Geometric morphometric analyses of worn cheek teeth help identify extant and extinct gophers (Rodentia,Geomyidae)

Studies of the biostratigraphy and palaeoecology of fossil vertebrate assemblages require large samples of accurately identified specimens. Such analyses can be hampered by the inability to assign isolated and worn remains to specific taxa. Entoptychine gophers are a diverse group of burrowing rodents found in Oligo‐Miocene deposits of the western United States. In both entoptychines and their extant relatives the geomyines, diagnostic characters of the occlusal surface of the teeth are modified with wear, making difficult the identification of many isolated fossil teeth. We use geometric morphometrics to test the hypothesis that tooth shape informs taxonomic affinities and expected levels of morphological variation across gopher taxa. We also incorporate data from microcomputer tomography to investigate changes in occlusal surface shape through wear within individuals. Our analyses demonstrate the usefulness of our approach in identifying extant geomyines to the genus, subgenus and species levels, and fossil entoptychines to the genus and, in some cases, the species level. Our results cast doubt on the validity of some species within Entoptychus and suggest future revisions to entoptychine taxonomy. The amounts of morphological divergence observed among fossil and extant genera are similar. Fossil species do not differ greatly from extant ones in that regard either. Further work evaluating the morphological variation within and across entoptychine species, including unworn teeth and osteological material, will allow revised analyses of the biostratigraphy and palaeoecology of important Oligo‐Miocene mammalian assemblages of the western United States and help to infer the phylogenetic relationships and evolution of gophers.     

Seasonal variation in molar outline of bank voles: An effect of wear?

Morphometric characters can be of use for elucidating the evolutionary history of species by providing an insight into the selective pressure related to the character of interest, and by allowing integration of fossil specimens. This potential interest of phenotypic characters, however, depends on how much other sources of variation, such as the life-history of the animal, may blur an evolutionary signal. For instance, age structure varies along the year, causing in turn various assemblages of wear stages in the teeth sampled at a given place and time. In this context, we investigated the season of trapping as potential source of variation in the size and shape of the molar occlusal surface of the bank vole, Clethrionomys glareolus.The size and shape of the occlusal surface of the third upper molar was quantified using outline analysis in 60 bank voles from Finland, trapped at the same study site in successive spring and autumn. The occlusal surface clearly differed in size and shape between the two seasons of trapping. Using 3D imaging as a visual support, we interpret this difference as the result of differential wear. The population in autumn is dominated by young specimens with unworn teeth whereas spring populations are composed of old animals with worn down molars. The range of seasonal variation in tooth size and shape appears to be of the same order of magnitude as biogeographic variation, demonstrating that differential wear may have a strong impact on biogeographic and evolutionary studies. Yet, beyond the effect of trapping season, a biogeographic signal still emerged, related to the genetic lineages evidenced in other studies. In consequence, morphometric characters such as size and shape of molar occlusal surfaces appear as valuable tracers of biogeographic differentiation, but future studies should take seasonal variations into account for more robust interpretation.     

To What Extent is Primate Second Molar Enamel Occlusal Morphology Shaped by the Enamel-Dentine Junction?

The form of two hard tissues of the mammalian tooth, dentine and enamel, is the result of a combination of the phylogenetic inheritance of dental traits and the adaptive selection of these traits during evolution. Recent decades have been significant in unveiling developmental processes controlling tooth morphogenesis, dental variation and the origination of dental novelties. The enamel-dentine junction constitutes a precursor for the morphology of the outer enamel surface through growth of the enamel cap which may go along with the addition of original features. The relative contribution of these two tooth components to morphological variation and their respective response to natural selection is a major issue in paleoanthropology. This study will determine how much enamel morphology relies on the form of the enamel-dentine junction. The outer occlusal enamel surface and the enamel-dentine junction surface of 76 primate second upper molars are represented by polygonal meshes and investigated using tridimensional topometrical analysis. Quantitative criteria (elevation, inclination, orientation, curvature and occlusal patch count) are introduced to show that the enamel-dentine junction significantly constrains the topographical properties of the outer enamel surface. Our results show a significant correlation for elevation, orientation, inclination, curvature and occlusal complexity between the outer enamel surface and the enamel dentine junction for all studied primate taxa with the exception of four modern humans for curvature (p<0.05). Moreover, we show that, for all selected topometrical parameters apart from occlusal patch count, the recorded correlations significantly decrease along with enamel thickening in our sample. While preserving tooth integrity by providing resistance to wear and fractures, the variation of enamel thickness may modify the curvature present at the occlusal enamel surface in relation to enamel-dentine junction, potentially modifying dental functionalities such as blunt versus sharp dental tools. In terms of natural selection, there is a balance between increasing tooth resistance and maintaining efficient dental tools. In this sense the enamel cap acts as a functional buffer for the molar occlusal pattern. In primates, results suggest a primary emergence of dental novelties on the enamel-dentine junction and a secondary transposition of these novelties with no or minor modifications of dental functionalities by the enamel cap. Whereas enamel crenations have been reported by previous studies, our analysis do not support the presence of enamel tubercles without dentine relief nuclei. As is, the enamel cap is, at most, a secondary source of morphological novelty.     

The Neanderthalian molar from Hunas, Germany.

In this paper, we present a well-preserved isolated human molar found in 1986 in the Hunas cave ruin, south-east Bavaria. The tooth was located at the bottom of layer F2, which belongs to a long stratigraphic sequence comprising faunal remains as well as archaeological levels (Mousterian). A stalagmite from layer P at the base of the stratigraphic sequence was recently dated to 79.373+/-8.237 ka (base) and 76.872+/-9.686 ka (tip) by TIMS-U/Th (Stanford University). We identified the tooth as a right (possibly third) mandibular molar. Characteristic parameters such as crown and root morphology, fissure pattern, enamel thickness, occlusal and interproximal wear, dental dimensions and indices, and radiological features indicate that the Hunas molar represents the tooth of a Neanderthal. This is corroborated by both the palaeontological and archaeological findings (Mousterian) of layer F2.     

A dental topographic analysis of chimpanzees

Molar tooth morphology is generally said to reflect a compromise between phylogenetic and functional influences. Chimpanzee subspecies have been reported to exhibit differences in molar dimensions and nonmetric traits, but these have not been related to differences in their diets. And in fact, observations to date of the diets of chimpanzees have not revealed consistent differences among subspecies. This study uses dental topographic analyses shown to reflect diet-related differences in occlusal morphology among primate species, to assess within-species variation among chimpanzee subspecies. High-resolution casts from museum collections were examined by laser scanning, and resulting data were analyzed using GIS algorithms and a two-factor ANOVA model. Although differences were noted between wear stages within subspecies in surface slope, relief, and angularity, none were found to distinguish the subspecies from one another in these attributes. This might reflect limitations in the ability of this method to detect diet-related differences, but is also consistent with a lack of differences in functionally relevant aspects of occlusal morphology among chimpanzee subspecies.     

Brief communication: Identification reassessment of the isolated tooth Krapina D58 through occlusal fingerprint analysis

High variability in the dentition of Homo can create uncertainties in the correct identification of isolated teeth. For instance, standard tooth identification criteria cannot determine with absolute certainty if an isolated tooth is a second or third maxillary molar. In this contribution, using occlusal fingerprint analysis, we reassess the identification of Krapina D58 (Homo neanderthalensis), which is catalogued as a third maxillary molar. We have hypothesized that the presence/absence of the distal occlusal wear facets can be used to differentiate second from third maxillary molars. The results obtained confirm our hypothesis, showing a significant difference between second and third maxillary molars. In particular we note the complete absence of Facets 7 and 10 in all third molars included in this analysis. The presence of these facets in Krapina D58 eliminates the possibility that it is a third maxillary molar. Consequently it should be reclassified as a second molar. Although this method is limited by the degree of dental wear (i.e., unworn teeth cannot be analyzed) and to individual molars in full occlusion, it can be used for tooth identification when other common criteria are not sufficient to discriminate between second and third maxillary molars. Am J Phys Anthropol 143:306–312, 2010. © 2010 Wiley‐Liss, Inc.     

Technical note: Occlusal fingerprint analysis: Quantification of tooth wear pattern

Information about food ingestion and mastication behavior during the lifespan of an individual is encoded in the dental occlusal wear pattern. To decode this information, we describe a new method called occlusal fingerprint analysis (OFA). Structural parameters of wear facets on the occlusal surface of teeth are quantified from digitized casts for the interpretation of occlusal aspects. The OFA provides an individual three‐dimensional dental occlusal compass that indicates the major pathways of interaction between antagonists, revealing information about development, spatial position, and enlargement of wear facets. Humans develop a very similar overall pattern of crown contacts, although specific characteristics of wear facets reflect an individual's occlusal relationships and masticatory behavior. We hypothesize that the wear pattern is a unique character and therefore valuable for individual identification. Furthermore we suggest that OFA, when further developed, may be useful for identification of behavioral, biological, and chemical factors affecting crown morphology. Am J Phys Anthropol, 2009. © 2009 Wiley‐Liss, Inc.     

Ontogenetic variation in occlusal shape of evergrowing molars in voles: An intravital study in Microtus gregalis (Arvicolinae,Rodentia)

In order to reveal patterns of ontogenetic change in occlusal shape of evergrowing molars in arvicolines, an intravital tooth printing method was applied to 20 individuals of Microtus gregalis born in captivity. Complexity patterns of the first lower molar were assessed by morphotype analysis of the anteroconid complex. Morphotype dental patterns were monitored using tooth prints at 0.5, 1, 2, 3 months of age, and postmortem. Ontogenetic changes in molar complexity and bilateral symmetry among right and left molars of the same individual during the process of tooth wear were assessed. Our results suggested that morphotype dental patterns could not be clearly established in half-month old animals due to presence of juvenile characters. For animals of 1 month and older, age differences in morphotype dental patterns were non-significant and negligible compared to among-individual variation. Within-individual differences among right and left molars, when present, were not related to age of an animal suggesting that bilateral asymmetry of morphotype dental pattern could be regarded as inherent characteristic of an individual persisting during post-juvenile tooth wear.     

Population systematics of chimpanzees using molar morphometrics

When dental morphological variation within extant species is used as a guideline to partition variation within fossil samples into species, the underlying assumption is that fossil species are equivalent to extant species. This is the case despite the fact that dental morphology, which is commonly used to differentiate fossil species, is rarely used to differentiate extant species. Aspects of external morphology, ecology, behavior, breeding patterns, and molecular structure that are used to delineate living species are generally not available for fossils. In this paper, the utility of dental evidence for sorting fossil samples into species is evaluated by testing whether molar occlusal morphology is capable of sorting populations of Pan into the species and subspecies already well-established by nondental evidence. The dentitions of 341 chimpanzee individuals, sampled from regions throughout equatorial Africa, were sorted into 16 populations using rivers to demarcate the boundaries between populations. Digital-imaging software was used to measure 15 traits on the occlusal surface of each upper molar and 19 on each lower molar. After applying size adjustments, size-transformed and untransformed variables were subjected to discriminant analysis, with separate analyses carried out for each molar type. Results indicate that populations of Pan troglodytes and Pan paniscus are well differentiated at all molar positions. Populations of P. t. verus are distinct from other populations of P. troglodytes. Populations of P. t. troglodytes and P. t. schweinfurthii show close dental similarity. A distinct population is recognized at the Nigeria-Cameroon border, indicating the presence of P. t. vellerosus. The concordance between the patterns of diversity recognized by this study and other molecular and nonmolecular studies indicates that paleontological species that are similar to species of Pan in terms of size and patterns of diversification may be differentiated using molar morphology.     

Dietary adaptations in the teeth of murine rodents (Muridae): a test of biomechanical predictions

Functional dental theory predicts that tooth shape responds evolutionarily to the mechanical properties of food. Most studies of mammalian teeth have focused on qualitative measures of dental anatomy and have not formally tested how the functional components of teeth adapt in response to diet. Here we generated a series of predictions for tooth morphology based on biomechanical models of food processing. We used murine rodents (Old World rats and mice) to test these predictions for the relationship between diet and morphology and to identify a suite of functional dental characteristics that best predict diets. One hundred and five dental characteristics were extracted from images of the upper and lower tooth rows and incisors for 98 species. After accounting for phylogenetic relationships, we showed that species evolving plant‐dominated diets evolved deeper incisors, longer third molars, longer molar crests, blunter posteriorly angled cusps, and more expanded laterally oriented occlusal cusps than species adapting to animal‐dominated diets. Measures of incisor depth, crest length, cusp angle and sharpness, occlusal cusp orientation, and the lengths of third molars proved the best predictors of dietary adaptation. Accounting for evolutionary history in a phylogenetic discriminant function analysis notably improved the classification accuracy. Molar morphology is strongly correlated with diet and we suggest that these dental traits can be used to infer diet with good accuracy for both extinct and extant murine species.     

The relation of canine size to pattern and extent of attrition in baboons

For most genera of animals the association between dental morphology and diet is such that inferences concerning the diet can be made on the basis of the dentition alone. The canine is the one tooth that appears exempt from such generalisation and exhibits a wide range of variability of size and shape in all groups. In order to determine the effect of dimorphism of the canine on the dental apparatus, male and female specimens of Theropithecus and Papio baboons were examined. Occlusal relationships and dental pathology for 21 Theropithecus and 40 Papio skulls were recorded, and crown height measurements obtained for maxillary incisors, buccal and lingual molar cusps. Attrition was the most common and severe cause of abscess formation in older animals: the pattern of attrition differed in adult males and females, the latter showing more wear of the incisor and lingual molar cusps. Partial correlations for incisor, buccal and lingual molar cuspal crown height show a significant correlation between incisor and lingual cusp attrition in juveniles of both sexes and adult females (p < 0.01). Adult males show no correlation of attrition. It is proposed that the correlation of incisor and lingual molar cusp attrition is associated with anterior-posterior grinding movements, such as take place during incision, that the large canine present in the male limits such movements, the sharp blade-like canine being employed as a cutting tool. This use of the canine by reducing functional demands on other teeth, prolongs the utility of the dental apparatus, and hence the lifespan of its possessor.     

The study of dental occlusion in ancient skeletal remains from Mallorca (Spain): A new approach based on dental clinical practice

Occlusal characteristics, fundamental to assess the presence of malocclusion, have been often unexplored in bioarchaeological analyses. This is largely due to the fragmented condition of the skeletal remains. By applying a method that considers dental and maxillary features useful to evaluate occlusion in ancient fragmentary material, the purpose of this work is to define the occlusal features and explore the causes of malocclusion in a mediaeval population from Mallorca. The findings of this study suggest that normocclusion was present in ca. 60% of the individuals (N = 31), and that some characteristics, such as molar relationship, were slightly different from those of modern populations. The analysis of the occlusal features revealed for example that open-bite was absent in 85% of the sample, posterior open-bite was completely absent and overbite and overjet were normal in around 90% of the individuals. Statistically significant correlations between canine and molar relationships and between molar relationship and dental wear of the superior and inferior canines and incisors were observed. In addition, wear could affect the curve of Spee. All these findings strengthen the hypothesis that in ancient times malocclusion was not as generalized as in modern times. Although the factors that lead to malocclusion throughout centuries could have several causes, we suggest that in this population dental wear, which is strongly associated with the diet, was the fundamental causing factor.     

Gaining New Insights into How Genetic Factors Influence Human Dental Development by Studying Twins

Many previous attempts to quantify the contribution of genetic factors to human dental variation using the classical twin design have been based on untested assumptions that lead to unreliable estimates of heritability. We have applied structural equation modelling to several different dental phenotypes in a sample of over 600 pairs of Australian twins, enabling the goodness-of-fit of the data to be tested against genetic models incorporating different components of genetic and environmental variance. Our results indicate that the contribution of additive genetic effects to phenotypic variation differs considerably between different dental traits. Heritability estimates for intercuspal distances of molar teeth and for incisal overbite and overjet are low to moderate in magnitude, whereas heritabilities for overall molar crown size and arch dimensions are moderate to high. We propose that after formation of the enamel knots during odontogenesis, the emerging pattern of molar cusps results from a cascade of local epigenetic events, rather than being under direct genetic control. Variation in molar crown size is explained best by a model incorporating additive genetic effects, as well as environmental influences that are both unique and common to co-twins. These environmental influences presumably operate in utero during the early stages of molar odontogenesis prior to crown calcification. The relatively low heritabilities noted for occlusal traits are consistent with the importance of masticatory activity and muscle function in determining the interrelationships between teeth in opposing dental arches. We believe that well-designed studies of twins, coupled with modern genome-scanning approaches, offer great potential to identify key “dental” genes and to clarify how these genes interact with the environment during development.     

Hunter-Schreger band orientation in interproximal enamel of modern human molars with complex morphological traits

A recent paper concerning characteristic groove-shaped wear in interproximal attritional facets of Neandertal posterior teeth correlated groove formation with deep enamel structural traits (Villa & Giacobini, 1995). Further studies were carried out on modern human teeth in order to evaluate a possible correlation between deep enamel structure and some crown complex morphological features. Seventy-five isolated molars from medieval and recent ossuaries as well as five molars recently extracted for therapeutic purpose were examined using scanning electron and optic microscope ground sections of interproximal enamel. The results showed possible correlations between deep enamel structural characteristics (i.e., Hunter-Schreger band verticalization) and some crown complex traits (i.e., occlusal groove pattern, mesial and distalfovea, mesial and distal accessory tubercules, interproximal marginal ridges). Observations reported in this study showed a significantly higher frequency of Hunter-Schreger band verticalization in lower molars with an occlusal complex pattern (i.e. primitive fissure pattern “Y” or “+”). This observation suggests a positive correlation among crown complex traits (which occur frequently in Neandertal teeth) with deep enamel structural characteristics. In addition, analysis of teeth grouped according to individual showed crown morphological traits and deep enamel structural characteristics corresponding to the same individual. This observation supports a genetic basis in occlusal shape and microstructural dental traits.     

Dental trait expression at the enamel-dentine junction of lower molars in extant and fossil hominoids

Discrete dental traits are used as proxies for biological relatedness among modern human populations and for alpha taxonomy and phylogeny reconstruction within the hominin clade. We present a comparison of the expression of lower molar dental traits (cusp 6, cusp 7, trigonid crest pattern, and protostylid) at the enamel-dentine junction (EDJ) in a variety of extant and fossil hominoid taxa, in order to assess the contribution of the EDJ to the morphology of these traits at the outer enamel surface (OES). Molars (n=44) were imaged nondestructively using high-resolution microCT, and three-dimensional surface models of the EDJ and OES were created to compare trait expression at each surface. Our results indicate that these dental traits originate at the EDJ, and that the EDJ is primarily responsible for their degree of expression at the OES. Importantly, variable trait morphology at the EDJ (often not easily recognizable at the OES) indicates that different developmental processes can produce traits that appear similar at the enamel surface, suggesting caution in intra- and intertaxonomic comparisons. The results also highlight the importance of the EDJ for understanding the morphological development of discrete traits, and for establishing graded scales of variation to compare trait frequency among groups for the purpose of taxonomic and/or phylogenetic analysis. Finally, this study demonstrates that imaging the EDJ of both worn and unworn fossil hominin teeth provides a novel source of information about tooth development and variation in crown morphology.     

Dental wear and oral pathology: possible evidence and consequences of habitual use of teeth in a Swedish Neolithic sample

Atypical wear and oral lesions were studied in the dental remains from the Middle Neolithic Pitted Ware Culture site Ajvide on the island of Gotland in the Baltic Sea. Teeth (n = 764) from 17 males and 11 females were examined microscopically to document unusual wear, assess wear patterns and oral lesions as evidence of habitual behavior, and determine their effect on the oral health of this population. Five atypical wear types were observed: occlusal facets, occlusal excessive load, labial vertical striae, labial horizontal striae, and interproximal striae. Three oral lesions were recorded: chipping, periapical lesions, and dental tilting. Results indicate that teeth were used in a habitual manner at Ajvide, based on the morphology and regularity of the patterns of atypical wear. Differences were observed between the sexes, indicating gender-related differences in the habitual use of teeth. Some wear categories showed a significant correlation with age, signifying increased or accumulated wear with age. Statistically significant positive correlations were found in the molars between occlusal excessive load wear and periapical lesions as well as tilting. Other apparent links were also observed between chipping and vertical striae as well as excessive load, although these were not significant. This suggests a relationship between dental wear and dental pathologies at this site, suggesting that habitual use of teeth indirectly affected the general oral health at the site. Wear patterns, furthermore, seem to mirror both frequent activities as well as single events.     

中国近代人群上颌前臼齿釉质-齿质连接面形状的三维几何形态测量

牙齿的釉质-齿质连接面(EDJ或Enamel-dentine junction)是釉质表面(OES或Outer enamel surface)形态的发生基础,其形态特征在牙齿发育早期形成,与遗传因素密切相关。为探讨EDJ形状在近代人群中的变异特点,本文使用显微断层扫描技术(micro-CT或micro-computed tomography)扫描了100例采自华中地区近代农业人群的上颌前臼齿(P~3和P~4各50例),并复原了EDJ表面三维结构。采用基于30个标志点(landmark)和半标志点(semi-landmark)的三维几何形态测量量化了上颌前臼齿EDJ表面形状。结果显示,牙齿内部舌侧尖区域变异程度较颊侧尖大。在人群内部,上颌前臼齿的变异方式主要表现在1)颊舌尖相互靠近或远离造成的咬合面深浅的差别;2)颊舌尖齿质最高点(dentine horn)相对高度的差异;3)舌侧尖近远中方向尺寸的变化;4)P~3颊侧尖近中脊的内收与外扩造成的整个轮廓形状的对称性变化;5)P~4整个咬合面轮廓MD/BL比值的大小差别。基于以上发现,本文进一步探讨了上颌前臼齿EDJ形状在两性或不同时代标本之间是否存在差异。平均形状的比较发现男性上颌前臼齿的舌尖相对较宽,颊侧尖近中脊相对较低。但主成分分析(Principal component analysis)和置换检验(Permutation test)显示两性差异未达到显著水平。同样,从新石器时代以来的各样本组之间在EDJ形状上的差别也没有达到统计上的显著水平。这一结果提示中国近代人群上颌前臼齿EDJ表面形状的变异特点至少可以追溯到全新世早期(本文使用标本最早来自距今6000-7000年前的新石器时代阶段)。未来EDJ的三维几何形态测量可通过扩大标本数量进一步探讨不同性别、不同地区人群、不同演化阶段之间的差异。     

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.     

Modular Wear Facet Nomenclature for mammalian post-canine dentitions

Abstract

Dental wear facets on the occlusal surface of premolars and molars are traces of their main function, the mastication and therefore reflect masticatory movements and also paramasticatory (i.e. non-dietary use of teeth) behavior. Here we present the Modular Wear Facet Nomenclature applicable to most mammalian dentitions. Topographic positions of wear facets in relation to the major cusps and crests of the teeth are used to designate the areas of the occlusal surface the facets occupy (e.g. their mesial, distal, lingual, or buccal position). Previous published systems for labeling wear facets have been inconsistent with each other. Therefore, we provide a synoptic review of the most widely-used terminologies, and introduce the alternative Modular Wear Facet Nomenclature. This nomenclature aims to overcome the difficulties caused by the existing inconsistent wear facet terminologies. Our new approach is applicable to dentitions where the occlusal morphology does not change significantly for most of the lifetime of the animal. In those dentitions, the primary occlusal surfaces are not significantly modified as wear facets become more extensive with wearing. This appears to be a common pattern in pre-tribosphenic, tribosphenic molars, and the teeth derived from tribosphenic precursors (e.g. bunodont molar morphologies). In teeth where the secondary occlusal surface is functionally intensely modified (i.e. high-crowned and evergrowing teeth with large areas of dentine exposed) any facet labeling system appears to be challenging, since the identification of individual facets is blurred and their spatial position may be indeterminable.