Determination of the mesio-distal tooth width via 3D imaging techniques with and without ionizing radiation: CBCT, MSCT, and µCT versus MRI.

Objective: The purpose of this study was to estimate the feasibility and accuracy of mesio-distal width measurements with magnetic resonance imaging (MRI) in comparison to conventional 3D imaging techniques [multi-slice CT (MSCT), cone-beam CT (CBCT), and µCT]. The measured values of the tooth widths were compared to each other to estimate the amount of radiation necessary to enable orthodontic diagnostics. Material and Methods: Two pig skulls were measured with MSCT, CBCT, µCT, and MRI. Three different judges were asked to determine the mesio-distal tooth width of 14 teeth in 2D tomographic images and in 3D segmented images via a virtual ruler in every imaging dataset. Results: Approximately 19% (27/140) of all test points in 2D tomographic slice images and 12% (17/140) of the test points in 3D segmented images showed a significant difference (P ≤ 0.05). The largest significant difference was 1.6mm (P < 0.001). There were fewer significant differences in the measurement of the tooth germs than in erupted teeth. Conclusions: Measurement of tooth width by MRI seems to be clinically equivalent to the conventional techniques (CBCT and MSCT). Tooth germs are better illustrated than erupted teeth on MRI. Three-dimensional segmented images offer only a slight advantage over 2D tomographic slice images. MRI, which avoids radiation, is particularly appealing in adolescents if these data can be corroborated in further studies.

Tooth replacement without a dental lamina: the search for epithelial stem cells in Polypterus senegalus.

Most actinopterygians replace their teeth continuously throughout life. To address the question of where and how replacement teeth form in actinopterygians, it is advisable to investigate well-chosen representatives within the lineage. The African bichir, Polypterus senegalus, belongs to the earliest diverged group of the actinopterygian lineage with currently living representatives. Its well characterized dentition, together with its phylogenetic position, make this species an attractive model to answer following questions: (1) when and where does the replacement tooth form and how is it connected with the dental organ of the predecessor, and (2) is there any evidence for the presence of epithelial stem cells, hypothesized to play a role in replacement? Serial sections show that one tooth family can contain up to three members, which are all interconnected by dental epithelium. Replacement teeth develop without the presence of a successional dental lamina. We propose that this is the plesiomorphic condition for tooth replacement in actinopterygians. BrdU pulse-chase experiments reveal cells in the outer and middle dental epithelium, proliferating at the time of initiation of a new replacement tooth. It is tempting to assume that these cell layers provide a stem cell niche. The observed absence of label-retaining cells after long chase times (up to 8 weeks) is held against the light of divergent views on cell cycling properties of stem cells. At present, our data do not support, neither reject, the hypothesis on involvement of epithelial stem cells within the process of continuous tooth replacement.

Differential expression of cxcl-14 during eruptive movement of rat molar germs.

Tooth eruption at the early postnatal period is strictly controlled by the molecules secreted mainly from follicular tissues, which recruit monocytes for osteoclast formation. In this study, it was hypothesized that different molecules can be expressed according to the stages of tooth eruption. Rat molar germs together with follicles were extracted and DD-PCR was performed from the root formation stage 2nd molars germs (after eruptive movement) and cap stage 3rd molar germs (before movement) at postnatal day 9. Cxcl-14, a potent chemoattractant, was detected as one of the differentially expressed molecules from DD-PCR. Its expression increased significantly at the root formation stage, compared with the cap or crown formation stage at both transcription and translation levels. The expression patterns of cxcl-14 were consistent with those of MCP-1 and CSF-1, and opposite to OPG. Immunofluorescence showed that cxcl-14 was localized in the dental follicular tissues only at the root formation stage overlaying the proximo-occlusal region of the molar germs. Many osteoclasts appeared on the surface of the alveolar bone which overlayed the occlusal region of the root formation stage 2nd molar germs and underwent resorption. Cxcl-14 expression was reduced considerably at both the translation and transcription levels by an alendronate treatment. These results suggest that cxcl-14 may be implicated in the formation of the eruptive pathway of tooth germs via osteoclastogenesis.

Morphogenesis and bone integration of the mouse mandibular third molar.

The mouse third molar (M3) develops postnatally and is thus a unique model for studying the integration of a non-mineralized tooth with mineralized bone. This study assessed the morphogenesis of the mouse M3, related to the alveolar bone, comparing M3 development with that of the first molar (M1), the most common model in odontogenesis. The mandibular M3 was evaluated from initiation to eruption by morphology and by assessing patterns of proliferation, apoptosis, osteoclast distribution, and gene expression. Three-dimensional reconstruction and explant cultures were also used. Initiation of M3 occurred perinatally, as an extension of the second molar (M2) which grew into a region of soft mesenchymal tissue above the M2, still far away from the alveolar bone. The bone-free M3 bud gradually became encapsulated by bone at the cap stage at postnatal day 3. Osteoclasts were first visible at postnatal day 4 when the M3 came into close contact with the bone. The number of osteoclasts increased from postnatal day 8 to postnatal day 12 to form a space for the growing tooth. The M3 had erupted by postnatal day 26. The M3, although smaller than the M1, passed through the same developmental stages over a similar time span but showed differences in initiation and in the timing of bone encapsulation.

Pediatric maxillary fractures.

Pediatric craniofacial structures differ from those of adults in many ways. Because of these differences, management of pediatric craniofacial fractures is not the same as those in adults. The most important differences that have clinical relevance are the mechanical properties, craniofacial anatomy, healing capacity, and dental morphology. This article will review these key differences and the management of pediatric maxillary fractures. From the mechanical properties' perspective, pediatric bones are much more resilient than adult bones; as such, they undergo plastic deformation and ductile failure. From the gross anatomic perspective, the relative proportion of the cranial to facial structures is much larger for the pediatric patients and the sinuses are not yet developed. The differences related to dentition and dental development are more conical crowns, larger interdental spaces, and presence of permanent tooth buds in the pediatric population. The fracture pattern, as a result of all the above, does not follow the classic Le Fort types. The maxillomandibular fixation may require circum-mandibular wires, drop wires, or Ivy loops. Interfragmentary ligatures using absorbable sutures play a much greater role in these patients. The use of plates and screws should take into consideration the future development with respect to growth centers and the location of the permanent tooth buds. Pediatric maxillary fractures are not common, require different treatments, and enjoy better long-term outcomes.

Advances in the identification of deciduous molar tooth germs.

In forensic anthropology, correct identification of human deciduous teeth is of paramount importance for age-at-death estimation and relies on detailed anatomical descriptions. Yet literature is scarce on indications: details on the morphology of molar tooth germs of fetuses and newborns, developing from multiple mineralized centers that will eventually coalesce, are scant. This paper presents new anatomical elements for practitioners to identify human molar tooth germs at early developmental stages. 126 deciduous molars from 22 modern skeletons of fetuses and newborns (with a known age-at-death ranging between 0 days and 2 months and 21 days postnatal), without reported or observed dental pathological signs, were selected from the Collezione Antropologica LABANOF (CAL) documented skeletal collection. Gross anatomical descriptions of the morphology and configuration of the centers were provided, considering the number of mineralized centers, the shape and the outline of the occlusal plane at different stages. Three different developmental stages were observed in the maxillary first and second molar and the mandibular first molar, whereas in the mandibular second molar four stages were observed. For each stage, we provide additional detailed morphological descriptions, sketches outlining the shape of the tooth germ, and a picture of the tooth; also, indications for siding the teeth are presented. This information can be used by forensic anthropologists and odontologists for a proper identification when tooth germs are not found in anatomical connection within the dental sockets. Further analyses that encompass more age groups on a larger sample would allow to map the entire crown development of deciduous molars.

Insulin-like growth factor 1 modulates bioengineered tooth morphogenesis.

Regenerative therapy to replace missing teeth is a critical area of research. Functional bioengineered teeth have been produced by the organ germ method using mouse tooth germ cells. However, these bioengineered teeth are significantly smaller in size and exhibit an abnormal crown shape when compared with natural teeth. The proper sizes and shapes of teeth contribute to their normal function. Therefore, a method is needed to control the morphology of bioengineered teeth. Here, we investigated whether insulin-like growth factor 1 (IGF1) can regulate the sizes and shapes of bioengineered teeth, and assessed underlying mechanisms of such regulation. IGF1 treatment significantly increased the size of bioengineered tooth germs, while preserving normal tooth histology. IGF1-treated bioengineered teeth, which were developed from bioengineered tooth germs in subrenal capsules and jawbones, showed increased sizes and cusp numbers. IGF1 increased the number of fibroblast growth factor (Fgf4)-expressing enamel knots in bioengineered tooth germs and enhanced the proliferation and differentiation of dental epithelial and mesenchymal cells. This study is the first to reveal that IGF1 increases the sizes and cusp numbers of bioengineered teeth via the induction of enamel knot formation, as well as the proliferation and differentiation of dental epithelial and mesenchymal cells.

Correlation between the pattern of facial growth and the position of the mandibular third molar.

PURPOSE: The purpose of this study was to examine the correlation between variables that determine the position of the third molar (M3) and correlation between the pattern of facial growth and examined variables. MATERIALS AND METHODS: Material for the study consisted of 130 panoramic radiographs and lateral radiographs of subjects' heads in whom orthodontic therapy had been started. Analysis of the position of the mandibular M3 and its relation to the bone and other teeth were determined by 4 variables: evaluation of the space for both M3, spatial relation between the second molar and M3, vertical position of the M3 in relation to the alveolar ridge, and inclination of the germ of the M3. RESULTS: In boys, significant correlation was determined on the right side of the jaw, between the retromolar area and the vertical position of M3. Significant correlation was determined in girls, between the retromolar area and the vertical position of M3 on both sides, retromolar area and M3 inclination on the left side, and retromolar area and spatial relation of M3 on the right side. Analysis of correlation between facial growth pattern and 4 variables that determinate the position of M3 showed positive correlation only for the lower right M3 inclination in subjects with anterior facial rotation. CONCLUSION: The present study showed that the amount of retromolar space for the position of the M3 is not a sign of its normal development. No significant differences were determined between the position of M3 and type of facial growth.

Bioengineered Tooth Buds Exhibit Features of Natural Tooth Buds.

Tooth loss is a significant health issue currently affecting millions of people worldwide. Artificial dental implants, the current gold standard tooth replacement therapy, do not exhibit many properties of natural teeth and can be associated with complications leading to implant failure. Here we propose bioengineered tooth buds as a superior alternative tooth replacement therapy. We describe improved methods to create highly cellularized bioengineered tooth bud constructs that formed hallmark features that resemble natural tooth buds such as the dental epithelial stem cell niche, enamel knot signaling centers, transient amplifying cells, and mineralized dental tissue formation. These constructs were composed of postnatal dental cells encapsulated within a hydrogel material that were implanted subcutaneously into immunocompromised rats. To our knowledge, this is the first report describing the use of postnatal dental cells to create bioengineered tooth buds that exhibit evidence of these features of natural tooth development. We propose future bioengineered tooth buds as a promising, clinically relevant tooth replacement therapy.

Primary enamel knot cell death in Apaf-1 and caspase-9 deficient mice.

During molar development, apoptosis occurs in a well-characterised pattern suggesting several roles for cell death in odontogenesis. However, molecular mechanisms of dental apoptosis are only poorly understood. In this study, Apaf-1 and caspase-9 knockouts were used to uncover the engagement of these members of the apoptotic machinery during early tooth development, concentrating primarily on their function in the apoptotic elimination of primary enamel knot cells. Molar tooth germ morphology, proliferation and apoptosis were investigated on frontal histological sections of murine heads at embryonic days (ED) 15.5, the stage when the primary enamel knot is eliminated apoptotically. In molar tooth germs of both knockouts, no apoptosis was observed according to morphological (haematoxylin-eosin) as well as biochemical criteria (TUNEL). Morphology of the mutant tooth germs, however, was not changed. Additionally, knockout mice showed no changes in proliferation compared to wild type mice. According to our findings on knockout embryos, Apaf-1 and caspase-9 are involved in apoptosis during tooth development; however, they seem dispensable and not necessary for proper tooth shaping. Compensatory or other mechanisms of cell death may act to eliminate the primary enamel knot cells in the absence of Apaf-1 and caspase-9.

The characteristics of adjacent anatomy of mandibular third molar germs: a CBCT study to assess the risk of extraction.

This study aims to investigate the characteristics of adjacent anatomy of mandibular third molar germs (MTMGs). Three hundred Chinese patients aged 12 to 17 years old who received cone-beam computed tomography (CBCT) were enrolled. The continuity of cortical outline of inferior alveolar canals (IACs) in the region of MTMGs, the integrity of lingual bone cortex and the relationship between hard tissue part of MTMGs and IACs were investigated by observing CBCT data via the NNT viewer software. The age, degree of dental development, gender and location were recorded as variables. The associations between different variables and the observed data were analysed. The possibilities of disrupted cortical outline of IACs or the hard tissue part of MTMGs contacting IACs were significantly lower in 12 or 13 age groups, lower in Nolla stage ≤ 6. Males were significantly less than females in the incidence of disrupted cortical outline of IACs. As to the perforation of lingual bone cortex, no significant differences were observed in gender, ages, location or development stages. According to the CBCT images, anatomical factors contributed the lest to the risk of inferior alveolar nerve and lingual nerve injury in the 12 to 13 age group during removing the MTMG removal.

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.

Histological description of tooth formation in adult Eretmodus cf. cyanostictus (Teleostei, Cichlidae).

The Eretmodini, a tribe of closely related cichlids (Teleostei, Cichlidae) originating from Lake Tanganyika, possess oral tooth shapes ranging from conical (in Tanganicodus) over cylindrical (in Spathodus) to spatulate (in Eretmodus). Prior to a study aiming to understand how these distinctly different tooth shapes can be acquired in such closely related taxa, a detailed histological study was required of tooth formation in a representative of the eretmodines. Here, we present a histological description of replacement tooth development in Eretmodus cf. cyanostictus. Using light-microscopic observations on semithin as well as on ground sections, microradiographs and stereo-microscopic observations of both alizarine red S stained and unstained jaws we can conclude that tooth formation in adult E. cf. cyanostictus roughly corresponds with what is known for teleost tooth development in general. Remarkable features include the localization and shape of the epithelial downgrowth, the transient presence of a layer intermediate between inner dental epithelium (IDE) and outer dental epithelium (ODE), the asymmetric shape of the enamel organ, the fact that the pulp cavity recedes in front of the forming enameloid during enameloid formation, and finally, the pattern of matrix mineralisation and maturation, and the presence of pigment in the enameloid. The observation that the enamel organ in adult E. cf. cyanostictus develops asymmetrically is significant for understanding tooth shape variation in the Eretmodini.

On the non-existence of compensatory tooth size interaction in a contemporary human population.

Compensatory tooth size interactions between early and later developing teeth within the same tooth class were empirically evaluated in a sample of 125 study casts of Caucasoid children. Mean buccolingual and mesiodistal diameters for first and second molars, pre-molars, and incisors were calculated, and those first developing teeth that were either larger of smaller than the mean were identified. Pearsonian correlation coefficients and chi-square tests revealed highly significant positive correlations between smaller of larger early developing teeth and their later developing neighbors. This total lack of compensatory tooth size interaction was also confirmed when outsized teeth (larger of smaller than one standard deviation from the mean) were used. Similar results were obtained when tooth size was corrected for arcade length, hence allowing for the rejection of Sofaer's model of compensatory tooth size interaction.

Progressive mineralization pattern of developing enamel during the maturation stage.

The maturation stage of developing enamel may be divided into three substages: First, a secondary mineralization increase appears from the surface toward the deeper layer; then, a tertiary mineralization increase takes place from the deeper layer toward the surface; and finally, the narrow subsurface layer mineralizes heavily and attains the highest degree of mineralization of all layers.

Deciduous tooth chronology in the mandible of the domestic pig.

Fetuses of known age, collected from 20 days' gestation to term, were used to characterize the chronology of deciduous tooth development within the right mandible of swine. Tooth development was first observed at 32 days' embryonic development, with the differentiation of the deciduous third molar. Bud stages for the remaining deciduous teeth differentiated within the period of 32 to 38 days of embryonic development. Although the initial histological appearance of these teeth covered a short period of time, it was apparent that each tooth continued to develop at its own rate. The deciduous second incisor and first molar reached a stage of enamel formation by the 80th and 86th day of fetal development. This is a much later stage than previously recorded for beginning enamel formation. The stages of tooth development and enamel formation for each tooth are summarized. A previous report on the distribution of the dental lamina and deciduous tooth development in the mandible of the domestic pig combined with the information presented in this report on tooth chronology provide much of the information required for future studies using the domestic pig in dental research. A fetus observed at the 74th day of development demonstrated a tooth bud for the deciduous first premolar. The development of this tooth was followed closely throughout the remainder of fetal development with the cap stage representing its most definitive form at 110 days' development. The suggested deciduous origin for this tooth could result in a reevaluation of the nomenclature for the dental formula of swine.

Larval vs. adult pharyngeal dentition in some Japanese cyprinid fishes.

The development of the pharyngeal dentition was examined in 13 species of five subfamilies of the family Cyprinidae. A previously described difference between the larval and adult dentition in Gnathopogon caerulescens was observed in 11 species of Gobioinae, Cyprininae, Leuciscinae, and Danioinae, but was not seen in two species of Acheilognathinae. The adult dentition is usually complete by the later larval or juvenile period. In the adult dentition, the functioning teeth are generally shed at each position, when the replacement tooth has been ankylosed to the bone, or when the germ of that tooth has grown sufficiently. In the larval dentition, however, the replacement tooth is ankylosed medial to the functioning tooth, so the older functioning tooth is retained after ankylosis of the replacement tooth. That is why the dentigerous surface of the bone grows rapidly during the larval period. Each tooth row represents a single replacement wave. The distribution and pattern of the central teeth are exactly the same in all types of the larval dentition. However, those of the anterior teeth vary between and within different species. The larval dentition develops into the major row of the adult dentition through tooth replacements. The number of tooth families in the larval dentition is completely consistent with the tooth number of the major row in the adult dentition. Therefore, the number of major row teeth owes its variation to that in the appearance pattern of the anterior teeth.

The visualization of the patterns of ameloblast modulation by the glyoxal bis(2-hydroxyanil) staining method.

Several red stripes appeared on the surface of the rat incisor enamel at the maturation stage when stained with a modified glyoxal bis (2-hydroxyanil) method (GBHA). The stripes running across the maturation enamel were correlated directly, morphologically, and indirectly, using 45Ca autoradiography, with the bands of overlying smooth-ended ameloblasts. In addition, GBHA strain revealed similar stripes on the maturation enamel of the developing teeth from a variety of animals (rat molar, bovine incisor and molar, porcine canine, and monkey incisor), indicating that the maturation of the mammalian tooth enamel, in general, is under the control of two types of maturation ameloblasts which undergo cyclic morphologic changes.

Tooth allografts fail to stimulate immunologic memory in mice.

Tooth transplants should not preclude future transplants in the recipient. In this study teeth failed to stimulate immunologic memory in weakly disparate mice. The teeth did carry transplantation antigens and were rejected after second-set skin grafts. The teeth probably enhanced their own survival through some immunoregulatory mechanism.

Influence of serum on cultured murine tooth organ allotransplants.

Previous investigations indicated that in vitro culture of fetal tooth germs before allotransplantation prolonged graft survival. This study assessed the influence of different sources of serum in culture medium on post-transplant development of neonatal tooth organs. The results indicate that recipient-strain serum, but not donor-strain serum or calf serum, increased tooth survival compared with that of uncultured controls, which were rejected by the fourteenth post-transplant day. The survival curve for cultured tooth organs was shifted to the right by two days. No tooth transplant survived beyond three wk.