An experimental approach to modeling the strength of canine teeth

The strength of canine teeth in several carnivores is found through direct fracture experiments. The average forces required to break the canines of adult animals are coyote 1170 N, red fox 533 N, bobcat 737 N and raccoon 512 N. Stresses created in teeth at the breaking load are predicted by finite-element analysis and beam theory. The ultimate tensile stress sustainable in these teeth is 338 MPa in adult animals. The large pulp cavity in the canines of young animals significantly weakens the bases of their teeth (by about 25%), but as the animal ages the pulp cavity decreases and has little effect on overall tooth strength. The tooth material of young of the year is significantly weaker than that from older animals (by about 35%). With the experimentally derived ultimate tensile stress, finite-element analysis can estimate the breaking load of canines for several carnivores. A significant allometric relationship exists between log of body weight and log of strength of tooth (slope=0.81).     

Sexual dimorphism in modern human permanent teeth

On average, males possess larger tooth crowns than females in contemporary human populations, although the degree of dimorphism varies within different populations. In previous studies, different amounts of either enamel or dentine were implicated as the cause of this dimorphism. In this study, we attempt to determine the nature of sexual dimorphism in the crowns of permanent modern human teeth and to determine if two contrasting tooth types (permanent third molars and canines) show identical patterns of dimorphism in enamel and dentine distribution. We estimated the relative contributions of both enamel and dentine to total crown size, from buccolingual sections of teeth. Our sample consisted of a total of 144 mandibular permanent third molars and 25 permanent mandibular canines of known sex. We show that sexual dimorphism is likely due, in part, to the presence of relatively more dentine in the crowns of male teeth. However, whatever the underlying cause, dimorphism in both tooth root and tooth crown size should produce measurable dimorphism in tooth weight, though this has not been previously explored. Therefore, we provide some preliminary data that indicate the usefulness of wet tooth weight as a measure of sexual dimorphism. Both male permanent third molars and canines are significantly heavier than those of females. The weight dimorphism reported here for both classes of teeth may prove a useful finding for future forensic studies. In particular, weights of canines may be more useful as a means of sexing modern human skeletal material than linear or area measurements of teeth.     

Tusk abnormalities in wild boar (<Emphasis Type="Italic">Sus scrofa</Emphasis> L.)

This paper describes pathological alterations in the permanent canines (tusks) of four male wild boars. The mandibular tusks of all individuals, and also some of the maxillary tusks, exhibited an extended enamel hypoplasia in their apical portion, denoting an impairment of secretory ameloblast function. Moreover, the pulp cavities of the mandibular tusks were exposed through cleft-like openings in the wear (whetting) surfaces of the teeth. Presence of a plug of reparative dentine within the pulp cavity was observed in a split mandibular tusk of one individual. In a second boar, the presence of a plug of reparative dentine within the pulp cavity of the mandibular tusks was indicated radiographically. These findings suggested a reparation process attempting to demarcate a vital, apical pulp portion from a necrotic, incisal portion. The enamel hypoplasias observed in the teeth are regarded to be sequelae of the pulp inflammation caused by bacterial invasion in the mandibular tusks. Most likely, bacterial invasion of the dental pulp occurred through the cleft-like openings in the tusks whetting surfaces, the openings resulting from insufficient formation of secondary dentine. It is, however, also conceivable that pulp inflammation and partial necrosis occurred as a consequence of bacterial invasion of patent dentinal tubules, and that the openings in the whetting surface developed secondarily as a consequence of the pulp changes. One mandibular tusk showed marked signs of resorption apically, suggesting a spread of the inflammation from the pulp into the periodontium.     

Tissue contributions to sex and race: differences in tooth crown size of deciduous molars.

This study describes size of constituent deciduous tooth crown components (enamel, dentine, and pulp) to address the manner in which males characteristically have larger teeth than females, and the observation that teeth of American blacks are larger than those of American whites. Measurements were collected (n = 333 individuals) from bitewing radiographs using computer-aided image analysis. Tissue thicknesses (enamel, dentine, pulp) were measured at the crown's mesial and distal heights of contour. Deciduous mesiodistal molar crown length is composed of about 1/7 enamel, 1/3 dentine, and 1/2 pulp. Details differ by tooth type, but males typically have significantly larger dentine and pulp dimensions than females; there is no sexual dimorphism in marginal enamel thickness. Males scale isometrically with females for all variables tested here. Blacks significantly exceed whites in size of all tissues, but tissue types scale isometrically with blacks and whites with one exception: enamel thickness is disproportionately thick in blacks. While the absolute difference is small (5.56 mm of enamel in blacks summed over all four deciduous molar tooth types vs. 5.04 mm in whites), the statistical difference is considerable (P < 0.001). Aside from enamel, crown size in blacks is increased proportionately vis-à-vis whites. Principal components analysis confirmed these univariate relationships and emphasizes the statistical independence of crown component thicknesses, which is in keeping with the sequential growth and separate embryonic origins of the tissues contributing to a tooth crown. Results direct attention to the rates of enamel and dentine deposition (of which little is known), since the literature suggests that blacks (with larger crowns and thicker enamel) spend less time in tooth formation than whites.     

Comparison of teeth and dermal denticles (odontodes) in the teleost Denticeps clupeoides (Clupeomorpha)

The present work is a contribution to an extensive comparative structural and developmental study we have undertaken to understand the evolution of the dermal skeleton in osteichthyans. We have investigated the structure of developing and functional tooth-like dermal denticles located on the head of Denticeps clupeoides, a clupeomorph, and compared their features to those of oral teeth. Morphological (scanning electron microscopy) and structural (light microscopy and transmission electron microscopy) observations clearly demonstrate that these small, sharp, conical and slightly backward-oriented denticles are true odontodes, i.e., homologous to oral teeth. They are composed of a dentine cone surrounding a pulp cavity, the top being covered by a hypermineralized cap. These odontodes are attached to a circular pedicel of attachment bone by a ligament that mineralizes, and the attachment bone matrix merges with that of the bony support. The pedicel of attachment bone surrounds a vascular cavity that is connected to the pulp cavity which is devoid of blood vessels and of nerve endings. Once the odontode is functional, the deposition of collagen matrix (called circumpulpar dentine) continues against the dentine, ligament, and attachment bone surfaces, thereby provoking a narrowing of the pulp cavity. Odontodes are shed by resorption occurring at the base, but their pedicels of attachment bone persist at the bone surface and become embedded in the bone matrix, within which they are clearly visible. The oral teeth are similar in shape, size, and structure to the odontodes, and they show only small differences probably related to the different function of these elements: They are more firmly anchored to the attachment bone, and the amount of dentine is relatively smaller than in odontodes. Despite their different functions, this close structural agreement between teeth and odontodes in Denticeps suggests that 1) competent cells from the same (ecto)mesenchymal population might be involved and 2) the genetic control of the developmental processes could be identical. It is suggested that the odontode expression in extra-oral positions is a relatively late novelty in this lineage. J. Morphol. 237:237–255, 1998. © 1998 Wiley-Liss, Inc.     

EVALUATION OF AN EFFECTIVE METHOD TO ESTIMATE AGE OF CAPE FUR SEALS USING GROUND TOOTH SECTIONS

Teeth of known-age Cape fur seals Arctocephalus pusillus pusillus were used to validate age estimated from ground sections. In the canines, dentine growth layer groups (GLGs) reflected age accurately but no reliable readings could be obtained from GLGs in the cementum. Upper canines were the most suitable for age estimation. By contrast, in the postcanines where the cementum is thicker, only GLGs in the cementum could be used for age determination, but not with the same accuracy as for dentine in the canines. Therefore, it is recommended that GLGs in the dentine be used to determine age in the Cape fur seal. However, pulp cavities in canines closed at about 13 yr and consequently GLGs in the cementum of the postcanines should be used where the pulp cavities of canines are closed. Accurate estimation of age is not possible from the dentine of older animals.     

Comparison of Mexican Wolf and Coyote Diets in Arizona and New Mexico

ABSTRACT Interactions between wolves (Canis lupus) and coyotes (C. latrans) can have significant impacts on their distribution and abundance. We compared diets of recently translocated Mexican wolves (C. l. baileyi) with diets of resident coyotes in Arizona and New Mexico, USA. We systematically collected scats during 2000 and 2001. Coyote diet was composed mostly of mammalian species, followed by vegetation and insects. Elk (Cervus elaphus) was the most common item in coyote scats. Mexican wolf diet had a higher proportion of large mammals and fewer small mammals than coyote diet; however, elk was also the most common food item in Mexican wolf scats. Our results suggest that Mexican wolf diet was more similar to coyote diet than previously reported, but coyotes had more seasonal variation. Considering results in other areas, we expect that Mexican wolves will have a negative impact on coyotes through direct mortality and possibly competition. Reintroduction of Mexican wolves may have great impacts on communities by changing relationships among other predators and their prey.     

Ontogeny of canine dimorphism in extant hominoids.

Many behavioral and ecological factors influence the degree of expression of canine dimorphism for different reasons. Regardless of its socioecological importance, we know virtually nothing about the processes responsible for the development of canine dimorphism. Our aim here is to describe the developmental process(es) regulating canine dimorphism in extant hominoids, using histological markers of tooth growth. Teeth preserve a permanent record of their ontogeny in the form of short- and long-period incremental markings in both enamel and dentine. We selected 52 histological sections of sexed hominoid canine teeth from a total sample of 115, from which we calculated the time and rate of cuspal enamel formation and the rate at which ameloblasts differentiate along the future enamel-dentine junction (EDJ) to the end of crown formation. Thus, we were able to reconstruct longitudinal growth curves for height attainment in male and female hominoid canines. Male hominoids consistently take longer to form canine crowns than do females (although not significantly so for our sample of Homo). Male orangutans and gorillas occasionally take up to twice as long as females to complete enamel formation. The mean ranges of female canine crown formation times are similar in Pan, Gorilla, and Pongo. Interspecific differences between female Pan canine crown heights and those of Gorilla and Pongo, which are taller, result from differences in rates of growth. Differences in canine crown heights between male Pan and the taller, more dimorphic male Gorilla and Pongo canines result both from differences in total time taken to form enamel and from faster rates of growth in Gorilla and Pongo. Although modern human canines do not emerge as significantly dimorphic in this study, it is well-known that sexual dimorphism in canine crown height exists. Larger samples of sexed modern human canines are therefore needed to identify clearly what underlies this.     

Canine tooth strength and killing behaviour in large carnivores

Bending strength of upper canine teeth is examined among living canids, felids, hyaenids and several extinct species including sabretooth cats, borophagine dogs and the dire wolf, Canis dirus. The tooth is modelled as a cantilever with an elliptical cross-section. Using beam theory, the bending strength of the upper canine is calculated given a constant force applied to the canine tip. Results indicate that felids and hyaenids have relatively stronger canines than canids, particularly in bending about the anteroposterior (AP) rather than the mediolateral axis. It is suggested that canine shape reflects the forces produced during killing and feeding. As shown by an analysis of jaw muscle moment arms, felids and hyaenids have relatively stronger bites than canids. Moreover, the canines of hyaenids and felids are perhaps more likely to contact bone during feeding and killing and consequently may be subjected to larger and more frequent bending moments about the AP axis. The canines of sabretooth cats are shown to be more similar in shape and strength characteristics to those of living canids than felids, whereas those of the borophagine dogs and the dire wolf are closer to modern hyaenas.     

Sexual dimorphism of the dental tissues in human permanent mandibular canines and third premolars

Methods of measuring tissue area from images of longitudinal thin tooth sections have been used to assess sexual dimorphism in the permanent dentition. The aim of this study was to demonstrate the extent of sexual dimorphism within the coronal tissue proportions of permanent mandibular canines and premolars, using area measurements of the enamel and dentine-pulp core. The sample consisted of embedded "half-tooth" sections from 45 individuals, all of known age-at-death and sex, collected from the St. Thomas' Anglican Church historic (1821-1874) cemetery site in Belleville, ON, Canada. The relative dentine-pulp area of the third premolars and canines displayed high levels of sexual dimorphism, as well as statistically significant mean differences between the sexes. The male canines and premolars have significantly more dentine than their female counterparts, as well as relatively more dentine with respect to overall crown size. The female canines and premolars have significantly more enamel relative to overall crown area than those of the males. These results suggest that relative area measures of crown tissues are more predictable measures of sexual dimorphism than absolute measures, and tissue proportions may remain constant despite intrasex variation in overall tooth crown size.     

Teeth of extant Polypteridae and Amiidae have plicidentine organization

The study of teeth of the lower jaws of Amia calva and Polypterus senegalus, with non -destructive X-ray tomography, has revealed that there are dentine folds in the tooth pulp cavity in both species. These folds are simple and present only in the base of the pulp cavity where they strengthen the fixation of teeth on the jaw. So the teeth of these two basal actinopterygian taxa have a simplexodont type of plicidentine like the extinct †Cheirolepis and various extant teleostean predators, whereas the extant Lepisosteids, the sister group of Amiidae, have polyplocodont plicidentine. The phylogenetic/adaptive significance of this simplexodont plicidentine is discussed.     

Comparative bite forces and canine bending strength in feline and sabretooth felids: implications for predatory ecology

The sabretooth felids were widespread across much of the world in the Late Tertiary, and appear to have been an important group of large predators. Owing to the substantially different skull morphology of derived sabretooths compared with extant felids, there has been considerable debate over the killing mode, bite forces, and bending strength of the large upper canines, and over the implications of these characteristics on feeding ecology. Debates have, however, usually been based on indirect comparisons of force vectors. In this paper, I provide assessments of the estimated force output from the jaw adductor muscles, based on estimates of muscle cross-sectional areas and force vectors, along with canine bending strengths, in a variety of sabretooth felids, in comparison with extant felids. In general, sabretoothed felids had moderately powerful bites, albeit with less jaw adductor power for their body sizes compared with extant felids, sometimes markedly so. Less derived sabrecats appear to have had proportionally higher bite forces than derived forms. The length of the upper canines seemingly compromised their bending strength at any given body size, and again this was most marked in derived forms. However, compared with estimated jaw adductor forces, the canines of sabrecats appear, if anything, to have been stronger than those of extant conical-toothed felids. It has previously been suggested that large sabretoothed felids hunted large prey with a canine shearing bite, powered in part by the jaw adductors and in part by the muscles of the upper neck–occipital region. The present results of canine bending strengths versus the predicted bite force from the jaw adductors supports this suggestion.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 151 , 423–437.     

Esthetic reconstruction of teeth in patient with dentinogenesis imperfecta--a case report

Dentinogenesis imperfecta (DI) is the result of a dominant genetic defect and affects both the deciduous and permanent dentitions. It is characterized by opalescent teeth composed of irregularly formed and undemineralized dentin which obliterates pulp chamber and root canal. DI can appear as a separate disorder or with osteogenesis imperfecta (OI). The teeth with DI show a grayish-blue to brown hue with dislodged enamel, dysplastic dentine with irregular dentinal tubules and interglobular dentine, short roots and pulpal obliteration, which all may lead to rapid and extensive attrition which require adequate crown reconstruction. The aim of this study was to show a reconstruction of frontal teeth in upper jaw with direct composite veneers in young adult patient with DI.     

Coyote Abundance,Sheep Predation,and Wild Prey Correlates Illuminate Mediterranean Trophic Dynamics

ABSTRACT Sheep predation by coyotes (Canis latrans) is a major problem for sheep producers in North America. Solutions are facilitated by a basic understanding of the trophic dynamic context of this problem, one that likely varies geographically in important qualitative ways. Little is known about vertebrate trophic dynamics in Mediterranean ecosystems, where prey are diverse and their biomass is strongly influenced multi-annually by variable rainfall. We used long-term data sets from north-coastal California, USA, to investigate whether wild prey fluctuations caused immediate negative effects on sheep predation via a reduction in the coyote functional response or delayed positive effects on sheep predation via a numerical response by coyote predators. Because we could not measure prey biomass directly, we used variables associated with lower trophic levels (e.g., annual plant productivity, vole abundance, rainfall) as proxies for wild prey biomass. Coyote population growth rate was positively correlated with lower-trophic-level variables of the previous year, suggesting a numerical response, and sheep (ad F + lambs) predation was positively correlated with coyote abundance in the current year. Sheep predation also was negatively correlated with lower-trophic-level variables of the current year, suggesting an immediate buffering effect of wild prey on sheep predation. Together, coyote abundance and lower-trophic-level variables explained 47% of the multi-annual variation in sheep kills. The negative pathway between lower-trophic-level variables and sheep predation was stronger than the positive pathway, possibly due to the erratic nature of multi-annual fluctuations in lower-trophic-level variables, which could prevent the numerical response from reaching its full potential. Monthly analyses revealed a type III functional response of coyotes to lambs, which is expected to enhance buffering effects of wild prey on sheep predation. Our findings suggest the dominant effect of wild prey biomass on sheep predation by coyotes in this Mediterranean-type community is as a buffer.     

Rice straw-wood particle composite for sound absorbing wooden construction materials

In this study, rice straw-wood particle composite boards were manufactured as insulation boards using the method used in the wood-based panel industry. The raw material, rice straw, was chosen because of its availability. The manufacturing parameters were: a specific gravity of 0.4, 0.6, and 0.8, and a rice straw content (10/90, 20/80, and 30/70 weight of rice straw/wood particle) of 10, 20, and 30 wt.%. A commercial urea-formaldehyde adhesive was used as the composite binder, to achieve 140-290 psi of bending modulus of rupture (MOR) with 0.4 specific gravity, 700-900 psi of bending MOR with 0.6 specific gravity, and 1400-2900 psi of bending MOR with a 0.8 specific gravity. All of the composite boards were superior to insulation board in strength. Width and length of the rice straw particle did not affect the bending MOR. The composite boards made from a random cutting of rice straw and wood particles were the best and recommended for manufacturing processes. Sound absorption coefficients of the 0.4 and 0.6 specific gravity boards were higher than the other wood-based materials. The recommended properties of the rice straw-wood particle composite boards are described, to absorb noises, preserve the temperature of indoor living spaces, and to be able to partially or completely substitute for wood particleboard and insulation board in wooden constructions.     

Asymptotic analysis of the stress field in adhering dental restorations

Polymer-based composites are widely used in restorative dentistry as alternatives to metals and ceramics to fill cavities in teeth. They adhere to the walls of the cavity in the tooth, thus forming a composite body consisting of dentine, enamel, and composite resin. Geometric discontinuities along the interfaces between these materials can induce singularities in the stress field, which in turn lead to premature failure of the restoration. In the present investigation, a complex stress function technique is employed to derive the order of the stress singularity. It is shown that the order of the singularity depends on both the material properties of the restorative material and the local geometry of the cavity. It is also shown that the singularity in the stress field can be avoided through careful design of the cavity shape. The results presented correlate well with experimental results reported in the literature.     

Development of larval and transformed teeth in Ambystoma mexicanum (Urodela, Amphibia): an ultrastructural study

Odontogenesis of early larval non-pedicellate teeth, late larval teeth with a more or less distinct dividing zone and fully transformed pedicellate teeth in Ambystoma mexicanum (Urodela) was studied to obtain insights into the development of differently structured teeth in lower vertebrates. Using transmission electron microscopy we investigated five developmental stages: (1) papilla; (2) bell stage (secretion of the matrix begins); (3) primordium (mineralization and activity of ameloblasts starts); (4) replacement tooth (young, old); and (5) established, functional tooth. Development of the differently structured teeth is largely identical in the first three stages. Mineralization takes place in apico-basal direction up to the (prospective) pedicel (early and some late larvae) or up to the zone that divides the late larval and transformed tooth in pedicel and dentine shaft (pedicellate condition). Mineralization starts directly at the collagen and by means of matrix vesicles. First odontoblasts develop small processes that extend to the basal lamina of the inner epithelial layer of the enamel organ. The processes are small and lack organelles in early larval teeth, but become larger, arborescent, and contain some organelles in late larval and transformed teeth. The processes are surrounded by unmineralized matrix (predentine). Odontoblasts at the basis of the teeth, at the pedicel, and in the zone of division do not develop significant cytoplasmic processes that extend into the matrix. Cells of the inner enamel epithelium differentiate to ameloblasts that secrete the enamel. In the early larval tooth they show an extensive basal labyrinth that becomes regressive when the enamel layer is completed. In late larval and transformed teeth, however, a large cavity arises between the basal ruffled border of ameloblasts and their basal lamina. This cavity appears to mediate amelogenesis. A small apical zone in early, but not in late larval teeth directly below the thin enamel layer consists of enameloid and is free of dentine channels.     

Spatial distribution of lead in enamel and coronal dentine of wistar rats

Lead is one of the most hazardous environmental toxins known. The assessment of lead in dental hard tissues is important in the understanding of its toxic effects on oral tissues and in estimating exposure and body burden in individuals exposed to lead from the environment. However, current information on the uptake and distribution of lead in enamel and dentine is limited. The aim of this project was to study, at high resolution, the spatial distribution of lead in enamel and coronal dentine using an experimental rat model. A dose of 40 mg/L of lead nitrate was administered to pregnant female rats during the periods of gestation and lactation through drinking water. First mandibular molar teeth were removed from their 15-d-old pups and the distribution of lead was studied using a nuclear microprobe (NMP). The distribution of lead in enamel and coronal dentine showed four distinct zones with significantly different mean lead concentrations (p<0.05). High levels of lead were observed in the superficial regions of enamel and in the dentine directly adjacent to the pulp. Additionally, the results confirmed that the NMP is capable of mapping the distribution of lead in teeth at micron resolutions with a detection limit of approx 1 microg/g.     

Canine size, shape, and bending strength in primates and carnivores

Anthropoid primates are well known for their highly sexually dimorphic canine teeth, with males possessing canines that are up to 400% taller than those of females. Primate canine dimorphism has been extensively documented, with a consensus that large male primate canines serve as weapons for intrasexual competition, and some evidence that large female canines in some species may likewise function as weapons. However, apart from speculation that very tall male canines may be relatively weak and that seed predators have strong canines, the functional significance of primate canine shape has not been explored. Because carnivore canine shape and size are associated with killing style, this group provides a useful comparative baseline for primates. We evaluate primate maxillary canine tooth size, shape and relative bending strength against body size, skull size, and behavioral and demographic measures of male competition and sexual selection, and compare them to those of carnivores. We demonstrate that, relative to skull length and body mass, primate male canines are on average as large as or larger than those of similar sized carnivores. The range of primate female canine sizes embraces that of carnivores. Male and female primate canines are generally as strong as or stronger than those of carnivores. Although we find that seed-eating primates have relatively strong canines, we find no clear relationship between male primate canine strength and demographic or behavioral estimates of male competition or sexual selection, in spite of a strong relationship between these measures and canine crown height. This suggests either that most primate canines are selected to be very strong regardless of variation in behavior, or that primate canine shape is inherently strong enough to accommodate changes in crown height without compromising canine function.