Tooth development and replacement in the Atlantic Cutlassfish,Trichiurus lepturus,with comparisons to other Scombroidei

Atlantic Cutlassfish, Trichiurus lepturus, have large, barbed, premaxillary and dentary fangs, and sharp dagger-shaped teeth in their oral jaws. Functional teeth firmly ankylose to the dentigerous bones. We used dry skeletons, histology, SEM, and micro-CT scanning to study 92 specimens of T. lepturus from the western North Atlantic to describe its dentition and tooth replacement. We identified three modes of intraosseous tooth replacement in T. lepturus depending on the location of the tooth in the jaw. Mode 1 relates to replacement of premaxillary fangs, in which new tooth germs enter the lingual surface of the premaxilla, develop horizontally, and rotate into position. We suggest that growth of large fangs in the premaxilla is accommodated by this horizontal development. Mode 2 occurs for dentary fangs: new tooth germs enter the labial surface of the dentary, develop vertically, and erupt into position. Mode 3 describes replacement of lateral teeth, in which new tooth germs enter a trench along the crest of the dentigerous bone, develop vertically, and erupt into position. Such distinct modes of tooth replacement in a teleostean species are unknown. We compared modes of replacement in T. lepturus to 20 species of scombroids to explore the phylogenetic distribution of these three replacement modes. Alternate tooth replacement (in which new teeth erupt between two functional teeth), ankylosis, and intraosseous tooth development are plesiomorphic to Bluefish + other Scombroidei. Our study highlights the complexity and variability of intraosseous tooth replacement. Within tooth replacement systems, key variables include sites of formation of tooth germs, points of entry of tooth germs into dentigerous bones, coupling of tooth germ migration and bone erosion, whether teeth develop horizontally or immediately beneath the tooth to be replaced, and how tooth eruption and ankylosis occur. Developmentally different tooth replacement processes can yield remarkably similar dentitions.     

Teeth of Embryos in Lamniform Sharks (Chondrichthyes: Elasmobranchii)

The dentitions of lamniform sharks possess a unique heterodonty, the lamnoid tooth pattern. However, in embryos, there are 'embryonic' and 'adult' dentitions. The teeth in the embryonic dentition are peg-like and appear to be attached to the jaw in an acrodont fashion. The adult dentition is characterized by the presence of replacement tooth series with the lamnoid tooth pattern. The embryonic–adult transition in dentitions appears at around 30–60cm TL. Tooth replacement generally begins before birth in embryos with adult dentitions. The adult dentition becomes functional just before or after parturition. An embryo of one species (Lamna nasus) shows a tooth directly on the symphysis of the upper jaws, marking the first record of a medial tooth for the order Lamniformes.     

The cusp of evolution and development: a model of cichlid tooth shape diversity

Tooth shape is a hallmark of repeated evolutionary radiations among cichlid fishes from East Africa. Cusp shape and number vary both within populations and among closely related species with different feeding behaviors and ecologies. Here, we use histology and scanning electron microscopy to chart the developmental trajectory of tooth shape differences in fishes from Lake Malawi. We demonstrate that species with bi- or tricuspid adult (replacement) teeth initially possess a first-generation unicuspid dentition. Notably, the timing of turnover from first-generation to replacement teeth differs among species and is correlated with feeding ecology. Next, we use field data for cichlid species with adult unicuspid, bicuspid, and tricuspid teeth to demonstrate a strong and positive relationship between the number of teeth in a row and tooth shape. We discuss cichlid tooth ontogeny in the context of morphogenetic models designed to explain the developmental basis of tooth shape variation in mammals. We suggest that the dramatic differences in cichlid dentitions can be explained by variation in the expression of common activators and inhibitors acting at multiple stages of odontogenesis.     

Ontogeny, anatomy and attachment of the dentition in mosasaurs (Mosasauridae: Squamata)

Aspects of mosasaur dental ontogeny are well preserved in many fossils of these giant marine squamates. Replacement teeth on the tooth-bearing elements (TBEs) first appear as small enamel crowns positioned posterolingual to the attached tooth (posterolabial for the pterygoid). Several developing crowns, of progressively larger size, are aligned in rows relating to a specific tooth position. The crowns rest in a dental groove that varies in width and depth depending on the TBE. The crown closest to the attached tooth is always the largest and is found in a small resorption pit. As resorption proceeds, the pit expands in volume (cementum and alveolar bone), and the crown increases in size and settles into the pit. Once mature crown size is achieved, the dentine root and cementum portion of the root develop rapidly, the attached tooth is lost and the replacement tooth erupts out of the alveolus. Mosasaurid teeth develop along a 'zig-zag'-shaped movement path: horizontally along the dental groove, down into the alveolus, and up and out of the alveolus prior to attachment to the alveolar wall. At no point in mosasaurid tooth development are the crowns observed in a horizontal position. The mosasaurid dental lamina appears to have been a continuous strip of dental epithelium as it is in other squamates. Mosasaurid tooth attachment is thecodont (histologically and geometrically) not subpleurodont. Most aspects of mosasaurid tooth attachment and ontogeny are autapomorphic for the group.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 149 , 687–700.     

Structure, attachment, replacement and growth of teeth in bluefish, Pomatomus saltatrix (), a teleost with deeply socketed teeth

Tooth replacement poses many questions about development, pattern formation, tooth attachment mechanisms, functional morphology and the evolution of vertebrate dentitions. Although most vertebrate species have polyphyodont dentitions, detailed knowledge of tooth structure and replacement is poor for most groups, particularly actinopterygians. We examined the oral dentition of the bluefish, Pomatomus saltatrix, a pelagic and coastal marine predator, using a sample of 50 individuals. The oral teeth are located on the dentary and premaxillary bones, and we scored each tooth locus in the dentary and premaxillary bones using a four-part functional classification: absent (A), incoming (I), functional (F=fully ankylosed) or eroding (E). The homodont oral teeth of Pomatomus are sharp, deeply socketed and firmly ankylosed to the bone of attachment. Replacement is intraosseus and occurs in alternate tooth loci with long waves of replacement passing from rear to front. The much higher percentage of functional as opposed to eroding teeth suggests that replacement rates are low but that individual teeth are quickly lost once erosion begins. Tooth number increases ontogenetically, ranging from 15–31 dentary teeth and 15–39 premaxillary teeth in the sample studied. Teeth increase in size with every replacement cycle. Remodeling of the attachment bone occurs continuously to accommodate growth. New tooth germs originate from a discontinuous dental lamina and migrate from the lingual (dentary) or labial (premaxillary) epithelium through pores in the bone of attachment into the resorption spaces beneath the existing teeth. Pomatomus shares unique aspects of tooth replacement with barracudas and other scombroids and this supports the interpretation that Pomatomus is more closely related to scombroids than to carangoids.     

Structure, attachment, replacement and growth of teeth in bluefish, Pomatomus saltatrix (Linnaeus, 1776), a teleost with deeply socketed teeth

Tooth replacement poses many questions about development, pattern formation, tooth attachment mechanisms, functional morphology and the evolution of vertebrate dentitions. Although most vertebrate species have polyphyodont dentitions, detailed knowledge of tooth structure and replacement is poor for most groups, particularly actinopterygians. We examined the oral dentition of the bluefish, Pomatomus saltatrix, a pelagic and coastal marine predator, using a sample of 50 individuals. The oral teeth are located on the dentary and premaxillary bones, and we scored each tooth locus in the dentary and premaxillary bones using a four-part functional classification: absent (A), incoming (I), functional (F=fully ankylosed) or eroding (E). The homodont oral teeth of Pomatomus are sharp, deeply socketed and firmly ankylosed to the bone of attachment. Replacement is intraosseus and occurs in alternate tooth loci with long waves of replacement passing from rear to front. The much higher percentage of functional as opposed to eroding teeth suggests that replacement rates are low but that individual teeth are quickly lost once erosion begins. Tooth number increases ontogenetically, ranging from 15–31 dentary teeth and 15–39 premaxillary teeth in the sample studied. Teeth increase in size with every replacement cycle. Remodeling of the attachment bone occurs continuously to accommodate growth. New tooth germs originate from a discontinuous dental lamina and migrate from the lingual (dentary) or labial (premaxillary) epithelium through pores in the bone of attachment into the resorption spaces beneath the existing teeth. Pomatomus shares unique aspects of tooth replacement with barracudas and other scombroids and this supports the interpretation that Pomatomus is more closely related to scombroids than to carangoids.     

Tooth replacement pattern of Coloborhynchus robustus (Pterosauria) from the Lower Cretaceous of Brazil

The well preserved anterior upper and lower jaw fragment of an adult specimen of Coloborhynchus robustus (Pterosauria: Ornithocheiridae), SMNK 2302 PAL, allowed investigations of the replacement pattern of the dentition macroscopically and by using CT scans. The quantification of the dentition by Zahnreihen, Z-Spacing, and replacement waves indicates a complex pattern of different replacement stages in which large gaps within the dentition were avoided. The specialized prey-catching apparatus of Coloborhynchus thus could retain its function even following tooth replacement. The replacement process in the specimen took about 2/3 of the total life-time of a tooth, and damaged teeth in the anterior jaw region may have been replaced more rapidly than posterior teeth. The distolingual replacement of the functional teeth delayed the time of their shedding in comparison with the circular resorption present in crocodiles. In contrast to these, the distolingual position of the replacement tooth did not decrease the biomechanical stability of the functional tooth, which can also be observed as a convergence in other thecodont dentitions, e.g., recent carnivore mammals. Teeth were shed when their replacement had reached about 60% of the full-grown height. A comparison of the observed pattern is constricted by the preservation and preparation of other specimens. Unfortunately, no known specimen in public collections reaches the quality of Coloborhynchus robustus, SMNK 2302 PAL, so that comparable patterns in other specimens are not likely to be detected.     

Early development of rostrum saw-teeth in a fossil ray tests classical theories of the evolution of vertebrate dentitions

In classical theory, teeth of vertebrate dentitions evolved from co-option of external skin denticles into the oral cavity. This hypothesis predicts that ordered tooth arrangement and regulated replacement in the oral dentition were also derived from skin denticles. The fossil batoid ray Schizorhiza stromeri (Chondrichthyes; Cretaceous) provides a test of this theory. Schizorhiza preserves an extended cartilaginous rostrum with closely spaced, alternating saw-teeth, different from sawfish and sawsharks today. Multiple replacement teeth reveal unique new data from micro-CT scanning, showing how the ‘cone-in-cone’ series of ordered saw-teeth sets arrange themselves developmentally, to become enclosed by the roots of pre-existing saw-teeth. At the rostrum tip, newly developing saw-teeth are present, as mineralized crown tips within a vascular, cartilaginous furrow; these reorient via two 90° rotations then relocate laterally between previously formed roots. Saw-tooth replacement slows mid-rostrum where fewer saw-teeth are regenerated. These exceptional developmental data reveal regulated order for serial self-renewal, maintaining the saw edge with ever-increasing saw-tooth size. This mimics tooth replacement in chondrichthyans, but differs in the crown reorientation and their enclosure directly between roots of predecessor saw-teeth. Schizorhiza saw-tooth development is decoupled from the jaw teeth and their replacement, dependent on a dental lamina. This highly specialized rostral saw, derived from diversification of skin denticles, is distinct from the dentition and demonstrates the potential developmental plasticity of skin denticles.     

The tooth of perfection: functional and spatial constraints on mammalian tooth shape

This paper addresses the question of how close mammalian teeth are to ideal functional forms. An 'ideal' form is a morphology predicted to be the best functional shape according to information of the relationships between shape and function. Deviations from an ideal form are likely to indicate the presence of developmental or genetic constraints on form. Model tools were constructed to conform to functional principles from engineering and dental studies. The final model shapes are very similar to several mammalian tooth forms (carnassial teeth and tribosphenic-like cusps), suggesting that these tooth forms very closely approach ideal functional forms. Further evidence that these tooth forms are close to ideal comes from the conservation over 140 million years, the independent derivation and/or the occurrence over a size range of several orders of magnitude of these basic tooth forms. One of the main functional shapes derived here is the 'protoconoid', a fundamental design for double-bladed tools that fits a large number of functional parameters. This shape occurs in tooth forms such as tribosphenic, dilambdodont and zalambdodont. This study extends our understanding of constraints on tooth shape in terms of geometry (how space influences tooth shape) and function (how teeth divide food).  © 2003 The Linnean Society of London . Biological Journal of the Linnean Society , 2003, 78 , 173–191.     

The Vertebrate Tooth Row: Is It Initiated by a Single Organizing Tooth?

Teeth are one of the most fascinating innovations of vertebrates. Their diversity of shape, size, location, and number in vertebrates is astonishing. If the molecular mechanisms underlying the morphogenesis of individual teeth are now relatively well understood, thanks to the detailed experimental work that has been performed in model organisms (mainly mouse and zebrafish), the mechanisms that control the organization of the dentition are still a mystery. Mammals display simplified dentitions when compared to other vertebrates with only a single tooth row positioned in the anterior part of the mouth, whereas other vertebrates exhibit tooth rows in many locations. As proposed 60 years ago, tooth rows can be formed sequentially from an initiator tooth. Recent results in zebrafish have now largely confirmed this hypothesis. Here this observation is generalized upon and it is suggested that in most vertebrates tooth rows could form sequentially from a single initiator tooth.     

Early development and replacement of the stickleback dentition

Teeth have long served as a model system to study basic questions about vertebrate organogenesis, morphogenesis, and evolution. In nonmammalian vertebrates, teeth typically regenerate throughout adult life. Fish have evolved a tremendous diversity in dental patterning in both their oral and pharyngeal dentitions, offering numerous opportunities to study how morphology develops, regenerates, and evolves in different lineages. Threespine stickleback fish (Gasterosteus aculeatus) have emerged as a new system to study how morphology evolves, and provide a particularly powerful system to study the development and evolution of dental morphology. Here, we describe the oral and pharyngeal dentitions of stickleback fish, providing additional morphological, histological, and molecular evidence for homology of oral and pharyngeal teeth. Focusing on the ventral pharyngeal dentition in a dense developmental time course of lab‐reared fish, we describe the temporal and spatial consensus sequence of early tooth formation. Early in development, this sequence is highly stereotypical and consists of seventeen primary teeth forming the early tooth field, followed by the first tooth replacement event. Comparing this detailed morphological and ontogenetic sequence to that described in other fish reveals that major changes to how dental morphology arises and regenerates have evolved across different fish lineages. J. Morphol. 277:1072–1083, 2016. © 2016 Wiley Periodicals, Inc.     

Variation in body size and trophic morphology within and among genetically differentiated populations of the cichlid fish, Metriaclima zebra, from Lake Malawi

1. The cichlid fish Metriaclima zebra , common in Lake Malawi, feeds by filtering plankton from the water and by brushing items from sediment covered substrata. It inhabits isolated rocky reefs among which community structure, resource availability and gene pools are likely to differ. We speculated that body size and trophic morphology of M. zebra might vary concomitantly.
2. We quantified the extent of genetic, body size and trophic variation within and between populations of M. zebra from southern Lake Malawi. Specifically, we tested the hypotheses that: (i) local populations are genetically differentiated, (ii) local populations differ in jaw morphology, dentition and standard length (SL), and (iii) variation in size is correlated with variation in trophic morphology.
3. Local populations of M. zebra differed in mean SL and were genetically differentiated. Moreover, populations exhibited dissimilar oral jaw morphologies and dentitions, perhaps related to differences in feeding biology. Variation in jaw shape was largely restricted to the curvature of the distal tip of the dentary. Populations were characterised by individuals with oblique, upward or downward directed gapes. Dental patterns differed in the proportion of unicuspid teeth in all rows of each jaw (dentaries and premaxillae) and the spacing of teeth in affected rows.
4. Within populations, jaw and tooth shapes were correlated with body size. Smaller individuals possessed upward curving jaws and closely packed multicusped teeth, while larger individuals exhibited relatively downward-directed jaws with increasing numbers of widely spaced unicuspid teeth.
5. Metriaclima zebra populations have increased in mean SL over the last decade, in contrast to a decline among Lake Malawi pelagic cichlids. Differences in size may contribute to variation in trophic morphology and may track local environmental dynamics in this lacustrine system.     

Dental ontogeny of a white shark embryo

Unlike most viviparous vertebrates, lamniform sharks develop functional teeth during early gestation. This feature is considered to be related to their unique reproductive mode where the embryo grows to a large size via feeding on nutritive eggs in utero. However, the developmental process of embryonic teeth is largely uninvestigated. We conducted X‐ray microcomputed tomography to observe the dentitions of early‐, mid‐, and full‐term embryos of the white shark Carcharodon carcharias (Lamniformes, Lamnidae). These data reveal the ontogenetic change of embryonic dentition of the species for the first time. Dentition of the early‐term embryos (∼45 cm precaudal length, PCL) is distinguished from adult dentition by 1) the presence of microscopic teeth in the distalmost region of the paratoquadrate, 2) a fang‐like crown morphology, and 3) a lack of basal concavity of the tooth root. The “intermediate tooth” of early‐term embryos is almost the same size as the adjacent teeth, suggesting that lamnoid‐type heterodonty (lamnoid tooth pattern) has not yet been established. We also discovered that mid‐term embryos (∼80 cm PCL) lack functional dentition. Previous studies have shown that the maternal supply of nutritive eggs in lamnoid sharks ceases during mid‐ to late‐gestation. Thus, discontinuation of functional tooth development is likely associated with the completion of the oophagous (egg‐eating) phase. Replacement teeth in mid‐term embryos include both embryonic and adult‐type teeth, suggesting that the embryo to adult transition in dental morphology occurs during this period. J. Morphol. 278:215–227, 2017. © 2016 Wiley Periodicals,Inc.     

Developmental mechanisms underlying tooth patterning in continuously replacing osteichthyan dentitions

The dentition of osteichthyans presents an astonishing diversity with regard to the distribution of teeth in the oral cavity, tooth numbers, arrangements, shapes, and sizes. Taking examples from three unrelated teleosts--the most speciose group of osteichthyans--and from the literature, this study explores how the initial tooth pattern is set up, and how this relates to the establishment and maintenance (or modification) of the tooth replacement pattern. In teleosts, first-generation teeth (the very first teeth in ontogeny to develop at a particular locus) are commonly initiated in adjacent or in alternate (odd and even) positions. The mechanisms responsible for these divergent developmental patterns remain to be elucidated, in particular, whether they reflect a field or local type of control. However, patterns of adjacent or alternate tooth initiation, set up by the first-generation teeth, can easily turn into replacement patterns where new teeth are initiated simultaneously every second, or even every third position, by synchronizing the formation of new first-generation teeth to the formation of replacement teeth at older loci. Our observations suggest that, once established, the replacement pattern appears to be maintained, as a kind of "default" state. Variations and modifications in this pattern are nevertheless common and suggest that tooth replacement is under local control, exerted at the level of the initiation of replacement teeth. Further studies are needed to test the hypothesis that regular replacement patterns are more frequent in association with the plesiomorphic condition of extramedullary replacement (replacement on the surface of the dentigerous bone) and more rare in the derived condition of intramedullary replacement (replacement within the medullary cavity of the dentigerous bone).     

Tooth and consequences: Heterodonty and dental replacement in piranhas and pacus (Serrasalmidae)

Tooth replacement in piranhas is unusual: all teeth on one side of the head are lost as a unit, then replaced simultaneously. We used histology and microCT to examine tooth‐replacement modes across carnivorous piranhas and their herbivorous pacu cousins (Serrasalmidae) and then mapped replacement patterns onto a molecular phylogeny. Pacu teeth develop and are replaced in a manner like piranhas. For serrasalmids, unilateral tooth replacement is not an “all or nothing” phenomenon; we demonstrate that both sides of the jaws have developing tooth rows within them, albeit with one side more mineralized than the other. All serrasalmids (except one) share unilateral tooth replacement, so this is not an adaptation for carnivory. All serrasalmids have interlocking teeth; piranhas interdigitate lateral tooth cusps with adjacent teeth, forming a singular saw‐like blade, whereas lateral cusps in pacus clasp together. For serrasalmids to have an interlocking dentition, their teeth need to develop and erupt at the same time. We propose that interlocking mechanisms prevent tooth loss and ensure continued functionality of the feeding apparatus. Serrasalmid dentitions are ubiquitously heterodont, having incisiform and molariform dentitions reminiscent of mammals. Finally, we propose that simultaneous tooth replacement be considered as a synapomorphy for the family.     

Connecting morphology, function and tooth wear in microchiropterans

A key objective in understanding the dentition of mammals is the ability to predict the function of teeth from their shape. Very few studies have used dental measurements that allow the prediction of comparative tooth effectiveness, particularly when modification in shape due to tooth wear is considered. Here, dental parameters are used in which a change in the parameter is readily interpretable in terms of change in factors such as increased force or energy required for cusps or crests to break down food. The functional parameters were measured for 3-D digital tooth reconstructions of the upper molars of the microchiropteran Chalinolobus gouldii at various stages of tooth wear. The changes in the majority of the parameters, such as decreased tip, edge and cusp sharpnesses, cusp occlusion relief, rake angle and fragment clearance, predict a deterioration in efficacy with increased wear. This conclusion has not been possible with alternative approaches; for instance, there was no significant change in crest length with wear, and so no change in function would be predicted from that measure. Some of the parameters did not change significantly with heavy wear, such as capture area of a crest, pointing to geometrical and design characteristics for the maintenance of shape with wear in the dilambdodont tooth form. Attrition and abrasion can be considered as wear on the relief and rake surfaces of tribosphenic-like crests, respectively. The differences in function of these two surfaces account for the differences in wear patterns.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 81–96.     

Costs of carnivory: tooth fracture in Pleistocene and Recent carnivorans

Large, carnivorous mammals often break their teeth, probably as a result of tooth to bone contact that occurs when carcasses are consumed more fully, a behaviour likely to occur under conditions of food stress. Recent studies of Pleistocene predators revealed high numbers of teeth broken in life, suggesting that carcass utilization and, consequently, food competition was more intense in the past than at present. However, the putative association between diet and tooth fracture frequency was based on a small sample of large, highly carnivorous species. In the present study, a greater diversity of extant carnivorans is sampled, including insectivorous, omnivorous, and carnivorous forms, ranging in size from weasels to tigers. Species that habitually consume hard foods (bones, shells) had the highest fracture frequencies, followed by carnivores, and then insectivorous and/or omnivorous species. Predator and prey sizes were not associated with tooth fracture frequency, but more aggressive species did break their teeth more often. Comparison of the modern sample with five Pleistocene species confirms the previous finding of higher tooth breakage in the past, although some extant species have fracture frequencies that approach those of extinct species. Thus, the Pleistocene predator guild appears to have been characterized by relatively high levels of competition that are rarely observed today.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 68–81.     

扁圆吻鲴下咽齿的个体发生及替换规律

扁圆吻鲴下咽齿的个体发生可分为三个阶段：初齿期、过渡齿期和成齿期。初步期符合鲤科鱼类的一般规律;过渡齿期相当延长,产生全部齿位,６或７枚齿,齿的发生存在两种类型;成齿与幼齿的替换规律完全不同,发育进入成齿阶段后,主行齿由奇数齿位与偶数齿位交错替换转变为相二枚齿进行替换,替换公式为１－４,２－５,３－６或１－４－７,２－５,３－６（主行齿６枚或７枚）,全部替换一次分三列替换波完成,可将扁圆吻鲴下咽齿的发育模式视为新的类型,副行齿在过渡齿期出现,与主行齿的发展模式不同,替换形式始终为相令齿位交错进行,本文还探讨了咽骨的发育及其对下咽发生的影响。     

The development and replacement of teeth in viviparous caecilians.

Tooth development and replacement in fetal and adult viviparous caecilians (Amphibia: Gymnophiona) are described and analyzed according to current theories of tooth succession. The fetal dentition differs from that of the adult in morphology, position, and function. Teeth are used by fetuses to scrape the oviducal epithelium, thus stimulating the secretion of a nutrient substance. Fetal dentitions vary in morphology and position in different species. The ontogeny of teeth of several species is described and the patterns of addition of loci and of replacement are analyzed. Loci are added both posteriorly along the jaw and between existing loci as the jaw grows prior to ossification; subsequently addition is restricted to the posterior part of the jaw. Tooth replacement is alternate. The several rows and patches of teeth are the result of retention of replacement series on the dentigerous elements. Tooth development and replacement in a series of juveniles and adults of different sizes in a single species are also considered. Post-fetal patterns of development and replacement are similar to those seen in larvae and adults of oviparous species. Variation in numbers of teeth and proportions of teeth at particular stages occurs ontogenetically and among individuals of the same size, though proportions occur in a similar pattern throughout the series. The general pattern of tooth replacement in fetuses and adults can be explained by either Edmund's Zahnreihen theory or by Osborn's Tooth Family theory, but replacement in fetal tooth patches and the fetal-adult dentitional transition are explained by neither.     

Concepts of occlusion: Australian evidence

Longitudinal studies of aboriginal children over a 20-year period have drawn attention to the wide variation in morphological features of the dentition and the way in which occlusal relationships develop. This paper summarizes some important determinants of optimal occlusal development, namely, tooth size relationships within and between dentitions, the patterns of alveolar growth, and tooth migrations during the transition from primary to permanent teeth and the nature of growth changes in the dental arches. Dental occlusion constantly changes throughout life in response to changing functional requirements. Observations limited to cross-sectional material provide an incomplete, and sometimes misleading, concept of dental occlusion and masticatory function.