Population studies on southwestern Indian tribes. V. Tooth morphology as an indicator of biological distance

The value of phylogenetic comparisons between populations based on tooth morphology depends on a knowledge of the extent to which the observed morphological variation is genetic in origin. This knowledge can be derived unequivocally only from the analysis of family data. However, in the absence of such knowledge the ability of tooth morphology to distinguish biological differences can be evaluated directly by testing its discriminating power in practice on populations between which the degrees of genetic difference are already known. The results of such an evaluation show that different degrees of subjectivity of scoring are associated with different characters, but that moderately good correspondence between known genetic differences and differences based on tooth morphology can be achieved when characters showing the least subjectivity of scoring are used.     

Maxillary molar occlusal polygons in five human samples

Angular and linear measurements of maxillary first molar occlusal polygons are given for young San (Bushmen), Sotho, Asiatic Indians, Whites, and Papago Indians. Angular and linear measurements are inseparably related. Much greater variation occurs in widths than in lengths. Maximum variation occurs between San and Papago. Papago maxillary first molars are separable from Old World molar samples in two of four angles and eight of 13 indices.     

Changing occlusal variation in Pima Amerinds

Occlusal variables and arch measurements have been recorded on 341 Pima Amerinds pertaining to two samples, one of older individuals raised on traditional diets, the other of younger individuals raised on refined commercial foods that are typical of modern urbanized people. Permanent dental occlusion is significantly more variable from defined ideals in the younger sample, despite their fewer deformities resulting from progressive aging. The youths had relatively narrower palates, correlating with a general trend among industrialized populations and also among experimental animals fed soft diets. Relative rate of deciduous tooth loss and replacement did not correlate with any occlusal variable.     

Patterns of dental wear in the Lengua Indians of Paraguay

Wear patterns were examined on dental casts of 202 living Lengua Indians from the Chaco area of Paraguay. Consideration was given to the development of the molar helicoidal plane, age-related changes in occlusal attrition, coalescence of dentine exposures, interproximal attrition, and erupted crown height. This study lends support to Osborn's theory of the helicoidal plane development by showing that attrition enhances rather than modifies posteruption molar occlusal planes. The rate of interproximal attrition was found to slow down with the eruption and functional initiation of the third molars. Sinuous and cavo-convex interproximal contact areas that are generated with age, however, appeared to be less abrasion resistant than straight surfaces, hence leading to an increase in interproximal attrition rates with advanced age. Maximum crown height reduction occurred between the ages of 20 and 40 years in central incisors, canines, and first molars. Kruskal-Wallis tests and log linera models failed to demonstrate significant sexually dimorphic or antimeric differences in wear patterns of Lengua teeth.     

Comparative genetic variance and heritability of dental occlusal variables in U.S. and Northwest Indian twins

Genetic variance analysis of 15 dental occlusal and arch variables is based on cross-cultural comparison of twin variances (U.S. Whites and Northwest Indian Punjabis). Both samples exhibit high genetic versus environmental partition of variance. However, monozygotes and dizygotes have unequal variance, which invalidates conventional genetic variance ratios. The pattern of environmental biases on the zygosities is quite different in the two groups. Revised estimates that acknowledge zygosity heterogeneity (hence unequal environmental influences) are generally much lower for occlusal traits, whereas arch size measurements are unaffected.     

Form and patterning of anterior tooth wear among aboriginal human groups

Form and severity of dental attrition was assessed in aboriginal human groups including hunter-gatherers (Eskimos, Australians) and those with dependence to a varying degree on food production (Southwest U.S. and Ohio American Indians). Wear on anterior teeth was both relatively and absolutely greater in the hunter-gatherers, as indicated by comparisons of wear on anterior and posterior teeth which come into occlusion at roughly the same time. Distinct differences in form of anterior wear were also apparent: The hunter-gatherers exhibited steadily increasing incidences of labially rounded wear with greater functional age, while the food-producing groups showed little or no rounding but instead high frequencies of heavily cupped wear (especially in those with premature loss of posterior teeth). These differences were attributed to nonmasticatory utilization of the front teeth in hunter-gatherers and to employment of the anterior teeth in masticatory (grinding) activities necessitated by large-scale molar loss in food producers.     

An energy dissipation and cross shear time dependent computational wear model for the analysis of polyethylene wear in total knee replacements

The cost and time efficiency of computational polyethylene wear simulations may enable the optimization of total knee replacements for the reduction of polyethylene wear. The present study proposes an energy dissipation wear model for polyethylene which considers the time dependent molecular behavior of polyethylene, aspects of tractive rolling and contact pressure. This time dependent – energy dissipation wear model was evaluated, along with several other wear models, by comparison to pin-on-disk results, knee simulator wear test results under various kinematic conditions and knee simulator wear test results that were performed following the ISO 14243-3 standard. The proposed time dependent – energy dissipation wear model resulted in improved accuracy for the prediction of pin-on-disk and knee simulator wear test results compared with several previously published wear models.     

Stereophotogrammetric analysis of occlusal morphology of extant hominoid molars: phenetics and function

Because teeth are commonly preserved in the fossil record, dental remains have often been employed in estimating evolutionary relationships among fossil hominoids. This is appropriate, however, only to the extent that dental morphology is phylogenetically informative. I have used phenetic analytic techniques to assess whether hominoid molars are likely to be useful for phylogenetic inference. Thirty-four occlusal landmarks for first and second molars were chosen; seven on each maxillary and ten on each mandibular tooth. Three-dimensional locations of these points were determined from stereophotographs of dental arcades of more than 260 specimens from six taxa (gorilla, chimpanzee, human, orangutan, siamang, and gibbon). Analytic emphasis was on canonical variates analyses of landmark coordinates for mandibular and maxillary second molars, adjusted for intergroup size differences. There is little correspondence between the systematic implications of hominoid molar morphometrics and reliable estimates of evolutionary propinquity based on interhominoid biomolecular similarities. The former seem to have been determined largely by dietary constraints. Although this suggests the possibility of using the protocol employed here to infer diets of fossil hominoids, molar crown measurements seem unlikely to serve well as phylogenetic indicators in the Hominoidea.     

Age-related nuclear size variability of thyreocytes in thyroid aspirates

Variations in nuclear areas in thyroid aspirates may be caused by many different pathologic conditions of the thyroid gland. Our experience in routine thyroid cytology has suggested that the age of the patient could also be a factor that can influence the nuclear size of thyroid epithelial cells. Planimetric measurements of nuclear areas of cytologically normal thyroid nuclei from patients with normal thyroid glands and from those with cold thyroid nodules, with each category containing two different age groups, revealed both a significant increase in nuclear areas in normal thyroid tissue from older patients and a significant increase in nuclear size variability among older patients with nodular goiters. This finding seems to indicate that patient age is another factor that exercises an influence upon the variability of nuclear areas, even in histologically normal thyroid glands.     

Three-dimensional measurement of the occlusal surfaces of lower first molars of Australian aboriginals

The occlusal surfaces of lower first molars of Australian Aboriginals were measured in three dimensions with the aid of Moiré contourography. Molar cuspal heights in this population were higher than in Japanese (Mongoloid) but lower than in Dutch (Caucasoid) populations. Intercuspal distances were considerably larger than those in the two other populations. Populational differences in occlusal features may influence both craniofacial structures and jaw movements in the three populations. Low correlations between the cuspal heights and the intercuspal distances in the other two populations were also found in this population, indicating that human molar cuspal height is independent of the transverse size of the crown. Mean values for the height of the three principal cusps in lower first molars were less than those in upper ones. However, the height of the hypoconid, which was the highest in the lower molar cusps, showed almost the same mean value as the height of the upper three principal cusps, indicating that the height of the main functional cusp, in both upper and lower first molars, was almost the same.     

Finite element simulation of early creep and wear in total hip arthroplasty

Polyethylene wear particulate has been implicated in osteolytic lesion development and may lead to implant loosening and revision surgery. Wear in total hip arthroplasty is frequently estimated from patient radiographs by measurement of penetration of the femoral head into the polyethylene liner. Penetration, however, is multi-factorial, and includes components of wear and deformation due to creep. From a clinical perspective, it is of great interest to separate these elements to better evaluate true wear rates in vivo. Thus, the aim of this study was to determine polyethylene creep and wear penetration and volumetric wear during simulated gait loading conditions for variables of head size, liner thickness, and head–liner clearance. A finite element model of hip replacement articulation was developed, and creep and wear simulation was performed to 1 million gait cycles. Creep of the liner occurred quickly and increased the predicted contact areas by up to 56%, subsequently reducing contact pressures by up to 41%. Greater creep penetration was found with smaller heads, thicker liners, and larger clearance. The least volumetric wear but the most linear penetration was found with the smallest head size. Although polyethylene thickness increases from 4 to 16 mm produced only slight increases in volumetric wear and modest effects on total penetration, the fraction of creep in total penetration varied with thickness from 10% to over 50%. With thicker liners and smaller heads, creep will comprise a significant fraction of early penetration. These results will aid an understanding of the complex interaction of creep and wear.     

A correlation of tooth wear and age among modern Igloolik eskimos.

The level of molar wear can be estimated reliably by measuring the cusp height. A correlation between age and the level of molar wear, expressed by a normalizing index (TWI) of cusp height, was found to exist in a sample of modern Igloolik Northwest Territories Eskimos. Not only was it possible to derive linear regression models to test the degree of correlation in the sample of 46 female and 39 male maxillary casts of Igloolik Eskimos, but the models were capable of accurately predicting the age of natives of the neighboring Hall Beach community. Sexual dimorphism in molar wear, perhaps attributable to differential bruxism, was demonstrated for the Igloolik sample. Based on the combined estimate of slopes for each maxillary molar pair for females and males, it was discovered that the male maxillary molars are worn approximately 30% more rapidly than female maxillary molars.     

Non-occlusal dental microwear variability in a sample of Middle and Late Pleistocene human populations from Europe and the Near East

Non-occlusal, buccal tooth microwear variability has been studied in 68 fossil humans from Europe and the Near East. The microwear patterns observed suggest that a major shift in human dietary habits and food processing techniques might have taken place in the transition from the Middle to the Late Pleistocene populations. Differences in microwear density, average length, and orientation of striations indicate that Middle Pleistocene humans had more abrasive dietary habits than Late Pleistocene populations. Both dietary and cultural factors might be responsible for the differences observed. In addition, the Middle Paleolithic Neanderthal specimens studied show a highly heterogeneous pattern of microwear when compared to the other samples considered, which is inconsistent with a hypothesis of all Neanderthals having a strictly carnivorous diet. The high density of striations observed in the buccal surfaces of several Neanderthal teeth might be indicative of the inclusion of plant foods in their diet. The buccal microwear variability observed in the Neanderthals is compatible with an overall exploitation of both plant and meat foods on the basis of food availability. A preliminary analysis of the relationship between buccal microwear density and climatic conditions prevailing in Europe during the Late Pleistocene has been attempted. Cold climatic conditions, as indicated by oxygen isotope stage data, seem to be responsible for higher densities of microwear features, whereas warmer periods could correspond to a reduced pattern of scratch density. Such a relationship would be indicative of less abrasive dietary habits, perhaps more meat dependent, during warmer periods.     

In vitro wear simulation on the RandomPOD wear testing system as a screening method for bearing materials intended for total knee arthroplasty

The 16-station RandomPOD wear test system, previously validated for prosthetic hip wear, was used in the simulation of knee wear mechanisms with a ball-on-flat test configuration. This consisted of a CoCr pin with a ground and polished spherical bearing surface (radius 28 mm) against a conventional, gamma-sterilized UHMWPE disk in serum lubrication. The biaxial motion, consisting of x and y translations, and the load was non-cyclic. Relative to the disk, the center of contact wandered within a circle of 10 mm diameter, and the average sliding velocity was 15.5 mm/s (ranging from 0 to 31 mm/s). The load varied non-cyclically between 0 and 142 N (average 73 N). In the 60-day test with 16 similar wear couples, moderate adhesive wear, the principal wear mechanism of a well-functioning prosthetic knee, dominated. This showed as a burnished, circular wear mark (diameter 13.2 mm, area 137 mm²). The wear factor was 2.04±0.03×10⁻⁶ mm³/N m (mean±95 percent confidence limit). For the first time a truly multidirectional, realistic and uniform, large capacity pin-on-disk simulation of knee wear mechanisms was implemented.     

Influence of kinematics on the wear of a total ankle replacement

Total ankle replacement (TAR) is an alternative to fusion, replacing the degenerated joint with a mechanical motion-preserving alternative. Minimal pre-clinical testing has been reported to date and existing wear testing standards lack definition. Ankle gait is complex, therefore the aim of this study was to investigate the effect on wear of a range of different ankle gait kinematic inputs. Five Zenith (Corin Group) TARs were tested in a modified knee simulator for twelve million cycles (Mc). Different combinations of IR rotation and AP displacement were applied every 2Mc to understand the effects of the individual kinematics. Wear was assessed gravimetrically every Mc and surface profilometry undertaken after each condition. With the initial unidirectional input with no AP displacement the wear rate measured 1.2±0.6 mm³/Mc. The addition of 11° rotation and 9 mm of AP displacement caused a statistically significant increase in the wear rate to 25.8±3.1 mm³/Mc. These inputs seen a significant decrease in the surface roughness at the tibial articulation. Following polishing three displacement values were tested; 0, 4 and 9 mm with no significant difference in wear rate ranging 11.8–15.2 mm³/Mc. TAR wear rates were shown to be highly dependent on the addition of internal/external rotation within the gait profile with multidirectional kinematics proving vital in the accurate wear testing of TARs. Prior to surface polishing wear rates were significantly higher but once in a steady state the AP displacement had no significant effect on the wear.     

Differences in interproximal and occlusal tooth wear among prehistoric Tennessee Indians: implications for masticatory function

Breadth of the interproximal wear facet between lower P2 and M1 and between lower M1 and M2 was measured in human skeletal samples representing the Archaic, Woodland, and Mississippian periods of Tennessee River Valley prehistory, with the aim of assessing relative magnitudes of applied masticatory forces. When stratified by level of occlusal wear, mean interproximal facet breadth was consistently larger in the Archaic sample than in the Mississippi sample, with the Woodland sample intermediate. An analysis of covariance demonstrated that there was significant (p less than or equal to 0.01) differences in facet size among the three groups even when differencs in crown breadth were taken into account. Similar results were obtained in regressions of facet size on chronological age (Archaic larger than Mississippian at P less than or equal to 0.01). Since rate of occlusal wear appears to be somewhat greater in the Archaic sample than in the later samples, the differences in interproximal wear are probably underestimated. It is suggested that the high levels of interproximal wear in the Archaic are indicative of the large occlusal forces and repetitive chewing required to masticate a diet of seeds, wild plant foods, and small animals, for which prior preparation (e.g., grinding, cooking) was minimal or nonexistent (as indicated by paleofecal samples). The lower amounts of interproximal wear observed in the Woodland and Mississippian samples imply considerable reductions in strenous mastication, perhaps due to the widespread adoption during these period of pottery and the earth oven, together with ethnographically-documented techniques of food preparation that transformed most foods to a soft consistency.     

Age-related variability of serum protein antigens in sturgeons (Acipenseridae, Acipenseriformes)

We studied the variability of antigenic properties of proteins in two sturgeon species at different stages of postembryonic development. The deepest changes occurred in individual components of albumins and beta-globulins (transferrins) and were mostly related to an increased proportion of the protein accounting for these antigens. Transformation of the main component of albumins A1 into adult antigens was completed in 5-month old fry. The main component of beta-globulins A (component of transferrins) appeared in the blood flow much later than other proteins and could retain the fry features until the age of 3-4 years. Other antigens belonging to alpha1- and alpha2-globulins and the second component of transferrins were more stable and did not undergo substantial changes. The direction of ontogenetic variability of serum antigens in sturgeon fry did not depend on the habitat of adult fish in fresh or sea water.     

Release of neutral proteinases from mononuclear phagocytes and synovial cells in response to cartilaginous wear particles in vitro

Cartilaginous wear particles were retrieved from synovial fluid aspirates of human diarthrodial joints and added to cultures of human or murine mononuclear phagocytes or human synovial cells. In each case, addition of the wear particles elevated the production of proteinases active at neutral pH against collagen, gelatin, azocasein and the synthetic pentapeptide phenylazobenzyloxycarbonyl-L-Pro-L-Leu-Gly-L-Pro-D-Arg. Synovial cells secreted more than five times as much collagenase as the same number of the other cells. All types of cell secreted significant quantities of enzymes active against the noncollagenous substrates. Mild treatment of the spent media with trypsin stimulated all of these enzymic activities. The spent culture media of synovial cells which had been exposed to cartilaginous wear particles released hydroxyproline and glycosaminoglycan from powdered cartilage, indicating the production of enzymes which degrade both the collagen and proteoglycan of the cartilaginous matrix. Cultures of mononuclear phagocytes, in contrast, while solubilizing chondroitin sulphate from cartilage, released very little hydroxyproline. The ability of wear particles to elicit these effects suggests a role for them in the pathogenesis of oesteoarthritis and other types of joint deterioration.     

Dietary boron does not affect tooth strength,micro-hardness,and density,but affects tooth mineral composition and alveolar bone mineral density in rabbits fed a high-energy diet

The objective of this study was to determine whether dietary boron (B) affects the strength, density and mineral composition of teeth and mineral density of alveolar bone in rabbits with apparent obesity induced by a high-energy diet. Sixty female, 8-month-old, New Zealand rabbits were randomly assigned for 7 months into five groups as follows: (1) control 1, fed alfalfa hay only (5.91 MJ/kg and 57.5 mg B/kg); (2) control 2, high energy diet (11.76 MJ and 3.88 mg B/kg); (3) B10, high energy diet + 10 mg B gavage/kg body weight/96 h; (4) B30, high energy diet + 30 mg B gavage/kg body weight/96 h; (5) B50, high energy diet + 50 mg B gavage/kg body weight/96 h. Maxillary incisor teeth of the rabbits were evaluated for compression strength, mineral composition, and micro-hardness. Enamel, dentin, cementum and pulp tissue were examined histologically. Mineral densities of the incisor teeth and surrounding alveolar bone were determined by using micro-CT. When compared to controls, the different boron treatments did not significantly affect compression strength, and micro-hardness of the teeth, although the B content of teeth increased in a dose-dependent manner. Compared to control 1, B50 teeth had decreased phosphorus (P) concentrations. Histological examination revealed that teeth structure (shape and thickness of the enamel, dentin, cementum and pulp) was similar in the B-treated and control rabbits. Micro CT evaluation revealed greater alveolar bone mineral density in B10 and B30 groups than in controls. Alveolar bone density of the B50 group was not different than the controls. Although the B treatments did not affect teeth structure, strength, mineral density and micro-hardness, increasing B intake altered the mineral composition of teeth, and, in moderate amounts, had beneficial effects on surrounding alveolar bone.     

Tooth wear, Neanderthal facial morphology and the anterior dental loading hypothesis

The Anterior Dental Loading Hypothesis states that the unique Neanderthal facial and dental anatomy was an adaptive response to the regular application of heavy forces resulting from both the masticatory and cultural use of the anterior teeth. Heavy anterior tooth wear frequently observed in Neanderthal specimens is cited as a main source of evidence for heavy forces being applied to these teeth. From this, it might be predicted that the wear shown on the anterior teeth of Neanderthals would greatly exceed that of the posterior teeth and that this differential would be greater than in other hominins with different facial morphologies.In this paper, a new method of examining tooth wear patterns is used to test these predictions in a large assemblage of Late Pleistocene hominins and a group of recent hunter-gatherers from Igloolik, Canada. The results show that all Late Pleistocene hominins, including Neanderthals, had heavily worn anterior teeth relative to their posterior teeth but, contrary to expectations, this was more pronounced in the modern humans than in the Neanderthals. The Igloolik Inuit showed heavier anterior tooth wear relative to their posterior teeth than any Late Pleistocene hominins. There was, however, a characteristic Neanderthal pattern in which wear was more evenly spread between anterior teeth than in modern humans. Overall, the evidence presented here suggests that all Late Pleistocene hominins habitually applied heavy forces between their anterior teeth and that Neanderthals were not exceptional in this regard. These results therefore does not support the Anterior Dental Loading Hypothesis.