On the relative frequencies of hominid maxillary and mandibular teeth and jaws as taphonomic indicators

In southern African samples of early hominid remains, maxillary and mandibular teeth (deciduous-plus-permanent) have a virtually equal chance of accumulating in the dolomitic limestone cave deposits, of being preserved therein and recovered therefrom. Thus, of 1066 fossil teeth ofAustralopithecus spp. plusHomo habilis, 51.9 per cent are maxillary and 48.1 per cent mandibular. On the other hand, the East African sample of 847 early hominid, deciduous-plus-permanent teeth, departs more strikingly from a 1∶1 ratio: it comprises 41.0 per cent maxillary and 59.0 per cent mandibular teeth. It is inferred that mandibular teeth have a somewhat better chance of accumulating and being preserved in, and being recovered from, the open, fluvial, lacustrine and deltaic sedimentary environments of the East African sites. The dental proportions are approximately matched by the proportions of jaws. For example, the maxilla: mandible proportions at Koobi fora in northern Kenya are 33.0∶67.0 for teeth and 21.6∶78.4 for jaws. In other words, the preponderance in favour of mandibular remains is somewhat more marked in the case of jaws than of teeth, this distinction doubtless reflecting the more fragile bony structure of the maxilla and the sturdier construction of the mandible. This first study known to the author of the differential distribution of maxillary and mandibular teeth of the Plio-Pleistocene hominids leads the author to hypothesize that, where environmental conditions at the place and time of the death of the hominids have been non-destructive, non-dispersive, relatively mild and protective, maxillae and mandibles may be expected to have been conserved and recovered in approximately equal proportions—and likewise of maxillary and mandibular teeth. On the other hand, the more brutal and destructive the sedimentary environment and other taphonomic influences have been, at the place and time when the hominid individuals died, the more likely it is that the maxillary and mandibular remains of jaws and teeth will deviate from equality of proportions, generally at the expense of the maxillae and upper teeth. Hence, it is proposed that the upper jaw/low jaw ratio (Mx/Mn jaw ratio) and the maxillary teeth/mandibular teeth ratio (Mx/Mn dental ratio) may serve as two useful new gauges of the rigour of palaeo-ecological and taphonomic conditions.     

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.     

Interspecies difference in placement of developing teeth and its relationship with cross-sectional geometry of the mandibular symphysis in four primate species including modern humans

The form of the anthropoid mandibular symphysis has recently been addressed in association with spatial requirements for the forming anterior teeth. To evaluate potential relationships between the symphyseal shape and teeth further, the growth patterns of the symphyseal region and the positioning of the tooth crypts were examined using CT data, comparing four primate species (modern humans, chimpanzees, Japanese monkeys, and hamadryas baboons) with varied symphyseal curvature and tooth size. First, results showed that interspecies differences in overall mandibular shape including symphyseal inclination and bicanine width are consistently expressed throughout postnatal ontogeny, although local symphyseal configurations related to the superior transverse torus (STT) tended to change considerably during growth in chimpanzees. Second, the four species were found to exhibit differentiated formation positions of the incisor and canine crypts. In particular, I2 developed between I1 and C in humans with a broad bicanine space and small teeth, whereas it was positioned posterior to I1 and above C in the cercopithecines with an extremely narrow bicanine space. In chimpanzees, despite the large bicanine width, I1 and I2 grew with a large antero-posterior overlap owing to their large size. These results indicate that the dental positioning is determined in concert with the size balance of the available mandibular space and forming teeth. Finally, the positions/contours of I2 crypt were shown to correspond strongly with the STT across the taxa. This suggests that interspecies differences in symphyseal shape should be interpreted partially by the species-specific positional relationships of the developing anterior teeth.     

Sex discriminatory effectiveness using combinations of root lengths and crown diameters

Using optical-scanner (OPTOCOM) and radiogrammetric measurements on mandibular permanent teeth, root length alone affords sex-discriminatory effectiveness equal to or exceeding conventional crown diameters. Combinations of root lengths and crown dimensions yield up to 80% accuracy in sexing with as few as two teeth, and discriminatory effectiveness of 87% with mandibular teeth alone.     

Deletion of the Pitx1 genomic locus affects mandibular tooth morphogenesis and expression of the Barx1 and Tbx1 genes

Pitx1 is a bicoid-related homeodomain factor that exhibits preferential expression in the developing hindlimb, mandible, pituitary gland and teeth. Pitx1 gene-deleted mice exhibit striking abnormalities in morphogenesis and growth of both hindlimb and mandible, suggesting a proliferative defect in these two structures. Here, we studied the expression and regulation of Pitx1 in both mandible and developing teeth and analyzed tooth morphology, cell proliferation, apoptosis and expression of Pitx2, Barx1 and Tbx1 in dental tissues of Pitx1−/− mouse embryos. Pitx1 expression is restricted to the epithelium of the growing tooth anlagen. Tissue recombination and bead implantation experiments demonstrated that bone morphogenetic protein-4 down-regulates Pitx1 expression in both mandibular mesenchyme and dental epithelium. Deletion of the Pitx1 locus results in micrognathia and abnormal morphology of the mandibular molars. Although Pitx2 expression in teeth of Pitx1−/− embryos is not altered, expression of Barx1 decreased in the mesenchyme of the mandibular molars. Furthermore, Pitx1 deletion results in suppression of Tbx1 expression in dental epithelium. Taken together, these results indicate that independent genetic pathways in mandibular and maxillary processes determine tooth development and morphology.     

Two-dimensional finite element analysis of stresses developed in the supporting tissues under complete dentures using teeth with different cusp angulations

Statement of problem: The selection of appropriate teeth for complete denture occlusion is very important for long‐term success, and adequate maintenance of the residual alveolar ridge. Purpose: The purpose of this study was to determine the stress generated underneath the complete denture by altering the cuspal angulations of the denture teeth. Material and methods: A two‐dimensional finite element model of a coronal section of maxillary and mandibular complete dentures, mucosa and alveolar bone in the first molar region was designed. The occlusal aspect of the denture teeth was altered to make 33°, 20°, 0° cuspal angulation. All the nodes at the bases of maxillary and mandibular alveolar bone of finite element analysis models were restrained in all directions. A functional occlusal load of 50 N was applied through the mandibular model base. To design these models and to analyse them, EMRC’s NISA II finite element analysis computer software was used. In these models, the elements were selected (a, b, c, d, e, f) in the region where it was necessary to determine the stresses generated in both the maxillary and mandibular portions. Results: The results were interpreted as Von Mises stresses and were observed in pre‐defined areas. The stress patterns observed within model with each type of posterior occlusion, showed unique variations as well as some similarities. Conclusion: Stresses of greater magnitude were observed in cuspal teeth, 33° and 20° respectively, where as 0° teeth showed a slightly less magnitude of stress generated.     

Aging and food source effects on mandibular stylets teeth wear of phytophagous stink bug (Heteroptera: Pentatomidae)

Studies were conducted to test the effect of age and food sources on wear of the mandibular teeth of the phytophagous pentatomid, Euschistus heros (F.). The total length (μm) of the area bearing the mandibular teeth, the length of the 1st tooth, and the height of the 2nd tooth for teneral (< 1 day-old) adults were significantly greater than that of adults fed on natural [green bean, Phaseolus vulgaris pods, raw shelled peanuts, Arachis hypogaea, and mature soybean, Glycine max seeds] for 30 or 60 days. Adults fed on artificial dry diet showed, in general, similar results to those of teneral adults. Force (Newtons) required penetrating the natural foods was significantly greater than that required penetrating the artificial diet. The greater hardness of the natural foods caused increased mandibular serration wear.     

Human mandibular incisors from the late Middle Pleistocene locality of Hoedjiespunt 1, South Africa.

The Hoedjiespunt 1 locality is an archaeological and palaeontological site located on the Hoedjiespunt Peninsula at Saldanha Bay, South Africa. In 1996 two human teeth, a left central mandibular incisor and a left lateral mandibular incisor, were discovered during excavations in the late Middle Pleistocene palaeontological layers. These teeth are described and are found to belong to a single subadult individual. Despite their developmental stage, these incisors already display early signs of wear. Their crown diameters are larger than modern and archaeological African comparative material and are most closely comparable with crown diameters of an early Middle Pleistocene and late Middle Pleistocene dental sample from Africa, Europe and Asia. In the light of this metrical evidence, data on two previously excavated maxillary molars, most probably belonging to the same individual, were re-examined. It was found that the Hoedjiespunt 1 hominid possessed dental metrical features (large anterior teeth and small molars) comparable with other African and European hominids referred to the Middle Pleistocene.     

Data on morphometric analysis of anterior teeth from Hazaribag College of Dental Sciences and Hospital,jharkhand

It is of interest to document data on morphometric (measurement of external form) analysis of maxillary and mandibular anterior teeth collected from a dental set up using mesio-distal (MD) dimension. The mesiodistal dimensions of all permanent anterior teeth (central incisor, lateral incisor and canine) of 25 males and 25 females patients were recorded using digital vernier calipers. Data were charted and statistical analysis was done using Mann Whitney U test. Data shows sexual dimorphism for every tooth between males and females. However, dimorphism was exhibited only in maxillary and mandibular canine, mandibular central incisors, and lateral incisor. Hence,odontometric parameters offer simple, reliable and cost-effective in forensic investigation for recording gender discrimination.     

GRADUAL CHANGE IN HUMAN TOOTH SIZE IN THE LATE PLEISTOCENE AND POST-PLEISTOCENE

Starting with the onset of the last glaciation approximately 100,000 years ago and continuing to the end of the Late Pleistocene approximately 10,000 years ago, human tooth size began to reduce at a rate of 1% every 2,000 years. Both the mesial-distal and the buccal-lingual dimensions of mandibular and maxillary teeth were undergoing the same rate of reduction. From the beginning of the Post-Pleistocene until the present, the overall rate of dental reduction doubled, becoming approximately 1% per thousand years. Buccal-lingual dimensions are now reducing twice as fast as mesial-distal dimensions, and maxillary teeth are reducing at an even more rapid rate than mandibular teeth. Late Pleistocene rates are comparable in Europe and the Middle East. The Post-Pleistocene rates are also the same for Europe, the Middle East, China, Japan, and Southeast Asia. It is suggested that the cookery at the beginning of the Late Pleistocene allowed the earlier changes to occur. The use of pottery within the last 10,000 years further reduced the amount of selection that had previously maintained usable tooth substance. Reduction then occurred as a consequence of the Probable Mutation Effect (Brace, 1963; McKee, 1984).     

Nouvelles découvertes de dents d’hominidés dans le membre Kaitio de la formation de Nachukui (1,65–1,9 Ma), Ouest du lac Turkana (Kenya)

New hominid teeth from the Kaitio member (1.65–1.9 Myr) in West Turkana (Kenya). New hominid teeth have been recovered from the archaeological sites of Kokiselei 1 and Naiyena Engol 1. These two sites are located in the west side of the Turkana Basin and belong to the Kaitio member of the Nachukui Formation. They are dated between 1.65-1.79 and 1.7-1.8 Myr respectively. The four teeth (left maxillary canine and first molar, right maxillary third molar and left mandibular third molar) discovered in Kokiselei 1 are attributed to Australopithecus boisei. The right mandibular first premolar found in Naiyena Engol 1 is referred to Homo sp. aff. ergaster. To cite this article: S. Prat et al., C. R. Palevol 2 (2003).     

Effect of double flasking and investing methods on artificial teeth movement in complete dentures processing

doi: 10.1111/j.1741‐2358.2011.00494.x
Effect of double flasking and investing methods on artificial teeth movement in complete dentures processing Purpose: The aim of this study was to evaluate linear dimensional alterations of artificial teeth for complete dentures when using different investment and flasking techniques. Background: Dimensional changes in the vertical dimension may occur owing to changes in artificial teeth positioning caused by different investing and flasking techniques. Materials and methods: Thirty pairs of the complete dentures were manufactured and randomly divided into three groups (n = 10): (1) invested with type III stone in monomaxillary PVC flask; (2) invested with type III stone in bimaxillary PVC flask; and (3) invested with laboratory silicone in bimaxillary PVC flask. Dentures were polymerised by microwave, and 12 linear distances were measured before and after denture processing. Data were analysed by one‐way anova , considering manufacturing technique as the study factor. Tukey’s HSD was used as post hocanova (p = 0.05). Results: Most of the linear distances were comparable for all groups. All transversal maxillary and mandibular distances were higher for group 1 compared with groups 2 and 3 (p < 0.05), except the distance 3–6 for mandibular arch, in which no difference was found between groups (p < 0.05). Both maxillary diagonal distances were higher in group 1 (p < 0.05), and no differences were found among all groups for mandibular measurements. Conclusions: Double flasking technique independent on the investment material is shown to be the most effective method to reduce changes in artificial teeth positioning.     

A twin study of dental dimension. II. Independent genetic determinants

To demonstrate the presence of independent genetic determinants of multiple correlated tooth dimensions from twin data, a multivariate analysis was performed on the covariance matrices of monozygotic and dizygotic within-pair differences for mesiodistal and buccolingual dimensions of 28 teeth of the secondary dentition. The results provided strong evidences that the correlation among tooth dimensions is primarily genetic in origin, probably attributable to the pleiotropic action of either independent genes or groups of genes. Among the genetic factors that were identified, one appeared to affect the maxillary teeth in general while a second influenced primarily the anterior mandibular teeth. There was a striking tendency for homologous measurements on the right and left sides to be associated with the same genetic factor. In contrast, genetic determination of the maxillary and mandibular dentition seemed to be independent of each other, and a wider range of genetic factors were found to influence the mandibular than the maxillary teeth, suggesting that a differential degree of evolutionary stability may have been achieved in the teeth of the two jaws.     

Geratodontology and horn growth of the impala (Aepyceros melampus)

Examination of the jaws of an impala population showed advanced wear on mandibular M1 compared with other ungulates which have been examined. This could lead to an erroneous interpretation of age if based upon mandibular tooth wear alone. Explanations are offered for this pattern in terms of the apparent pattern of wear of the impala molar teeth. Suggestions are also put forward for a method of determining specific age, from a conceptual wear model, when only extreme parameters are known. Horn growth in the male is also described.     

The stress model of abutment tooth and periodontal tissues with unilateral mandibular dissociation and loss by precision extracoronal attachment

In order to explore the application of the precision extracoronal attachment based on three-dimensional finite element stress model in the repair of unilateral mandibular dissociation and loss, the stress distribution of the butment and periodontal tissues when the precision extracoronal attachment was used in unilateral mandibular dissociation and loss was analyzed, so as to provide reference for the application of materials in clinical repair. In this study, the biomechanics of oral cavity and its attachment were analyzed to provide theoretical basis for model construction. Because the degree of periodontal tissue absorption and the number of abutment teeth affected the restoration effect of the coronal precision attachment, the models were established from these two perspectives. The results showed that when the periodontal tissue absorption of both abutment teeth exceeded 1/3, the method of double abutment restoration was not recommended. When three abutments were used, there was a significant decrease compared with the absorption of the periodontal tissue of the double abutment. In clinic, the stress distribution of the distal abutment teeth and its periodontal tissues can be improved by increasing the number of abutment tooth. However, since increasing the number of abutments required an increase in the amount of healthy tooth tissue, it couldn’t be blindly selected in the clinic. After comprehensive consideration, it is appropriate to choose two abutment teeth for restoration.     

牛河梁红山文化人群龋齿的统计与分析

本文通过对牛河梁遗址出土的31例红山文化时期人类牙齿龋病的统计与分析, 获知: 1)牛河梁遗址男女两性的患龋率、龋齿率没有明显的性别差异; 2)他们的患龋率和龋齿率有随年龄增长逐步增高的趋势; 3)上颌的龋齿罹患率高于下颌; 4)龋齿的发生主要集中在臼齿,且以咬合面部位为主; 5)他们的患龋率和龋齿率均较低。牛河梁红山文化人群相对偏低的龋齿率可能暗示出他们的经济生活方式还处在以采集狩猎为主体的模式中, 农耕经济可能处于较低层次的状态。     

Variation in the developing root cone angle of the permanent mandibular teeth of modern man and certain fossil hominids

The radiographic appearance of the developing root apex of 461 mandibular teeth was studied using ellipsopantomographs of 77 individuals. The angle formed by the mesial and distal aspects of the developing root cone was measured for each quarter of root development in the permanent mandibular teeth of each subject. Large values for this angle in the more coronal part of the root gradually decreased towards the root apex where values were small in all teeth studied. This gradual decrease in the angle of the developing root cone is concordant with the faster increase in root length but slower rates of dentinogenesis reported for the apical region of human teeth in the literature, as the decrease is likely to reflect the increasing numbers of odontoblasts that become involved in root formation as it proceeds apically. The developing root cone angles of one of the five fossil hominid specimens studied (KMN-ER 820) fall outside the range for the developing root cone angle of the developing premolar and permanent second molar roots in modern Homo sapiens and is evidence of a faster rate of root elongation than is typical for modern man.     

The size and morphology of the Nasioi dentition

Dental impressions were obtained on 240 Nasioi, a Melanesian population living on the island of Bougainville. Odontometric data are presented for both the permanent and deciduous teeth, and the former teeth are also examined morphologically. The results show that the Nasioi have large permanent teeth like other Australoid populations whereas the deciduous teeth are only of moderate size. The coefficients of variation are large in the permanent teeth compared to other populations but the sexual dimorphism in tooth size and variability is not remarkable. Morphologically, the permanent teeth of the Nasioi are characterized by a cusp number pattern, a high frequency of the Dryopithecus + pattern on the first mandibular molar, few individuals with a Cusp of Carabelli, and a moderate expression of shovelled-shaped anterior teeth.     

Cephalometric evaluation of the changes in mandibular symphysis after 7 years of denture wearing

Objective: To evaluate changes in mandibular symphysis during 7 years of complete denture wearing following extraction of natural anterior teeth. Design: Comparison among measurements taken at four different occasions in a prospective cephalometric study. Setting: The study was conducted at the Dental School of Athens University. Subjects: 10 complete denture wearers (5 women, 5 men) with average age of 53.2 years, at the beginning of the study. Measures: Linear and area measurements of the mandibular symphysis. Results: The overall reduction in the anterior mandibular height was 7.87 mm and in the mandibular symphysis area 54.8 mm² (p<0.05). Females presented higher total average reduction in both variables tested, and more rapid bone loss during the first two years of denture wear, compared to men. Superimposition of the tracings revealed considerable individual variation in mandibular symphysis changes. Conclusion: Results are in line with the findings of other authors indicating continuous reduction and dramatic inter-subject variation in the mandibular alveolar bone, following extraction of natural teeth and wearing of complete dentures.     

Characterization of the orchid bee Euglossa viridissima (Apidae: Euglossini) and a novel cryptic sibling species,by morphological,chemical, and genetic characters

In orchid bees, males signal their availability as mates by fanning ‘perfumes’, i.e. blends of volatiles that are collected from environmental sources and stored in hind leg pouches. The chemical composition of such perfumes in males with either two or three mandibular teeth has previously led to the discovery of two sympatric, cryptic lineages within Euglossa viridissima Friese on the Yucatan peninsula, Mexico. Here, we combine chemical, morphological, and genetic data for an integrated characterization of the two lineages. The lectotype of E. viridissima Friese in the Museum of Natural History in Vienna has two mandibular teeth, and the species name viridissima must thus be assigned to the predominantly bidentate lineage, whereas the completely tridentate lineage is described as a novel species, Euglossa dilemma sp. nov. Bembé & Eltz. Chemical profiling and microsatellite genotyping revealed that E. viridissima males can occasionally (～10% of individuals) express a third mandibular tooth, but this tooth is not positioned centrally on the mandible as in E. dilemma, but is displaced towards the tip. Thus, males of the two lineages can be unambiguously diagnosed by mandibular characters alone. Based on 889 bp of CO1 sequence data, we confirm that E. viridissima and E. dilemma constitute a monophyletic group within the genus Euglossa. However, CO1 alone failed to separate these two lineages due to the lack of parsimony‐informative sites. Both species occur in broad sympatry across Central America, but the orchid bees recently introduced to Florida have three mandibular teeth in males, i.e. belong to E. dilemma. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163 , 1064–1076.