Development of deciduous and permanent dentitions in the upper jaw of the house shrew (Suncus murinus)

The diphyodont tooth replacement in mammals is characterized by a single replacement of a deciduous dentition by a permanent dentition. Despite its significance in mammalian biology and paleontology, little is known about the developmental mechanisms regulating the diphyodont replacement. Because the mouse never replaces its teeth, this study used the house shrew, Suncus murinus, as a model to investigate the control of the diphyodont replacement of a deciduous dentition by successions and additions of permanent teeth. Using morphological and gene expression analyses of serial sections, we have demonstrated the development of the upper dentition of the house shrew. In this species, the deciduous tooth germs are formed but soon become vestigial, whereas the successional and accessional (molar) germs are subsequently formed and developed. There are distinct Shh expression domains in the deciduous, successional, and accessional tooth germs, and those of the latter two germs are identified from the appearance of their primary enamel knots. The developmental sequence of tooth germs in the house shrew indicates that two adjacent primary enamel knots of the successional and accessional germs do not develop simultaneously, but with a constant time lag. We suggest that this mode of tooth succession and accession can be explained by a sequential inhibitory cascade model in which the timing of initiation and the spacing of tooth development are determined by the inhibition from the primary enamel knots of developmentally preceding adjacent tooth germs.     

Development of heterodont dentition in house shrew (Suncus murinus)

Mammalian heterodont dentition comprises incisors, canines, premolars, and molars. Although there has been intensive research, the patterning of these specific tooth types has not yet been elucidated. In order for the gene expression data to be linked with tooth type determination, it is first necessary to determine precisely the incisor-, canine-, premolar-, and molar-forming regions in the jaw primordia. To accomplish this, we studied dentition development in the house shrew (Suncus murinus), which has retained all the tooth types, using three-dimensional reconstructions from serial histological sections and the Sonic hedgehog (Shh) expression patterns. Before the appearance of morphological signs of odontogenesis, Shh expression localized to the presumptive tooth-forming regions, in which the mesial and distal expression domains corresponded to the incisor- and premolar-forming regions, respectively. The upper incisor region was found to extend across the boundary between the frontonasal and the maxillary processes. The canine-forming regions later appeared in the intermediate portions of the maxillary and the mandibular processes. The molar-forming regions later appeared distal to the initially demarcated tooth-forming regions by secondary extension of the distal ends. The demarcation visualized by the Shh expression pattern in the jaw primordia of the house shrew probably represents the basic developmental pattern of mammalian heterodont dentition.     

Early regression of the dental lamina underlies the development of diphyodont dentitions

Functional tooth germs in mammals, reptiles, and chondrichthyans are initiated from a dental lamina. The longevity of the lamina plays a role in governing the number of tooth generations. Monophyodont species have no replacement dental lamina, while polyphyodont species have a permanent continuous lamina. In diphyodont species, the dental lamina fragments and regresses after initiation of the second tooth generation. Regression of the lamina seems to be an important mechanism in preventing the further development of replacement teeth. Defects in the complete removal of the lamina lead to cyst formation and has been linked to ameloblastomas. Here, we show the previously unknown mechanisms behind the disappearance of the dental lamina, involving a combination of cell migration, cell-fate transformation, and apoptosis. Lamina regression starts with the loss of the basement membrane, allowing the epithelial cells to break away from the lamina and migrate into the surrounding mesenchyme. Cells deactivate epithelial markers (E-cadherin, cytokeratin), up-regulate Slug and MMP2, and activate mesenchymal markers (vimentin), while residual lamina cells are removed by apoptosis. The uncovering of the processes behind lamina degradation allows us to clarify the evolution of diphyodonty, and provides a mechanism for future manipulation of the number of tooth generations.     

Degeneration of tooth germ in the developing dentition of the gray short-tailed opossum (Monodelphis domestica)

The aim of this study was to examine the developmental aspects of the dental lamina and the tooth germ of the marsupial opossum (Monodelphis domestica), and to clarify the dental formula of this animal. Specimens were 12-, 16-, and 18-d-old opossums. 3-D reconstructions were constructed from frontal serial sections. In these animals, the tooth germs of the deciduous maxillary and mandibular canine, deciduous third premolar and first molar, and the deciduous maxillary first incisor and second molar had a successional dental lamina and a replacement tooth germ. The tooth germ of the deciduous maxillary fourth incisor and the mandibular first incisor were reduced. The dental lamina was continuous in each jaw except for the deciduous maxillary first incisor. The first dentition (deciduous dentition) remained as the permanent dentition on the deciduous maxillary first incisor, and the deciduous maxillary and mandibular canine and first molar. The maxillary fourth incisor and the mandibular first incisor were the second dentition (successional dentition). Only the deciduous third premolars were replaced. These results showed monophyodonty caused by both deciduous and replacement tooth germ degeneration.     

Morphological Characteristics of Upper Jaw Dentition in a Gobiid Fish (Sicyopterus japonicus): A Micro-computed Tomography Study

Using micro-computed tomography (micro-CT), scanning electron microscopy, contact microradiography, and light microscopy, we investigated the morphological characteristics of the upper dentition of the gobiid fish Sicyopterus japonicus. Three-dimensional (3-D) micro-CT reconstruction demonstrated many close-set densely packed rows of replacement teeth within the dental sac behind a row of functional teeth located on the labial margin of the premaxillae. Cross-slices of the 3-D micro-CT image revealed that functional teeth and numerous replacement teeth were arranged in a semicircular-like strand. In ground as well as histological cross-sections made in a similar plane as seen in the micro-CT image, each tooth family consisted of about 35 replacement teeth in the fish, ranging in standard length (SL) from 50.8 to 60.5 mm, and a tooth germ was initiated at the most disto-labial end of a tooth family, with the functional tooth situated at the opposite end. Between them, many replacement teeth were arranged in orderly fashion, with each replacement tooth being a little less developed than its proximal neighbor.The present study demonstrates that in the upper jaw dentition of adult S. japonicus, consecutive development of replacement teeth in a tooth family can be monitored simultaneously in the same section by appropriate histological sectioning. These results suggest that the upper jaw dentition of this fish provides a suitable as well as unique system for the study of consecutive development of replacement teeth in adult fish.     

Early morphogenesis of heterodont dentition in minipigs

The minipig provides an excellent experimental model for tooth morphogenesis because its diphyodont and heterodont dentition resemble that of humans. However, little information is available on the processes of tooth development in the pig. The purpose of this study was to classify the early stages of odontogenesis in minipigs from the initiation of deciduous dentition to the late bell stage when the successional dental lamina begins to develop. To analyze the initiation of teeth anlagens and the structural changes of dental lamina, a three-dimensional (3D) analysis was performed. At the earliest stage, 3D reconstruction revealed a continuous dental lamina along the length of the jaw. Later, the dental lamina exhibited remarkable differences in depth, and the interdental lamina was shorter. The dental lamina grew into the mesenchyme in the lingual direction, and its inclined growth was underlined by asymmetrical cell proliferation. After the primary tooth germ reached the late bell stage, the dental lamina began to disintegrate and fragmentize. Some cells disappeared during the process of lamina degradation, while others remained in small islands known as epithelial pearls. The minipig can therefore, inter alia, be used as a model organism to study the fate of epithelial pearls from their initiation to their contribution to pathological structures, primarily because of the clinical significance of these epithelial rests.     

Odontogenesis in the Veiled Chameleon (Chamaeleo calyptratus)

ObjectiveReplacement teeth in reptiles and mammals develop from a successional dental lamina. In monophyodont (single generation) species such as the mouse, no successional lamina develops. We have selected a reptilian monophyodont species – the Veiled Chameleon (Chamaeleo calyptratus) – to investigate whether this is a common characteristic of species that do not have replacement teeth. Furthermore, we focus on the sequence of tooth initiation along the jaw, and tooth attachment to the bones.DesignEmbryos of the Veiled Chameleon were collected during the first 6 months of incubation (from the 5th to 24th week) at 7-day intervals.ResultsAfter five weeks of incubation, an epithelial thickening was present as a shallow protrusion into the mesenchyme. A week later, the epithelium elongated more deeply into the mesenchyme to form the dental lamina. The formation of all tooth germs along the jaw was initiated from the tip of the dental lamina. Development of a successional dental lamina was initiated during the pre-hatching period but this structure became markedly reduced during juvenile stages. MicroCT analysis showed the presence of a heterodont dentition in young chameleons with multicuspid teeth in the caudal jaw area and simpler monocuspid teeth rostrally. Unlike the pleurodont teeth of most reptilian species, chameleon teeth are acrodontly ankylosed to the bones of the jaw. Odontoblasts produced a layer of predentine that connected the dentine to the supporting bone, with both tooth and bone protruding out of the oral cavity and acting as a functional unit.ConclusionsChameleons may provide new and useful information to study the molecular interaction at the tooth–bone interface in physiological as well as pathological conditions.     

The homology of the premolar teeth in Setonix brachyurus (Macropodidae: Marsupialia)

The development of the premolar teeth of Setonix brachyurus was studied using eight pouch-young specimens sectioned in a plane transverse to the jaws, one specimen being sectioned horizontally. Sections were stained in Masson's trichrome.

The replacing third premolar developed from the dental lamina lying between the second premolar and the deciduous premolar and not from a lingual downgrowth of dental lamina by the side of the deciduous premolar. In the oldest specimen examined, the third premolar had become displaced from its developmental position; in the upper jaw it was situated to the lingual side of the posterior portion of the second premolar and in the lower jaw to the lingual side of the anterior portion of the deciduous premolar. This displacement appeared to result from two separate growth patterns; an intrinsic growth pattern caused the third premolar to become deeply situated in the jaw and was produced by the stalk of attachment which attained remarkable dimensions, and an extrinsic growth pattern resulted in the second premolar and deciduous premolar lying in close approximation thereby obliterating the area of origin of the third premolar.

Two anterior non-functional cheek teeth, probably representing a canine and a first premolar tooth, developed in the upper jaw, and one non-functional tooth, probably representing a canine or a first premolar tooth, developed in the lower jaw.

The undifferentiated lingual downgrowths of dental lamina by the sides of the enamel organs were not regarded as positive evidence of a replacing series of teeth, but interpreted as constituting the residual free end of the dental lamina. Possible errors in the interpretation of the origin of the third premolar are mentioned. Three possible interpretations concerning the homology of the premolar teeth are given and the significance of the findings in relation to the evolution of the diphyodont condition of placentals discussed.     

A longitudinal study on growth and development of dental arches of primary, mixed and permanent dentitions

In dental clinic for children, criteria for growth and developmental changes related to increases in the width and length of the dental arch at the primary, mixed, and permanent dentition stages are essential. This study was carried out to measure the width and the length of normal dental arch and to make detailed observations of growth and developmental processes in the dental arch at each dentition stage. Materials were serial study casts of the maxilla and the mandible taken every 2 month from 127 children (74 boys and 54 girls). The casts were made from 6 months after birth until the age of 15. Measurements of the width of the dental arch were made between bilateral teeth of the same tooth type, both deciduous and permanent. The length of the dental arch was measured on the basis of the perpendicular distance from the contact point of mesial surfaces of central incisors to a line between bilateral teeth of the same tooth type. Measured values were categorized according to either chronological age or tooth age on the basis of the eruption of the central permanent incisors. The indices of the dental arch with relation to the width and the length at each dentition stage were calculated for the sake of partial and total observations of alterations in dental arch form. The results were as follows: 1) In terms of chronological age, until 1 year before the eruption of permanent replacements, the width of the dental arch gradually decreased in both the maxilla and the mandible in the regions of the deciduous central and lateral incisors. Increasing slightly from about the age of 6 years and the period of mixed dentition, the width of the dental arch remained stable until the permanent dentition stage. From the primary dentition stage, the width of the dental arch in the region of the maxillary and mandibular canines and first and second molars gradually increased. Therefore it remained stable until the eruption of permanent dentition. The width in the region of the permanent maxillary and mandibular first molars gradually increased and attained a stable condition at about 12 years of age. In males, the width in the area of the maxillary secondary molars decreased slightly and tended to decrease in the mandible. In females, on the other hand, the width showed a tendency to increase with advancing ages. With the exception of the second permanent molars, the width between the distance of bilateral teeth were consistently larger in males than in females.(ABSTRACT TRUNCATED AT 400 WORDS)     

Incidence of caries and periodontal condition in patients with cleft lip and cleft palate]

The data relative to caries experience, provided dental care, periodontal condition, oral hygiene and pocket depth obtained from 158 patients with cheilognathopalatoschisis were recorded. According to age, the findings were subdivided into three groups: deciduous dentition, mixed dentition and permanent dentition group. The data obtained from the upper jaw were compared to those from the lower jaw. Furthermore, the data relative to the different types of tooth and the region of the cleft were compared to the findings from teeth non-neighbouring the cleft. The results permit to draw conclusions as to noteworthy aspects of the orthodontic and the general dental care of patients with cheilognathopalatoschisis.     

Histogenesis and disappearance of the teeth of the Mekong giant catfish, Pangasianodon gigas (Teleostei)

Juveniles of the Mekong giant catfish, Pangasianodon gigas (Teleostei), have 3 sorts of tooth-upper and lower jaw teeth, palatal teeth, and pharyngeal teeth--but adults are toothless. To investigate the histogenesis and disappearance of the teeth, we made serial sections of the mouth and teeth of juvenile fish at 10 developmental stages (from ca. 8.5 to ca. 30 cm in total length) and examined them under scanning electron microscope and light microscope. Observations of teeth and surrounding tissues in the serial sections revealed the process of tooth resorption by active odontoclast-like cells. Numbers of jaw and palatal teeth decreased with age. When the fish reached ca. 14 cm in total length, the numbers of functional upper jaw teeth and successional tooth germs decreased rapidly, and the developmental rate of successional tooth germs slowed. When the fish reached ca. 24 cm, no teeth existed in the upper jaw. It is clear that tooth disappearance results from the shedding of functional teeth and the lack of replacement tooth germs.     

A step-by step guide for autotransplantation of teeth

Tooth loss is an adverse consequence of oral diseases and traumatic dental injuries. Although several treatment options exist to treat a missing or hopeless tooth, especially in young individuals, most of the existing alternatives (such as orthodontic treatment, removable or fixed partial dentures, and dental implants) impose a challenge in children due to the nature of the developing jaw bones. Tooth autotransplantation is the replacement of a tooth with another functional tooth within the patient's dentition. Autotransplantation can serve as a promising treatment alternative in cases of tooth loss not only in children and adolescents but also in adult patients. Autotransplantation is a technique-sensitive procedure, that requires proper and thorough planning as well as careful and knowledgeable execution in order to improve the chances for long-term success and survival of the transplanted tooth. Thus, the aim of this article was to provide a step-by-step clinical guide, emphasizing key points and highlights for planning and performing a successful autotransplantation procedure. Autotransplantation is a very predictable treatment modality that can serve as a viable option to replace a missing tooth, especially in young patients. Proper planning and careful execution of the procedure are important to achieve optimal long-term results.     

Satisfaction with the dentition related to dental functional status and tooth replacement in an adult Bulgarian population: a cross-sectional study

Objectives

The purpose of this study is to assess satisfaction with the dentition in general, dental esthetics, and chewing function related to dental functional status and tooth replacement in subjects, dentate in both jaws.

Materials and methods

Dentitions of subjects (n?=?2,437) aged ≥20 years were categorized in a hierarchical functional classification system, with and without tooth replacements, according to four dental conditions: ‘≥10 teeth in each jaw’, ‘complete anterior regions’, ‘sufficient premolar regions’ (≥3 occluding pairs), and ‘sufficient molar regions’ (bilaterally ≥1 occluding pair). Likelihood ratios (LR) were used to express the ability of these conditions to discriminate between satisfied and not satisfied subjects. Odds ratios (OR) were calculated to evaluate associations between satisfaction, the four dental conditions separately, and tooth replacement.

Results

In the hierarchical system, subjects having ‘<10 teeth’ were more likely of being not satisfied with their dentitions (LR 4.09), esthetics (LR 3.51), and chewing (LR 5.49). As a separate condition, ‘≥10 teeth’ was significantly associated only with satisfaction with chewing. The conditions ‘complete anterior regions’ and ‘sufficient’ premolar and molar regions’ were associated with all satisfaction variables (ORs 1.47–2.96, p values ≤0.012). When dental conditions were determined on the basis of natural teeth only, having teeth replaced was positively correlated with satisfaction; when determined on the basis of natural plus replaced teeth, subjects having teeth replaced tended to be less satisfied than their counterparts with natural teeth only.

Conclusions

Satisfaction was strongly associated with dental functional status.

Clinical relevance

Dental configurations comprising both natural and artificial teeth were less likely to provide the same level of satisfaction as equivalent dental configurations comprising natural teeth only.     

Origin and developmental fate of vestigial tooth primordia in the upper diastema of the field vole (Microtus agrestis, Rodentia)

OBJECTIVE: Odontogenesis in voles is a convenient model to test hypotheses on tooth development generated from investigations in the mouse. Similar to other rodents, the functional dentition of the vole includes a toothless diastema. At its mesial end, a vestigial tooth bud has been found in the upper jaw of vole embryos. The aim of this study was to analyse the developmental dynamics of vestigial tooth structures in the upper diastema of the field vole and to compare it with the situation in the mouse. DESIGN: The development of odontogenic structures in the upper diastema of the field vole was investigated using serial histological sections and three-dimensional (3D) computer-aided reconstruction. RESULTS: A transient continuous dental lamina in the upper diastema of the field vole extended mesially to the first molar primordium, but was not continuous with the dental lamina in the incisor region. At its mesial limit, a large vestigial tooth primordium was regularly present. A further distinct vestigial bud was located mesially to the first molar primordium. The segmentation of the dental lamina suggested a potential to give rise to further vestiges in the upper diastema of the vole. CONCLUSIONS: In the prospective diastema of the vole exists as in the mouse a continuous dental lamina. Beside the prominent vestigial tooth bud in the mesial diastema, a further large bud was transiently located in front of the molars. The incorporation of dental epithelium into the first upper molar (M(1)) primordium in the vole differs from that in the mouse.     

The effect of age on tooth replacement patterns in piranhas (Pisces: Characidae)

Patterns of tooth replacement were observed in two living piranha fish (Serrasalmus) by recording the state of the dentition twice weekly over a period of approximately 9 months. Since similar studies had been carried out on the same two fish 3 yr earlier, it was possible to determine whether any significant changes had occurred with age. Though all the teeth within any jaw quadrant were still replaced synchronously, significant changes in tooth replacement patterns occurred with age. The jaw quadrants were affected unequally in both fish and this could be regarded as indicative of the fact that replacement patterns may, in part, be under control of local rather than general mechanisms. In older fish the teeth remained functional for longer periods than in the younger fish.     

Eruption times of permanent teeth in children and young adolescents in Athens (Greece)

In a study in Athens, Greece, during the summer of 2003, 2,304 patients (1,168 boys and 1,176 girls) were examined by a young dentistry. The examination occurred within the framework of a routine dental check-up performed at the National and Kapodistrian University of Athens. The age span ranged from 3.00 to 24.93 years of age. Sex, age and present permanent teeth were recorded. Wisdom teeth were excluded. The sequence of tooth eruption differs significantly in the lower and upper jaw, whereas no significant differences existed when comparing the sides of each jaw. The tooth eruption in the lower and upper jaw of male and female probands is symmetrical. In comparing the upper and the lower jaw of both genders, it becomes evident that there is a tendency for earlier tooth eruptions in the lower jaw. In respect to the tooth eruption sequence, a change was noted in the upper jaw. Contrary to the reports of other authors, the second premolar has changed places with the canine and erupts prior to this tooth. This could also be demonstrated in recent studies from New York and Bremen (Germany). Otherwise no major differences concerning the sequence of tooth eruptions were observed, when compared with the results gained from other populations. Concerning the entire dentition, no acceleration of the tooth eruption could be noted. The computed differences of teeth eruption as a mean value calculated over all teeth was ±1 year at maximum, compared with studies from different continents. Oral examination of teeth is a simple tool to calculate tooth eruption intervals. This first investigation in a population of Athens revealed a change in the eruption sequence of permanent teeth. These findings are relevant for dental treatment planning and should be reconfirmed at certain intervals.     

Overview: The Mechanisms Controlling Root Morphogenesis in Mammalian Molars: —Morphological Relevance of the Tooth Root and Crown,Developmental Mechanisms,and Phylogenetic Aspect of the Tooth Roots—

Diet is one of the most important factors driving the process of natural selection in evolution. The dentition is adapted for the diet, contributing to the diversification and adaptation of extant vertebrates. Importantly, the structure of the molar shows marked variation in extant mammals to facilitate the processing of many kinds of food and support the occlusal force effectively. A tooth root is an important element, connecting a tooth with the jaw to support the occlusal force. However, morphological studies on teeth mainly focus on the crown, whereas there has been an insufficient accumulation of information on the morphogenic control mechanism of tooth root structures. There have been some reports on the root form in humans due to clinical demand, and recent studies on Hertwig's epithelial root sheath (HERS), which plays an important role in root development, have progressed rapidly. However, studies on the regulatory mechanism of the tooth root structure in relation to the jaw and crown are still awaited. In this paper, we highlight the following three issues : the morphological relevance of the tooth root and crown, and developmental mechanisms and phylogenetic aspects of the tooth roots. HERS produces several signaling molecules including bone morphogenic protein (BMP), Sonic Hedgehog (Shh), Wnt, ectodysplasin (Eda), and fibrobast growth factor (FGF). These factors regulate the closure of the pulp chamber floor to determine the numbers and width of the tooth roots, and then regulate the fusion, curve, and length. The tooth root differentiates and develops in conjunction with its crown. However, few studies have examined the tooth root from an evolutionary perspective. We need to advance research on the tooth root including the whole tooth in developmental biology, evolutionary biology, and comparative odontology.     

Increased apoptosis during morphogenesis of the lower cheek teeth in tabby/EDA mice

In wild-type (WT) mice, epithelial apoptosis is involved in reducing the embryonic tooth number and the mesial delimitation of the first molar. We investigated whether apoptosis could also be involved in the reduction of tooth number and the determination of anomalous tooth boundaries in tabby (Ta)/EDA mice. Using serial histological sections and computer-aided 3D reconstructions, we investigated epithelial apoptosis in the lower cheek dentition at embryonic days 14.5-17.5. In comparison with WT mice, apoptosis was increased mainly mesially in Ta dental epithelium from day 15.5. This apoptosis showed a similar mesio-distal extent in all 5 morphotypes (Ia,b,c and IIa,b) of Ta dentition and eliminated the first cheek tooth in morphotypes IIa,b. Apoptosis did not appear to play any causal role in positioning inter-dental gaps. Analysis of the present data suggests that the increased apoptosis in Ta mice is a consequence of impaired tooth development caused by a defect in segmentation of dental epithelium.     

Selectively preventing development of third molars in rats using electrosurgical energy

BACKGROUND: Third molars are teeth with questionable value. People who never develop third molars avoid confronting the disease and pain these teeth often cause. Since third molars do not begin to develop until children are approximately five years of age, a window of opportunity exists to therapeutically prevent this tooth's development. The dentition of neonate rats possess developmental stages of molars similar to that of five-year-old children. This pilot study tests the hypothesis that third molars can be selectively prevented from developing. METHODS: Thirty-three neonate rats received a momentary pulse of electrosurgical energy to one of their maxillary tuberosities. The tuberosities on the contralateral sides received no treatment. Intraoral and radiographic examinations of sacrificed animals occurred when they were between 47 and 52 days old. Several tuberosity areas from sacrificed animals underwent histologic examination. RESULTS: Ten rats showed no intraoral or radiographic evidence of third molar development, and six developed smaller-than-normal third molars. Development of the maxilla also was affected frequently. One treated tuberosity area that was missing a third molar showed no histologic evidence of tooth-forming tissues, cyst formation or other significant abnormal tissue changes. CONCLUSIONS: Maxillary third molars can be selectively prevented from developing in rat pups at or near the time of tooth bud initiation; however, electrosurgical energy is too powerful and uncontrollable to reliably confine its damage to only the tooth-forming tissues. CLINICAL IMPLICATIONS: Third molars may be able to be selectively prevented from developing in growing children near the time of tooth bud initiation if less-differentiated precursor tooth-forming tissues can be selectively targeted.