Wear Gradient Research Articles

Variability in molar crown morphology and cusp wear in two Western chimpanzee populations.

Chimpanzees (Pan troglodytes) possess a relatively generalized molar morphology allowing them to access a wide range of foods. Comparisons of crown and cusp morphology among the four subspecies have suggested relatively large intraspecific variability. Here, we compare molar crown traits and cusp wear of two geographically close populations of Western chimpanzees, P. t. verus, to provide further information on intraspecific dental variability. Micro-CT reconstructions of high-resolution replicas of first and second molars of two Western chimpanzee populations from Ivory Coast (Taï National Park) and Liberia, respectively were used for this study. First, we analyzed projected tooth and cusp 2D areas as well as the occurrence of cusp six (C6) on lower molars. Second, we quantified the molar cusp wear three-dimensionally to infer how the individual cusps alter with advancing wear. Both populations are similar in their molar crown morphology, except for a higher appearance rate of a C6 in Taï chimpanzees. In Taï chimpanzees, lingual cusps of upper molars and buccal cusps of lower molars possess an advanced wear pattern compared to the remaining cusps, while in Liberian chimpanzees this wear gradient is less pronounced. The similar crown morphology between both populations fits with previous descriptions for Western chimpanzees and provides additional data on dental variation within this subspecies. The wear pattern of the Taï chimpanzees are in concordance with their observed tool rather than tooth use to open nuts/seeds, while the Liberian chimpanzees may have consumed hard food items crushed between their molars.

Microwear textures associated with experimental near-natural diets suggest that seeds and hard insect body parts cause high enamel surface complexity in small mammals

In mammals, complex dental microwear textures (DMT) representing differently sized and shaped enamel lesions overlaying each other have traditionally been associated with the seeds and kernels in frugivorous diets, as well as with sclerotized insect cuticles. Recently, this notion has been challenged by field observations as well as in vitro experimental data. It remains unclear to what extent each food item contributes to the complexity level and is reflected by the surface texture of the respective tooth position along the molar tooth row. To clarify the potential of seeds and other abrasive dietary items to cause complex microwear textures, we conducted a controlled feeding experiment with rats. Six individual rats each received either a vegetable mix, a fruit mix, a seed mix, whole crickets, whole black soldier fly larvae, or whole day-old-chicks. These diets were subjected to material testing to obtain mechanical properties, such as Young’s modulus, yield strength, and food hardness (as indicated by texture profile analysis [TPA] tests). Seeds and crickets caused the highest surface complexity. The fruit mix, seed mix, and crickets caused the deepest wear features. Moreover, several diets resulted in an increasing wear gradient from the first to the second molar, suggesting that increasing bite force along the tooth row affects dental wear in rats on these diets. Mechanical properties of the diets showed different correlations with DMT obtained for the first and second molars. The first molar wear was mostly correlated with maximum TPA hardness, while the second molar wear was strongly correlated with maximum yield stress, mean TPA hardness, and maximum TPA hardness. This indicates a complex relationship between chewing mechanics, food mechanical properties, and observed DMT. Our results show that, in rats, seeds are the main cause of complex microwear textures but that hard insect body parts can also cause high complexity. However, the similarity in parameter values of surface textures resulting from seed and cricket consumption did not allow differentiation between these two diets in our experimental approach.

Dental microwear texture gradients in guinea pigs reveal that material properties of the diet affect chewing behaviour.

Dental microwear texture analysis (DMTA) is widely used for diet inferences in extant and extinct vertebrates. Often, a reference tooth position is analysed in extant specimens, while isolated teeth are lumped together in fossil datasets. It is therefore important to test whether dental microwear texture (DMT) is tooth position specific and, if so, what causes the differences in wear. Here, we present results from controlled feeding experiments with 72 guinea pigs, which received either fresh or dried natural plant diets of different phytolith content (lucerne, grass, bamboo) or pelleted diets with and without mineral abrasives (frequently encountered by herbivorous mammals in natural habitats). We tested for gradients in dental microwear texture along the upper cheek tooth row. Regardless of abrasive content, guinea pigs on pelleted diets displayed an increase in surface roughness along the tooth row, indicating that posterior tooth positions experience more wear compared with anterior teeth. Guinea pigs feedings on plants of low phytolith content and low abrasiveness (fresh and dry lucerne, fresh grass) showed almost no DMT differences between tooth positions, while individuals feeding on more abrasive plants (dry grass, fresh and dry bamboo) showed a gradient of decreasing surface roughness along the tooth row. We suggest that plant feeding involves continuous intake and comminution by grinding, resulting in posterior tooth positions mainly processing food already partly comminuted and moistened. Pelleted diets require crushing, which exerts higher loads, especially on posterior tooth positions, where bite forces are highest. These differences in chewing behaviour result in opposing wear gradients for plant versus pelleted diets.

Finite element 3D numerical simulation study of car braking systems and brake disc/drum – pad/shoe friction couple materials

Our study uses the finite element method of modeling and analyzing the functioning of a braking system for a modern vehicle, in terms of stress ditributions, structural deformation, wear and thermal gradient of the brake disc and drum. The 3D geometric model of system brake is designed using Solidworks, and the coupled thermal and structural analysis is performed with the ANSYS Workbench R16 program. The brake was applied when the car was 85.7 km / h (ω = 125 rad · s-1), the duration of braking until the car stopped was t = 5 s. For the given example, the coefficient of average friction during braking, considering the pressure on the pad p = 7.5 MPa, is μ = 0.35. It was discovered that the relative deformations of the plate and disc are larger in the area of the outer diameter than that of the inner diameter. This is also outlined by the fact that the pressure is higher on the outer sides than on the inner sides of the plate, the highest value being in the central axis zone of the outer side. Knowing the thermophysical characteristics of the disc and the plate and the working conditions, it was possible to determine the temperature variation during braking. The results of the numerical research revealed that an increase of the contact pressure and / or the relative speed between the contact surfaces implies an increase of the amplitude of the stick-slip phenomenon.

Anatomy, Relationships, and Paleobiology of Cambaytherium (Mammalia, Perissodactylamorpha, Anthracobunia) from the lower Eocene of western India

ABSTRACT The anatomy of Cambaytherium, a primitive, perissodactyl-like mammal from the lower Eocene Cambay Shale Formation of Gujarat, India, is described in detail on the basis of more than 350 specimens that represent almost the entire dentition and the skeleton. Cambaytherium combines plesiomorphic traits typical of archaic ungulates such as phenacodontids with derived traits characteristic of early perissodactyls. Cambaytherium was a subcursorial animal better adapted for running than phenacodontids but less specialized than early perissodactyls. The cheek teeth are bunodont with large upper molar conules, not lophodont as in early perissodactyls; like perissodactyls, however, the lower molars have twinned metaconids and m3 has an extended hypoconulid lobe. A steep wear gradient with heavy wear in the middle of the tooth row suggests an abrasive herbivorous diet. Three species of Cambaytherium are recognized: C. thewissi (∼23 kg), C. gracilis (∼10 kg), and C. marinus (∼99 kg). Body masses were estimated from tooth size and long bone dimensions. Biostratigraphic and isotopic evidence indicates an age of ca. 54.5 Ma for the Cambay Shale vertebrate fauna, the oldest Cenozoic continental vertebrate assemblage from India, near or prior to the initial collision with Asia. Cambaytheriidae (also including Nakusia and Perissobune) and Anthracobunidae are sister taxa, constituting the clade Anthracobunia, which is sister to Perissodactyla. We unite them in a new higher taxon, Perissodactylamorpha. The antiquity and occurrence of Cambaytherium—the most primitive known perissodactylamorph—in India near or before its collision with Asia suggest that Perissodactyla evolved during the Paleocene on the Indian Plate or in peripheral areas of southern or southwestern Asia.

Double Reinforcement of Al–Fe Intermetallic Composites Fabricated by Friction Stir Processing

A double reinforced layer on an aluminum alloy surface was produced using friction stir processing (FSP) by adding 34CrNiMo6 powder into Al (AA2024) substrate for better wear resistance and gradient transitions. The microstructures of the composites were analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The phase composition was examined by X-ray diffraction (XRD). The results show that the double reinforced layer of the Al13Fe4 intermetallic compound could be successfully fabricated via FSP. The volume fraction of Al13Fe4 in the double reinforced layer was higher than in the single reinforced layer due to adding 34CrNiMo6 powder and reinforced twice, and the Al13Fe4 particles were dispersed more homogeneously in the double reinforced layer. The interfaces between the double and single reinforced layer had a good metallurgical bond. The microhardness of the double reinforcement layer was significantly increased. Compared with the AA2024 substrate, the microhardness of the double and single reinforced layers increased five- (576 HV) and two-fold (254 HV), respectively.

Effect of gas phase composition on functional-gradient coatings formation by supersonic cold gas dynamic spraying

The paper develops method for manufacturing wear and corrosion-resistant gradient coating. A special feature of the proposed method is the creation of chemical composition gradient due to controlled variation of the gas phase composition when applying supersonic cold gas-dynamic spraying. This ensures high adhesive strength of the composite coatings of the metal-non-metal system in combination with high micro-hardness of the peripheral layers. Such functional gradient coatings have wide practical applications.

Mastication and enamel microstructure in Cambaytherium, a perissodactyl-like ungulate from the early Eocene of India

The dentition of Cambaytherium was investigated in terms of dental wear, tooth replacement and enamel microstructure. The postcanine tooth row shows a significant wear gradient, with flattened premolars and anterior molars at a time when the last molars are only little worn. This wear gradient, which is more intensive in Cambaytherium thewissi than in Cambaytherium gracilis, and the resulting flattened occlusal surfaces, may indicate a preference for a durophagous diet. The tooth replacement (known only in C. thewissi) shows an early eruption of the permanent premolars. They are in function before the third molars are fully erupted. During the dominant phase I of the chewing cycle the jaw movement is very steep, almost orthal, with a slight mesiolingual direction and changes into a horizontal movement during phase II. The enamel microstructure shows Hunter-Schreger-bands (HSB) in the inner zone of the enamel. In some teeth the transverse orientation of the HSB is modified into a zig-zag pattern, possibly an additional indicator of a durophagous diet.

Dental wear and age grading at Roonka, South Australia.

In many hunter-gatherer populations, the teeth are used as a third hand or a tool. Much attention has been paid to wear and its relationship to gendered division of labor, but age is also a significant organizing factor in many societies. In this article, I analyze whether the pattern of wear at Roonka, Australia, reflects the age-graded acquisition of tasks. The remains analyzed come from Roonka and date from c6000 BP to 150 BP. In total 126 adults and juveniles were analyzed. Wear gradients were calculated for each tooth relative to wear on the first molar. Data were compared using nonparametric statistics and cluster analysis to assess the degree of patterning within the sample. Dental wear proceeded rapidly. There is no evidence of sex differences in the pattern of wear. Age differences do occur. While disproportionate anterior wear occurs among juveniles and young adults, by middle adulthood the pattern is less variable and involves the premolars. Old adults have a much flatter pattern of wear. The pattern of wear is consistent with ethnographic observations, which suggest a degree of latitude in the activities of juveniles and young adults. By middle age variability between individuals declines reflecting shared tasks and more intensive use of the teeth. The pattern of wear amongst old adults, however, is much flatter presumably due to changes in occlusion. While dental wear is informative about the organization of labor there is a need to take into account both patterns of activity and occlusion.

Comparative analyses of tooth wear in free-ranging and captive wild equids.

Captive breeding has played a crucial role in the conservation of threatened equid species. Grazing ruminants and rhinoceros in captivity have less abrasion-dominated tooth wear than their free-ranging conspecifics, with potential negative consequences for their health. However, a similar study on wild equids in captivity is missing. The aim was to establish if different tooth wear patterns are exhibited by free-ranging and captive equids. Cross-sectional study of museum specimens comparing free-ranging and captive equids. Dental casts of maxillary cheek teeth of 228 museum specimens (122 from free-ranging and 106 from captive individuals) of 7 wild equid species were analysed using the extended mesowear method. Although teeth showing specific abnormalities were not scored, the presence of focal overgrowths (hooks) of the rostral premolars (106, 206) was recorded. Captive Equus ferus przewalskii, E. grevyi, E. hemionus, E. quagga boehmi and E. zebra hartmannae have less abrasion-dominated tooth wear on their premolars than their free-ranging conspecifics (P<0.001). Fewer differences were exhibited between populations in the molars. No differences were exhibited in the distal cusp of the molars (110, 210) between populations, except in a small sample of E. kiang. Captive equids exhibited more homogeneous wear along the tooth row whereas free-ranging equids exhibited a tooth wear gradient, with more abrasion on premolars than molars. There were more rostral hooks on the premolars (106, 206) in the captive than the free-ranging population (P = 0.02). Captive equids did experience less abrasion-dominated tooth wear than their free-ranging conspecifics, but the differences in tooth wear were less pronounced than those between captive and free-ranging wild ruminant and rhinoceros species. This indicates that feeding regimes for captive equids deviate less from natural diets than those for captive ruminants and rhinoceros but that factors leading to hook formation, in particular feeding height, should receive special attention. The Summary is available in Chinese - see Supporting information.

Mastication and Wear inLophiodon(Perissodactyla, Mammalia) Compared with Lophodont Dentitions in Some other Mammals

Three functional aspects (jaw movement, collapse of lophs by wear, and molar wear gradient) are described for Lophiodon and compared with typical lophodont dentitions in other mammals, e.g., Macropus, Pyrotherium and Deinotherium. The jaw movement is deduced from striations and guiding rails. In Lophiodon only phase I of the power stroke is documented by facets, whereas a minor phase II occurs in Macropus. During phase I the lophs perform two functions: cutting when the crests are passing each other, and compressing the bolus during further interlocking. When dentine is exposed the lophs collapse and lose their trenchant function and are grinding only. The sudden collapse of the lophs is partially due to the abrasion within the compression chamber, as seen in Dendrolagus. The molar wear gradient (the differential wear between the first and last molars) is low in Pyrotherium, intermediate in Lophiodon, and Deinotherium as compared with a low molar wear gradient in Tapirus or a high gradient in Macropus.

Tooth wear in captive rhinoceroses (Diceros, Rhinoceros, Ceratotherium: Perissodactyla) differs from that of free-ranging conspecifics

Tooth wear can affect body condition, reproductive success and life expectancy. Poor dental health is frequently reported in the zoo literature, and abrasion-dominated tooth wear, which is typical for grazers, has been reported in captive browsing ruminants. The aim of this study was to test if a similar effect is evident in captive rhinoceros species. Dental casts of maxillary cheek teeth of museum specimens of captive black (Diceros bicornis; browser), greater one-horned (Rhinoceros unicornis; intermediate feeder) and white rhinoceroses (Ceratotherium simum; grazer) were analysed using the recently developed extended mesowear method for rhinoceroses. Captive D. bicornis exhibited significantly more abrasion-dominated tooth wear than their free-ranging conspecifics (p&lt;0.001), whereas captive C. simum exhibited significantly less abrasion-dominated tooth wear, particularly in the posterior cusp of the second molar (p=0.005). In R. unicornis, fewer differences were exhibited between free-ranging and captive animals, but tooth wear was highly variable in this species. In both free-ranging and captive D. bicornis, anterior cusps were significantly more abrasiondominated than posterior cusps (p&lt;0.05), which indicates morphological differences between cusps that may represent functional adaptations. By contrast, tooth wear gradients between free-ranging and captive animals differed, which indicates ingesta- specific influences responsible for inter-tooth wear differences. Captive D. bicornis exhibited more homogenous tooth wear than their free-ranging conspecifics, which may be caused by an increase in the absolute dietary abrasiveness and a decrease in relative environmental abrasiveness compared to their freeranging conspecifics. The opposite occurred in C. simum. The results of this study suggest that diets fed to captive browsers are too abrasive, which could result in the premature loss of tooth functionality, leading to reduced food acquisition and processing ability and, consequently, malnourishment.

Detecting Inter-Cusp and Inter-Tooth Wear Patterns in Rhinocerotids

Extant rhinos are the largest extant herbivores exhibiting dietary specialisations for both browse and grass. However, the adaptive value of the wear-induced tooth morphology in rhinos has not been widely studied, and data on individual cusp and tooth positions have rarely been published. We evaluated upper cheek dentition of browsing Diceros bicornis and Rhinoceros sondaicus, mixed-feeding R. unicornis and grazing Ceratotherium simum using an extended mesowear method adapted for rhinos. We included single cusp scoring (EM(R)-S) to investigate inter-cusp and inter-tooth wear patterns. In accordance with previous reports, general mesowear patterns in D. bicornis and R. sondaicus were attrition-dominated and C. simum abrasion-dominated, reflecting their respective diets. Mesowear patterns for R. unicornis were more attrition-dominated than anticipated by the grass-dominated diet, which may indicate a low intake of environmental abrasives. EM(R)-S increased differentiation power compared to classical mesowear, with significant inter-cusp and inter-tooth differences detected. In D. bicornis, the anterior cusp was consistently more abrasion-dominated than the posterior. Wear differences in cusp position may relate to morphological adaptations to dietary regimes. Heterogeneous occlusal surfaces may facilitate the comminution of heterogeneous browse, whereas uniform, broad grinding surfaces may enhance the comminution of physically more homogeneous grass. A negative tooth wear gradient was found in D. bicornis, R. sondaicus and R. unicornis, with wear patterns becoming less abrasion-dominated from premolars to molars. No such gradients were evident in C. simum which displayed a uniform wear pattern. In browsers, premolars may be exposed to higher relative grit loads, which may result in the development of wear gradients. The second premolar may also have a role in food cropping. In grazers, high absolute amounts of ingested abrasives may override other signals, leading to a uniform wear pattern and dental function along the tooth row, which could relate to the observed evolution towards homodonty.

基于小波包和Niblack法的枪号图像二值化算法

Aiming at the characteristics of the gun code image that characters are easy to wear and contrast gradient is too large or too small,a binarization method based on wavelet packet filter floating threshold and Niblack method is proposed.Firstly,the image is filtered using wavelet packet filter and binarized with the low pass image after filtering.Then,the image is binarized with the Niblack method to obtain the second fusing image.Finally,two fusing images are merged based on the minimum principle of image gray values to get the final binarization image.Experimental results show that the method has a good performance in binarization effect and adaptation range and can imply in many situation.

Estimating age from adult occlusal wear: A modification of the miles method

The Miles method of age estimation relies on molar wear to estimate age and is widely used in bioarcheological contexts. However, because the method requires physical seriation and a sample of subadults to estimate wear rates it cannot be applied to many samples. Here, we modify the Miles method by scoring occlusal wear and estimating molar wear rates from adult wear gradients in 311 hunter-gatherers and provide formulae to estimate the error associated with each age estimate. A check of the modified method in a subsample (n = 22) shows that interval estimates overlap in all but one case with age categories estimated from traditional methods; this suggests that the modifications have not hampered the ability of the Miles method to estimate age even in heterogeneous samples. As expected, the error increases with age and in populations with smaller sample sizes. These modifications allow the Miles method to be applied to skeletal samples of adult crania that were previously only amenable to cranial suture age estimation, and importantly, provide a measure of uncertainty for each age estimate.

Interproximal wear facets and tooth associations in the Paşalar hominoid sample

Interproximal wear facets were examined on hominoid teeth from the middle Miocene site at Paşalar, Turkey. The aim was to find matches between adjacent premolar and molar teeth from single individuals that were collected in the field as isolated teeth and use them to reconstruct tooth rows. These were then used to investigate: (1) the wear gradient on the molar teeth; (2) the dispersal of teeth from single mandibles and maxillae; (3) the size ratios among the molars; and (4) the number of individuals represented by the hominoid sample. Facets were scored for size and shape and were assessed visually using photographs and superimposed outline drawings on acetate transparencies. Out of a sample of approximately 1500 teeth collected between 1983 and 1996, 532 molars and 258 premolars produced apparent matches making up 160 tooth rows. These were then examined rigorously for morphological consistency and state of wear, and, employing the criterion that only the most unequivocal associations should be used, the final number was reduced to 48 tooth rows—31 mandibular and 17 maxillary. The tooth associations represent a minimum of 21 individuals and probably as many as 34. Molar wear was rapid, with M1s having almost twice as much wear as M3s, as measured by a wear-gradient index. The M2s are intermediate but generally closer to M1s in degree of wear, as are P4s. This wear pattern suggests either delayed eruption of M3s or extremely abrasive diets causing rapid, heavy wear. There is some indication that the wear patterns in Griphopithecus alpani and Kenyapithecus kizili are different, with the latter perhaps having a lower wear gradient, but the K. kizili sample is very small. In both species, the M2 is the largest molar and the M1 is the smallest. Separation of individual teeth in the 48 tooth associations varied from widely separated—up to 8.5 m apart—to within a few centimeters of each other. One tooth row (D922) was found with the teeth in contact but the maxillary bone had dissolved away. Two dispersal mechanisms have been identified from earlier taphonomic work: transport of disarticulated elements to the fossil site and reworking of sediments by spring action.

Functional Characterization of Ungulate Molars Using the Abrasion-Attrition Wear Gradient: A New Method for Reconstructing Paleodiets

The analysis of fossil ungulate cheek teeth has long been one of the main sources of information about the terrestrial environments of the Cenozoic, but the methods used to extract this information have been either imprecise or prohibitively laborious. Here we present a method based on relative facet development that is quantitative, robust, and rapid. This method, which we term mesowear analysis, is based on the physical properties of ungulate foods as reflected in the relative amounts of attritive and abrasive wear that they cause on the dental enamel of the occlusal surfaces. Mesowear was recorded by examining the buccal apices of molar tooth cusps. Apices were characterized as sharp, rounded, or blunt, and the valleys between them either high or low. The method has been developed only for selenodont and trilophodont molars, but the principle is readily extendable to other crown types. Mesowear analysis is insensitive to wear stage as long as the very early and very late stages are excluded.Cluster analysis of the mesowear variables produces clusters reflecting four main groups from abrasion-dominated to attrition-dominated: grazers, graze-dominated mixed feeders, browse-dominated mixed feeders, and browsers. Most of the relatively few apparent anomalies are explained by more detailed dietary information. Mesowear analysis provides resolution within the main dietary classes and the clustering is virtually identical with and without the index of hypsodonty. Discriminant analysis using all mesowear variables and hypsodonty showed an overall correct classification of 76% of 64 species of living ungulates into the conventional dietary categories of browser, grazer, and mixed feeder, while a smaller set of 27 “typical” species was correctly classified at 96%. Alternative “conservative” and “radical” dietary classifications that were employed to accommodate cases where dietary information was controversial or unclear produced only marginally different results. Mesowear analysis successfully resolved a test case using the Serengeti grazing succession and appears to be superior to microwear analysis in two cases where the diet of fossil ungulates has been previously studied by microwear and other conventional methods.

Design criteria and correction factors for field wear testing

Some general criteria for wear testing are presented. Laboratory wear tests can be designed to meet the criteria but test results generally do not accurately predict wear under field conditions. Field wear testing is needed to optimize the final selection of materials for the given application. The concept of wear gradient is introduced. Wear gradients, with respect to time and location, are small and reproducible in laboratory tests but generally are significant and fluctuate under field conditions. Field tests are classified as sequential series, concurrent series, and concurrent group tests. The use of reference specimens for establishing time-averaged wear gradients is discussed and formulae for correcting the test specimen wear for non-uniform triboconditions over the test area are presented. A field test for abrasive wear of a linear array of specimens is described. The corrected wear values of duplicate specimens agree within 5% of the mean.

Differences in molar wear gradient between adult macaques and langurs

Interspecific differences in the amount and form of molar wear in nonhuman primates are only beginning to be documented and understood. The purpose of this study was to look at the wear gradient between M1 and M2 in a sample of macaques and langurs to determine if differences in wear gradient could be related to differences in diet. A skeletal collection of wild shot Macaca fascicularis, Presbytis cristata, and Presbytis rubicunda from the Museum of Comparative Zoology at Harvard University was examined using photogrammetric techniques. X, Y, and Z coordinates were used to compute areas of dentin exposure on the buccal occlusal surfaces of M1 and M2. The relationship between these variables was examined using Bartlett’s three-group method and least-squares regression. Interspecific comparisons of the resultant y intercepts indicate that (I) M. fascicularis (as compared with P. cristata or P.) has more dentin exposed on M1 when there is none exposed on M2, and (2) P. cristata (as compared with P. rubicunda) has more dentin exposed on M1 when there is none exposed on M2. Factors that might be responsible for these differences are (a) differences in dentin/enamel structure, (b) differences in molar eruption timing, and (c) differences in behavior. An unusual intercusp sequence of dentin exposure in the langurs makes precise interpretations difficult. However, at the present time, behavioral differences among the species deserve further consideration as a cause of the observed differences in molar wear gradient.

Differences in molar wear gradient between juvenile macaques and langurs

AbstractInterspecific differences in the amount and form of molar wear in nonhuman primates are only beginning to be documented and understood. The purpose of this study was to look at the wear gradient between M1 and dm2 in a sample of macaques and langurs to determine if differences in wear gradient could be related to differences in diet. A skeletal collection of wild shot Presbytis cristatus and Macaca fascicularis from the Museum of Comparative Zoology at Harvard University was examined using stereophotogrammetric techniques. X, Y, and Z coordinates were used to compute the areas of dentin exposure on the buccal cusps of M1 and the buccal cusps of dm2. The relationship between these variables was examined using Bartlett's three group method and least squares regression. Intergeneric comparisons of the resultant y‐intercepts indicate that the macaques have more dentin exposed on dm2 when there is none exposed on M1. Factors that might be responsible for this difference include differences in dentin/enamel structure, differences in molar eruption timing, and differences in behavior. At the present time, behavioral differences between the genera appear to be the most likely cause of the difference in wear gradient.