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

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

Individual tooth macrowear pattern guides the reconstruction of Sts 52 (Australopithecus africanus) dental arches

The functional restoration of the occlusal relationship between maxillary and mandibular tooth rows is a major challenge in modern dentistry and maxillofacial surgery. Similar technical challenges are present in paleoanthropology when considering fragmented and deformed mandibular and maxillary fossils. Sts 52, an Australopithecus africanus specimen from Sterkfontein Member 4, represents a typical case where the original shape of the dental arches is no longer preserved. It includes a partial lower face (Sts 52a) and a fragmented mandible (Sts 52b), both incomplete and damaged to such an extent to thwart attempts at matching upper and lower dentitions. We show how the preserved macrowear pattern of the tooth crowns can be used to functionally reconstruct Sts 52's dental arches. High‐resolutiondental stone casts of Sts 52 maxillary and mandibular dentition were mounted and repositioned in a dental articulator. The occlusal relationship between antagonists was restored based on the analysis of the occlusal wear pattern of each preserved tooth, considering all dental contact movements represented in the occlusal compass. The reconstructed dental arches were three‐dimensional surface scanned and their occlusal kinematics tested in a simulation. The outcome of this contribution is the first functional restoration of A. africanus dental arches providing new morphometric data for specimen Sts 52. It is noteworthy that the method described in this case study might be applied to several other fossilspecimens. Am J Phys Anthropol, 2013. © 2013 Wiley Periodicals, Inc.     

Age-related variability in occlusal wear planes

Investigation of two populations of 136 individuals shows several patterns of occlusal wear plane change which are positively correlated with age. For individuals up to the age of 18, there is a characteristic pattern in which the occlusal wear planes of the mandibular teeth are lingually sloped and those of the maxillary dentition buccally sloped, with the exception of the maxillary premolars, which are also lingually sloped. The long axes of the mandibular teeth give them a lingual orientation relative to the maxillary teeth, and the long axes of the maxillary molars, by contrast, are buccally oriented. In the 18-30 age range for all sexes, the mandibular M1 becomes buccally sloped on its occlusal surface while the occlusal wear plane on the maxillary M1 becomes lingually sloped. Later age changes indicate a trend for the mandibular premolars to become buccally sloped, while the wear planes of the maxillary premolars remain lingually sloped. There is a corresponding tendency for the maxillary and mandibular second molars to undergo changes in the initial orientation of the occlusal wear planes.     

郑州汪沟遗址仰韶文化居民的牙齿磨耗及口腔健康状况

对汪沟遗址出土的174例仰韶文化居民的2816枚牙齿进行统计与分析,计算出牙齿的平均磨耗等级和前后部牙齿磨耗差别指数,统计特殊磨耗、龋齿、骨质隆起在样本中的出现率。结果显示,汪沟组牙齿平均磨耗等级为3.403262级,男性牙齿平均磨耗等级为3.63级,女性为3.61级;男女两性牙齿磨耗差异不显著(p>0.05);前后部牙齿磨耗差别指数比达到1:1;出现26例由于深覆■导致的特殊磨耗;臼齿咬合面凹坑式磨耗出现率为2.50%;龋齿患病率68.97%,龋齿率26.56%,龋均4.30;骨质隆起的出现率为5.20%,颌骨粗壮程度不显著。汪沟人群的牙齿磨耗程度总体偏轻,牙齿磨耗程度与河南下王岗组居民接近。基于以上特点,我们认为中原地区仰韶文化人群在饮食结构和用牙习惯上存在一定的共性。     

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.     

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.     

Mastication and enamel microstructure in <Emphasis Type="Italic">Cambaytherium</Emphasis>, 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.     

Canine role in dental wear patterns: Macaca nemestrina

A study of variables and patterns in dental wear among 30 individuals in a colony of Macaca nemestrina shows that consideration of age and sex are crucial for understanding differential wear degrees on molar occlusal planes. With advanced age, this species of non-human primate undergoes obliteration of initial morphological characteristics through the gradual erosion of enamel. Wear gradients are differential from PM1-M3 in both sexes. It appears that there is a functional relationship between degrees of occlusal plane wear and the degree of wear on the canines, and that females show a greater degree of wear changes relative to males of equivalent age because of initial differences in canine length and robusticity due to sexual dimorphism. It appears that there is a direct relationship between occlusal wear plane changes and the degree of wear on the canines, with advanced differential wear showing up in individuals in whom years of maxillary canine honing, canine damage, and the normal wear of mastication has reduced dimensions of unworn permanent canines. Other considerations included in this study are the honing functions of the deciduous first mandibular molars and molar cusp height relative to canine function.     

Dental wear study in a 14th century skull of the Sao tribe, Cameroon

The aim of this work was to study the wear affecting the almost complete dentition of a Sao individual fossil from Cameroon prehistory (XIVth century). Occlusal surfaces of the fossil fragile pieces were plaster replicated with an original technique adapted from usual dental impression methods (silicon elastomer polymerising by addition). Axial macro-photographs of both sectional dental casts and original pieces made it possible to produce drawings of the occlusal areas on transparencies in order to superimpose the lateral hemiarch counterparts in their optimal intercuspal position. The study of interarch contacts was completed by confronting and observing the occluding position of hemiarch replicas. The occlusal analysis revealed that the wear extent was equivalent on left and right molars. Hall's occlusal wear index and Van Reenen and Reinach's classification of proximal wear allow assessment of the degree of wear extent on premolar and molar sections in relation to the side or the arch observed. The even bilateral proximal and occlusal wears observed on the different kinds of homologous teeth appeared as the main contributor to this well-balanced interarch occlusion. The mandibular incisor losses and the particular type of wear affecting lower canines led to the conclusion of the presence of a labret, a great number of which was found in the area. According to Miles' method of age assessment based on tooth wear, the pieces studied belonged to an individual between 30 and 40 years old.     

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.     

Unravelling the Functional Biomechanics of Dental Features and Tooth Wear

Most of the morphological features recognized in hominin teeth, particularly the topography of the occlusal surface, are generally interpreted as an evolutionary functional adaptation for mechanical food processing. In this respect, we can also expect that the general architecture of a tooth reflects a response to withstand the high stresses produced during masticatory loadings. Here we use an engineering approach, finite element analysis (FEA), with an advanced loading concept derived from individual occlusal wear information to evaluate whether some dental traits usually found in hominin and extant great ape molars, such as the trigonid crest, the entoconid-hypoconulid crest and the protostylid have important biomechanical implications. For this purpose, FEA was applied to 3D digital models of three Gorilla gorilla lower second molars (M₂) differing in wear stages. Our results show that in unworn and slightly worn M₂s tensile stresses concentrate in the grooves of the occlusal surface. In such condition, the trigonid and the entoconid-hypoconulid crests act to reinforce the crown locally against stresses produced along the mesiodistal groove. Similarly, the protostylid is shaped like a buttress to suffer the high tensile stresses concentrated in the deep buccal groove. These dental traits are less functional in the worn M₂, because tensile stresses decrease physiologically in the crown with progressing wear due to the enlargement of antagonistic contact areas and changes in loading direction from oblique to nearly parallel direction to the dental axis. This suggests that the wear process might have a crucial influence in the evolution and structural adaptation of molars enabling to endure bite stresses and reduce tooth failure throughout the lifetime of an individual.     

Enlarged occlusal surfaces on first molars due to severe attrition and hypercementosis: examples from prehistoric coastal populations of Texas

During an examination of prehistoric samples from the Texas coast, individuals consistently exhibited a suite of traits on the first molars that included severe wear, hypercementosis, and resorption of the buccal margin of the alveolus. The occlusal surface of the tooth was worn below the cervical margin, with the subsequent incorporation of the buccal surface of the buccal roots into the occlusal plane. This expanded occlusal surface, which extends the buccal surface beyond the normal edge of the tooth, is composed of a combination of original enamel, secondary dentin, and cementum. There is a marked rounding of the buccal aspect of the occlusal surface. These conditions were noted in both maxillary and mandibular first molars. The resorption of alveolar bone surrounding the buccal roots resembles resorption associated with periodontal infection and is thought to be the result of severe levels of stress being applied to this portion of the dentition.     

On deflecting wrinkles and the Dryopithecus pattern in human mandibular molars

The utility of the traditional Dryopithecus pattern observations on mandibular molars in hominid dental analysis has been challenged recently from several points of view. Both fossil and contemporary evidence suggest the independence of cusp number and groove pattern on mandibular molars and the quality of dentitions which are normally available for study make it difficult to determine both aspects of pattern (cusp number, groove pattern) equally. Now this paper shows that one of the polymorphisms on the occlusal surface of mandibular molars, the “deflecting wrinkle,” may be responsible for the spurious appearance of a Y molar pattern. It presence serves to insure a “2–3 contact” and hence the identification of the Y molar pattern. While seldom reported in traditional dental data, the wrinkle varies in frequency from 7% in South African white first permanent molars to 78.5% in Bushmen. Elsewhere, Hanihara has proposed that it be considered part of the “Mongoloid dental complex”.     

Loss of molar occlusion and mandibular morphology in adults in an ancient human population consuming a coarse diet

The purpose of the study is to investigate the link between number of molar teeth retained in occlusion and mandibular morphology in adults in an ancient, high dental wear human population. The study material comprises skeletons from Mediaeval Wharram Percy, England (N = 50 female, 69 male adults). It was hypothesized that adults retaining fewer occluding molars would show reduction in mandibular dimensions, particularly in the ascending ramus and gonial regions where the main muscles of mastication have their insertions. Molar occlusal status is assessed using the concept of functional units. Mandibular morphology is assessed using a suite of ten linear measurements plus the mandibular angle. Results show no evidence for any association between number of molars retained in occlusion and mandibular angle. There was an association between mandibular size and number of molars retained in occlusion, with smaller mandibular dimensions in those retaining fewer occluding molars. Some measurements were affected more than others so that there was also some shape alteration. Alteration of mandibular dimensions was more clearly demonstrable in females than in males. Only in females could significant reduction in the ascending ramus and gonial regions be demonstrated. Reasons for the apparent difference in response to loss of molar occlusion between male and female mandibles are unclear, but sex differences in bony metabolism mediated by hormonal factors may be implicated. Results suggest that care should be exercised when including mandibles from individuals showing loss of molar occlusion in morphological studies. Am J Phys Anthropol 152:383–392, 2013. © 2013 Wiley Periodicals, Inc.     

Dental wear,wear rate,and dental disease in the African apes

The African apes possess thinner enamel than do other hominoids, and a certain amount of dentin exposure may be advantageous in the processing of tough diets eaten by Gorilla. Dental wear (attrition plus abrasion) that erodes the enamel exposes the underlying dentin and creates additional cutting edges at the dentin‐enamel junction. Hypothetically, efficiency of food processing increases with junction formation until an optimal amount is reached, but excessive wear hinders efficient food processing and may lead to sickness, reduced fecundity, and death. Occlusal surfaces of molars and incisors in three populations each of Gorilla and Pan were videotaped and digitized. The quantity of incisal and molar occlusal dental wear and the lengths of dentin–enamel junctions were measured in 220 adult and 31 juvenile gorilla and chimpanzee skulls. Rates of dental wear were calculated in juveniles by scoring the degree of wear between adjacent molars M1 and M2. Differences were compared by principal (major) axis analysis. ANOVAs compared means of wear amounts. Pearson correlation coefficients were calculated to compare the relationship between molar wear and incidence of dental disease. Results indicate that quantities of wear are significantly greater in permanent incisors and molars and juvenile molars of gorillas compared to chimpanzees. The lengths of dentin–enamel junctions were predominantly suboptimal. Western lowland gorillas have the highest quantities of wear and the most molars with suboptimal wear. The highest rates of wear are seen in Pan paniscus and Pan t. troglodytes, and the lowest rates are found in P.t. schweinfurthii and G. g. graueri. Among gorillas, G. b. beringei have the highest rates but low amounts of wear. Coefficients between wear and dental disease were low, but significant when all teeth were combined. Gorilla teeth are durable, and wear does not lead to mechanical senescence in this sample. Am. J. Primatol. 72:481–491, 2010. © 2010 Wiley‐Liss, Inc.     

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

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

Changes in food processing and occlusal dental wear during the early agricultural period in northwest Mexico

Crown dimensions and occlusal surface wear rate and wear plane were evaluated using paired first and second mandibular molars from a sample of 84 Early Agricultural period (1600 B.C.-A.D. 200) skeletons from northwest Mexico. Although this period represents a major shift in subsistence strategies in the Sonoran Desert, from food-foraging to agriculture, archaeological and dental pathology studies have identified this period as one of relative dietary stability. It was therefore predicted that very little variation in occlusal wear would have occurred between the early phase (San Pedro: 1600-800 B.C.) and late phase (Cienega: 800 B.C.-A.D. 200). Comparison of crown diameters identified some phenotypic differences between sexes but not between archaeological phases. Molar occlusal surfaces were then divided into four quadrants, and wear scores recorded for each quadrant. Principle axis analysis was performed between total wear scores of paired, adjacent first and second mandibular molars to assess rate and occlusal wear plane over time. The analysis demonstrated that both wear rate and wear plane increased from the early to the late phase of the Early Agricultural period. These results indicate that although diet may have indeed remained stable during this period in the Sonoran Desert increases in the rate of wear and wear plane may reflect changes in food-processing techniques. It is suggested that more intensive processing of agricultural products during the Cienega phase simultaneously softened the diet to create more tooth-contact wear and introduced more grit to cause faster and more angled wear on the molar occlusal surfaces.     

Dental morphology of Jews from Yemen and Cochin

60 dental plaster casts of Jewish adolescents, half of them children of immigrants from Yemen and half of them from Cochin (India), were investigated as to tooth measurements and morphologic traits. Each group was composed of an equal number of males and females. Cochini showed a sex specific dimorphism in tooth size, a relatively larger bucco-lingual diameter of upper and lower first premolars, lower frequency of Carabelli's tuberculum and in males larger tooth measurements than their Yemenite counterparts. The variability of ²I² was significantly higher in females than in males, and in Yemenite girls than in Cochini. The molar patterns were similar in both groups with regard to number and development of cusps and occlusal form of the mandibular molars.     

Occlusal relief changes with molar wear in Pan troglodytes troglodytes and Gorilla gorilla gorilla

Most research on primate tooth form-function relationships has focused on unworn teeth. This study presents a morphological comparison of variably worn lower second molars (M(2)s) of lowland gorillas (Gorilla gorilla gorilla; n=47) and common chimpanzees (Pan troglodytes troglodytes; n=54) using dental topographic analysis. High-resolution replicas of occlusal surfaces were prepared and scanned in 3D by laser scanning. The resulting elevation data were used to create a geographic information system (GIS) for each tooth. Occlusal relief, defined as the ratio of 3D surface area to 2D planometric area of the occlusal table, was calculated and compared between wear stages, taxa, and sexes. The results failed to show a difference in occlusal relief between males and females of a given taxon, but did evince differences between wear stages and between taxa. A lack of significant interaction between wear stage and taxon factors suggests that differences in occlusal relief between chimpanzees and gorillas are maintained throughout the wear sequence. These results add to a growing body of information on how molar teeth change with wear, and how differences between primate species are maintained at comparable points throughout the wear sequence. Such studies provide new insights into form-function relationships, which will allow us to infer certain aspects of diet in fossils with worn teeth.     

Brief communication: correcting overestimation when determining two-dimensional occlusal area in human molars

The robustness index (RI) is determined by multiplying dental mesiodistal and buccolingual diameters, and is used to estimate occlusal area. However, because teeth are not rectangular its calculation consistently causes overestimations. Moreover, teeth, in particular molars, are not identically shaped so overestimations vary. The current study seeks to determine the extent to which overestimations are affected by tooth shape and to improve RI's efficacy. Initially, 120 molars were sorted into six shape groups, which were determined by hypocone/hypoconulid expression. Three maxillary and three mandibular shape groups were set using the Arizona State University Dental Anthropology System. ANOVA results determined that RI overestimations, which averaged around 20%, were not the same for each shape category. Maxillary molars with large hypocones and mandibular molars with no hypoconulids were overestimated significantly less than the other molar groups. Regression-based correction formulae were generated and applied to the original sample. These formulae far more precisely estimated tooth area than RI and there were no differences in estimation based upon tooth shape. A subsequent validation study of 24 additional molars was undertaken to test the formulae on teeth not from the original sample. Overestimation/underestimation averaged 0.5% and was about the same for each of the tooth shape groups. Finally, six new correction formulae were generated using all 144 molars. The correction formulae provide, what is termed here, an adjusted robustness index (ARI), and it is recommended that ARI is used in future studies of molar occlusal area.