An immunocytochemical study of the innervation of developing human fetal teeth using protein gene product 9.5 (PGP 9.5)

Innervation and osteoclast distribution in the inferior pharyngeal jaw of the cichlid Nile tilapia (Oreochromis niloticus)

In addition to an oral jaw, cichlids have a pharyngeal jaw, which is used for crushing and processing captured prey. The teeth and morphology of the pharyngeal jaw bones adapt to changes in prey in response to changes in the growing environment. This study aimed to explore the possible involvement of the peripheral nervous system in remodeling the cichlid pharyngeal jaw by examining the innervation of the inferior pharyngeal jaw in the Nile tilapia, Oreochromis niloticus. Vagal innervation was identified in the Nile tilapia inferior pharyngeal jaw. Double staining with tartrate-resistant acid phosphatase and immunostaining with the neuronal markers, protein gene product 9.5, and acetylated tubulin, revealed that osteoclasts, which play an important role in remodeling, were distributed in the vicinity of the nerves and were in apposition with the nerve terminals. This contact between peripheral nerves and osteoclasts suggests that the peripheral nervous system may play a role in remodeling the inferior pharyngeal jaw in cichlids.

Expect the unexpected: The course of the inferior alveolar artery - Preliminary results and clinical implications

INTRODUCTION

The anatomical position of the inferior alveolar artery (IAA) within the mandibular canal and in relation to the substructures of the neurovascular mandibular bundle has been sparsely described to date. More detailed information on the exact IAA position would be beneficial for both dental and maxillofacial surgical procedures to minimize complications such as bleeding, nerve compression hematoma, and sensory deficiency.

MATERIAL AND METHODS

In 31 Thiel-preserved and fresh-frozen cadaver hemimandibles the position of the IAA in relation to the structures of the inferior alveolar neurovascular bundle and the mandible borders was analyzed anatomically and histologically.

RESULTS

In 77.4% of the cases, rotation of the IAA around the mental nerve was apparent, resulting in a typical site-dependent IAA position. While the IAA was situated buccally within the pterygomandibular space, buccal-inferior in the mandibular foramen, superior in the molar region, and lingually in the premolar region. In 12.9% of the cases, a persistent lingual position of the IAA was observed for the entire mandibular canal. In one case, an additional mandibular canal and an accessory IAA were identified.

DISCUSSION

This study provides new and encompassing information on the complete course and position of the IAA. This course is of practical use for oral implantology and various surgical procedures in dental- and maxillofacial surgery. Variations in the typical IAA course and site-dependent positional changes may be referred to as mandible growth and functional adaption to occlusion anomalies. This report helps enhance the morphological and functional understanding of IAA relationship during mandible development.

[Ectoderm, mesoderm and neuroectoderm are tissue types of importance for understanding and preventing root resorption. Clinical guidelines]

INTRODUCTION

This three-part article summarizes ideas already described elsewhere by the author. Part 1. New way of diagnosing the dentition. For diagnostic purposes origin and appearance of the three tissue types - ectoderm, mesoderm (ectomesenchyme) and peripheral nerves - are depicted on orthopantomograms. Same tissue types are marked on the root surface (peri-root sheet). Part 2. Factors provoking root resorption. Resorption can be explained from the composition of the peri-root sheet. Deviations (inborn or acquired) in each of the three tissue layers can provoke inflammation, resulting in resorption. Orthodontic forces resulting in resorption can occur in normal peri-root sheets, but also in peri-root sheets with inborn deviations, important to diagnose. Part 3. How to prevent root resorption - Clinical guidelines. General diseases and different dental morphologies are signs predisposing for root resorption (ectoderm and mesoderm), so are local or general virus attacks (neuroectoderm). Resorption often occurs in dentitions never treated orthodontically.

MATERIAL AND METHOD

The author performed a review of the literature in order to present a new diagnostic approach incorporating histological and embryological concepts.

RESULTS

The review revealed different etiologies and sites involved in root resorption. Patients presenting variations of the peri-root sheet are most exposed to root resorption.

DISCUSSION

At this stage, it is difficult to diagnose these variations. The author offers diagnostic recommendations to be followed prior to orthodontic treatment. Even when no orthodontic treatment is given, root resorption can occur unexpectedly. In these cases, resorption prevention is currently impossible.

Mechanism of human tooth eruption: review article including a new theory for future studies on the eruption process

Human eruption is a unique developmental process in the organism. The aetiology or the mechanism behind eruption has never been fully understood and the scientific literature in the field is extremely sparse. Human and animal tissues provide different possibilities for eruption analyses, briefly discussed in the introduction. Human studies, mainly clinical and radiological, have focused on normal eruption and gender differences. Why a tooth begins eruption and what enables it to move eruptively and later to end these eruptive movements is not known. Pathological eruption courses contribute to insight into the aetiology behind eruption. A new theory on the eruption mechanism is presented. Accordingly, the mechanism of eruption depends on the correlation between space in the eruption course, created by the crown follicle, eruption pressure triggered by innervation in the apical root membrane, and the ability of the periodontal ligament to adapt to eruptive movements. Animal studies and studies on normal and pathological eruption in humans can support and explain different aspects in the new theory. The eruption mechanism still needs elucidation and the paper recommends that future research on eruption keeps this new theory in mind. Understanding the aetiology of the eruption process is necessary for treating deviant eruption courses.

Regional aggressive root resorption caused by neuronal virus infection

During orthodontic treatment, root resorption can occur unexplainably. No clear distinction has been made between resorption located within specific regions and resorption occurring generally in the dentition. The purpose is to present cases with idiopathic (of unknown origin) root resorption occurring regionally. Two cases of female patients, 26 and 28 years old, referred with aggressive root resorption were investigated clinically and radiographically. Anamnestic information revealed severe virus diseases during childhood, meningitis in one case and whooping cough in the other. One of the patients was treated with dental implants. Virus spreading along nerve paths is a possible explanation for the unexpected resorptions. In both cases, the resorptions began cervically. The extent of the resorption processes in the dentition followed the virus infected nerve paths and the resorption process stopped when reaching regions that were innervated differently and not infected by virus. In one case, histological examination revealed multinuclear dentinoclasts. The pattern of resorption in the two cases indicates that innervation is a factor, which under normal conditions may protect the root surface against resorption. Therefore, the normal nerve pattern is important for diagnostics and for predicting the course of severe unexpected root resorption.

The human periodontal membrane: focusing on the spatial interrelation between the epithelial layer of Malassez, fibers, and innervation

OBJECTIVE

The purpose of the present study was to map the spatial interrelation of fibers, peripheral nerves, and epithelial layer of Malassez in human periodontal membrane in areas close to the root surfaces.

MATERIAL AND METHODS

Four healthy permanent teeth extracted from four patients during puberty due to orthodontic treatment planning were analyzed. The extracted teeth, fixed in 4% neutral buffered formaldehyde for 5 days, were decalcified in 0.5 M EDTA. Paraffin blocks were sagittally cut in 5 microm thick serial sections and mounted on Superfrost Plus microscope slides. For survey, every fifth slide was stained with Alcian Blue/Van Gieson. Immunohistochemical reactions: Cytokeratin (wide spectrum screening) for epithelium, anti-vimentin for fibers, and anti-neuronal nuclei (NeuN) for innervation.

RESULTS

The study indicates that the epithelial layer of Malassez is a border between different fiber morphologies and innervation patterns. Innervation is identified predominantly in the periodontal layer with tightly packed fibers close to the root surface.

CONCLUSION

It is suggested that the genetic composition of the epithelial layer of Malassez in the periodontal membrane may be the key to understanding the different functions of the periodontal membrane and also the individual differences of these functions.

Clear cell odontogenic carcinoma: case report with immunohistochemical findings adding support to the challenging diagnosis

Clear cell odontogenic carcinoma (CCOC) is a rare odontogenic tumor associated with aggressive clinical behavior, metastasis, and low survival. We report a case of CCOC affecting the mandible of a 39-year-old man. The tumor presented a biphasic pattern composed of clear cell nests intermingled with eosinophilic cells and separated by collagenous stroma. Immunoreactivity to cytokeratin (CK), specifically AE1/AE3 and CK 8, 14, 18, and 19 was found, as well as to epithelial membrane antigen (EMA). The tumor cells were negative for S100 protein, CK 13, vimentin, smooth muscle actin, laminin and type IV collagen. Low labeling indices for the proliferation markers Ki-67 and proliferating cell nuclear antigen and to p53 protein might predict a favorable prognosis for the lesion. A surgical resection was performed, followed by adjuvant radiotherapy. A 2-year follow-up has shown no signs of recurrence. The significance of histochemical and immunohistochemical resources in the correct diagnosis of CCOC is analyzed.

Comparative evaluation of neural tissue antigens--neurofilament protein (NF), peripherin (PRP), S100B protein (S100B), neuron-specific enolase (NSE) and chromogranin-A (CgA)--in both normal and inflamed human mature dental pulp

The immunohistochemical detection of neurofilament protein (NF), peripherin (PRP), S100B protein (S100B), neuron-specific enolase (NSE) and chromogranin-A (CgA) has been studied in nerve fibres and bundles of human dental pulp. This was done in order to identify possible differences in the distribution pattern of the above markers between normal and inflamed pulp and, further, to evaluate their potential use as peripheral markers of dental innervation as well as objective markers for the determination of the extent of inflammation. Both normal and inflamed human dental pulp showed positive immunolabelling for NF, S100B and NSE and lack of labelling for PRP and CgA protein. An increased density of NF, S100B and NSE immunoreactive nerve fibres was observed in inflamed pulp samples compared to non-inflamed. The findings of this study suggest the possible application of NF, S100B and NSE as markers of dental innervation. Furthermore, they may be useful for the determination of the extent of pulpal inflammation, and might be utilized in alternative modalities of biological pulp therapy to reduce the inflammation process. The absence of CgA immunolabelling implies the presumptive absence of neuroendocrine antigens, while further research is required in order to clarify the involvement of PRP in dental pulp.

Quantitative histological and ultrastructural features of opercula of normally erupting human teeth

Tooth eruption across the mucosa in humans has been studied rarely, although there are disturbances of eruption that are attributed specifically to failure of the supraosseous eruptive migration. The aim of this study was to analyze the soft tissues covering normally erupting teeth so as to get an insight into the supraosseous phase of tooth eruption and to provide the basis for comparison with cases of eruption disturbances. Six opercula covering normally erupting permanent molars (primary opercula) and six of succedaneous teeth (secondary opercula) were surgically removed from 10 patients aged 7.5-17.5 years. Specimens were examined light and electron microscopically and analyzed morphometrically. All opercula contained strands and islands of odontogenic epithelium, prominent numbers of high endothelial venules, nerves, and mast cells. Nerves comprised normally structured, 1.5-3.5 microm thick myelinated (Adelta) and thinner unmyelinated (C) fibers. In primary opercula, the proportions of blood vessels and nerves were three- and sevenfold higher than the respective values for the secondary opercula. Furthermore, primary opercula contained multinucleated, fibroblast-like giant cells that were not observed in secondary opercula. As all teeth under investigation were erupting normally, neither the presence of the giant cells nor the atypical proportions of blood vessels and nerves appeared to be decisive in the eruption process. These conspicuous tissue components of opercula seem merely to accompany the eruptive tooth movement.

The influence of jaw innervation on the dental maturation pattern in the mandible

OBJECTIVES

To explore the relationship between mandibular dental maturation and the pattern of jaw innervation.

SETTING AND SAMPLE POPULATION

The sample included 365 panoramic radiographs taken in the period 1965-1969 in a Danish municipality.

DESIGN

For assessing dental maturity, the seven left mandibular teeth (M2, M1, P2, P1, C, I2, I1) were given a dental maturity score according to a method introduced by Demirjian. Spearman correlation coefficients between the maturity score of an index tooth (one of each teeth) and the maturity score of the 6 other teeth was calculated and illustrated.

RESULTS

All the correlation coefficients were larger than 0.5 indicating a rather high level of association between the development of mandibular teeth in the same individual. Thus, associations between the pattern of dental maturation and jaw innervation were not obvious.

CONCLUSION

When the correlation between the dental maturity stages was analysed, no significant relation was found between dental maturation and jaw innervation in the mandible. This is interesting considering the results presented in a recent study, which showed that the clinical observed tooth eruption was closely related to the pattern of jaw innervation. Those authors suggested that the factors influencing the eruption might be associated with jaw innervation. In our study, the stepwise dental maturation process, however, is not equally associated with jaw innervation.

Molecular cloning, characterization, and distribution of the gerbil angiotensin II AT2 receptor

We isolated a cDNA clone encoding the gerbil AT2 receptor (gAT2) gene from a gerbil adrenal gland cDNA library. The full-length cDNA contains a 1,089-bp open reading frame encoding 363 amino acid residues with 90.9, 96.1, and 95.6% identity with the human (hAT2), rat (rAT2), and mouse AT2 (mAT2) receptors, respectively. There are at least seven nonconserved amino acids in the NH2-terminal domain and in positions Val196, Val217, and Met293, important for angiotensin (ANG) II but not for CGP-42112 binding. Displacement studies in adrenal sections revealed that affinity of the gAT2 receptor was 10-20 times lower for ANG II, ANG III, and PD-123319 than was affinity of the rAT2 receptor. The affinity of each receptor remained the same for CGP-42112. When transfected into COS-7 cells, the gAT2 receptor shows affinity for ANG II that is three times lower than that shown by the hAT2 receptor, whereas affinities for ANG III and the AT2 receptor ligands CGP-42112 and PD-123319 were similar. Autoradiography in sections of the gerbil head showed higher binding in muscles, retina, skin, and molars at embryonic day 19 than at 1 wk of age. In situ hybridization and emulsion autoradiography revealed that at embryonic day 19 the gAT2 receptor mRNA was highly localized to the base of the dental papilla of maxillary and mandibular molars. Our results suggest selective growth-related functions in late gestation and early postnatal periods for the gAT2 receptor and provide an essential basis for future mutagenesis studies to further define structural requirements for agonist binding.

Development of innervation in primary incisors in the foetal period

Sections from the frontal part of the mandible of 43 human foetuses from 9 to 39 weeks of prenatal age, which contained two, three and sometimes four lower incisors were immunohistochemically examined using protein gene product and neuron specific enolase (NSE) antibodies in order to establish the time of appearance of nerve fibres in the developing tooth germ and to define their topography. Nerve fibres were first detected in the dental follicle in the 11th week of intrauterine life. Their presence in the dental papilla was confirmed in the 18th week when the first layers of dentine and enamel were deposited. In the 24th week of intrauterine life, the nerve fibres first reached the subodontoblastic region. In the subsequent weeks, an increase in the number of nerve fibres accompanying blood vessels in the central portion of the dental papilla resulted in the formation of neuro-vascular bundles. Moreover, the progressive deposition of enamel and dentine was accompanied by branching of papillary nerves, which thereby formed a fan-pattern. In the foetal period, no evidence was found for the formation of a subodontoblastic plexus. However, we did observe single nerve fibres in close proximity to the odontoblast layer at the end of intrauterine life. Nerve fibres were not detected in either predentine or dentine throughout foetal life.

Biological interpretation of the correlation of emergence times of permanent teeth

The eruption mechanism is not fully understood. It is known that the dental follicle is essential and that experimentally provoked denervation influence the process of eruption. Accordingly, the purpose of this study was to elucidate the eruption pattern in a human population and relate this pattern to the pattern of jaw innervation. The eruption pattern was evaluated from the correlation between the emergence times of different teeth in the permanent dentition based on longitudinal data from a large national registry (12,642 boys and 12,095 girls). Correlations coefficients were generally high (>0.5) and higher between teeth within the same tooth groups (i.e. incisors, canines and premolars, and molars) than between teeth from different tooth groups. It was shown that the correlation in emergence of teeth closely followed the pattern of innervation of the jaws. Thus the study supported the hypothesis concerning a possible association between eruption and innervation.

Alteration in the expression of heat shock protein (Hsp) 25-immunoreactivity in the dental pulp of rat molars following tooth replantation

The regeneration process of dental pulp following tooth replantation in rat molars was investigated by immunocytochemistry for heat shock protein (Hsp) 25 and protein gene product 9.5 (PGP 9.5). In control teeth at postnatal 4 weeks, the odontoblasts showed intense Hsp 25-immunoreactivity in the coronal dental pulp, but little or no immunoreactivity in the root and floor pulp. In contrast, the Hsp 25-negative odontoblasts in the latter areas displayed immunoreactivity for PGP 9.5. Tooth replantation caused loss of Hsp 25- and PGP 9.5-immunoreactions in the dental pulp during postoperative days 1-3. At postoperative day 5, plump cells with clear nucleoli and several fine processes--presumably newly differentiated odontoblasts--at the pulp-dentin border became immunopositive for Hsp 25. These data suggest that the expression of Hsp 25- and PGP 9.5-immunoreactivity reflects the status of differentiation of the odontoblasts. Furthermore, some pulpal nerve fibers as well as the Schwann cells in the dental pulp, ordinarily negative in Hsp 25-immunoreaction, acquired their immunoreactivity by postoperative day 5, but lost it thereafter, suggesting the involvement of Hsp 25 in the regeneration of pulpal nerve fibers. In the case of bone-like tissue formation in the pulp space, on the other hand, no Hsp 25-immunoreactive odontoblasts were recognized in the pulp-dentin border. Thus, the alignment of Hsp 25-immunopositive odontoblasts along the pulp-dentin border indicates a decisive factor for inducing the reparative dentin formation after tooth replantation.

The transforming growth factor-beta 3 knock-out mouse: an animal model for cleft palate

The recent report of a transforming growth factor-beta 3 (TGF-beta 3) knock-out mouse in which 100 percent of the homozygous pups have cleft palate raised the question as to the potential usefulness of these animals as a model for cleft palate research. The specific aim in this study was to carefully document the anatomy of the cleft palate in the TGF-beta 3 knock-out mice as compared with wild type controls. Special attention was paid to the levator veli palatini muscle, the tensor veli palatini muscle, and their respective innervation. Because the TGF-beta 3 knock-out is lethal in the early perinatal period and because the heterozygotes are phenotypically normal, polymerase chain reaction was required to genotype the animals before mating. Time-mated pregnancies between proven heterozygotes were then delivered by cesarean section at gestational day 18.5 to prevent maternal cannibalism of homozygote pups. All delivered pups were killed and their tails processed by polymerase chain reaction to verify genotype. The heads were then fixed and sectioned in axial, coronal, or sagittal planes. Sections were stained with hematoxylin and eosin or processed for immunohistochemistry with nerve specific protein gene product 9.5 and calcitonin gene-related peptide antibodies. Sections were analyzed in a serial fashion. Nine wild type control animals were analyzed along with nine TGF-beta 3 knock-out homozygotes. Time matings between proven heterozygotes yielded wild type pups, heterozygote pups, and homozygote knock-out pups in the expected mendelian ratios (28 percent to 46 percent to 26 percent; n = 43). The results demonstrated 100 percent clefting in the homozygous TGF-beta 3 knock-out pups. Complete clefting of the secondary palate was seen in four of nine and incomplete clefting was seen in five of nine. The levator veli palatini and tensor veli palatini muscles were demonstrated coursing parallel to the cleft margin in all cleft mice. The orientation of these muscles differs from the normal transverse sling of the levator veli palatini muscle and the normal palatine aponeurosis of the tensor veli palatini muscle at the soft palate in control animals. Innervation of the levator veli palatini muscle by cranial nerve IX and the tensor veli palatini muscle by cranial nerve V were demonstrated in both cleft and control animals by use of immunohistochemistry with nerve-specific antibodies. Demonstration of a teratogen-free, reproducible animal model of clefting of the palate with a known, single-gene etiology is an important step in the systematic understanding of a congenital defect whose multifactorial etiology has hampered previous research efforts. This study presents a detailed anatomic description of such a model, including a description of the muscular anatomy and the innervation of the muscles of the palate. Because of early perinatal mortality, this model has limited applications for postnatal studies.

Molecular signaling and pulpal nerve development

The purpose of this review is to discuss molecular factors influencing nerve growth to teeth. The establishment of a sensory pulpal innervation occurs concurrently with tooth development. Epithelial/mesenchymal interactions initiate the tooth primordium and change it into a complex organ. The initial events seem to be controlled by the epithelium, and subsequently, the mesenchyme acquires odontogenic properties. As yet, no single initiating epithelial or mesenchymal factor has been identified. Axons reach the jaws before tooth formation and form terminals near odontogenic sites. In some species, local axons have an initiating function in odontogenesis, but it is not known if this is also the case with mammals. In diphyodont mammals, the primary dentition is replaced by a permanent dentition, which involves a profound remodeling of terminal pulpal axons. The molecular signals underlying this remodeling remain unknown. Due to the senescent deterioration of the dentition, the target area of tooth nerves shrinks with age, and these nerves show marked pathological-like changes. Nerve growth factor and possibly also brain-derived neurotrophic factor seem to be important in the formation of a sensory pulpal innervation. Neurotrophin-3 and -4/5 are probably not involved. In addition, glial cell line-derived neurotrophic factor, but not neurturin, seems to be involved in the control of pulpal axon growth. A variety of other growth factors may also influence developing tooth nerves. Many major extracellular matrix molecules, which can influence growing axons, are present in developing teeth. It is likely that these molecules influence the growing pulpal axons.

Immunohistochemical expression of neural tissue markers (neuron-specific enolase, glial fibrillary acidic protein, S100 protein) in ameloblastic fibrodentinoma: a comparative study with ameloblastic fibroma

Formalin-fixed paraffin-embedded sections of three cases of ameloblastic fibrodentinoma (AFD) were studied by the avidin-biotin-peroxidase complex method using antibodies against neuron-specific enolase (NSE), glial fibrillary acidic protein (GFAP) and S100 protein and the results were compared with those in ameloblastic fibroma (AF). A striking histopathological characteristic of AFD was the formation of abortive dentin with various degrees of maturation at the epithelial-mesenchymal tissue interface. Central cells of enamel organ-like epithelia with various stages of abortive dentin induction in AFD were generally positive for NSE. Dental lamina-like epithelial cells also showed positive staining in some areas. No cells were positive for NSE in AF. Positive staining for GFAP was observed in the juxta-epithelial mesenchymal tissue of the formation stage of immature dentin with various numbers of entrapped cells in AFD, but GFAP staining was negative in other mesenchymal and epithelial tissues at other stages. In AF, no GFAP-positive cells were found. There were a few S100 protein-positive cells found in the foci of epithelial components in both AFD and AF. Mesenchymal cells showing a dendritic or spindle shape were positive for S100 protein in some areas of AFD and AF. Although such cells in the mesenchymal component of pigmented AFD were more numerous than in non-pigmented AFD and AF, their distribution pattern in the former condition was basically similar to that in the latter. Although the present results, obtained from conventional immunohistochemical procedures, do not directly reflect the expression of neural crest-derived cells in the dentinogenesis of AFD, such results do not disprove the possibility of the expression of neural proteins probably related to neural crest-derived cells in dentinogenesis under certain pathologic conditions in odontogenic mixed tumors. Such a phenomenon may also occur during dentinogenesis in other odontogenic mixed tumors and in normal tooth differentiation, but at an undetectable level.

Prenatal development of the alveolar bone of human deciduous incisors and canines

The formation of the human alveolar process around the incisors and canines is a hitherto unreported aspect of fetal oral development. The question is how, where, and when the alveolar process is formed. The purpose of this study was to elucidate the questions where and when and hence to analyze the pattern of formation of the alveolar bone around developing human deciduous canine and incisor teeth. The study was conducted with material selected from a sample of 61 normal human fetuses, legally or spontaneously aborted. Fertilization ages ranged from 9 to 22 weeks, crown-rump Length from 25 to 205 mm, and foot length from 4 to 34 mm. From this material, 7 maxillae and 10 mandibles were selected for the study according to developmental stages of the canines and incisors and according to the orientation of the histological sections. The skeletal investigation consisted of macroscopic and microscopic analysis of the mandibles and maxillae. The investigations revealed the absence of bone between the central and lateral incisors in the mandibles and maxillae of fetuses below the ages of 21 and 22 weeks, respectively. In three specimens, alveolar bone between the central and lateral incisors was recorded (21, 21, and 22 weeks of fertilization). Absence of bone labial to the canine was recorded in all fetuses investigated. In all other regions, alveolar bone occurred as a regular finding. The present study has shown that alveolar bone formation is strictly coordinated with tooth formation. Alveolar bone occurs later in the area labial to the canine and in the region between the central and lateral incisors than it does in other areas associated with the incisor/canine regions. Knowledge of this pattern in the formation of the alveolar process seems to be of importance for a future elucidation of how the alveolar process is initially formed.

Neuro-osteology

Neuro-osteology stresses the biological connection during development between nerve and hard tissues. It is a perspective that has developed since associations were first described between pre-natal peripheral nerve tissue and initial osseous bone formation in the craniofacial skeleton (Kjaer, 1990a). In this review, the normal connection between the central nervous system and the axial skeleton and between the peripheral nervous system and jaw formation are first discussed. The early central nervous system (the neural tube) and the axial skeleton from the lumbosacral region to the sella turcica forms a unit, since both types of tissue are developmentally dependent upon the notochord. In different neurological disorders, the axial skeleton, including the pituitary gland, is malformed in different ways along the original course of the notochord. Anterior to the pituitary gland/sella turcica region, the craniofacial skeleton develops from prechordal cartilage, invading mesoderm and neural crest cells. Also, abnormal development in the craniofacial region, such as tooth agenesis, is analyzed neuro-osteologically. Results from pre-natal investigations provide information on the post-natal diagnosis of children with congenital developmental disorders in the central nervous system. Examples of these are myelomeningocele and holoprosencephaly. Three steps are important in clinical neuro-osteology: (1) clinical definition of the region of an osseous or dental malformation, (2) embryological determination of the origin of that region and recollection of which neurological structure has developed from the same region, and (3) clinical diagnosis of this neurological structure. If neurological malformation is the first symptom, step 2 results in the determination of the osseous region involved, which in step 3 is analyzed clinically. The relevance of future neuro-osteological diagnostics is emphasized.

Expression of GDNF and its receptors in developing tooth is developmentally regulated and suggests multiple roles in innervation and organogenesis

Glial cell line-derived neurotrophic factor (GDNF) is a recently identified survival factor for several populations of neurons in the central and peripheral nervous system that also regulates kidney development. To study the roles of GDNF in the regulation of tooth innervation and formation, we analyzed by in situ hybridization the expression patterns of GDNF and its receptors Ret, GDNF family receptor alpha-1 (GFRalpha-1), and GFRalpha-2 from the initiation of first molar formation to the completion of crown morphogenesis. At the time of trigeminal axon ingrowth, GDNF mRNAs were expressed in the mesenchyme around the tooth germ (i.e., target field of the dental innervation), suggesting that it is involved in the regulation of the embryonic tooth innervation. This hypothesis was supported by the ability of GDNF to induce neurite outgrowth from embryonic day 12 (E12) to E15 trigeminal ganglia. This timing correlated with the appearance of Ret in the subset of cells in the trigeminal ganglion at E12, whereas GFRalpha-1 and GFRalpha-2 receptors were constantly expressed in trigeminal ganglion during E11-E15. After birth, GDNF expression showed apparent correlation with the ingrowth and presence of trigeminal nerve fibers in the tooth, suggesting that GDNF is involved in the regulation of innervation of the dental papilla and dentin postnatally. Ret, GFRalpha-1, and GFRalpha-2 mRNAs were expressed in the dental epithelial and mesenchymal cells at stages when epithelial-mesenchymal signalling regulates critical steps of tooth morphogenesis. Ret and GFRalpha-2 were colocalized in the dental mesenchyme during bud and cap stages. Expression of GFRalpha-1 associated with the formation of the epithelial enamel knot, which is a putative embryonic signalling center regulating tooth shape. During postnatal development, GDNF and its receptors were expressed in dental papilla mesenchyme. In addition, GDNF and GFRalpha-1 transcripts were seen in the preodontoblasts and odontoblasts, suggesting that they may be involved in differentiation and maintenance of functional properties of the odontoblasts. Taken together, these results suggest that GDNF acts as a target-derived neurotrophic factor during tooth innervation. In addition, GDNF and its receptors may have nonneuronal organogenetic functions during tooth morphogenesis.

Neurotrophin mRNA expression in the developing tooth suggests multiple roles in innervation and organogenesis

To analyze the roles of neurotrophins during early development of rat teeth, we studied the expression of neurotrophin mRNAs from the initiation of first molar formation to the completion of crown morphogenesis. With RNAase protection assay all neurotrophin mRNAs were detected in embryonic teeth. In situ hybridization analysis revealed developmentally changing, distinct expression patterns for nerve growth factor (NGF) and neurotrophin-3 (NT-3), which were shown not to be regulated by or dependent on peripheral innervation. NGF mRNAs appeared in the mesenchymal target field of the tooth at the time of the trigeminal axon ingrowth (embryonic days 14-15: E14-E15), and they were also present along the pathway taken by growing trigeminal axons. NT-4/5 mRNAs were uniformly expressed in all epithelial cells, but brain-derived neurotrophic factor (BDNF) transcripts were not detected. All neurotrophins induced neurite outgrowth from E13-E16 trigeminal ganglion explants. These results suggest that NGF is involved in the guidance of trigeminal axons to embryonic teeth. In postnatal teeth, expression of NGF mRNAs, but not other neurotrophins, correlated with trigeminal axon ingrowth, proposing that NGF is involved in local sprouting and establishment of the final innervation pattern of the dental papilla and dentin. These results suggest that NGF is required for tooth innervation and that other neurotrophins may also have regulatory roles. In addition, the expression patterns of NGF, NT-3, and NT-4/5 as well as of neurotrophin receptors suggest that the neurotrophin system may also serve non-neuronal functions during tooth development.

Localization of nerve cells in the developing rat tooth

Earlier studies have shown that mammalian tooth formation can take place in the absence of peripheral nerve fibers. This has been taken to indicate that neurons are not needed for mammalian tooth development. However, our recent localization of peripherin, which is a neuronal cell marker, has suggested that neuronal cell bodies may be associated with developing teeth. In this study, we have analyzed in vivo and in vitro the presence of neuronal cells in developing rat tooth germs. When E14 and E16 rat first molars (thickening of presumptive dental epithelium and bud-stage tooth germ, respectively) were cultured in vitro, peripheral trigeminal axons degenerated. However, with antibodies against peripherin and L1 neural cell adhesion protein, we detected neuronal cell bodies and their axons in the explants. Next, the expression of neurofilament light-chain (NF-L) mRNAs was studied by in situ hybridization of embryonic E12 first branchial arches and tooth germs from initiation to completion of crown morphogenesis (E13, five-day post-natal teeth). NF-L transcripts were first seen at the bud stage (E15) next to the dental epithelium at the buccal side of the tooth germ. At the cap stage (E18), NF-L mRNAs were located under the oral epithelium at some distance from dental epithelium. These expression patterns correlate to the previous localization of peripherin-positive cells and suggest that NF-L expression also revealed neuronal cells. Taken together, these results demonstrate that, in addition to projections of peripheral neurons, neuronal cells are associated with the developing teeth. Hence, it is possible that neuronal cells may participate in the regulation of mammalian tooth formation.

Immunohistochemical localization of nerve fibres during development of embryonic rat molar using peripherin and protein gene product 9.5 antibodies

Nerve fibres were localized during the initiation and early morphogenesis of the first molar tooth in rat embryos by immunoperoxidase detection of the intermediate-filament protein peripherin and protein gene product 9.5 (PGP 9.5). Nerve fibres from the trigeminal ganglion were detected in the developing first branchial arch of E12-14 embryos. Nerves were not seen in the vicinity of the developing tooth germ before the buid stage (E15), when they were seen around the condensed dental mesenchyme. During transition from the bud to the cap stage (E15), nerve fibres were detected not only in the area of the future dental follicle but also in the mesenchyme next to dental epithelium on the buccal side of the tooth germ. During later cap and bell stages nerve fibres persisted in the dental follicle, but they were not seen in the epithelial dental organ or dental papilla mesenchyme. Absence of trigeminal nerve fibres from the presumptive tooth-bearing area indicates that they are not involved in the initiation of rat tooth development. In addition, the localization of nerve fibres shows that there are some differences in the innervation of rat teeth compared with human and mouse teeth. These results provide data for further studies on the regulation of embryonic rat tooth innervation.

Luteinizing hormone-releasing hormone and innervation pathways in human prenatal nasal submucosa: factors of importance in evaluating Kallmann's syndrome

A previous study has demonstrated that luteinizing hormone-releasing hormone (LHRH) is localized in the human bilateral vomeronasal organs in the nasal septum during a 4-week period of intrauterine life (22). The purpose of the present study was to elucidate the location of LHRH-expressing cells outside the vomeronasal organs, with special emphasis on the submucosa of the medial wall and roof of the nasal cavity. An additional aim was to study the innervation pathways in the same regions. Both regions can be affected in Kallmann's syndrome, which is characterized by hypogonadotropic hypogonadism (lack of LHRH) and often associated with anosmia. Histological sections of craniofacial regions (49 normal human fetuses, 6-19 weeks) were examined by immunohistochemical techniques for LHRH and for neuronal tissue (protein gene product 9.5, PGP 9.5). LHRH reactions were only seen in the septal submucosa extending from the vomeronasal organs to the olfactory bulb. There was a close spatiotemporal association between the occurrence of LHRH and neuronal tissue. From the rhino-olfactory epithelium separate nerve tissue extended to the olfactory bulb. It is suggested that the medial region of the nasal placode giving rise to the septal wall is always affected in Kallmann's syndrome, and in cases in which the phenotypic features are associated with anosmia, also the more lateral part of the nasal placode, from which the rhino-olfactory region originates, is affected.

The human mandibular canal arises from three separate canals innervating different tooth groups

The purpose of this study was to describe the prenatal formation of the human mandibular canal. Since bony canals develop in prenatal life around the nerve paths, it was assumed that the canal pattern could reflect the pattern of innervation of the dentition. Mapping of this early canal pattern does not appear to have been undertaken before. The material consisted of anthropological mandibles from the National Institute of Anthropology and History, Mexico City. A total of 302 human hemimandibles from the latter half of the prenatal period was investigated. The length, measured from the mental symphysis to the mandibular condyle, ranged from 28 to 60 mm. The dento-alveolar maturity was classified in two stages according to the appearance of alveolar sockets of deciduous and first permanent molars. The mandibles were radiographed with guttapercha points inserted into the canal openings (foramina) on the lingual surfaces of the mandibular rami. The study showed that the canal to the incisors appeared first, followed by the canal to the primary molars, and last by the one or more canals to the first permanent molars. In the most mature group, three different canals always occurred in each hemimandible. The canals were directed from the lingual surface of the mandibular ramus toward the different tooth groups. The inferior alveolar nerve presumably occurs in the mandible as three individual nerve paths originating at different stages of development. It is suggested that rapid prenatal growth and remodeling in the ramus region result in a gradual coalescence of the canal entrances that is obvious at birth. It is hypothesized that the pattern of tooth agenesis within the three groups of teeth is related to the three separate paths of innervation of the dentition.

Etiologic aspects and orthodontic treatment of unilateral localized arrested tooth-development combined with hearing loss

In this study a case has been presented involving localized, arrested maxillary tooth development, asymmetric maxillary development, and unilateral loss of hearing. No similar case seems to have been described before. The orthodontic treatment comprised extraction of four permanent tooth germs in the maxilla and autotransplantation of mandibular teeth, followed by the use of fixed orthodontic appliances and a one-unit bridge restoration. Etiologic aspects are discussed. It is suggested that a severe attack of mumps that involved massive swelling of the parotid glands immediately after chicken pox and measles at the age of 4 to 5 years, may have resulted in a neurologic reduction of hearing and arrested tooth development. The teeth in which root development in relation to mumps does not appear to have been reported previously, whereas hearing loss after mumps has been reported. In the search for verification of this possible connection, children with arrested tooth development should be examined for reduction of hearing, and children with hearing loss after mumps ought to have their dental development checked.

Human prenatal craniofacial development related to brain development under normal and pathologic conditions

A survey is given of current knowledge of the interrelationship between facial, cranial and brain development in humans. First, normal facial, cranial (mandible, maxilla, palatine bone, cranial base, theca cranii, dentition), and brain development are described separately. Then, developmental interrelationships are illustrated under normal and pathologic conditions (cleft lip and palate, holoprosencephaly, anencephaly, amniotic band sequence). New observations are described in detail, and references are given to previously published articles. A close interconnection exists between the development of the face, the craniofacial skeleton, and the brain. This is illustrated by new observations in cleft palate fetuses and new theories about the etiology of holoprosencephaly and tooth agenesis. The survey focuses, moreover, on the importance of the face and the cranial base in endocrine development. Borderlines between face regions and cranial regions with different developmental origin are set up for future elucidation of the etiology behind syndromes involving the craniofacial regions.

Nerve fibres and cells immunoreactive to neurochemical markers in developing rat molars and supporting tissues

The distribution of nerve fibres immunoreactive to calcitonin gene-related peptide (CGRP), substance P (SP) and neuropeptide Y (NPY) was compared to the general neurochemical markers for nerves and neuroendocrine cells protein gene product 9.5 (PGP 9.5) and neurone-specific enolase (NSE), by use of the avidin-biotin peroxidase complex method in developing dental structures in rats aged 13 to 27 days. A substantially greater part of the nerve fibres was immunoreactive to CGRP and SP than to NPY. In the bell stage, nerve fibres immunoreactive to PGP 9.5, CGRP and SP were found in the dental follicle but not in the dental papilla and stellate reticulum. In the advanced bell stage, after initiation of dentine and enamel formation, PGP 9.5, CGRP- and SP-immunoreactive fibres were found in the dental papilla, while the first NPY-immunoreactive fibres were observed in the papilla when root formation started. Concomitant with the beginning of root development, a subodontoblastic nerve plexus was gradually formed and PGP 9.5-, CGRP- and SP-immunoreactive fibres were found within the dentinal tubules. From the start of root formation, CGRP-, SP- and NPY-immunoreactive nerves were shown in the developing periodontal ligament, although a mature distribution pattern was not observed until root formation was nearly completed. Ameloblasts, odontoblasts and cell-like structures in the outer enamel epithelium and within the dental lamina were PGP 9.5-immunoreactive at the bell stage. As the tooth matured, the immunolabelling gradually decreased, but was still present in some odontoblasts after tooth eruption. NSE-immunoreactive, cell-like structures were found in the periphery of the dental follicle, and persisted close to alveolar bone in the periodontal ligament when the tooth reached occlusion. Hence, it may be concluded that sensory nerves containing SP and CGRP are present in the pulp in advance of sympathetic nerves immunoreactive to NPY.