This chapter reviews phylogenetic and intraspecific variations in tooth sequence polymorphism. The sequence of eruption of the permanent teeth shows a remarkable shift through the order primates. At one end, in the insectivores, the posterior or molar teeth add themselves to the dental arcade before the deciduous anterior teeth even begin replacement. At the other end, typified by the textbook European, the deciduous anterior teeth are largely replaced by their permanent successors before the second and third molar teeth extend the effective size of the dental arch. This distinction in eruption order between early primate and modern man is paralleled by a less dramatic but comparable difference between ape and man. The discovery of immature paleoanthropic hominids directed attention to their still-developing if fossilized teeth. There appeared to be a neat developmental difference that put paleoanthropic man in one eruption set and neanthropic man in another, except perhaps for the copper-age Greeks. But this neat differentiation between fossil and modern hominids based on the presumed order of eruption in a few juvenile fossil mandibles and the average age at eruption from norms for Europeans proved to be one of the credible but incorrect myths. In living apes, or preserved specimens, gingival eruption has been the point of record. Available data and data summarizations, thus, combine alveolar eruption, gingival eruption, estimates of eruption order based on the relative heights of the erupted teeth, and radiological assessments.

This chapter reviews the dentition in the assessment of individual age in skeletal material. Evidence of age may be deduced from the bones or the teeth, which tend to survive much longer than other parts of the skeleton, provide the sole basis for an age estimation. Most of the published work refers to the forensic aspects of this subject and shows that age can be assessed from the teeth during the period of tooth development that is up to about 18 years of age with a fairly high degree of accuracy. In assessing age from dentitions that are immature, use is commonly made of a chart prepared by Schour and Massler (1941), published in slightly modified form by the American Dental Association and reproduced in many textbooks. In recent years, there has been an accumulation of information about the progression of tooth growth by means of which revision of the chart could be undertaken. Little appears to be known about possible racial differences in the chronology of tooth development and tooth growth. Racial differences could, however, reasonably be expected to be of small degree because the times of tooth eruption, which are more affected than tooth growth by sex differences, hormonal disturbances, and dietary deficiencies show only relatively slight racial differences.

This chapter reviews crown characters of the deciduous dentition of the Japanese–American hybrids. Since 1949, studies of the physical traits of Japanese–American hybrids have been carried out by the members of the Department of Anthropology, University of Tokyo, under the direction of Professor Suda. The children studied were born of Japanese mothers and American fathers, including both Whites and Negroes, after World War II. They were brought up in one of the institutions for such orphans, the Elizabeth Sanders Home at Oiso, located some fifty miles southwest of Tokyo. Anthropological studies of these children have been undertaken twice a year. In addition to recording anthropometric data, X-ray studies of hand and foot bones, skin color tests, motor performance tests, dental studies, and psychiatric tests were also done. The hybrid groups generally show an intermediate pattern of distribution between the racial groups of their parents. In some characters, however, they show a closer resemblance or inclination to one of the parents. The hybrid groups are closer to the Japanese as regards the cusp development of the deciduous upper first molars but are nearer to the Americans when considering Carabelli's cusp in the deciduous upper second molars.

This chapter explores the variations in the microstructure and biochemistry of human teeth, focusing on considerations such as previous studies of ancient teeth. Ancient teeth are always hard and brittle, and any section that can be prepared for microscopic examination will be correspondingly fragile. It was only when plastic material was used as an embedding matrix that the inherent difficulties were eventually overcome. Technical advances have now made the microscopic study of fossil, also recent, teeth a practical undertaking. These recent studies allow an understanding of the nature and distribution of the microscopic postmortem canals. Sognnaes pointed out that the degree of postmortem change in teeth is no reliable criterion of the age of the particular specimen. He undertook an exploratory histological survey of the developmental quality of ancient human teeth originating from Paleolithic man in Palestine, prehistoric Greeks, Predynastic Egyptians, the ancient Irish, medieval Norsemen, and early American Indians.

This chapter presents information regarding the frequency of shovel-shaped incisors in ten relatively homogeneous groups of people, namely, Romano-British, Anglo-Saxon (Early British), Danes, Swedes, Norwegian Lapps, Bantu, Arabs, Indians, East Greenland Eskimo, and a combined Japanese, Chinese and Tibetan series. It also presents statistical analysis of the correlation of shovel morphology between the median and lateral incisors. The chapter highlights the incidence of the shovel-trait in earlier forms of man. A major aspect of the study of human dentition is the recognition and assessment of morphological variations. One such characteristic is the presence of structural formations referred to as shovel-shape, manifested by the prominence of the mesial and distal ridges enclosing a central fossa in the lingual surface of incisor teeth, differentiating them from types without the shovel character. Shovel-shaped incisors are frequently found among the upper incisors and occasionally among the lower incisors. Generally, they are bilateral, although in rare instances, they are not. The mode, origin, inheritance, and phylogenetic significance of shovel-shaped incisors are not yet understood, and there is still much data to be collected on the various racial groups. An evaluation of the degree of shovel character is to some extent largely subjective, and discrepancies in results gathered from the same ethnic groups by different workers certainly occur.

This chapter discusses the congenital absence of teeth in human populations. Congenital absence of one or a number of teeth in humans, which can be referred to as hypodontia, is not so uncommon. This may affect both the anterior and posterior teeth, and just one type of tooth. Salzmann (1957) gives the order of frequency of missing teeth as third molars, maxillary lateral incisors, maxillary or mandibular second premolars, mandibular central incisors, and maxillary first premolars—absence of other teeth being too infrequent to classify. In the majority of cases, only one or two teeth are missing, as shown for example by the most commonly affected teeth, the third molars. No significant differences between the frequencies of hypodontia in the two sexes have yet been established. Heredity is certainly the most important determinant of hypodontia, whether many teeth are affected or only one or two. Considering all forms of hypodontia together, there is clearly a wide range of genetic factors with which it may be associated.

This chapter presents a radiographic study of the Neanderthal teeth from Krapina, Croatia. The application of radiographic techniques in the study of fossil hominid remains, particularly teeth, is by no means a recent facet of palaeontological studies. Gorjanović-Kramberger (1906) in his original work on the Krapina remains and Schoetensack's (1908) study of Homo heidelbergensis include radiographic details. On the basis of remnants of jaws and fragments of ascending ramus, it is possible to say that the Krapina finds probably represent 28 individuals, of which 23 are quite certain. Based on a detailed radiography analysis, the dental variability seen in the Krapina group similar detailed studies of other fossil human teeth can be possibly done. Now for the Krapina group, in the permanent incisors, there is absolutely no evidence of the double root canal variant, which can be found in recent populations of man. The deciduous incisors do not display any marked radiographic differences in comparison with recent teeth. The canines display the development of the pulp chamber, where, on the upper canine (extreme left), the chamber reaches the width of 7–8 millimeters and has a somewhat taurodont appearance. An unusual, perhaps transitional form, to be seen in the Krapina series is a lower premolar with two roots.

This chapter reviews double-rooted human lower canine teeth. Double-rooted lower canines may occur in the permanent dentition of man as a variation in the form of the root. They have been considered a rare phenomenon conceived either as a lusus naturae or as an atavism reproducing conditions seen in some Mesozoic mammals. In no specimens of fossil Hominoidea have double-rooted canines been found, but the lack of adequate fossil material prevents any final decision as yet on the theory of atavism. The sporadic existence of double-rooted canines in several groups of recent primates seems to be rather incidental. This view might need modification, however, when more material has been examined. The knowledge of regional displacement during evolution of traits occurring in metameric organs such as teeth allows for the conclusion to be made that the varying extent of the region of multi-rooted teeth in the jaws of primates may sometimes incorporate the region of the canine, which might likewise have happened to some extent in the evolutionary stages leading to Homo sapiens.

This chapter explores the molar crowns of the primary dentition both in the soft tissue stage prior to initial calcification and in the various stages during the calcification process. The monographs and general texts devoted to fossil man and the adaptive radiation of the primates could scarcely have been undertaken without serious attention to the morphology of the teeth, particularly the molars. The eventual morphology of the molar crown is dependent upon at least two types of growth. The folding of the inner enamel epithelium, which is itself a phenomenon of differential rates of mitotic activity, may be regarded as the primary and most fundamental step in the ultimate determination of the crown morphology. A secondary, but important, contributing process to the final configuration of the crown is the deposition of enamel, which has been demonstrated to proceed at different rates in different parts of the tooth

This chapter reviews tooth morphology and appreciation of primate evolution by a study of tooth morphology. In primates, the processes of fossilized bone destruction are particularly important; skeletons, even skulls, are rare, and in most cases all that is available is teeth and jaws. It is fortunate that the teeth, developing early in life inside the jaws, protected from external environmental influences, reflect the genetic constitution of the individual to a high degree. In practice, it has been found that, if adequately interpreted, teeth provide a reliable basis for the discussion of evolutionary relationships. However, the adequate interpretation of fossil teeth is by no means a simple matter. The number of specimens from any one locality is usually small, and it is difficult to make adequate allowance for variation. Thus, there is a need to know more about what teeth can do in the way of evolutionary change. This necessitates more knowledge acquisition regarding the ontogeny of the bone dentition, particularly the ontogenetic basis of variation and how the ontogeny is modified genetically.