads

Human activities are changing habitats and climates and causing species' ranges to shift. Range expansion brings into play a set of powerful evolutionary forces at the expanding range edge that act to increase dispersal rates. One likely consequence of these forces is accelerating rates of range advance because of evolved increases in dispersal on the range edge. In northern Australia, cane toads have increased their rate of spread fivefold in the last 70 years. Our breeding trials with toads from populations spanning the species' invasion history in Australia suggest a genetic basis to dispersal rates and interpopulation genetic variation in such rates. Toads whose parents were from the expanding range front dispersed faster than toads whose parents were from the core of the range. This difference reflects patterns found in their field-collected mothers and fathers and points to heritable variance in the traits that have accelerated the toads' rate of invasion across tropical Australia over recent decades. Taken together with demonstrated spatial assortment by dispersal ability occurring on the expanding front, these results point firmly to ongoing evolution as a driving force in the accelerated expansion of toads across northern Australia.     

Strength requirements for internal and external prostheses

Throughout the history of development of joint replacement implants and external prostheses there have been mechanical failures due to a discrepancy between material strength, cross-sectional characteristics and the loads developed in normal or abnormal function by the patient utilising the device. Particularly for internal prostheses attention is being paid at the present time to wear characteristics and the requirements for the articulating surfaces and the volume of wear particles produced during tests simulating the use of the device within the patient. The particular importance of the wear particles is that they seem to be associated with accelerated resorption of bone at areas essential for successful fixation of the implant within it. This article will consider joint replacements at the knee and hip and external prostheses for the leg. If failure due to external trauma is ignored the loads to be considered in testing standards correspond in implants to the muscular and ligamentous forces related to the forces developed between ground and foot and to the bending moments in the structure of leg prostheses. Generally it can be assumed that the treatment of the patient following trauma is more easily accomplished and more likely to be successful if the prosthesis has failed and not the bony structure of the patient. However, the author is unaware that these devices have ever been designed to have lower intrinsic strength than the anatomical structures to which they are connected; indeed in many cases particularly for implants they are much stronger than the bone to which they are connected. The major difficulty in rational design of prosthetic devices has been uncertainty about the importance of occasionally applied loads of a high value relative to those on a frequent basis and also to the frequency of application of these overloads. In this paper consideration is given to methods of determination of load systems relevant to the mechanical performance of implanted joint replacements at the hip and the knee and external prostheses for leg amputees. New data are presented relating to walking, other daily activities and the corresponding frequency of occurrence of these. Loading data on implants obtained by various biomechanical models is compared and related to the loads actually measured by implanted transducers. The philosophy of the standardised test load systems and the performance requirements is reviewed.     

Combined Use of FSR Sensor Array and SVM Classifier for Finger Motion Recognition Based on Pressure Distribution Map

For controlling dexterous prosthetic hand with a high number of active Degrees of Freedom (DOF),it is necessary to reliably extract control volitions of finger motions from the human body.In this study,a large variety of finger motions are discriminated based on the diversities of the pressure distribution produced by the mechanical actions of muscles on the forearm.The pressure distribution patterns corresponding to the motions were measured by sensor array which is composed of 32 Force Sensitive Resistor (FSR) sensors.In order to map the pressure patterns with different finger motions,a multiclass classifier was designed based on the Support Vector Machine (SVM) algorithm.The multi-subject experiments show that it is possible to identify as many as seventeen different finger motions,including individual finger motions and multi-finger grasping motions,with the accuracy above 99％ in the in-session validation.Further,the cross-session validation demonstrates that the performance of the proposed method is robust for use if the FSR array is not reset.The results suggest that the proposed method has great application prospects for the control of multi-DOF dexterous hand prosthesis.     

How well can spring-mass-like telescoping leg models fit multi-pedal sagittal-plane locomotion data?

Idealized mathematical models of animals, with point-mass bodies and spring-like legs, have been used by researchers to study various aspects of terrestrial legged locomotion. Here, we fit a bipedal spring-mass model to the ground reaction forces of human running, a horse trotting, and a cockroach running. We find that, in all three cases, while the model captures center-of-mass motions and vertical force variations well, horizontal forces are less well reproduced, primarily due to variations in net force vector directions that the model cannot accommodate. The fits result in different apparent leg stiffnesses in the three animals. Assuming a simple fixed leg-angle touch-down strategy, we find that the gaits of these models are stable in different speed-step length regimes that overlap with those used by humans and horses, but not with that used by cockroaches.     

Direct Measurements of Drag Forces in C. elegans Crawling Locomotion

With a simple and versatile microcantilever-based force measurement technique, we have probed the drag forces involved in Caenorhabditis elegans locomotion. As a worm crawls on an agar surface, we found that substrate viscoelasticity introduces nonlinearities in the force-velocity relationships, yielding nonconstant drag coefficients that are not captured by original resistive force theory. A major contributing factor to these nonlinearities is the formation of a shallow groove on the agar surface. We measured both the adhesion forces that cause the worm’s body to settle into the agar and the resulting dynamics of groove formation. Furthermore, we quantified the locomotive forces produced by C. elegans undulatory motions on a wet viscoelastic agar surface. We show that an extension of resistive force theory is able to use the dynamics of a nematode’s body shape along with the measured drag coefficients to predict the forces generated by a crawling nematode.     

Pure passive hyperextension of the human cadaver knee generates simultaneous bicruciate ligament rupture

Knee hyperextension has been described as a mechanism of isolated anterior cruciate ligament (ACL) tears, but clinical and experimental studies have produced contradictory results for the ligament injuries and the injury sequence caused by the hyperextension loading mechanism. The hypothesis of this study was that bicruciate ligament injuries would occur as a result of knee hyperextension by producing high tibio-femoral (TF) compressive forces that would cause anterior translation of the tibia to rupture the ACL, while joint extension would simultaneously induce rupture of the posterior cruciate ligament (PCL). Six human knees were loaded in hyperextension until gross injury, while bending moments and motions were recorded. Pressure sensitive film documented the magnitude and location of TF compressive forces. The peak bending moment at failure was 108?N?m±46?N?m at a total extension angle of 33.6?deg±11?deg. All joints failed by simultaneous ACL and PCL damages at the time of a sudden drop in the bending moment. High compressive forces were measured in the anterior compartments of the knee and likely produced the anterior tibial subluxation, which contributed to excessive tension in the ACL. The injury to the PCL at the same time may have been due to excessive extension of the joint. These data, and the comparisons with previous experimental studies, may help explain the mechanisms of knee ligament injury during hyperextension. Knowledge of forces and constraints that occur clinically could then help diagnose primary and secondary joint injuries following hyperextension of the human knee.