Structure and formation of ankylosis in Xenopus laevis

The structure of ankylotic teeth in Xenopus laevis was studied by light, transmission, and scanning electron microscopy as well as by microradiography in decalcified and undecalcified specimens. The mature teeth of Xenopus laevis are calcified from the crown to the base, fused to the jaw bone, and have no uncalcified area, such as a fibrous ring separating the tooth into the crown and pedicle. Microradiography shows that the mature tooth and jaw bone appear as an X-ray opaque area, except for the basal region of the dentine. This region is composed of an X-ray translucent area and an X-ray opaque thin layer on the lingual side of the translucent area. The mature tooth is composed of two differently calcified areas: (1) a highly calcified area, which makes up almost all of the tooth and contains a thin layer of the basal dentine on the lingual side, and (2) a lowly calcified basal dentine, which is fused to the jaw bone. Therefore, the lowly calcified area does not completely separate the dentine and jaw bone. Repeating banding patterns among the collagen fibrils differ among the dentine-forming area and the matrices of dentine and jaw bone. During the formation of ankylosis of the tooth germ, collagen bundles in the dentine-forming area accumulate directly on the surface of the jaw bone. Consequently, the mature teeth of Xenopus laevis fuse to the jaw bone directly without the mediation of the other structures.     

Surface changes in the naturally ankylosed teeth of the frog Rana pipiens during growth and maturation: an SEM study

An SEM study of the surface morphology of the major stages of mature and developing teeth of the leopard frog was made using anorganic preparations of the teeth and jaws. After initial development, the crown area changed little during subsequent tooth eruption, ankylosis and maturation. The thin enamel covering extended further down the shaft than expected. After ankylosis, the surfaces of the tooth continued to mature. The unmineralized gap between the crown and the pedestal, which is prominent in most amphibians, gradually filled in as the ankylosed tooth aged. The upper portion of the pedestal initially formed a dentine surface which was globular in appearance due to partial calcification of the surface collagen fibres but became smooth with uniformly calcified fibres as the ankylosed tooth matured. The lower portion of the pedestal was more variable and there was a gradual transition of dentine into a more cellular, bone-like tissue which contained lacunae and larger fibre bundles. This bone-like tissue was very distinct in surface morphology from the bone of the adjacent jaw, and as the tooth matured it changed from a coarse, woven appearance to one more like lamellar bone. Resorption bays were present in both the dentine and bony areas of teeth which were being shed. During development, the pedestal, which attaches the tooth to the jaw, formed as a separate calcification site and did not form a complete ring until fusion of its buccal surface with that of the overlying crown. A bony buccal lip formed early as part of the pedestal.     

Observations on the polyphyodont dentition of Hemiphractus proboscideus (Anura: Hylidae)

In Hemiphractus fang–like teeth are ankylosed to the premaxilla, maxilla and prevomer, and bony odontoids are found on the dentary, angular and palatine bones. The odontoids are small, but a larger pair at the front of the lower jaw project upwards and backwards into the mouth and fit into a diastema between the anterior premaxillary teeth when the mouth is closed.
The teeth are unipartite and monocuspid, and each consists of a strongly recurved and elongated cone of orthodentine, capped at the tip by a thin layer of enamel. The inner circumpulpal layer of the dentine is tubular, but no tubules are present in the outer pallial layer. During tooth development, dentine is formed before the enamel matrix is produced, and the tooth germs lie horizontally beneath the ventral surface of each dentigerous bone. On eruption, the tooth germs migrate horizontally and become ankylosed to the outer edge of the jaw bone by a layer of cellular cementum.
During tooth replacement, the vast majority of the dentine of each tooth, and the cementum at the tooth base, are resorbed by osteoclasts. It is not clear whether the tips of the teeth are shed or not.     

A morphometric study of bone and tooth volumes in the pipid frog Xenopus laevis (Daudin), with comments on the importance of tooth resorption during normal tooth replacement

Volumetric estimations of teeth and bone on serial sections using a semiautomatic image analyzer indicate that, in the polyphyodont dentition of the pipid anuran Xenopus laevis (Daudin), the mean volume of the dentine composing the teeth is about 23.5% of the volume of the supporting maxillae and premaxillae. During tooth replacement, osteoclasts resorb up to 98% of the dentine. Teeth may be resorbed rather than shed in order to conserve tooth constituents because, if shedding of complete teeth did occur, a quantity of calcified tissue equal to perhaps 45 times the volume of the bone of the upper jaw might be lost over an animal's projected life span of about 13-15 years.     

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.     

Nano- and micromechanical properties of dentine: Investigation of differences with tooth side

The soft zone in dentine beneath the dentino-enamel junction is thought to play an important role in tooth function, strain distribution and fracture resistance during mastication. Recently reported asymmetry in mechanical properties with tooth side may point at a basic property of tooth function. The aim of our study was to test if this asymmetry was reflected in the nano- and micromechanical properties of dentine. We investigated the mechanical properties of dentine on the buccal and lingual side of nine extracted human teeth using nano- and microindentation. Properties were analysed on the natural log scale, using maximum likelihood to estimate the parameters. Two-sided 0.05-level likelihood ratio tests were used to assess the influences of surface (buccal versus lingual) and dentine depth, measured from the DEJ in crown dentine and from the CDJ in root dentine. Results showed the well known gradual increase in mechanical properties with increasing distance from the DEJ. Coronal dentine showed higher elastic modulus and hardness on the lingual side of teeth for all measurements, while root dentine was harder on the buccal side. Due to the subtlety of these effects and the small number of teeth studied, results failed to reach statistical significance. Results suggest that dentine nano- and micromechanical properties vary with tooth side in agreement with recent literature using macroscopic methods. They also reveal that buccal-lingual ratios of hardness are in opposite directions in crown and root dentine, suggesting compensatory functions.     

Morphology of the tooth of the American alligator (Alligator mississippiensis): The fine structure and elemental analysis of the cementum

The fine structure and the concentration of trace elements in the cementum layer in functional teeth of subadult alligators (ca. 120 cm to 160 cm total length) was studied by using scanning electron microscopy (SEM), microradiography, and electron microprobe analysis (EMPA). The cementum layer was hypertrophic and consisted of two layers: the fibrous layer and the calcified layer. The two layers undergo developmental changes as a result of resorption and replacement. During the tooth replacement in the American alligator, trace elements decreased at the base of the dentine layer; the resorption of the alveolar bone occurred simultaneously at the tooth socket. We concluded that the resorption of the cementum in the alligator provided a useful indication of the mechanism of tooth replacement in crocodilian.     

Biomimetic Remineralization of Demineralized Dentine Using Scaffold of CMC/ACP Nanocomplexes in an In Vitro Tooth Model of Deep Caries

Currently, it is still a tough task for dentists to remineralize dentine in deep caries. The aim of this study was to remineralize demineralized dentine in a tooth model of deep caries using nanocomplexes of carboxymethyl chitosan/amorphous calcium phosphate (CMC/ACP) based on mimicking the stabilizing effect of dentine matrix protein 1 (DMP1) on ACP in the biomineralization of dentine. The experimental results indicate that CMC can stabilize ACP to form nanocomplexes of CMC/ACP, which is able to be processed into scaffolds by lyophilization. In the single-layer collagen model, ACP nanoparticles are released from scaffolds of CMC/ACP nanocomplexes dissolved and then infiltrate into collagen fibrils via the gap zones (40 nm) to accomplish intrafibrillar mineralization of collagen. With this method, the completely demineralized dentine was partially remineralized in the tooth mode. This is a bottom-up remineralizing strategy based on non-classical crystallization theory. Since nanocomplexes of CMC/ACP show a promising effect of remineralization on demineralized dentine via biomimetic strategy, thereby preserving dentinal tissue to the maximum extent possible, it would be a potential indirect pulp capping (IPC) material for the management of deep caries during vital pulp therapy based on the concept of minimally invasive dentistry (MID).     

Oxalate desensitising treatment of dentinal surface

It is well known that a typical painful feeling is caused by impact of different agents and by thermodynamic conditions upon the dentine layer of the tooth. Therefore the action by artificial solutions should be tested to study how the induced modifications might inhibit the pain. The aim of the present study is to evaluate by scanning electron microscopy (SEM) the morphology of dentine surface after different chemical treatments. Oxalate solutions are able to produce a layer of large crystals, while acid solutions remove the smear layer and open the dentinal tubules.     

A scanning electron microscope study of the odontoids and teeth in Hemiphractus proboscideus (Anura: Hylidae)

In Hemiphractus proboscideus odontoids are found on the dentary, angular and palatine bones. The morphology of all odontoids is similar, although there are minor variations. They grow by appositional growth, probably quite slowly and possibly seasonally. The odontoids are produced as a result of increase in width of the lamellae near the surface of their supporting bone, and seem to be capable of repair after damage in vivo . The teeth on the premaxilla, maxilla and prevomer are strongly recurved and are composed of dentine covered over their apical one-fifth by a thin layer of aprismatic enamel. The teeth are monocuspid but each possesses two small tubercles which are situated on the mesial and distal margins near the apex. The surface dentine is composed of longitudinal bundles of calcified fibres connected by horizontal interlocking fibres. During tooth replacement resorption bays are visible on the external and pulpal surfaces of the dentine.     

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.     

Tooth movements are guided by specific contact areas between the tooth root and the jaw bone: A dynamic 3D microCT study of the rat molar

Teeth sustain high loads over a lifetime and yet intact tooth failure is rare. The different structures of the tooth, jaw bone and the intervening soft periodontal ligament enable the tooth to endure repeated loading during mastication. Although mechanical and functional properties of the different components are thoroughly investigated, the manner in which the whole tooth functions under load is still enigmatic. A custom-made loading system inside a microCT scanner was used to directly visualize the root movements in relation to the jaw bone as the rat molar tooth was loaded. At low loads no contact was observed between the root surface and the bone, whereas at higher loads three specific contact areas between the root surface and the jaw bone were observed. These contact areas restrict tooth movement in the buccal-lingual direction, but enable the tooth to rock in a "seesaw" like manner in the distal-mesial direction. The contact areas appear to play a role in determining tooth motion and in turn define the manner in which the whole tooth moves when loaded. These observations are important for understanding basic structure-function relations of the tooth-PDL-bone system, and have direct implications for better understanding pathological and therapeutic processes in orthodontics, periodontics and jaw bone regeneration.     

Morphology and growth of lepidosirenid lungfish tooth plates (Pisces: Dipnoi)

The structure of the tooth plates of Protopterus and Lepidosiren was investigated to determine the causes and consequences of postlarval shape change. During growth, the basal area of the tooth plates increases, some cusps become more prominent, and shearing surfaces are sharpened. The jaw articulation restricts the range of movements of the lower jaw, and causes the tooth plates to occlude precisely; the resulting wear patterns are regular. The tooth plates are composed of enamel, trabecular dentine, and petrodentine. A petrodentine column forms the core of a tooth plate; it is flanked by trabecular dentine. Microhardness measurements show that trabecular dentine is comparable in hardness to mammalian dentine, whereas the petrodentine is comparable to enamel. The location and differential wear of these tissues produce the prominent cusps and self-sharpened blades of the adult tooth plates.     

Structure of alveolar bone during tooth eruption in the dog: preliminary findings

The structure of the alveolar bone during the tooth eruption in the young dog mandibles was investigated by microradiographic and polarized light techniques. Around the first erupting molar root a trabecular network of primary alveolar bone, less mineralized than the surrounding cortical one, was found. Numerous calcified spicules parallel one to others radiate out the spongiosa near the periodontal ligament. The collagen fiber bundles of the alveolar, woven, bone are continuous with the periodontal ligament ones. This finding indicates that the alveolar bone increases by ossification of the periodontal ligament. Therefore the latter is the forming alveolar bone substratum. The trabeculae of the occlused premolar alveolar bone are ticker and more mineralized. This modification of the occlused tooth alveolar bone could be related to the occlusal stresses.     

Origin and evolution of gnathostome dentitions: a question of teeth and pharyngeal denticles in placoderms

The fossil group Placodermi is the most phylogenetically basal of the clade of jawed vertebrates but lacks a marginal dentition comparable to that of the dentate Chondrichthyes, Acanthodii and Osteichthyes (crown-group Gnathostomata). The teeth of crown-group gnathostomes are part of an ordered dentition replaced from, and patterned by, a dental lamina, exemplified by the elasmobranch model. A dentition recognised by these criteria has been previously judged absent in placoderms, based on structural evidence such as absence of tooth whorls and typical vertebrate dentine. However, evidence for regulated tooth addition in a precise spatiotemporal order can be observed in placoderms, but significantly, only within the group Arthrodira. In these fossils, as in other jawed vertebrates with statodont, non-replacing dentitions, new teeth are added at the ends of rows below the bite, but in line with biting edges of the dentition. The pattern is different on each gnathal bone and probably arises from single odontogenic primordia on each, but tooth rows are arranged in a distinctive placoderm pattern. New teeth are made of regular dentine comparable to that of crown-gnathostomes, formed from a pulp cavity. This differs from semidentine previously described for placoderm gnathalia, a type present in the external dermal tubercles. The Arthrodira is a derived taxon within the Placodermi, hence origin of teeth in placoderms occurs late in the phylogeny and teeth are convergently derived, relative to those of other jawed vertebrates. More basal placoderm taxa adopted other strategies for providing biting surfaces and these vary substantially, but include addition of denticles to the growing gnathal plates, at the margins of pre-existing denticle patches. These alternative strategies and apparent absence of regular dentine have led to previous interpretations that teeth were entirely absent from the placoderm dentition. A consensus view emerged that a dentition, as developed within a dental lamina, is a synapomorphy characterising the clade of crown-group gnathostomes. Recent comparisons between sets of denticle whorls in the pharyngeal region of the jawless fish Loganellia scotica (Thelodonti) and those in sharks suggest homology of these denticle sets on gill arches. Although the placoderm pharyngeal region appears to lack denticles (placoderm gill arches are poorly known), the posterior wall of the pharyngeal cavity, formed by a bony flange termed the postbranchial lamina, is covered in rows of patterned denticle arrays. These arrays differ significantly, both in morphology and arrangement, from those of the denticles located externally on the head and trunkshield plates. Denticles in these arrays are homologous to denticles associated with the gill arches in other crown-gnathostomes, with pattern similarities for order and position of pharyngeal denticles. From their location in the pharynx these are inferred to be under the influence of a cell lineage from endoderm, rather than ectoderm. Tooth sets and tooth whorls in crown-group gnathostomes are suggested to derive from the pharyngeal denticle whorls, at least in sharks, with the patterning mechanisms co-opted to the oral cavity. A comparable co-option is suggested for the Placodermi.     

The method of age determination of the Pacific walrus (Odobenus rosmarus divergens) using the layered structure of functional teeth

The functional teeth of Pacific walruses that died or were harvested in the Retkyn Spit, Enmelen village, Kolyuchin Island, Vankarem Cape, Enurmino village, and Chegitun River region in 2005, 2007–2008, and 2010–2011 were examined. The definite structure was investigated in animals of their first year of life. The presence of a milk layer in the tooth dentine can be considered as a mark that all the cement layers have been preserved, and the age determination of an individual is precise. The annual increment of dentine significantly changed with age in different parts of the tooth (buccal, lingual, and central), and the annual growth of dentine decreased every year. The growth rate of the upper jaw teeth was significantly higher, and the duration of their growth was much longer than that in the lower jaw teeth. The wearing of dentine and cement layers was unequal in different parts of tooth. Several recommendations for choosing a tooth for the determination of the walrus’s age and for the estimation of age using the layered tooth structure are given.     

Specific immunohistochemical localization of osteonectin and collagen types I and III in fetal and adult porcine dental tissues

Affinity-purified antibodies have been used in combination with the peroxidase-antiperoxidase technique to study the distribution of osteonectin and collagen types I and III in porcine dental tissues. Tissue sections (2 mm thick), including unerupted (fetal) or erupted (adult) teeth, were fixed in periodate-lysine-paraformaldehyde, demineralized in 12% w/v ethylenediaminetetraacetic acid, and after embedding, 6 micron sections were prepared for immunolocalization. Strong staining for osteonectin was observed in dentine of unerupted teeth and in the associated alveolar bone. Light to moderate staining was observed in the dental pulp, stratum intermedium, stellate reticulum, and the reticular elements in the endosteal spaces. In erupted teeth, osteonectin staining in dentine was concentrated around dentinal tubules and the associated alveolar bone stained with variable intensity. Cementum was poorly stained. However, the periodontal ligament and reticular material in the endosteal spaces showed moderate to strong staining. Weaker staining was apparent in the pulp and lamina propria of the gingiva. In comparison, type I collagen showed a similar distribution to osteonectin in both fetal and adult tissues, whereas type III collagen was generally restricted to the periodontal ligament, reticular elements of the endosteal spaces, and Sharpey's fibers in bone and cementum. Both odontoblast and ameloblast layers in fetal tissues stained for osteonectin and type III collagen.     

Immunohistochemical distribution of collagens types IV, V, and VI and of pro-collagens types I and III in human alveolar bone and dentine

The aim of the present study was to characterize the composition of the organic matrix in alveolar jaw bone and dentine using antibodies against pro-collagens Types I and III and collagens Types IV, V, and VI. After demineralization of oral hard tissues in 0.2 N HCl, antigenicity was well preserved and the distribution of the pro-collagens and collagens could be demonstrated. Staining for pro-collagen Type I was prominent around osteoblasts and in pre-dentine, indicating active de novo synthesis of Type I pro-collagen. Pro-collagen Type I was ubiquitous but was less abundant in bone and dentine, whereas pro-collagen Type III was seen only in areas of bone remodeling, in peritubular spaces, and in pre-dentine. Type IV collagen was limited to the basement membranes of vessels in osteons and bone marrow. Type V collagen was detected neither in pre-dentine nor in bone. In contrast, Type VI collagen was found in dentine and bone, showing a faint but homogeneous staining which, similarly to pro-collagen Type III, was pronounced around osteoblasts and in pre-dentine, areas of active bone and dentine formation. This study showed that the organic matrix of dentine and bone contains Type VI as well as Type I collagen. Pro-collagen Type III (and to a lesser extent collagen Type VI) is transiently produced during new formation and remodeling of oral hard tissues, and disappears once the matrix calcifies. Type I pro-collagen qualifies as a general marker protein for increased osteoblastic activity. We conclude that immunostaining for the different collagen/pro-collagen types can be used to assess normal or abnormal stages of bone/dentine formation.     

Ultrastructural localization of dentine phosphoprotein in rat tooth germs by immunogold staining

Dentine phosphoprotein (DPP) was localized on thin frozen sections of fixed rat tooth germs by indirect immunogold staining. Antisera were directed against DPP and against glutaraldehyde-treated DPP and were characterized by immuno-electroblotting. In odontoblasts, DPP was found to be localized in the cisternae of the rough endoplasmic reticulum (RER) and the Golgi apparatus and in Golgi-associated vesicles. Odontoblastic processes were moderately positive for DPP and dentine was intensely labeled on frozen sections of unfixed tissue. Predentine showed a slight immunoreactivity. These results indicate the synthesis of DPP in the RER, its accumulation in the Golgi apparatus and its vesicular transport and secretion via the odontoblastic processes into dentine. The close association of the gold particles with the dentinal collagen fibres makes a role of DPP in linking mineral to collagen conceivable. Matrix vesicles were negative for DPP, suggesting that the protein is not present at the sites of matrix vesicle-associated nucleation.     

Prismatic dentine in the Australian lungfish, Neoceratodus forsteri (Osteichthyes: Dipnoi)

The Australian lungfish, Neoceratodus forsteri, has a dentition consisting of enamel, mantle dentine and bone, enclosing circumdenteonal, core and interdenteonal dentines. Branching processes from cells that produce interdenteonal dentine leave the cell surface at different angles, with collagen fibrils aligned parallel to the long axis of each process. In the interdenteonal dentine, crystals of calcium hydroxyapatite form within fibrils of collagen, and grow within a matrix of non-collagenous protein. Crystals are aligned parallel to the cell process, as are the original collagen fibrils. Because the processes are angled to the cell surface, the crystals within the core or interdenteonal dentine are arranged in bundles set at angles to each other. Apatite crystals in circumdenteonal dentine are finer and denser than those of the interdenteonal dentine, and form outside the fibrils of collagen. In mature circumdenteonal dentine the crystals of circumdenteonal dentine form a dense tangled mass, linked to interdenteonal dentine by isolated crystals. The functional lungfish tooth plate contains prisms of large apatite crystals in the interdenteonal dentine and masses of fine tangled crystals around each denteon. This confers mechanical strength on a structure with little enamel that is subjected to heavy wear.