Neural crest cells require Meis2 for patterning the mandibular arch via the Sonic hedgehog pathway.

Cranial neural crest cells (cNCCs) originate in the anterior neural tube and populate pharyngeal arches in which they contribute to formation of bone and cartilage. This cell population also provides molecular signals for the development of tissues of non-neural crest origin, such as the tongue muscles, teeth enamel or gland epithelium. Here we show that the transcription factor Meis2 is expressed in the oral region of the first pharyngeal arch (PA1) and later in the tongue primordium. Conditional inactivation of Meis2 in cNCCs resulted in loss of Sonic hedgehog signalling in the oropharyngeal epithelium and impaired patterning of PA1 along the lateral-medial and oral-aboral axis. Failure of molecular specification of PA1, illustrated by altered expression of Hand1/2, Dlx5, Barx1, Gsc and other markers, led to hypoplastic tongue and ectopic ossification of the mandible. Meis2-mutant mice thus display craniofacial defects that are reminiscent of several human syndromes and patients with mutations in the Meis2 gene.

[Orthodontic anomalies and secular trend in formation of the orofacial cranium]. / Ortodontické anomálie a sekulární trend v utvárení orofaciální oblasti.

BACKGROUND. The aim of the study was to compare craniofacial and dental characteristics of contemporary and historical populations and elucidate some etiological aspects of malocclusion. METHODS AND RESULTS. Con-temporary cohort of 703 university students and three historical samples (73 skulls from 9th century, 344 skulls from the 10th to 14th century and 210 skulls from the 14th to 18th century were examined. Measurements of craniometric and anthropometric points were done. The width of jaws was examined in Pont's points. Björk´s method for epidemiological registration of malocclusion was used; teleroentgenograms were examined as well. Broader dental arches regardless of the type of skull and significantly lower frequency of serious malocclusions were proven in historical population. CONCLUSION. The extreme increase of serious malocclusions in the contemporary population is more probably caused by civilisation factors than secular trend in formation of skull. .

Maxillary dental arch biometry: assessment with fetal MR imaging.

OBJECTIVE: To define normal growth of the fetal maxillary dental arch using magnetic resonance imaging. METHOD: Four hundred twenty-four consecutive fetuses (18 to 37 weeks) with a morphologically normal anatomy or only minor malformations, not affecting bone growth and face anatomy were included. On axial T2-weighted images the dental arch length and width were measured. The measurements were correlated with gestational age and the biparietal diameter (BPD) of the fetal head using correlation and regression analysis. RESULTS: A linear growth relationship was observed between the dental arch length and gestational age (r = 0.86; p = < 0.0001; y = -1.85 + 0.75 × gestational age) and the dental arch width and gestational age (r = 0.92; p = < 0.0001; y = -2.19 + 1.05 × gestational age). A significant correlation was found between the dental arch length and the BPD (r = 0.903; p = < 0.0001) and the dental arch width and the BPD (r = 0.927; p = < 0.0001). The interobserver variability showed good agreement for the dental arch length (intraclass coefficient 0.981; r = 0.963) and width (intraclass coefficient 0.987; r = 0.974), respectively. CONCLUSION: We present a nomogram for the in utero assessment of the fetal dental arch. These data may help in the early detection of abnormal dental arch development.

An investigation into the morphometric developments of the maxillary and mandibular arches during the fetal period.

OBJECTIVE: The objective of this study was to determine the developments, morphometric features, and shapes of the maxillary and mandibular arches during the prenatal period in a large series of fetal material. METHODS: The study was carried out on 225 human fetuses aged between 8 and 40 weeks of gestation. General, extraoral, and intraoral parameters were taken from each fetus. The width and depth measurements and the shapes of the maxillary and mandibular arches were achieved using the casts obtained. The arches were categorized according to the shapes of the anterior and posterior regions of the arches. RESULTS: Palatal and mandibular indices did not change during the prenatal period. Maxillary arch measurements were greater than the mandibular measurements. Moreover, width measurements of both arches were greater than the depth measurements during fetal life. We found that the frequencies of triangular maxillary and mandibular arches were highest in the first and second trimesters; whereas, the square model became more frequent in the third trimester and at full term. Classification of the arches according to their posterior regions showed that the tips of the arches shifted medially toward the term. There were significant correlations between width and depth parameters of the arches and extraoral parameters. CONCLUSION: Data obtained in the study would be useful for clinicians by presenting an objective scale related to the prenatal period as well as being helpful in assessing the development of this region, identifying the anomalies and pathologies, and assisting treatment.

Effects of induced premaxillary suture fusion on the craniofacial morphology in growing rats.

OBJECTIVE: Due to premaxillary rapid development and fusion with the maxilla at the fetus stage, the functions of the premaxillary suture still remain unclear. This study was designed to explore the effect of artificial induced premaxillary suture fusion on craniofacial morphology. METHODS: Thirty Sprague Dawley rats were divided into control and experimental groups, with 3 week, 5 week and 8 week subgroups of five animals each. An incision was made in each rat along the premaxillary suture and cyanoacrylate was administered to immobilize the exposed premaxillary suture for experimental rats. No glue was applied to controls. Weights, dental impressions and radiographs were taken before and after surgery until sacrifice and used to determine the differences between groups using the one-way ANOVA test. RESULTS: After immobilizing the premaxillary suture, significant changes in the craniofacial morphology were measured at the different time points. In the experimental groups, local changes occurred at the 3rd week. A global alteration in craniofacial morphology was apparent at the 8th week in the experimental group compared to the control. At each successive time point, craniofacial morphological alterations increased in rats with fused premaxillary sutures. CONCLUSIONS: Induced premaxillary suture fusion can inhibit the growth of the premaxilla and cause extensive craniofacial morphological changes. These findings suggest that premaxillary suture fusion may be related to craniofacial malformation or malocclusion and to the formation of the flattened craniofacial profile in humans.

Validation of biometric study of fetal mandibles by 3D tomodensitometric images.

We carried out a biometric study of the mandible during the last two trimesters of fetal life using three-dimensional tomodensitometric images. We first validated the method of fetal mandible measurement from three-dimensional reconstructions, and then compared these measurements with direct measurements on dissected mandibles. Thanks to the biometric technique on three-dimensional images, dissection of mandibles is no longer necessary, allowing the material to be conserved for later studies. Tomodensitometric images of the whole fetal skull can be obtained in 10 minutes, a much shorter time than that required for dissection of the fetal mandible. Another major advantage is the possibility of computerized image storage, which allows subsequent studies on the same material, its observation and manipulation as well as exchange of findings with the research community, with no risk of damage to the original material.

Characteristic forms of the upper part of the oral cavity in newborns with isolated cleft palate.

OBJECTIVE: To determine the functional and morphological compensation of the lack of integrity in the upper part of the oral cavity in newborns with isolated cleft palate. Integrity of the upper part of the oral cavity is required for the effective pumping of amniotic fluid, the essential mode of nutrition in intrauterine life. The adaptation could be seen immediately after birth. MATERIALS: Plaster casts of the upper part of the oral cavity in 60 newborns with isolated cleft palate of various extent and plaster casts of the upper part of the oral cavity in 27 newborns without cleft were used. A number of surface points were identified and used for a trigonometric morphological analysis. RESULTS: The parameters of the upper part of the oral cavity in four groups of newborns with various extent of isolated cleft palate were compared with newborns without cleft palate. The results indicate a shift of the functional oral cavity into the nasal cavity and the pharynx, depending on the extent of the cleft. CONCLUSION: The pumping activity of the tongue forms the upper part of the oral cavity and consequently the tongue moves into the nasal cavity and pharynx, depending on the extent of the cleft. In this way, effective pumping of amniotic fluid is possible despite the cleft. This is of vital importance for the fetus during intrauterine life. A poorly passable or even unpassable respiratory way is only of secondary importance during that time.

ARCOS PRECONTORNEADOS DE TRASNFORMACION A LA TEMPERATUTA VARIABLE

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Enhancement by hepatocyte growth factor of bone and cartilage formation during embryonic mouse mandibular development in vitro.

To elucidate the possible roles of hepatocyte growth factor (HGF) in the early development of mouse mandible, HGF was applied to an organ-culture system with chemically defined media. Mandibular arches microdissected from mouse embryos at the 10th day of gestation were cultured for 10 days with or without HGF, HGF plus HGF-receptor (c-met) antisense oligodeoxyribonucleotide, or HGF plus c-met sense oligodeoxyribonucleotide in the media. The cultured mandibles were then analysed, histologically in serial paraffin sections. In the absence of HGF, the tooth organs of bud stage, Meckel's cartilage and the tongue were formed, whereas only a slight amount of bone tissue was formed in the cultured mandible. The expression of intrinsic HGF and c-met in the cultured mandibles was confirmed by reverse transcriptase-polymerase chain reaction. Furthermore, immunohistochemistry demonstrated that both HGF and c-met were localized in areas of the mesenchymal tissue forming bone and cartilage. With HGF in the medium, the volume of both bone and cartilage increased significantly and dose-dependently. HGF also increased the rate of proliferation of osteogenic cells and chondrocytes. Addition of c-met antisense oligodeoxyribonucleotide partially inhibited the HGF-induced enhancement of bone and cartilage formation, whereas addition of c-met sense oligodeoxyribonucleotide had no effect. These results revealed that exogenous HGF enhances bone and cartilage morphogenesis in the cultured mandibles, suggesting physiological roles for intrinsic HGF in the early development of mouse mandible.

Dynamic interactions and the evolutionary genetics of dental patterning.

The mammalian dentition is a segmental, or periodically arranged, organ system whose components are arrayed in specific number and in regionally differentiated locations along the linear axes of the jaws. This arrangement evolved from simpler dentitions comprised of many single-cusp teeth of relatively indeterminate number. The different types of mammalian teeth have subsequently evolved as largely independent units. The experimentally documented developmental autonomy of dental primordia shows that the basic dental pattern is established early in embryogenesis. An understanding of how genetic patterning processes may work must be consistent with the different modes of development, and partially independent evolution, of the upper and lower dentition in mammals. The periodic nature of the location, number, and morphological structure of teeth suggests that processes involving the quantitative interaction of diffusible signaling factors may be involved. Several extracellular signaling molecules and their interactions have been identified that may be responsible for locating teeth along the jaws and for the formation of the incisor field. Similarly, the wavelike expression of signaling factors within developing teeth suggests that dynamic interactions among those factors may be responsible for crown patterns. These factors seem to be similar among different tooth types, but the extent to which crown differences can be explained strictly in terms of variation in the parameters of interactions among the same genes, as opposed to tooth-type-specific combinatorial codes of gene expression, is not yet known. There is evidence that combinatorial expression of intracellular transcription factors, including homeobox gene families, may establish domains within the jaws in which different tooth types are able to develop. An evolutionary perspective can be important for our understanding of dental patterning and the designing of appropriate experimental approaches, but dental patterns also raise basic unresolved questions about the nature of the evolutionary assumptions made in developmental genetics.

Location of alveolar clefts relative to the incisive fissure.

OBJECTIVE: The purpose of this study was to investigate, in a normal human fetal sample, the development of the anterior area of the palate. Emphasis has been placed on the bilateral epithelial fusion lines between the soft-tissue palatal shelves and the premaxillary mucosa, and on the relationship between these fusion lines and the locations of the inclusive fissures and of the tooth buds. The goal was to evaluate how the location of clefts in cleft lip and palate (CLP) patients interferes with tooth buds that are often affected in clefting. DESIGN: Nineteen maxillas of human fetuses underwent histologic examination after serial horizontal sectioning. Superimpositions of tracings from photographs of the histologic sections yielded information on the maxillary morphology at different levels. RESULTS: After elevation and fusion of the soft-tissue palatal shelves, the palatal fusions were Y-shaped. During subsequent osseous palate development, including formation of the incisive fissure and intermaxillary suture, the Y-shaped epithelial fusions disintegrated. The locations of the anterior arms of the epithelial Y and of the incisive fissure did not coincide. CONCLUSIONS: The incisive fissure is likely not the location of clefts in CLP. The location of anterior palatal clefting in CLP patients follows the original course of the epithelial fusion between the palatal shelves and the premaxillary mucosa found in the region of the lateral incisors.

Instruction by retinoic acid of incisor morphology in the mouse embryonic mandible.

Endogenous retinoids are present in the embryonic mouse mandible and reach a peak in concentration at the time of the formation of the dental lamina. All-trans retinoic acid is present in a 10-fold higher concentration in the future incisor region of the mouse embryonic mandible at day 11.5. It was found here that exogenous all-trans retinoic acid has pleiotropic effects on the pattern of odontogenesis when applied before the formation of the dental lamina. These effects include a change in the pattern of the dental lamina, supernumerary buds and incisors in the diastema region, and replacement of molars with incisors in the molar region. Thus retinoic acid appears to instruct incisor morphology in the mouse embryonic mandible.

Blockade of the initiation of murine odontogenesis in vitro by citral, an inhibitor of endogenous retinoic acid synthesis.

Endogenous retinoids are present in the embryonic mouse mandible and reach a concentration peak immediately before the formation of the dental lamina. Because exogenous retinoids alter the pattern of the dental lamina and the expression of epidermal growth factor mRNA (a transcript necessary for initiation of odontogenesis), the role of retinoic acid in the initiation of odontogenesis was studied here. Citral (3,7-dimethyl-2,6-octadienal), a known inhibitor of retinoic acid synthesis, was used to block the endogenous synthesis of retinoic acid in the mouse embryonic mandible before the formation of the dental lamina (gestational day 9). A 24-h exposure to citral totally blocked tooth formation in 7/10 mandibles. Reductions of endogenous retinoic acid concentrations were confirmed by high-performance liquid chromatography. Tooth formation was restored by simultaneous treatment with all-trans retinoic acid or 9-cis retinoic acid during the citral exposures (first 24 h of culture). Endogenous retinoic acid is necessary for the initiation of odontogenesis.

Osteogenesis of the mandibular arch in Ts16 mice.

Males and females homozygous for the Robertsonian translocation specific for chromosomes 16 and 17 Rb(16.17)Bnr and male and females homozygous for the Robertsonian translocation for chromosomes 6 and 16 Rb(6.16)24Lub were bred to produce double heterozygotes [Rb(16.17)Bnr/Rb(6.16)24Lub]. Experimental data were based on 156 features: 70 euploid (control), 86 trisomic. Affected fetuses were identified by decreased size, shortened faces (flattened snouts), oedema, petechiae, open eyelids, and dysplastic ears. Identification of trisomics was substantiated by karyotyping the metaphasic spreads. Five gestational days were studied (14-18). Fetal age was assumed to be accurate as fertilization occurred within half an hour of copulation. Euploid specimens followed normal developmental paths of chondrogenesis, osteogenesis and related tissues. In trisomics, developmental faults increased unequally between gestational days 15 and 17: some tissues were mildly and others acutely affected. Among the trisomic disorders were diminished growth, lagging mitotic activity, and retarded and poorly ordered tissue development, especially of bone. All of these contributed to hypoplasia, hypocellularity, reduced vascular supply and enlarged intercellular spaces. Intensities of the mandibular abnormalities varied among litters and littermates. The severity of the developmental disorders of an individual Ts16 specimen differed among the tissue components studied. Of the trisomic mandibular tissues, bone was most frequently involved and Meckel's cartilage least.

A well developed alveolabial sulcus of the intermaxilla in a complete bilateral cleft lip and palate.

An uncommon well developed alveolabial sulcus in a baby born with a complete bilateral cleft lip and palate is presented. The possible embryonic explanation for this extremely rare finding is discussed.

[Light microscope study of human dental morphogenesis]. / Studio al microscopio ottico sulla morfogenesi dentaria umana.

Human teeth morphogenesis was studied by optical microscopy from the 10th to 20th week of fetal life. Enamel, dentin and pulp development were analyzed. An important observation on mandibu teeth arises from this investigation that consists in a biforcation of mandibular ossification in two branches, this could allow to the teeth to develop inside the mandibular arch.

Effects of D-glucose and beta-hydroxybutyric acid on the in vitro development of (pre)chondrocytes from embryos of normal and diabetic rats.

In order to elucidate cellular mechanisms causing skeletal malformations in offspring of diabetic rats we studied the incorporation of thymidine and sulphate into embryonic (pre)chondrocytes exposed to increased levels of D-glucose and beta-hydroxybutyric acid for six days in vitro. The (pre)chondrocytes were prepared from embryos of normal or diabetic rats of a malformation-prone strain or from embryos of normal rats of a non-malformation-prone strain. Diabetic female rats of the former strain are known to produce a high proportion of offspring with mandibular and lumbosacral malformations. Increased beta-hydroxybutyric acid caused decreased thymidine incorporation in all types of chondrocytes, and decreased sulphate incorporation in limb bud cells from embryos of normal rats from both strains. Elevated D-glucose levels yielded a slight decrease in thymidine incorporation in mandibular arch cells from embryos of normal rats of the malformation-prone strain, and a marked decrease of both sulphate and thymidine incorporation in mandibular arch cells from embryos of diabetic rats of this strain. The observations suggest that elevated levels of D-glucose or beta-hydroxybutyric acid are able to inhibit the differentiation and growth of (pre)-chondrocytes and illustrate a selective sensitivity of mandibular arch (pre)chondrocytes to a diabetic environment. The data are compatible with the view that both D-glucose and beta-hydroxybutyric acid may cause aberrations in the development of rat mandibular arch chondrocytes, suggesting a role for these compounds in diabetic teratogenesis.

Crown area as an indicator of changing crown size in human pre-natal teeth.

This study deals with correlations of tooth size in human primary teeth. Traditionally, mesiodistal or buccolingual measurements have been used to express crown size. However, in this study, crown area was used as a reference parameter. Graphic reconstructions of 38 histologically prepared human fetuses with Crown-Rump Length (CRL) between 54 and 280 mm were used to obtain linear and area measurements. Based on clinical records and physical examinations, these fetuses were considered typical-for-age, or "normal". Correlation matrices indicated high levels of concordance among all developing deciduous tooth crowns and arch measurements. It was concluded that crown area is a statistically better trait to use in comparison of teeth rather than the traditional mesiodistal measurement.