A scanning electron-microscopic study of in vitro abrasion of mammalian tooth enamel under compressive loads

Reconstructing diets of hunted sika deer from Torihama Shell Midden site (ca. 6,000 years ago) by dental microwear texture analysis

Sika deer (Cervus nippon) is the most abundant ruminant in the Japanese archipelago and has been the primary hunting target, including during the prehistoric ages. Abundant skeletal remains of sika deer have been excavated from archeological sites of the Jomon periods (ca. 15,000–2,400 BP). We reconstructed the feeding habits of sika deer from the Torihama Shell Midden site in Fukui Prefecture, western Japan. The Torihama site is one of the most well-preserved archeological sites of the Jomon period, and we investigated materials from the layers of the Early Jomon period (ca. 6,000 BP). In this study, we obtained three-dimensional tooth surface texture from the lower molars of excavated deer and measured microwear texture using international surface roughness parameters (ISO 25178-2) to infer their habitat use. Next, we estimated the percentage of grasses in the diet by using the reference dataset for extant sika deer with known diets. The results show that the Torihama deer overlapped with mixed feeding and grazing sika deer populations. Moreover, the proportion of grasses in the diet was estimated to be 50.7% on average but showed a wide range among the Torihama deer. This result implied that Torihama deer were mixed feeders of dicot leaves and grasses and had a flexible diet adapted to the vegetation of its habitat. Our results support the paleoenvironmental estimation that the Torihama Shell Midden site contained mixed vegetation of evergreen, deciduous, and coniferous trees around the Mikata Five Lakes in the Early Jomon period. These findings provide insights into the highly plastic diets of the extant sika deer in the Japanese archipelago.

Experimental approaches to assess the effect of composition of abrasives in the cause of dental microwear

Dental microwear is used to investigate feeding ecology. Animals ingest geological material in addition to food. The full effect of geological abrasives on tooth wear is unknown. To evaluate mineralogical abrasives as tooth wear agents, rats were fed food manufactured with quartz silt, diatomaceous earth, and calcium carbonate. Rats were assigned to treatments and fed for 15 days. Molars were scanned with a Sensofar Plu Neox confocal microscope and evaluated using ISO-25178-2 parameters and traditional microwear variables using light microscopy. Using a pellet-diet as the control, all treatments had influence on microwear and discriminant function analyses indicated that unique surface textures had been produced. ISO variables with high discriminatory values were correlated to scratch and pit frequencies, but more ISO parameters identified changes associated with numbers of scratches than changes associated with pits. The microwear changes associated with the abrasive inclusions were co-dependent on the type of diet that the abrasives had been added to. The abrasives had less effect with pellets but produced more modified and more differentiated microwear when added to the transgenic dough. Although abrasives produce distinctive surface textures, some knowledge of the properties of food with the abrasives is needed to identify the abrasive agent.

Technical note: Artificial Resynthesis Technology for the experimental formation of dental microwear textures

Dental microwear formation on the posterior dentition is largely attributed to an organism's diet. However, some have suggested that dietary and environmental abrasives contribute more to the formation process than food, calling into question the applicability of dental microwear to the reconstruction of diet in the fossil record. Creating microwear under controlled conditions would benefit this debate, but requires accurately replicating the oral environment. This study tests the applicability of Artificial Resynthesis Technology (ART 5) to create microwear textures while mitigating the challenges of past research. ART 5 is a simulator that replicates the chewing cycle, responds to changes in food texture, and simulates the actions of the oral cavity. Surgically extracted, occluding pairs of third molars (n = 2 pairs) were used in two chewing experiments: one with dried beef and another with sand added to the dried beef. High-resolution molds were taken at 0, 50, 100, 2500, and 5000 simulated chewing cycles, which equates to approximately 1 week of chewing. Preliminary results show that ART 5 produces microwear textures. Meat alone may produce enamel prism rod exposure at 5000 cycles, although attrition cannot be ruled out. Meat with sand accelerates the wear formation process, with enamel prism rods quickly obliterated and "pit-and-scratch" microwear forming at approximately 2500 cycles. Future work with ART 5 will incorporate a more thorough experimental protocol with improved controls, pH of the simulated oral environment, and grit measurements; however, these results indicate the potential of ART 5 in untangling the complex variables of dental microwear formation.

Mechanical modelling of tooth wear

Different diets wear teeth in different ways and generate distinguishable wear and microwear patterns that have long been the basis of palaeodiet reconstructions. Little experimental research has been performed to study them together. Here, we show that an artificial mechanical masticator, a chewing machine, occluding real horse teeth in continuous simulated chewing (of 100 000 chewing cycles) is capable of replicating microscopic wear features and gross wear on teeth that resemble wear in specimens collected from nature. Simulating pure attrition (chewing without food) and four plant material diets of different abrasives content (at n = 5 tooth pairs per group), we detected differences in microscopic wear features by stereomicroscopy of the chewing surface in the number and quality of pits and scratches that were not always as expected. Using computed tomography scanning in one tooth per diet, absolute wear was quantified as the mean height change after the simulated chewing. Absolute wear increased with diet abrasiveness, originating from phytoliths and grit. In combination, our findings highlight that differences in actual dental tissue loss can occur at similar microwear patterns, cautioning against a direct transformation of microwear results into predictions about diet or tooth wear rate.

Tooth wear pattern analysis in a sample of Italian Early Bronze Age population. Proposal of a 3-D sampling sequence

OBJECTIVE

The purpose of this study was to assess the prevalence, distribution and intensity of tooth wear in a sample of an ancient Italian population in order to explain the pattern in terms of dietary habits and/or non-dietary tooth-use behaviors during the Early Bronze Age, with a focus on possible age-group and sex differences.

DESIGN

Well-preserved permanent teeth of individuals from the Bronze Age site of Ballabio (Lecco) in northern Italy were examined for tooth wear by different methods. Eight 3D models of teeth at increasing severity of wear were created.

RESULTS

In total, 357 permanent teeth belonging to male and female individuals were included in the study. Dental wear was present in 96.6% of the total sample. Males showed significantly greater levels of wear than females in the mandibular teeth. Both sexes exhibited a significantly different wear direction between the anterior (oblique and flat) and posterior (oblique and concave) teeth. Significant age differences were observed in the direction and level of wear in the incisors, canines and premolars, with higher wear in the older group. Complete and rotatable virtual 3D images of different wear patterns are proposed.

CONCLUSIONS

The findings of the present study confirm the data from archaeological studies on this site and on northern Italian habits during the Early Bronze Age suggesting a diet rich in vegetables. The observed wear patterns can be related both to the diet of this Bronze age population, based on hard and abrasive food requiring vigorous mastication, and to sex differences in cultural practices.

Age-related changes in molar topography and shearing crest length in a wild population of mountain Gorillas from Volcanoes National Park, Rwanda

OBJECTIVES

Great ape teeth must remain functional over long lifespans. The molars of the most folivorous apes, the mountain gorillas, must maintain shearing function for 40+ years while the animals consume large quantities of mechanically challenging foods. While other folivorous primates experience dental senescence, which compromises their occlusal surfaces and affects their reproductive success as they age, it is unknown whether dental senescence also occurs in mountain gorillas. In this article, we quantified and evaluated how mountain gorilla molars change throughout their long lifespans.

MATERIALS AND METHODS

We collected high-resolution replicas of M(1)s (n = 15), M(2)s (n = 13), and M(3)s (n = 11) from a cross-sectional sample of wild mountain gorilla skeletons from the Virunga Volcanoes, ranging in age from 4 to 43 years. We employed dental topographic analyses to track how aspects of occlusal slope, angularity, relief index, and orientation patch count rotated change with age. In addition, we measured the relative length of shearing crests in two- and three-dimensions.

RESULTS

Occlusal topography was found to decrease, while 2D relative shearing crest length increased, and 3D relative crest lengths were maintained with age.

DISCUSSION

Our findings indicate that shearing function is maintained throughout the long lifetimes of mountain gorillas. Unlike the dental senescence experienced by other folivorous primates, mountain gorillas do not appear to possess senesced molars despite their long lifetimes, mechanically challenging diets, and decreases in occlusal topography with age.

Technical note: An in vitro study of dental microwear formation using the BITE Master II chewing machine

Dental microwear has been used for decades to reconstruct the diets of fossil hominins and bioarchaeological populations. The basic theory has been that hard-brittle foods (e.g., nuts, bone) require crushing and leave pits as they are pressed between opposing cheek-tooth surfaces, whereas soft-tough foods (e.g., grass blades, meat) require shearing and leave scratches as they are dragged along opposing surfaces that slide past one another. However, recent studies have called into question the efficacy of microwear as an indicator of diet. One issue has been the limited number of in vitro studies providing empirical evidence for associations between microwear pattern and chewing behavior. We here describe a new study using a chewing simulator, the BITE Master II, to examine the effects of angle of approach between opposing teeth and food consistency on microwear surface texture. Results indicate that opposing teeth that approach one another: 1) perpendicular to the occlusal plane (crushing) result in pits; 2) parallel to the occlusal plane (shearing) result in striations in the direction of movement; and 3) oblique to the occlusal plane (45°) result in both striations and pits. Results further suggest that different food types and abrasive loads affect the propensity to accumulate microwear features independent of feature shapes.

Controlled feeding trials with ungulates: a new application of in vivo dental molding to assess the abrasive factors of microwear

Microwear, the quantification of microscopic scratches and pits on the occlusal surfaces of tooth enamel, is a commonly used as a paleodietary proxy. For ungulates (hoofed mammals), scratch-dominant microwear distinguishes modern grazers from browsers, presumably as a result of abrasion from grass phytoliths (biogenic silica). However, it is also likely that exogenous grit (i.e., soil, dust) is a contributing factor to these scratch-dominant patterns, which may reflect soil ingestion that varies with feeding height and/or environmental conditions (e.g., dust production in open and/or arid habitats). This study assesses the contribution of exogenous grit to tooth wear by measuring the effects of fine- and medium-grained silica sand on tooth enamel using a novel live animal tooth molding technique. This study therefore constitutes the first controlled feeding experiment using ungulates and the first in vivo experiments using abrasives of different sizes. Four sheep were fed three diet treatments: 1) a mixture of Garrison and Brome hay (control), 2) hay treated with fine-grained silica sand (180–250 µm), and 3) hay treated with medium-grained silica sand (250–425 µm). We found a significant increase in pit features that was correlated with an increase in grain size of grit, corroborating earlier chewing simulation experiments that produced pits through grit-induced abrasion (i.e., the ‘grit effect’). Our results support an interpretation of large silica grains fracturing to create smaller, more abundant angular particles capable of abrasion, with jaw movement defining feature shape (i.e., scratch or pit).

Mechanisms and causes of wear in tooth enamel: implications for hominin diets

The wear of teeth is a major factor limiting mammalian lifespans in the wild. One method of describing worn surfaces, dental microwear texture analysis, has proved powerful for reconstructing the diets of extinct vertebrates, but has yielded unexpected results in early hominins. In particular, although australopiths exhibit derived craniodental features interpreted as adaptations for eating hard foods, most do not exhibit microwear signals indicative of this diet. However, no experiments have yet demonstrated the fundamental mechanisms and causes of this wear. Here, we report nanowear experiments where individual dust particles, phytoliths and enamel chips were slid across a flat enamel surface. Microwear features produced were influenced strongly by interacting mechanical properties and particle geometry. Quartz dust was a rigid abrasive, capable of fracturing and removing enamel pieces. By contrast, phytoliths and enamel chips deformed during sliding, forming U-shaped grooves or flat troughs in enamel, without tissue loss. Other plant tissues seem too soft to mark enamel, acting as particle transporters. We conclude that dust has overwhelming importance as a wear agent and that dietary signals preserved in dental microwear are indirect. Nanowear studies should resolve controversies over adaptive trends in mammals like enamel thickening or hypsodonty that delay functional dental loss.

Dental evidence for the diets of Plio-Pleistocene hominins

Diet is fundamental to the interaction between an organism and its environment, and is therefore an important key to understanding ecology and evolution. It should come as no surprise then that paleoanthropologists have put a great deal of effort into reconstructing the diets of Plio-Pleistocene hominins. Most of this effort has focused on teeth; these durable parts of the digestive system are usually the most commonly preserved elements in vertebrate fossil assemblages. In this article, I review much of this work. Tooth size, occlusal morphology, enamel thickness, and microstructure provide evidence for the physical properties of the foods to which a species was adapted. Dental microwear can offer insights into the properties of foods that an individual ate on a day-to-day basis. Taken together, these lines of evidence can offer important insights into early hominin food choices and adaptations. New methods of analysis and theoretical perspectives are improving our understanding of the diets of Australopithecus, Paranthropus, and early Homo, and promise further progress long into the future.

Phase transformation of plasma-sprayed hydroxyapatite coating with preferred crystalline orientation

Highly oriented hydroxyapatite coatings (HACs) were obtained on titanium substrates through a radio-frequency thermal plasma spraying (TPS) method. XRD patterns showed that the HACs had crystallites with [001] preferred orientation vertical to the coating's surface. XRD results also indicated that tetracalcium phosphate crystallites in the as-sprayed HAC were oriented in the (100) direction. XRD peaks corresponding to tetracalcium phosphate, tricalcium phosphate and calcium oxide were absent after heat and hydrothermal treatment. The orientation degree of the HAC was influenced little by such post-heat treatments. Considering the crystallographic relationship between the tetracalcium phosphate in the as-sprayed HAC and the HA crystallites formed in the heat-treated HAC, these XRD results indicate that the tetracalcium phosphate in the as-prepared coatings transformed topotaxially into HA during the post-heat treatment. TEM and SEM analyses of the highly oriented HAC were conducted. The characteristic lamellar structure of TPS deposits was observed in cross-sections of the HAC. A prismatic texture was also observed in magnified SEM images. TEM observation showed that 200-800-nm-wide prismatic crystallites were formed in HA splats, and their longitudinal axis was oriented vertically to the coating's surface. SAD patterns showed that the longitudinal axis of the prismatic crystallites corresponded to the [001] zone axis of the HA crystal.

Inferring parrotfish (Teleostei: Scaridae) pharyngeal mill function from dental morphology, wear, and microstructure

Morphology, occlusal surface topography, macrowear, and microwear features of parrotfish pharyngeal teeth were investigated to relate microstructural characteristics to the function of the pharyngeal mill using scanning electron microscopy of whole and sectioned pharyngeal jaws and teeth. Pharyngeal tooth migration is anterior in the lower jaw (fifth ceratobranchial) and posterior in the upper jaw (paired third pharyngobranchials), making the interaction of occlusal surfaces and wear-generating forces complex. The extent of wear can be used to define three regions through which teeth migrate: a region containing newly erupted teeth showing little or no wear; a midregion in which the apical enameloid is swiftly worn; and a region containing teeth with only basal enameloid remaining, which shows low to moderate wear. The shape of the occlusal surface alters as the teeth progress along the pharyngeal jaw, generating conditions that appear suited to the reduction of coral particles. It is likely that the interaction between these particles and algal cells during the process of the rendering of the former is responsible for the rupture of the latter, with the consequent liberation of cell contents from which parrotfish obtain their nutrients.

Brief Communication: Intertooth and intrafacet dental microwear variation in an archaeological sample of modern humans from the Jordan Valley

Dental microwear was recorded in a Bronze-Iron Age (3570-3000 BP) sample of modern humans recovered from Tell es-Sa'idiyeh in the Jordan Valley. Microwear patterns were compared between mandibular molars, and between the upper and lower part of facet 9. The comparison revealed a greater frequency of pits and shorter scratches on the second and third molars, compared to the first. Pit frequency also increased on the lower part of the facet on the first molar, compared to the upper part. These results support previous calls for standardization when selecting a molar type for a diet-microwear study. Otherwise the microwear variations along the tooth row could mask any diet-microwear correlations. The results also suggest that there may be a need to choose a consistent location on a facet in order to enhance comparability among studies.

Effect of prism orientation and loading direction on contact stresses in prismatic enamel of primates: Implications for interpreting wear patterns

The ability of prisms to effectively dissipate contact stress at the surface will influence wear rates in teeth. The aim of this investigation was to begin to quantify the effect of prism orientation on surface stresses. Seven finite element models of enamel microstructure were created, each model differing in the angulation of prism orientation with regard to the wear surface. For validation purposes, the mechanical behavior of the model was compared with published experimental data. In order to test the enamel under lateral loads, a compressed food particle was dragged across the surface from the dentino-enamel junction (DEJ) towards the outer enamel surface (OES). Under these conditions, tensile stresses in the enamel model increased with increases in the coefficient of friction. More importantly, stresses were found to be lowest in models in which the prisms approach the surface at lower angles (i.e., more obliquely cut prisms), and highest when the prisms approached the surface at 60 degrees (i.e., less obliquely cut). Finally, the direction of travel of the simulated food particle was reversed, allowing comparison of the difference in behavior between trailing and leading edge enamels (i.e., when the food particle was dragged either towards or away from the DEJ). Stresses at the trailing edge were usually lower than stresses at the leading edge. Taken together with what is known about prism orientation in primate teeth, such findings imply greater wear resistance at the intercuspal region and less wear resistance at the lateral enamel at midcrown. Such findings appear to be supported by archeological evidence.

Error rates in dental microwear quantification using scanning electron microscopy

There is a degree of correlation between dietary habits and dental microwear in extant primates, and this has enabled inferences to be made about prehistoric diets. Several techniques have been used to quantify microwear, but the comparability of results derived from each has not been demonstrated. Moreover, neither intra- nor interobserver error rates in microwear quantification have been documented to date. We here assess intra- and interobserver error using Microware 4.0, and evaluate intertechnique comparability using the three methods that have been most widely employed in the field. This study documents an overall intraobserver error rate of about 7%, and an overall interobserver error rate of some 9%. Both intra- and interobserver error appears to be influenced substantially by the nature of the micrograph being measured. In no instance did the results obtained by different observers using Microware 4.0 differ significantly, and there was a reasonable degree of interobserver consistency in the rank ordering of micrographs in relation to any given parameter. The results obtained through the use of different quantitative techniques differed significantly, with an overall intertechnique error rate of approximately 19%. Several variables, including differences in magnification factor, scanning electron microscope kV settings, and specimen-detector relationships undoubtedly contribute to the differences among the three methods, but we were not able to assess their relative importance. Microwear quantification permits distinctions between broad dietary categories, but the margin of intra- and interobserver error should be taken into account when defining pattern differences between populations (or species) or when documenting seasonally mitigated differences within a taxon. In view of the error introduced by the use of different methods, we suggest that a consistent technique, such as offered by the Microware software package, be adopted by current researchers to establish a common microwear database.

Dental microwear evidence for a dietary shift between two nonmaize-reliant prehistoric human populations from Indiana

Several recent studies have demonstrated the efficacy of dental microwear analysis (DMA) for dietary reconstruction among nonhuman primates, early hominids, and prehistoric humans. The current study seeks microwear evidence for a paleobotanically suggested change in the types of foods that were consumed by two temporally distinct populations of the North American eastern woodlands. This particular dietary shift between the Late Archaic and the Early/Middle Woodland periods did not include the introduction of maize or any other tropical cultigen. In contrast, most dietary reconstructions from this area have compared later populations that consumed tropical cultigens (such as maize) with those that did not. High-resolution casts of adult mandibular second molar protoconid phase II wear facets were viewed via a scanning electron microscope at 500x. Photomicrographs of the microwear features were analyzed with specialized software, Microware 2.2 (Ungar [1995] Scanning 17:57-59). Analysis of variance statistical tests were performed, with one variable requiring rank-transformation. A dietary transition is evidenced by a statistically significant increase in the mean number of pits and concomitant decreases in scratch width and scratch length from the Late Archaic to the Early/Middle Woodland. Overall, the diet became harder and less abrasive. The implication here is that dental microwear analysis is able to discern relatively subtle dietary transitions in human populations that may not be as readily accessible by other means of dietary reconstruction.

Incisor microwear, diet, and tooth use in three Amerindian populations

Incisor microwear patterns have been shown to reflect aspects of diet and ingestive behaviors in a wide range of nonhuman primates. While some studies have suggested that anterior dental microwear might be used to infer unusual front tooth use practices in archaeological populations, quantitative work on modern human incisors has thus far been limited. In this study we examined dental microwear on the maxillary central incisors of three groups of humans: Aleutian Islanders (n = 16), Arikara from the Mobridge Site in South Dakota (n = 15), and a Late Woodland Bluff sample from Jersey County, Illinois (n = 17). High-resolution replicas were prepared and examined by scanning electron microscopy following conventional procedures. Photomicrographs were taken at consistent locations on the labial surface, and microwear was quantified using Microware 3.0 (Ungar, 1997). Statistical test results revealed significant differences among the groups in microwear feature densities, sizes, and shapes. The Aleut, Arikara, and Illinois Bluff samples showed a gradient of increasing microwear density, increasing linearity in feature shape, and decreasing feature size. These differences evidently correspond to amount of meat consumption, and apparently to degree of use of the incisors in heavy loading. No differences were observed between groups in heterogeneity of feature orientations, and no sex-related differences were found. Associations between incisor microwear on the one hand and subsistence practice and anterior tooth use on the other likely have important implications for the study of hominid paleobiology.

Dental microwear of Griphopithecus alpani

The examination of microscopic dental wear allows inferences to be made about diet in extinct species. This study reconstructs the diet of Griphopithecus alpani, a 15 Ma fossil hominoid from the Miocene site of Paşalar in north-western Turkey, using scanning electron microscopy (SEM) to examine the microscopic wear on its molar teeth. The microwear patterns of Griphopithecus are compared with those of three extant hominoid taxa-Gorilla gorilla gorilla, Pan troglodytes verus, and Pongo pygmaeus pygmaeus. The microwear on three occlusal wear surfaces is examined in this study, and sex and age differences are also included. Analysis of variance is performed on the following microwear variables-feature density, pit density, striation density, the ratio of pits relative to striations, pit widths, and striation widths. Griphopithecus has significantly higher microwear feature densities and higher percentages of pits than Gorilla. It also has larger pit frequencies and narrower striations than both Pan and Gorilla. There are no significant differences between the microwear patterns of Griphopithecus and Pongo. This suggests that the diet of Gripho-pithecus was more similar to that of Pongo, which consumes mainly fruit, and occasionally hard and unripe fruits and nuts, than to that of Pan and Gorilla. In addition, the high percentage of pits displayed by Griphopithecus may indicate that it was ingesting harder fruits and/or objects than the extant hominoids, although this is not a significant difference. There also are consistent variations in the microwear present on the three different wear facets examined in the study-Phase II facets display more microwear and pitting than the Phase I surface examined. The results of this study do not indicate variation in dental microwear according to sex or age.

Thegosis--a critical review

The evidence for tooth sharpening has been examined and it has been concluded that there is no evidence for a posterior tooth sharpening mechanism which is independent of masticatory function and improves the efficiency of that function. Anterior tooth sharpening may occur in some species as behavioural activity but it is not accepted that this sharpening is directed towards the production of new incisiform weapons as distinct from the improvement of existing caniniform weapons, or more efficient tools for the manipulation of food. Thegosis (from the Greek, thego to whet or sharpen) is a term which could be used to describe the sharpening of anterior teeth under specific often socially context driven situation. Stress is accepted as a cause of non-masticatory tooth to tooth contact as is the suggestion that excessive tooth grinding and clenching is pathological and stress related. Bruxism and pathological thegosis are suggested synonymous terms for this activity.

Dental microwear and microstructure in early oligocene primates from the Fayum, Egypt: implications for diet

Textbook descriptions usually portray the Fayum anthropoideans as frugivores, with Parapithecus grangeri including a folivorous component in its diet and Apidium a component of hard-object feeding. Recent work with modern mammals has shown that analyses of both dental microwear and dental microstructure may yield insights into diet and tooth use. The purpose of this study was to combine these two techniques to gain a better perspective on the paleobiology of the Fayum higher primates. Dental microwear analyses involved the use of high resolution epoxy casts of Aegyptopithecus, Parapithecus, and Apidium housed in the Duke University Primate Center. Scanning electron micrographs were taken at x500, and all microwear features in each micrograph were digitized. For microstructure analyses, molar teeth were sectioned in a variety of planes, lightly etched, and photographed in the SEM. Results of the dental microwear analyses indicate that the three Fayum anthropoideans all clustered with modern primate frugivores but that there were also significant differences between Aegyptopithecus and the other two Fayum genera. By contrast, dental microstructure analyses showed important differences between Apidium and the other two genera. The reason for these differences probably lies in a combination of body size and dietary differences, with Aegyptopithecus occasionally feeding on hard objects and Apidium maximizing wear resistance through a unique emphasis of radial (rather than decussating) enamel.