Three-Dimensional Surface Texture Characterization of In Situ Simulated Erosive Tooth Wear.

This in situ erosive tooth wear (ETW) study tested enamel 3-dimensional (3D) surface texture outcomes for the detection and differentiation of ETW lesions simulated in clinically relevant conditions. Twenty participants enrolled in this 3-arm crossover intraoral ETW simulation and wore their own partial denture for 14 d holding 2 human enamel specimens (per arm). In each arm, participants were assigned to 1 of 3 different dental erosion protocols: severe (lemon juice/pH 2.5), moderate (grapefruit juice/pH 3.5), and no erosion (bottled drinking water, control). Enamel specimens were evaluated by white-light scanning confocal profilometry for 3D surface texture and surface loss (ETW model validation). Individual point clouds were analyzed using standard dental microwear texture characterization protocols for surface roughness and anisotropy. Fractal complexity (Asfc), texture aspect ratio (Str), and arithmetical mean height (Sa) values were generated at baseline, 7 d, and 14 d. Data were analyzed by analysis of variance models suitable for the crossover design with repeated measurements, and correlation coefficients were used to examine the relationship between outcomes. Asfc and Sa differentiated ETW severity (no erosion < moderate < severe, P < 0.001) at days 7 and 14. Asfc and Sa were lower at baseline compared to days 7 and 14 (P < 0.001) for moderate and severe challenges. Asfc increased from day 7 to 14 (P = 0.042) for the severe challenge. For Str, ETW severity did not have a significant effect overall (P = 0.15). Asfc and Sa were highly positively correlated (r = 0.89, P < 0.001), while Asfc and Sa were not correlated overall with Str (r < 0.1, P ≥ 0.25). Enamel surface loss increased with ETW severity (no erosion < moderate < severe, P < 0.001) at days 7 and 14, validating the ETW simulation model. Complexity (Asfc) and roughness (Sa) outcomes were able to detect and differentiate ETW levels, with Asfc being able to monitor the progression of severe lesions. No clear characterization of ETW lesions could be provided by the anisotropy (Str) parameter.

Inference of Diets of Early Hominins from Primate Molar Form and Microwear.

Paleontologists use fossil teeth to reconstruct the diets of early hominins and other extinct species. Some evidence is adaptive: nature selects for tooth size, shape, and structure best suited to specific food types. Other evidence includes traces left by actual foods eaten, such as microscopic tooth wear. This critical review considers how molars work, how they are used, and how occlusal topography and dental microwear can be used to infer diet and food preferences in the past, particularly for hominins of the Pliocene and early Pleistocene. Understanding that cheek teeth function as guides for chewing and tools for fracturing allows us to characterize aspects of occlusal form that reflect mechanical properties of foods to which a species is adapted. Living primates that often eat leaves, for example, have longer crests and more sloping occlusal surfaces than those that prefer hard foods. Studies of feeding ecology have shown, however, that tooth shape does not always correspond to preferred food items. It often follows mechanically challenging foods whether eaten often or rarely. Other lines of evidence that reflect actual tooth use are required to work out food preferences. Microwear textures, for example, reflect foods eaten by individuals in the past such that hard seeds and bone tend to leave complex, pitted surface textures, whereas tough leaves and meat more often leave anisotropic ones covered in long, parallel scratches. The study of fossil hominin molars shows how these various attributes are combined to infer diet and food preference in the past. A trend in occlusal morphology suggests decreased dietary specialization from Australopithecus to early Homo, and increasing dispersion in microwear complexity values is consistent with this. On the other hand, occlusal morphology may suggest dietary specialization in Paranthropus, although different species of this genus have different microwear texture patterns despite similar craniodental adaptations.

Dental Surface Texture Characterization Based on Erosive Tooth Wear Processes.

The differential diagnosis of dental wear lesions affects their clinical management. We hypothesized that surface texture parameters can differentiate simulated erosion, abrasion, and erosion-abrasion lesions on human enamel and dentin. This in vitro study comprised 2 parts (both factorial 4 × 2), with 4 lesion types (erosion, abrasion, erosion-abrasion, and sound [no lesion; control]) and 2 substrates (enamel and dentin). Flattened/polished dental specimens were used in part 1, whereas natural dental surfaces were used in part 2. Testing surfaces were evaluated in blind conditions, using average surface roughness (Sa) and the following scale-sensitive fractal analysis parameters: area-scale fractal complexity (Asfc), exact proportion length-scale anisotropy of relief (eplsar), scale of maximum complexity (Smc), and textural fill volume (Tfv). Two-way analyses of variance, followed by Fisher's protected least significant difference tests (α = 0.05), were used to evaluate the effects of lesion and substrate. Classification trees were constructed to verify the strength of potential associations of the tested parameters. In part 1,Asfc, Sa, and Tfv were able to differentiate erosion and erosion-abrasion lesions from the sound (no lesion) control in both substrates; only Asfc differentiated erosion and erosion-abrasion enamel lesions (allP< 0.05). The best association of parameters correctly classified up to 84% and 94% of the lesions on enamel and dentin, respectively. In part 2, only Asfc differentiated erosion and erosion-abrasion lesions from the sound (no lesion) control in both substrates, whereas eplsar was able to differentiate erosion from erosion-abrasion (allP< 0.05). The association of parameters correctly classified up to 81% and 91% of the lesions in enamel and dentin, respectively.Asfc, Sa, and Tfv were able to differentiate erosion and erosion-abrasion lesions, despite their complicated surface textures. The association of parameters improved the differentiation of lesions for both enamel and dentin in polished or natural surfaces.

Dental microwear texture analysis of two families of subfossil lemurs from Madagascar.

This study employs dental microwear texture analysis to reconstruct the diets of two families of subfossil lemurs from Madagascar, the archaeolemurids and megaladapids. This technique is based on three-dimensional surface measurements utilizing a white-light confocal profiler and scale-sensitive fractal analysis. Data were recorded for six texture variables previously used successfully to distinguish between living primates with known dietary differences. Statistical analyses revealed that the archaeolemurids and megaladapids have overlapping microwear texture signatures, suggesting that the two families occasionally depended on resources with similar mechanical properties. Even so, moderate variation in most attributes is evident, and results suggest potential differences in the foods consumed by the two families. The microwear pattern for the megaladapids indicates a preference for tougher foods, such as many leaves, while that of the archaeolemurids is consistent with the consumption of harder foods. The results also indicate some intraspecific differences among taxa within each family. This evidence suggests that the archaeolemurids and megaladapids, like many living primates, likely consumed a variety of food types.

Mechanical defenses in leaves eaten by Costa Rican howling monkeys (Alouatta palliata).

Primate species often eat foods of different physical properties. This may have implications for tooth structure and wear in those species. The purpose of this study was to examine the mechanical defenses of leaves eaten by Alouatta palliata from different social groups at Hacienda La Pacifica in Costa Rica. Leaves were sampled from the home-ranges of groups living in different microhabitats. Specimens were collected during the wet and dry seasons from the same tree, same plant part, and same degree of development as those eaten by the monkeys. The toughness of over 300 leaves was estimated using a scissors test on a Darvell mechanical tester. Toughness values were compared between social groups, seasons, and locations on the leaves using ANOVA. Representative samples of leaves were also sun-dried for subsequent scanning electron microscopy and energy dispersive x-ray (EDX) analyses in an attempt to locate silica on the leaves. Both forms of mechanical defense (toughness and silica) were found to be at work in the plants at La Pacifica. Fracture toughness varied significantly by location within single leaves, indicating that measures of fracture toughness must be standardized by location on food items. Monkeys made some food choices based on fracture toughness by avoiding the toughest parts of leaves and consuming the least tough portions. Intergroup and seasonal differences in the toughness of foods suggest that subtle differences in resource availability can have a significant impact on diet and feeding in Alouatta palliata. Intergroup differences in the incidence of silica on leaves raise the possibility of matching differences in the rates and patterns of tooth wear.

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.

A review of interproximal wear grooves on fossil hominin teeth with new evidence from Olduvai Gorge.

Interproximal (approximal) grooves at the cementum-enamel junction of premolar and molar teeth have been observed in a broad range of human ancestors and related extinct species from 1.84 million years ago to the present. Many hypotheses have been presented to explain the aetiology of these grooves, though their form and positioning are most consistent with tooth-picking behaviours. This paper reviews occurrences of interproximal grooves in the cheek teeth of modern and fossil humans, evaluates hypotheses on their cause, and reports on a previously undescribed groove found in OH 60, a molar tooth from Olduvai Gorge. This specimen is among the earliest to show such grooving, and is most likely attributable to Homo erectus. It is concluded that, because interproximal grooves have been observed only on Homo teeth, they probably reflect a behaviour or behaviours unique to that genus.

Diet and the evolution of the earliest human ancestors.

Over the past decade, discussions of the evolution of the earliest human ancestors have focused on the locomotion of the australopithecines. Recent discoveries in a broad range of disciplines have raised important questions about the influence of ecological factors in early human evolution. Here we trace the cranial and dental traits of the early australopithecines through time, to show that between 4.4 million and 2.3 million years ago, the dietary capabilities of the earliest hominids changed dramatically, leaving them well suited for life in a variety of habitats and able to cope with significant changes in resource availability associated with long-term and short-term climatic fluctuations.

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.

Technical note: Modeling primate occlusal topography using geographic information systems technology.

Most functional analyses of primate tooth form have been limited to linear or area measurements. Such studies have offered but a limited glimpse at differences in occlusal relief among taxa. Such differences in dental topography may relate to tooth function and, so, have considerable implications for the inference of diet from fossil teeth. In this article, we describe a technique to model and compare primate molars in three dimensions using Geographic Resources Analysis Support System (GRASS) software. We examine unworn lower second molars of three extant hominoids with known differences in diet (Gorilla gorilla, Pan troglodytes, and Pongo pygmaeus), and two fossil forms, (Afropithecus turkanesis and Dryopithecus laietanus). First, we obtained approximately 400 landmarks on the occlusal surfaces of each tooth using an electromagnetic digitizer. Raster "terrain models" of occlusal surfaces were then created by interpolation of the coordinate data. We used GRASS terrain analysis automated techniques to quantify the volumes and slopes of individual cusps. We also used the GRASS watershed technique to identify the volume of liquid that would accumulate in each tooth's basin (a measure of basin area), and the directions and intensity of drainage over the occlusal surface. In sum, GRASS shows considerable potential for the characterization and comparison of tooth surfaces. Furthermore, techniques described here are not limited to the study of teeth, but may be broadly applicable to studies of skulls, joints, and other biological structures.

Neandertal incisor beveling.

In discussions of the Neandertals, there has been repeated emphasis on the accelerated rate of attrition and the frequent presence of labial beveling of their incisors. Interpretations of this dental attrition have related it to paramasticatory and dietary uses of their anterior teeth as well as to aspects of their facial morphology. In light of this, we examined the rate of beveling (the angle between the labial and incisal surfaces) of central incisors relative to tooth wear in samples of Neandertals, Inuits and Puebloan Amerindians. I1s show little change in the beveling angle with wear and no significant differences between the samples. I1s, however, exhibit a consistent pattern of increased beveling with dental attrition, progressing rapidly until the crown height approximates its labiolinguinal cervical diameter, and then proceeding at a slower rate. All three samples exhibit a similar pattern. However, the Neandertals have significantly greater beveling in more worn teeth than either recent human sample, and the Inuits have nonsignificantly increased beveling relative to the Puebloans in these more worn I1s. In this, it is the degree of development of beveling, not the pattern of beveling, which differentiates the Neandertals. It is hypothesized that the differences between the Neandertals and recent samples could be the product of: (1) contrast in initial incisor procumbency, (2) a labial separation of the maxillary and mandibular incisal occlusal surfaces during edge-to-edge bite, and/or (3) a greater degree of interproximal wear promoting increased "posterior tipping" of the maxillary incisors. The last appears most likely.

Preliminary examination of non-occlusal dental microwear in anthropoids: implications for the study of fossil primates.

Most studies of microscopic wear on non-human primate teeth have focused on the occlusal surfaces of molars. Recent analyses of the buccal surfaces of human cheek teeth have demonstrated an association between diet and dental microwear on the these surfaces as well. In the current study, we examine microwear on both the buccal and lingual surfaces of non-human primate molars to assess the potential of these surfaces to reveal information concerning anthropoid feeding behaviors. We compare frequency of microwear occurrence in 12 extant and 11 fossil anthropoid species. Among the living primates, the occurrence of microwear on nonocclusal surfaces appears to relate to both diet and degree of terrestriality. The implications of this research for the inference of feeding behaviors and substrate use in fossil cercopithecoids are discussed.

Dust accumulation in the canopy: a potential cause of dental microwear in primates.

Dental microwear researchers consider exogenous grit or dust to be an important cause of microscopic wear on primate teeth. No study to date has examined the accumulation of such abrasives on foods eaten by primates in the forest. This investigation introduces a method to collect dust at various heights in the canopy. Results from dust collection studies conducted at the primate research stations at Ketambe in Indonesia, and Hacienda La Pacifica in Costa Rica indicate that 1) grit collects throughout the canopy in both open country and tropical rain forest environments; and 2) the sizes and concentrations of dust particles accumulated over a fixed period of time differ depending on site location and season of investigation. These results may hold important implications for the interpretation of microwear on primate teeth.

The dietary adaptations of European Miocene catarrhines.

European Miocene "apes" have been known for nearly a century and a half but their phylogenetic significance is only now becoming apparent with the recent discovery of many relatively complete remains. Some appear to be close in time and morphology to the last common ancestor of modern great apes and humans. The current study is an attempt to reconstruct the diets of these fossils on the basis of quantitative data. Results suggest that these primates varied more greatly in their diets than modern apes, with adaptations ranging from hard-object feeding to soft-object frugivory to folivory.

A semiautomated image analysis procedure for the quantification of dental microwear II.

Paleontologists often examine microscopic scratches and pits that form on teeth for indications of the diets of past animals. Most researchers count and measure scratches and pits from photomicrographs to identify microwear patterns for comparison among samples. This paper describes an affordable, available semiautomated image analysis procedure for microwear quantification. An image is downloaded from a scanning electron microscope frame buffer to a microcomputer, and the user identifies microwear features with a mouse-driven pointer. Microwear feature density, dimensions, and orientations are then computed and stored as ASCII files for subsequent data analysis.

Patterns of ingestive behavior and anterior tooth use differences in sympatric anthropoid primates.

Little research has been directed towards the examination of ingestive behaviors in wild primates. This paper describes a naturalistic study of anterior tooth use in four sympatric anthropoid species: Hylobates lar, Macaca fascicularis, Pongo pygmaeus, and Presbytis thomasi. Instantaneous group scan data were collected during nearly 1,800 hours of observation between August 1990 and July 1991 at the Ketambe Research Station in the Gunung Leuser National Park, Sumatra, Indonesia. Ingestive behaviors are documented for specific food items and compared among the primate taxa. Results indicate significant differences among the species in preferred methods of food ingestion. These differences are related in part to dietary differences, and in part to other aspects of each primate's biology and ecology.

Incisor microwear of Sumatran anthropoid primates.

Several studies have suggested that incisor microwear reflects diet and feeding adaptations of anthropoids. However, such studies have been largely qualitative, and interpretations have relied on anecdotal references to diet and tooth use reported in the socioecology literature. The current study relates incisor microwear in four anthropoid primates to specific ingestive behaviors and food types. Central incisor casts of wild-shot museum specimens of Hylobates lar, Macaca fascicularis, Pongo pygmaeus, and Presbytis thomasi were examined by scanning electron microscopy, and analyzed using a semiautomated image analysis procedure. Microwear patterns were used to generate predictions regarding diet and anterior tooth use. These predictions were evaluated using data collected during a 1 year study of feeding behavior of these same taxa in the wild (Ungar, 1992, 1994a,b). Results suggest that (1) enamel prism relief is associated with the effectiveness of etching reagents in foods, (2) dental calculus buildup results from a lack of incisor use and perhaps the ingestion of sugar-rich foods, (3) striation density varies with degree of anterior tooth use in the ingestion of abrasive food items, (4) striation breadth is proposed to relate to the ratio of exogenous grit to phytoliths consumed; and (5) preferred striation orientation indicates the direction that food items are pulled across the incisors during ingestion. It is concluded that incisor microwear studies can contribute to the understanding of diets and feeding behaviors of extinct primates.

Reanalysis of the Lukeino molar (KNM-LU 335).

This paper details a reanalysis of KNM-LU 335, a hominoid mandibular first molar dated to about 6 Ma from the Lukeino Formation, Kenya. Researchers have argued that this molar closely resembles those of modern chimpanzees and may approximate the ancestral morphotype of humans and chimpanzees. The investigation presented here describes a morphometric study of the Lukeino molar and M1s of Homo sapiens, Pan troglodytes, and early australopithecines. Results indicate that KNM-LU 335 differs from both human and chimpanzee M1s in relative distances (measured in three dimensions) between crown fissure termini. Further, the Lukeino molar shares with early australopithecines a pronounced flaring of the buccal surface of the crown not seen for either modern sample. Results of this study do not exclude KNM-LU 335 as a potential ancestral morphotype for Pan and Homo but provide no evidence that this morphotype resembled modern chimpanzees.