Incisor Size Research Articles

The return of the unicorns: the natural history and conservation of the greater one-horned rhinoceros

Foreword, by George B. SchallerPrefaceIntroductionPart I: Vanishing Mammals, Vanishing Landscapes 1. Vanishing Mammals: The Rise and Fall of the Rhinoceroses2. Culture, Conservation, and the Demand for Rhinoceros Horn3. Vanishing Landscapes: The Flood Plain Ecosystem of ChitwanPart II: Biology of an Endangered Megaherbivore 4. Size and Sexual Dimorphism in Greater One-Horned Rhinoceros5. The Biology of an Extinction-Prone Species: Facing Demographic, Genetic, and Environmental Threats6. Life on the Flood Plain: Spacing and Ranging Behavior, Feeding Ecology, and Activity Patterns7. Male Dominance, Reproductive Success, and the Incisor Size Hypothesis8. Endangered Phenomena: Rhinoceros as Landscape ArchitectsPart III: The Recovery of Endangered Large Mammal Populations and their Habitats in Asia 9. Does Privately Owned Ecotourism Support Conservation of Charismatic Megafauna?10. Making Room for Megafauna: Promoting Local Guardianship of Endangered Species and Landscape-scale Conservation11. The Recovery of Rhinoceros and Other Asian Megafauna ConclusionAppendix A: MethodsAppendix B: Measurements and other Physical Features of greater one-horned rhinoceros captured in Royal Chitwan National Park, NepalAppendix C: Demographic and Genetic DataAppendix D: Seasonal Home Range and Daily MovementsAppendix E: A Profile of Rhinoceros BehaviorAppendix F: Reproductive Histories of Adult Female RhinocerosReferencesIndex

The mechanics of the first bite.

An analysis of the action of the incisor teeth in humans is presented in terms of the fracture of food particles. It is predicted that the resistance of foods with an essentially linear elastic response to an initial bite by the incisors will depend on the square root of the product of two food properties, Young's modulus and toughness. This quantity should be approximately equal to the product of the stress at cracking during a bite, and the square root of the length of a notch or indentation from which that crack initiates. As a test of the theory, the relationship between in vivo stresses and the depth of incisal penetration, measured during bites on seven 'snack' foods by 10 subjects, and food properties established from mechanical testing, was investigated. Theory and experiment were found to be in excellent agreement. A dimensionless index of the efficiency of incision is suggested, relating fracture performance by subjects to values from a testing machine. This appears to have a high level of inter-subject discrimination with efficiencies varying about threefold. The method appears to have potential applications in dentistry, food science and studies of human and primate evolution.

A comparison of the supra-alveolar pulp size of impeded and unimpeded mandibular rat incisors using micro-computed tomography

A comparison of the supra-alveolar pulp size of impeded and unimpeded mandibular rat incisors using micro-computed tomography

Tooth anomalies associated with failure of eruption of first and second permanent molars

The occurrence of tooth anomalies in association with failure of the first and second molars to erupt was assessed in a sample of 1520 nonsyndromic subjects with uncrowded dental arches (mean age, 14 years 4 months) and compared with the prevalence rate calculated in a matched control group of 1000 subjects. The tooth anomalies examined included infraocclusion of deciduous molars, palatal displacement of maxillary canines, rotation of maxillary lateral incisors, aplasia of second premolars, and small size of maxillary lateral incisors. Associations among arrested eruption of first and second permanent molars and anomalies in tooth eruption and position (infraoccluded deciduous molars, palatally displaced canines, rotated maxillary lateral incisors) were highly significant (P <.001). No significant association was found among the occurrence of molar eruption disturbances, aplasia of premolars, and small-sized laterals. These findings point to a common biologic cause for the appearance of failure of eruption of molar teeth and other disturbances in tooth eruption and position, most likely under genetic influence. (Am J Orthod Dentofacial Orthop 2000;118:608-10)

Species differentiation among muroid rodents on the basis of their lower incisor size and shape : ecological and taxonomical implications

Article Species differentiation among muroid rodents on the basis of their lower incisor size and shape : ecological and taxonomical implications was published on January 1, 2000 in the journal Mammalia (volume 64, issue 2).

Incisor size and community structure in rodents: Two tests of the role of competition

We used two different approaches to test for the effect of interspecific competition on community-wide patterns in the size of the upper incisor in six rodent communities. One tests for constancy of size ratios between adjacent species (Barton and David's test), and the other tests for minimum mean size overlap between species pairs (randomization test). The results of the two tests were more congruent for the radius of the upper incisor than for its diameter. Although a number of tests gave significant results, they led to a consistent rejection of the null hypothesis of a randomly generated pattern only in two communities from an African rainforest. Many factors are likely to disturb community structure, among which we identify recent species introductions and the presence of rare species. Our results also show that Hutchinson's rule of a limiting size similarity does not hold; the mean size ratio between adjacent species was correlated with the overall size range and the number of species in a community.

Effects of maternal acetazolamide treatment on body weights and incisor development of the fetal rat.

The incisor development of fetal rats on gestation day 19 was well correlated with their fetal weights. The number of odontoblasts in the mandibular incisors, an index of incisor development, increased more than that of the maxillary incisors with increase in fetal body weights. Maternal acetazolamide treatments were observed to suppress the mean fetal weight and to retard incisor development. A smaller incisor size, a thinner predentin layer, and fewer odontoblasts were characteristic of the acetazolamide group. There was also a good correlation between the fetal weights and the number of odontoblasts in the acetazolamide group. From these results, we postulated that the retarded incisor development of the fetal rats caused by the maternal acetazolamide treatment was related to their suppressed fetal weights. However, the regression coefficient of the fetal weights and the number of odontoblasts in the acetazolamide group was smaller than that of the vehicle control group. It may indicate that retarded incisor development in response to maternal acetazolamide treatment is to some extent independent of suppressed fetal weight.

Mixed dentition analysis for Hong Kong Chinese.

Using simple linear regression analyses, prediction equations for the combined mesiodistal crown diameters of canines and premolars based on lower incisor size were generated from 97 Hong Kong Chinese (51 males and 46 females, average age 12.31 years) out of a sample of 112. The mesiodistal crown diameters of the permanent teeth were measured using calipers and recorded to the nearest 0.01 mm. Significant sex differences were found for the combined diameters of the canine-premolar segments. The coefficients of correlation between combined diameters of canines and premolars and lower incisors ranged from 0.65 to 0.79. Significant sex differences of the regression equations were found and thus four simple linear regression equations were generated. Coefficients for the slope ranged from 0.58 to 0.66, and coefficients for the intercept ranged from 6.66 to 8.82. The R2 values, standard errors of estimate, and absolute mean errors revealed that prediction models for females were less precise than those for males. Probability tables were constructed from the results of the present study. The prediction equations were found to differ from those of Tanaka and Johnston. Accuracy in the mixed dentition analysis for southern Chinese would be improved by applying the prediction equations or probability tables generated from the present study.

Dinocephalians are not anomodonts

ABSTRACT Watson and Romer's (1956) proposal that dinocephalians, dicynodonts, and venjukoviomorphs comprise a monophyletic Anomodontia has been supported by King (1988) on the basis of four hypothesized synapomorphies: 1) loss of the coronoid bone, 2) non-terminal nostrils with a long posterior spur of the premaxilla, 3) a grooved palatal surface of the vomer, and 4) reduction or loss of the internal trochanter of the femur. These characters, however, appear to be plesiomorphic for therapsids (long internarial process of the premaxilla, and a grooved palatal surface of the vomer), related to incisor size and/or the degree to which the premaxillary alveolar margin is elevated, and show no consistent phylogenetic pattern (position of the external nares), homoplasies (convergent reduction or loss of the internal trochanter of the femur), or not even characteristic of dinocephalians (loss of the coronoid bone). There is no evidence to support inclusion of dinocephalians in the Anomodontia.

Incisor size and shape: implications for feeding behaviors in saber-toothed “cats”

ABSTRACT Although the great size and procumbency of the incisor teeth of many saber-toothed carnivorans have long been recognized, the potential functional significance of carnivoran incisor size and shape remains largely unexplored. Here, we explore upper incisor design and incisor arcade shape in living felids, canids, and hyaenids. In addition, we compare upper incisors of saber-toothed carnivorans with those of modern carnivorans and use these data to infer aspects of saber-tooth killing and feeding behaviors. Results demonstrate that the shape of individual upper incisors of extant carnivorans is intricately related to the dental arcade in which the teeth are rooted. Canids and hyaenids have robust incisors in parabolic arcades, whereas felid incisors are weaker, particularly in mediolateral bending, and are located in transversely linear arcades. It is proposed that the strength of the medial incisors is in part a consequence of arcade shape. Incisors in linear arcades can be weaker because they are...

Relationship of incisor size to diet and anterior tooth use in sympatric sumatran anthropoids.

Researchers often relate anthropoid incisor size to diet and ingestive behaviors. It is suggested that primates that frequently consume large, tough foods (i.e., fruits) require large incisors to process these items. This idea has been difficult to test because of a lack of data on anterior tooth use in wild primates, and a lack of understanding concerning the relationships between food properties and ingestive behaviors. The first field study of primate ingestive behaviors has recently been completed for four species of Sumatran anthropoids: Hylobates lar, Macaca fascicularis, Pongo pygmaeus, and Presbytis thomasi [Ungar, American Journal of Physical Anthropology 95:197-219, 1994; International Journal of Primatology 16:221-245, 1995]. This paper documents both relative and absolute incisor row width differences among these taxa, and evaluates the relationships between incisor size and feeding behaviors for specific taxa. Results indicate that differences in incisor size among these species cannot all be explained by degree of frugivory, food item size, or even degree of incisor use in ingestion alone. It is therefore suggested that inferences of dietary differences based on largely or solely on differences in incisor sizes of specific fossil anthropoid taxa should be approached with caution. © 1996 Wiley-Liss, Inc.

Genetic Covariance Structure of Incisor Crown Size in Twins

Previous studies of tooth size in twins and their families have suggested a high degree of genetic control, although there have been difficulties separating the various genetic and environmental effects. A genetic analysis of variation in crown size of the permanent incisors of South Australian twins was carried out, with structural equation modeling used to determine the relative contributions of genetic and environmental factors. Maximum mesiodistal crown dimensions of maxillary and mandibular permanent incisors were recorded from dental models of 298 pairs of twins, including 149 monozygous (MZ) and 149 dizygous (DZ) pairs. The analysis revealed that: (i) an adequate fit required additive genetic and unique environmental components; (ii) augmenting the model with non-additive genetic variation did not lead to a significant improvement in fit; (iii) there was evidence of shared environmental influences in the upper central incisors of males; (iv) the additive genetic component constituted a general factor loading on all eight teeth, with group factors loading on antimeric pairs of teeth; (v) unique environmental effects were mostly variable-specific; (vi) most factor loadings on antimeric tooth pairs could be constrained to be equal, indicating a symmetry of genetic and environmental influences between left and right sides; and (vii) estimated heritability of the incisor mesiodistal dimensions varied from 0.81 to 0.91.

The anterior dentition of Sivapithecus parvada, with comments on the phylogenetic significance of incisor heteromorphy in Hominoidea

Abstract A premaxillary fragment of Sivapithecus parvada preserving the germs of the right central and lateral incisors is described. The specimen was recovered in situ during excavation at locality Y311 in the upper Nagri Formation (ca. 9·2 m.y.a.) of the Siwalik Sequence, Potwar Plateau, Pakistan. The central incisor is approximately 35% larger than the next largest Swapithecus incisor, in keeping with the very large size of S. parvada compared to other Sivapithecus species, and is exceptionally long mesiodistally in relation to its breadth. It is also morphologically distinct, having a sharply angled distal margin and a distinct lingual tubercle. However, previous descriptions of Sivapithecus upper central incisors as having a continuous lingual shelf are in some cases erroneous and ignore the morphological variation present in the sample. In several features of anterior tooth size, morphology and proportionality, S. parvada resembles Pongo more than do other species of Sivapithecus. The I1/I2 length ratio of the new specimen is 2·12, the largest size disparity reported for any fossil catarrhine, and greater than any single value in a large sample of Pongo pygmaeus. Very great size disparity between upper central and lateral incisors is widely considered to be a synapomorphy of the orang-utan lineage. We conclude, however, that descriptions of upper incisor size heteromorphy in Pongo have in general been exaggerated and have failed to recognize substantial differences in this character between Bornean and Sumatran orang-utans. We further conclude, based on examination of a variety of Miocene hominoids and other Miocene catarrhine primates, that the character of I1/I2 proportionality has little if any phylogenetic utility within Hominoidea.

Resorbed lateral incisors adjacent to impacted canines have normal crown size

The importance of detecting maxillary canine impaction is that it may compromise dental health, particularly since a small but significant proportion of impacted canines is associated with the resorption of the roots of neighboring teeth. It has been shown that the existence of small and peg-shaped lateral incisors is highly correlated with maxillary canine palatal impaction. To date, however, it has not been established whether the root resorption that occurs has a similar correlation or a predilection for one or other types of lateral incisor crown structure. Accordingly, a group of patients with buccally or palatally impacted canines, in which root resorption of the lateral incisor could be diagnosed roentgenographically, was examined and compared with a group of cases with palatally impacted canines, none of which showed root resorption, which served as controls, The mesiodistal crown dimension of the lateral incisor in the experimental group was found to be normal in all patients except three (13%), which was significantly different from the distribution of lateral incisor size in the control group ( p < 0.001). In the majority of the cases, aggressive root resorption of the lateral incisor root had occurred. We would speculate that in these cases, the normal-sized and early developing lateral incisor root obstructs the deviated eruption path of the canine and consequently stands a considerably greater chance of being damaged by resorption.

Investigation into the relationship between perikymata counts and crown formation times

AbstractThis study reports on a sample of 12 modern human incisors (from two archaeological sites) that were viewed with a scanning electron microscope and whose perikymata were counted. These 12 incisors more than doubles the previously published sample size of modern human incisors that have served as the published standard for perikymata number in human incisors and have been employed to define taxonomic relationships in fossil hominids. All previously published fossil specimens fall within the expanded range of modern human perikymata counts and can no longer be considered distinctively nonhuman in dental formation time.Five neandertal incisors from the Krapina site in Croatia, Yugoslavia, were also examined. These incisors substantially expand the previous data base for counts of perikymata in Homo sapiens neanderthalensis, likewise overlapping the previously published modern human range.Finally, the validity of methods that have been employed for deriving crown formation times from perikymata counts in fossil hominines is called into question. Utilizing the presently known perikymata ranges for modern humans, these methods do not predict the range of known crown formation times of modern humans as assessed from studies of living children.

Heterosis for survival and dentition in Hereford, Angus, Shorthorn, and crossbred cows

Records of 328 Angus, Hereford, Shorthorn, and first-cross cows produced from 1960 to 1963 were used to estimate heterosis (h) and individual (gI) and maternal (gM) average breed effects on cumulative survival (CS) by ages to 12 yr, longevity (L), and size (SI) and condition of incisors at 10 to 15 yr of age. Reasons for cow disposal were also studied. The 155 cows born in 1960 and 1961 first calved at 3 yr of age, and the 173 born in 1962 and 1963 first calved at 2 yr of age. Analyses for CS and L were done for both actual culling of cows open in two consecutive years (AC) and imposed culling of any open cow (IC). The model for CS and L included cow birth year-breed of cow's sire (Y-S), sires within Y-S, breed of dam (D), and D x Y-S. For SI, the model included breed of cow, year of recording, and quadratic effect of age. Linear contrasts were used to estimate h, gI, and gM for quantitative variables, and chi-square was used for discrete variables. Under both AC (P less than .05) and IC, crossbreds exceeded straightbreds in CS to 12 yr (16.7 and 8.5%) and L (1.36 and .99 yr). Estimates of gI and gM for CS and L were generally small, except for the low (P less than .05) gM of Shorthorn cows under IC. Mortality and culling for emaciation, cancer eye, or prolapse was less for crossbreds than for straightbreds and increased with age. Crossbreds had longer (P less than .01) and better (P less than .001) teeth than straightbreds. The longer productive life of crossbred cows reduces rearing costs for replacements and increases sales of calves and cull cows.

Incisor size and wear in Australopithecus africanus and Paranthropus robustus

Comparisons based upon recent body size estimates indicate that the maxillary central incisors of Paranthropus robustus are relatively smaller than those of Australopithecus africanus. The MD diameters of A. africanus incisors are similar to expected values for a large-bodied catarrhine. The P. robustus crowns are noticeably smaller, being comparable to those of modern humans among extant catarrhines. This suggests that P. robustus may have ingested foods that required less extensive incisal preparation than the foods consumed by A. africanus. I 1 bevelling patterns suggest that a horizontal incisal wear surface was probably maintained in both taxa through posterior tipping of these teeth. This indicates that the incisal surfaces of differently worn crowns may be legitimately compared in microwear analyses. The ratio of microwear pits to scratches, scratch orientations and wear feature dimensions do not differ significantly between the two early hominid taxa. Indeed, the differences among the labial, incisal and lingual surfaces within each species are commonly more noticeable than the differences between the two species. Microwear feature densities in A. africanus, however, are significantly higher for all three I 1 surfaces. Comparisons with extant primates suggest that A. africanus incisors may have been employed to process a greater variety of foods, including larger, more abrasive items than were encountered by P. robustus.

Comparative studies of geographically isolated populations in Japan based on dental measurements.

In recent years, considerable attention has been paid on the physical characteristics of the Ainu and the Okinawa Islanders in connection with the origin of modern Japanese. In the present study, the metric traits of the dentition in the Tokunoshima Islanders, the Aogashima Islanders, the Okinawa Islanders and the Ainu were compared with each other and with those in the modern populations from Tokyo and Nagasaki, and the Aeneolithic Yayoi population. The first four populations have been isolated or at least nearly isolated for a long period from the populations of main island of Japan because of their geographic conditions.As regards the shape factors in the dentition, the four isolated populations are closely related to each other, and they show closer affinities to the Tokyo population than to the Nagasaki and the Yayoi populations. The shape factor in the latter two populations shows similar trends but is quite different from that in the other four isolated populations as well as the Tokyo population. Using the principal component analysis method, it is elucidated that the relative size of premolars and incisors plays an important role in difference of the shape factor among the populations. Taking all the results obtained into account, the characteristics of the dentition in the isolated populations are likely under the same genetic control which is common to the Neolithic Jomon population. The origin and affinity of modern Japanese are discussed on the basis of such findings.

Static intraspecific allometry of jaws and teeth in Cercopithecus aethiops

Adult static intraspecific allometry of jaw size and tooth area was evaluated in a sample of 100 Cercopithecus aethiops crania (50 male, 50 female). Tooth areas were calculated from mesiodistal and buccolingual measurements of all the teeth in both arcades and were scaled to four viscero‐cranial measurements: bimaxillary breadth, maxillo‐alveolar length, mandibular length and bigonial width. Allometric coefficients calculated for jaw dimensions alone indicate tighter viscerocranial integration in females than in males. A finding of note was that half of the variation in maxillo‐alveolar length may be accounted for by variation in mandibular length: females are isometric, males negatively allometric.A similar degree of allometric mosaicism was found when maxillary incisor size was scaled to maxillary length and width. In females, the relationship was negatively allometric, whilst incisor size in males was found to be unrelated to either. Negative allometry characterized the relationship of canine base area to jaw length in both sexes, with males additionally being positively allometric to mandibular width.The scaling of postcanine tooth areas to jaw length was characterized by a dichotomous pattern: males showed significant mandibular integration whilst females showed only significant maxillary integration. Compensatory tooth size interaction between maxillary canine base area and the summed incisor and postcanine areas was suggested by the significant negative allometric relation between them.

Tooth morphology and lower incisor alignment many years after orthodontic therapy

The dental models of seventy-seven orthodontically treated patients were evaluated to determine the contribution of lower incisor tooth dimensions to their alignment many years after treatment. Tooth dimensions included the maximum mesiodistal (MD) and faciolingual (FL) dimensions and the shape ratio represented by MD/FL. Incisor alignment was assessed by means of Little's irregularity index, and all measurements were recorded to the nearest 0.1 mm with modified dial calipers. Multiple regression analysis revealed that the total contribution of all these lower incisor dimensions accounted for only 7.4% of the variability in their alignment, which was not statistically significant. A similar lack of association between lower incisor tooth dimensions and their alignment was found in a sample of eighty-six adults with untreated malocclusions. It therefore appears that the size and shape of the lower incisors do not significantly contribute to their alignment many years after orthodontic treatment.