Heritable dentin defects: nosology, pathology, and treatment

Morphological and Ultrastructural Collagen Defects: Impact and Implications in Dentinogenesis Imperfecta

Collagen is the building block for the extracellular matrix in bone, teeth and other fibrous tissues. Osteogenesis imperfecta (OI), or brittle bone disease, is a heritable disorder that results from defective collagen synthesis or metabolism, resulting in bone fragility. The dental manifestation of OI is dentinogenesis imperfecta (DI), a genetic disorder that affects dentin structure and clinical appearance, with a characteristic feature of greyish-brown discolouration. The aim of this study was to conduct a systematic review to identify and/or define any ultrastructural changes in dentinal collagen in DI. Established databases were searched: Cochrane Library, OVID Embase, OVID Medline and PubMed/Medline. Search strategies included: Collagen Ultrastructure, DI and OI. Inclusion criteria were studies written in English, published after 1990, that examined human dental collagen of teeth affected by DI. A Cochrane data extraction form was modified and used for data collection. The final dataset included seventeen studies published from 1993 to 2021. The most prevalent findings on collagen in DI teeth were increased coarse collagen fibres and decreased fibre quantity. Additional findings included changes to fibre orientation (i.e., random to parallel) and differences to the fibre organisation (i.e., regular to irregular). Ultrastructural defects and anomalies included uncoiled collagen fibres and increased D-banding periodicity. Studies in collagen structure in DI reported changes to the surface topography, quantity, organisation and orientation of the fibres. Moreover, ultrastructural defects such as the packing/coiling and D-banding of the fibrils, as well as differences in the presence of other collagens are also noted. Taken together, this study provides an understanding of the changes in collagen and its impact on clinical translation, paving the way for innovative treatments in dental treatment.

Dentinogenesis Imperfecta and Caries in Osteogenesis Imperfecta among Vietnamese Children

Osteogenesis imperfecta (OI) is a genetic disorder characterized by increased bone fragility and low bone mass, caused mainly by mutations in collagen type I encoding genes. The current study aimed to evaluate dentinogenesis imperfecta (DI), oral manifestations and caries status of OI children. Sixty-eight children (41 males, 27 females) aged from 3 to 17 years old (mean 9 ± 4.13) participated in the study. Participants were classified into three OI type groups (I—2 cases, III—31 cases and IV—35 cases). Clinical examination and an orthopantomogram were used to obtain prevalences and associations of DI, caries status, malocclusion, crossbite, open bite, eruption, impaction and missing teeth with OI. The prevalence of DI among OI patients was 47.1%, more common in OI type III than type IV. The yellow-brown discoloration type was more vulnerable to attrition than the opalescent-grey one in the primary dentition. OI seemed not to have a high risk of caries; the prevalence of caries was 69.1%. A high incidence of malocclusion, crossbite and open bite was observed. In-depth oral information would provide valuable data for better dental management in OI patients. Parents and general doctors should pay more attention to dental care to prevent caries and premature tooth loss.

Dentinogenesis imperfecta type II: A case report with 17 years of follow-up

Dentinogenesis imperfecta is a dominant autosomal hereditary disorder of dentin formation that affects the deciduous and permanent teeth. Its etiology is characterized by inadequate cell differentiation during odontogenesis. The clinical characteristics of dentinogenesis imperfecta are discolored teeth with a translucency that varies from gray to brown or amber. Radiographically, the teeth exhibit pulp obliteration, thin and short roots, bell-shaped crowns, and periapical bone rarefaction. The aim of this report was to present a case of dentinogenesis imperfecta type II that was followed up over a 17-year period. This report also presents scanning electron microscopy images of the enamel and dentin, showing that both were altered in the affected teeth. The disease characteristics and the treatments that were administered are reported in this study to guide dentists with respect to the need for early diagnosis and adequate follow-up to avoid major sequelae.

Hereditary Dentin Defects

By the Shields classification, articulated over 30 years ago, inherited dentin defects are divided into 5 types: 3 types of dentinogenesis imperfecta (DGI), and 2 types of dentin dysplasia (DD). DGI type I is osteogenesis imperfecta (OI) with DGI. OI with DGI is caused, in most cases, by mutations in the 2 genes encoding type I collagen. Many genes are required to generate the enzymes that catalyze collagen’s diverse post-translational modifications and its assembly into fibers, fibrils, bundles, and networks. Rare inherited diseases of bone are caused by defects in these genes, and some are occasionally found to include DGI as a feature. Appreciation of the complicated genetic etiology of DGI associated with bony defects splintered the DGI type I description into a multitude of more precisely defined entities, all with their own designations. In contrast, DD-II, DGI-II, and DGI-III, each with its own pattern of inherited defects limited to the dentition, have been found to be caused by various defects in DSPP (dentin sialophosphoprotein), a gene encoding the major non-collagenous proteins of dentin. Only DD-I, an exceedingly rare condition featuring short, blunt roots with obliterated pulp chambers, remains untouched by the revolution in genetics, and its etiology is still a mystery. A major surprise in the characterization of genes underlying inherited dentin defects is the apparent lack of roles played by the genes encoding the less-abundant non-collagenous proteins in dentin, such as dentin matrix protein 1 ( DMP1), integrin-binding sialoprotein ( IBSP), matrix extracellular phosphoglycoprotein ( MEPE), and secreted phosphoprotein-1, or osteopontin ( SPP1, OPN). This review discusses the development of the dentin extracellular matrix in the context of its evolution, and discusses the phenotypes and clinical classifications of isolated hereditary defects of tooth dentin in the context of recent genetic data respecting their genetic etiologies.

Malformations of the tooth root in humans

The most common root malformations in humans arise from either developmental disorders of the root alone or disorders of radicular development as part of a general tooth dysplasia. The aim of this review is to relate the characteristics of these root malformations to potentially disrupted processes involved in radicular morphogenesis. Radicular morphogenesis proceeds under the control of Hertwig's epithelial root sheath (HERS) which determines the number, length, and shape of the root, induces the formation of radicular dentin, and participates in the development of root cementum. Formation of HERS at the transition from crown to root development appears to be very insensitive to adverse effects, with the result that rootless teeth are extremely rare. In contrast, shortened roots as a consequence of impaired or prematurely halted apical growth of HERS constitute the most prevalent radicular dysplasia which occurs due to trauma and unknown reasons as well as in association with dentin disorders. While odontoblast differentiation inevitably stops when growth of HERS is arrested, it seems to be unaffected even in cases of severe dentin dysplasias such as regional odontodysplasia and dentin dysplasia type I. As a result radicular dentin formation is at least initiated and progresses for a limited time. The only condition affecting cementogenesis is hypophosphatasia which disrupts the formation of acellular cementum through an inhibition of mineralization. A process particularly susceptible to adverse effects appears to be the formation of the furcation in multirooted teeth. Impairment or disruption of this process entails taurodontism, single-rooted posterior teeth, and misshapen furcations. Thus, even though many characteristics of human root malformations can be related to disorders of specific processes involved in radicular morphogenesis, precise inferences as to the pathogenesis of these dysplasias are hampered by the still limited knowledge on root formation.

Immunocytochemical detection of dentin matrix proteins in primary teeth from patients with dentinogenesis imperfecta associated with osteogenesis imperfecta

Dentinogenesis imperfecta determines structural alterations of the collagen structure still not completely elucidated. Immunohisto-chemical analysis was used to assay type I and VI collagen, various non-collagenous proteins distribution in human primary teeth from healthy patients or from patients affected by type I dentinogenesis imperfecta (DGI-I) associated with osteogenesis imperfecta (OI). In sound primary teeth, an organized well-known ordered pattern of the type I collagen fibrils was found, whereas atypical and disorganized fibrillar structures were observed in dentin of DGI-I affected patients. Expression of type I collagen was observed in both normal and affected primary teeth, although normal dentin stained more uniformly than DGI-I affected dentin. Reactivity of type VI collagen was significantly lower in normal teeth than in dentin from DGI-I affected patients (P<0.05). Expressions of dentin matrix protein-1 (DMP1) and osteopontin (OPN) were observed in both normal dentin and dentin from DGI-I affected patients, without significant differences, being DMP1 generally more abundantly expressed. Immuno labeling for chondroitin sulfate (CS) and biglycan (BGN) was weaker in dentin from DGI-I-affected patients compared to normal dentin, this decrease being significant only for CS. This study shows ultra-structural alterations in dentin obtained from patients affected by DGI-I, supported by immunocytochemical assays of different collagenous and non-collagenous proteins.

Dentinogenesis imperfecta type I: A case report with literature review on nomenclature system

Dentinogenesis imperfecta (DI) is an inherited disorder affecting dentin. Defective dentin formation results in discolored teeth that are prone to attrition and fracture. Mutation in dentin sialophosphoprotein (DSPP) has been found to cause the dentin disorders DI - I and II (shields II and III). Early diagnosis and treatment of DI is recommended as it may prevent or intercept deterioration of the teeth and occlusion and improve esthetics. Here, we report a case with characteristic clinical, radiological and histological features of DI-I. The etiology and classification followed in literature is confusing since dentinoenamel junction (DEJ) in DI seems to be structurally and functionally normal and DI is clearly a disorder distinct from osteogenesis imperfecta (OI), but we still relate etiology of DI to DEJ and follow Shields classification. Therefore, we have briefly reviewed etiology and nomenclature system of DI.

Clinical manifestations and dental management of dentinogenesis imperfecta associated with osteogenesis imperfecta: Case report

Dentinogenesis imperfecta (DI) associated with osteogenesis imperfecta (OI) is a genetic disorder that affects the connective tissues and results in dentine dysplasia. This case report discusses the systemic and dental manifestations of OI and DI in a 4-year-old child, with moderate presentation of both disorders, who was treated at King Fahd Military Medical Complex in Dhahran. Dental treatment included the use of strip and stainless-steel crowns under local anesthesia, as well as behavior modification techniques. Rigorous home care instructions, including reinforcement of the oral hygiene practice and avoidance of any episode that may lead to bone fracture, were discussed with the parents. The case was reevaluated at 3-month follow-up visits, wherein the medical and dental histories were updated, the child's growth was monitored, periodic clinical and radiographic examinations were performed, and the oral hygiene was evaluated via the debris index score and caries risk assessment. Further treatment of the permanent dentition may be needed in the future.

Treatment considerations for patient with Amelogenesis Imperfecta: a review

Amelogenesis imperfecta (AI) is a group of inherited disorders primary affecting the structural of enamel. Patients with AI experience poor esthetic, excessive tooth sensitivity and compromised chewing function that dental treatments are frequently required at early age. This review describes the non-enamel implications, stage-specific management strategies and outcomes of selected restorative materials based on literature evidence.

Case report: Rehabilitation of a child with dentinogenesis imperfecta and congenitally missing lateral incisors

BACKGROUND

Dentinogenesis imperfecta is one of the most common hereditary disorders of dentine formation. Opalescent teeth composed of irregularly formed and undemineralised dentine that obliterates pulp chambers and root canals characterize it. Complete-coverage crowns are usually the preferred restoration for patients with this condition.

CASE REPORT

A 9 year-old girl presented with dentinogenesis imperfecta, congenitally missing maxillary lateral incisors and maxillary right permanent second molar retention.

TREATMENT

The treatment comprised an initial approach to allow the correct eruption of the retained second molar. The use of low-fusion metal ceramic restorations comprised a second stage to improve the aesthetic appearance and decrease the risk of overload on teeth with limited value.

FOLLOW-UP

The patient has been recalled regularly and at the last visit, 10 years after initial prosthetic treatment, no problems or signs of complications have occurred. The patient is now aged 25 years and is still satisfied with the prosthetic rehabilitation.

CONCLUSION

This case illustrates the need for appropriate and timely restorative treatment to prevent deterioration of the dentition. This case will also demonstrate that low-fusion metal ceramic restoration is a viable esthetic treatment option for today's patients.

Dentinogenesis imperfecta in children with osteogenesis imperfecta: a clinical and ultrastructural study

AIM

The aim of this study was to assess the correlation between osteogenesis imperfecta (OI) and dentinogenesis imperfecta (DI) from both a clinical and histological point of view, particularly clarifying the structural and ultrastructural dentine changes.

DESIGN

Sixteen children (6-12 years aged) with diagnosis of OI were examined for dental alterations referable to DI. For each patient, the OI type (I, III, or IV) was recorded. Extracted or normally exfoliated primary teeth were subjected to a histological examination (to both optical microscopy and confocal laser-scanning microscopy).

RESULTS

A total of ten patients had abnormal discolourations referable to DI: four patients were affected by OI type I, three patients by OI type III, and three patients by OI type IV. The discolourations, yellow/brown or opalescent grey, could not be related to the different types of OI. Histological exam of primary teeth showed severe pathological change in the dentin, structured into four different layers. A collagen defect due to odontoblast dysfunction was theorized to be on the base of the histological changes.

CONCLUSIONS

There is no correlation between the type of OI and the type of discolouration. The underlying dentinal defect seems to be related to an odontoblast dysfunction.

Phenotype characterization and DSPP mutational analysis of three Brazilian dentinogenesis imperfecta type II families

The aim of this study was to perform phenotype analysis and dentin sialophosphoprotein (DSPP) mutational analysis on 3 Brazilian families diagnosed with dentinogenesis imperfecta type II (DGI-II) attending the Dental Anomalies Clinic in Brasilia, Brazil. Physical and oral examinations, as well as radiographic and histopathological analyses, were performed on 28 affected and unaffected individuals. Clinical, radiographic and histopathological analyses confirmed the diagnosis of DGI-II in 19 individuals. Pulp stones were observed in ground sections of several teeth in 2 families, suggesting that obliteration of pulp chambers and root canals results from the growth of these nodular structures. Mutational DSPP gene analysis of representative affected family members revealed 7 various non-disease-causing alterations in exons 1-4 within the dentin sialoprotein domain. Further longitudinal studies are necessary to elucidate the progression of pulpal obliteration in the DGI-II patients studied as well as the molecular basis of their disease.

Dentin dysplasia type I treated with onlay bone grafting, sinus augmentation, and osseointegrated implants

Dentin dysplasia is a defect of dentin development that was classified by Shields as type I and type II. The teeth in dentin dysplasia type I are characterized by normal enamel and abnormal dentin in the crown and root. For that reason, this disorder is characterized by dental caries, early exfoliation of the teeth and, consequently, maxillomandibular bony atrophy. In this report, we present a case of a young girl affected by dentin dysplasia type I, treated with a combination of onlay bone grafting and a sinus lift technique to accomplish implant placement. This case showed that onlay autogenous grafting and a sinus lift technique are well-tested methods of bony augmentation and can be useful in patients with congenital dentin defects, such as dentin dysplasia.

Dentinogenesis imperfecta associated with short stature, hearing loss and mental retardation: a new syndrome with autosomal recessive inheritance?

The follow-up history and oral findings in two brothers from consanguineous parents suggest that the association of dentinogenesis imperfecta (DI), delayed tooth eruption, mild mental retardation, proportionate short stature, sensorineural hearing loss and dysmorphic facies may represent a new syndrome with autosomal recessive inheritance. Histological examination of the dentin matrix of a permanent molar from one of the siblings reveals morphological similarities with defective dentinogenesis as presenting in patients affected with Osteogenesis Imperfecta (OI), a condition caused by deficiency of type I collagen. A number of radiographic and histological characteristics, however, are inconsistent with classical features of DI. These findings suggest that DI may imply greater genetical heterogeneity than currently assumed.

The natural history, including orofacial features of three patients with Ehlers-Danlos syndrome, dermatosparaxis type (EDS type VIIC)

Ehlers-Danlos syndrome (EDS) dermatosparaxis type (type VIIC) and the related disease of cattle dermatosparaxis, are recessively inherited connective tissue disorders, caused by a deficient activity of procollagen I N-proteinase, the enzyme that excises the N-terminal propeptide in procollagen type I, type II, and type III. Although well documented in cattle, to date only seven human cases have been recorded, most of them aged under 2 years. We document the natural history of three patients with EDS dermatosparaxis type, two of whom have been reported before the age of 2 years, and one new patient. The phenotype of the patients, and especially the facial resemblance, is striking, making this a clinically recognizable condition. The most consistent anomalies during the first years of life are premature rupture of the membranes, extreme skin fragility and easy bruising, large fontanels, blue sclerae, puffy eyelids, micrognathia, umbilical hernia, and short fingers. Joint hypermobility becomes more important with age. The children are at risk for rupture of internal organs due to soft tissue fragility, as is illustrated by different internal events in two of the three patients described here. Orofacial features include micrognathia, a frontal open bite, and gingival hyperplasia with varying degrees of hyperkeratosis. The deciduous dentition shows abnormal morphology of the molars, obliteration of the tooth pulp, and severe enamel attrition. The permanent dentition shows agenesis and microdontia of several teeth. Tooth discoloration, dysplastic roots, and tooth pulp obliteration are present in a restricted number of permanent teeth.

Unusual oral findings in dermatosparaxis (Ehlers-Danlos syndrome type VIIC)

A 13-year-old patient with dermatosparaxis (Ehlers-Danlos syndrome type VIIC), an autosomal recessive disorder of procollagen-I-N-proteinase, is presented. The oral findings comprise micrognathia, hypodontia, localized microdontia, opalescent tooth discoloration, root dysplasia, pulp obliteration, severe gingival hyperplasia, frontal open bite, and severe restriction of TMJ mobility. The reported anomalies suggest the need for expanding the present phenotypic spectrum. This is the first report on oral findings in the syndrome.

Apparently new osteodysplastic and primordial short stature with severe microdontia, opalescent teeth, and rootless molars in two siblings

A Thai man and his sister affected with a newly recognized syndrome of proportionate primordial short stature are reported. The patients had severe intrauterine and postnatal growth retardation, prominent nose and nasal bridge, small pinnae, large sella turcica, areas of hypo- and hyperpigmentation of skin, dry and thin scalp hair, and long and straight clavicles. Ivory epiphyses and cone-shaped epiphyses of the hands were found when they were young, but most of them disappeared as they grew up. Scaphoid and trapezium had angular appearance. The second toes were unusually long. Distal symphalangism of toes and barchymesophalangy of fingers were noted. The findings that appear to distinguish this syndrome from the previously reported syndromes are long second toes, opalescent and rootless teeth, severe microdontia, severely hypoplastic alveolar process, and unerupted tooth. The mode of inheritance is suspected to be autosomal recessive.

A newly recognized syndrome of skeletal dysplasia with opalescent and rootless teeth

A Thai girl with skeletal dysplasia and dental anomalies was seen. Her anomalies consisted of disproportionately short stature, short neck, broad and depressed nasal bridge, broad chest in the anteroposterior dimension, kyphosis, widely spaced nipples, and protruded abdomen. Radiographic testing indicated that she had a large sella turcica, platyspondyly, hypoplastic acetabulum, and a small body of mandible. Both her deciduous and permanent teeth were equally opalescent, and most were rootless, with root development of the mandibular teeth more severely affected. Some maxillary roots were extremely short and tapered. Hypodontia was also observed. These findings represent a unique and hitherto undescribed syndrome of skeletal dysplasia with concomitant dental anomalies.

Normal formation and development defects of the human dentition

Oral health and systemic health are intimately related, and a thorough evaluation of the oral health of children is critical in providing appropriate health care. By understanding the normal sequence and patterns of tooth development, clinicians can readily identify children who deviate from normal dental development and provide appropriate interventions or make appropriate referrals. Developmental defects of the human dentition are not uncommon and can severely adversely affect the physical and psychological health of children. Despite the severity of some developmental defects of the dentition, the ability to diagnose and manage these conditions, in most cases, allows children the benefit of optimal oral health.

Discrimination of morphological findings in dentine from osteogenesis imperfecta patients using combinations of polarized light microscopy, microradiography and scanning electron microscopy

OBJECTIVES

The aim of this study was to investigate the morphological appearance of dentine in teeth from individuals with osteogenesis imperfecta type I, III and IV using different histological techniques, and to correlate morphological findings to different types of osteogenesis imperfecta.

SAMPLE AND METHODS

Extracted or exfoliated primary and permanent teeth were collected from 15 patients with the osteogenesis imperfecta diagnoses I, III or IV, with or without the additional diagnosis dentinogenesis imperfecta. Ground and decalcified sections were prepared from the teeth. Histo-morphological studies of the dentine were performed utilizing light and polarized light microscopy, microradiography and scanning electron microscopy.

RESULTS

Characteristic findings were irregular tubules, remnants of capillary inclusions and obliterated pulps. All types of osteogenesis imperfecta exhibited similar types of dentine aberrations, but patients with type III or IV had a higher frequency of aberrations when compared to type I.

CONCLUSIONS

The combination of either polarized light microscopy or micro-radiography, together with scanning electron microscopy, gave the most amount of morphological information from dentine samples. In addition, aberrations in dentine structure were more clearly observable. Light microscopy was not critical for the analyses.

Evaluation of oral problems in an osteogenesis imperfecta population

OBJECTIVE

The incidence of craniofacial and dental anomalies in children with the more severe nonlethal forms of osteogenesis imperfecta was evaluated.

STUDY DESIGN

The study evaluated 40 children (age range, 1-17.5 years) with types III and IV osteogenesis imperfecta. In each case, the dentition was evaluated for the presence of dentinogenesis imperfecta, attrition, and caries, as well as for radiographic appearance, dental development, and malocclusion.

RESULTS

The incidence of dentinogenesis imperfecta was greater than 80% in the primary dentition. Clinically, the color of the dentition was of predictive value in appropriate management of the primary dentition. Tooth discoloration and attrition did not occur to the same extent in the permanent dentition as in the primary dentition in either group. Class III dental malocclusion occurred in 70% to 80% of this osteogenesis imperfecta population, with a high incidence of anterior and posterior cross bites and open bites. A delay in dental development was observed in 21% of patients type III osteogenesis imperfecta, whereas accelerated development was noted in 23% of the patients with type IV. In addition, ectopic eruption occurred in 13 patients.

CONCLUSIONS

In addition to dentinogenesis imperfecta, significant oral problems occur in types III and IV osteogenesis imperfecta. Other features that impact the dental management of this population are highlighted.

Immunoreactivity of tenascin-C in dentin matrix in dentinogenesis imperfecta associated with osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a heterogeneous group of heritable connective tissue disorders, assigned to different mutations in type I collagen genes. A variety of structural abnormalities of dentin have been described in dentinogenesis imperfecta (DI) associated with OI. To clarify further the constitution of the dentin matrix in OI, we immunostained frozen and paraffin sections of deciduous teeth from four patients, each from a different family, with two monoclonal antibodies (MAbs) to the matrix glycoprotein tenascin-C (TN-C). One of the MAbs recognizes an epitope common to all TN-C isoforms (BC-4), and the other is specific for a splicing variant (BC-2). Normal teeth, oral mucosa, and skin were analyzed for comparison. Staining patterns with the two MAbs did not differ markedly. Normal dentin matrix and odontoblasts were lacking reactivity, but the pulp stained clearly. TN-C reactivity was present in the dentin matrix of all teeth obtained from two patients with different OI phenotypes and DI, and in one out of three teeth from one patient who also had DI. The reactivity was distributed in layers, but the staining patterns varied from one patient to another and from tooth to tooth. Intratubular staining seen in a tooth from the patient with clinically and histologically normal teeth was comparable with that present in normal deciduous teeth. The variation in TN-C expression suggests that, besides genetic heterogeneity, epigenetic factors could influence the composition of the dentin matrix in OI.

Prenatal craniofacial development: new insights on normal and abnormal mechanisms

Technical advances are radically altering our concepts of normal prenatal craniofacial development. These include concepts of germ layer formation, the establishment of the initial head plan in the neural plate, and the manner in which head segmentation is controlled by regulatory (homeobox) gene activity in neuromeres and their derived neural crest cells. There is also a much better appreciation of ways in which new cell associations are established. For example, the associations are achieved by neural crest cells primarily through cell migration and subsequent cell interactions that regulate induction, growth, programmed cell death, etc. These interactions are mediated primarily by two groups of regulatory molecules: "growth factors" (e.g., FGF and TGF alpha) and the so-called steroid/thyroid/retinoic acid superfamily. Considerable advances have been made with respect to our understanding of the mechanisms involved in primary and secondary palate formation, such as growth, morphogenetic movements, and the fusion/merging phenomenon. Much progress has been made on the mechanisms involved in the final differentiation of skeletal tissues. Molecular genetics and animal models for human malformations are providing many insights into abnormal development. A mouse model for the fetal alcohol syndrome (FAS), a mild form of holoprosencephaly, demonstrates a mid-line anterior neural plate deficiency which leads to olfactory placodes being positioned too close to the mid-line, and other secondary changes. Work on animal models for the retinoic acid syndrome (RAS) shows that there is major involvement of neural crest cells. There is also major crest cell involvement in similar syndromes, apparently including hemifacial microsomia. Later administration of retinoic acid prematurely and excessively kills ganglionic placodal cells and leads to a malformation complex virtually identical to the Treacher Collins syndrome. Most clefts of the lip and/or palate appear to have a multifactorial etiology. Genetic variations in TGF alpha s, RAR alpha s, NADH dehydrogenase, an enzyme involved in oxidative metabolism, and cytochrome P-450, a detoxifying enzyme, have been implicated as contributing genetic factors. Cigarette smoking, with the attendant hypoxia, is a probable contributing environmental factor. It seems likely that few clefts involve single major genes. In most cases, the pathogenesis appears to involve inadequate contact and/or fusion of the facial prominences or palatal shelves. Specific mutations in genes for different FGF receptor molecules have been identified for achondroplasia and Crouzon's syndrome, and in a regulatory gene (Msx2) for one type of craniosynostosis. Poorly co-ordinated control of form and size of structures, or groups of structures (e.g., teeth and jaws), by regulatory genes should do much to explain the very frequent "mismatches" found in malocclusions and other dentofacial "deformities". Future directions for research, including possibilities for prevention, are discussed.

Prenatal craniofacial development: new insights on normal and abnormal mechanisms

Technical advances are radically altering our concepts of normal prenatal craniofacial development. These include concepts of germ layer formation, the establishment of the initial head plan in the neural plate, and the manner in which head segmentation is controlled by regulatory (homeobox) gene activity in neuromeres and their derived neural crest cells. There is also a much better appreciation of ways in which new cell associations are established. For example, the associations are achieved by neural crest cells primarily through cell migration and subsequent cell interactions that regulate induction, growth, programmed cell death, etc. These interactions are mediated primarily by two groups of regulatory molecules: "growth factors" (e.g., FGF and TGFalpha) and the so-called steroid/thyroid/retinoic acid superfamily. Considerable advances have been made with respect to our understanding of mechanisms involved in primary and secondary palate formation, such as growth, morphogenetic movements, and the fusion/merging phenomenon. Much progress has been made on the mechanisms involved in the final differentiation of skeletal tissues. Molecular genetics and animal models for human malformations are providing many insights into abnormal development. A mouse model for the fetal alcohol syndrome(FAS), a mild form of holoprosencephaly, demonstrates a mid-line anterior neural plate deficiency which leads to olfactory placodes being positioned too close to the mid-line, and other secondary changes. Work on animal models for the retinoic acid syndrome (RAS) shows that there is major involvement of neural crest cells. There is also major crest cell involvement in similar syndromes, apparently including hemifacial microsomia. Later administration of retinoic acid prematurely and excessively kills ganglionic placodal cells and leads to a malformation complex virtually identical to the Treacher Collins syndrome. Most clefts of the lip and/or palate appear to have a multifactorial etiology. Genetic variations in TGF alpha s, RAR alpha s, NADH dehydrogenase, an enzyme involved in oxidative metabolism, and cytochrome P-450, a detoxifying enzyme, have been implicated as contributing genetic factors. Cigarette smoking, with the attendant hypoxia, is a probable contributing environmental factor. It seems likely that few clefts involve single major genes. In most cases, the pathogenesis appears to involve inadequate contact and/or fusion of the facial prominences or palatal shelves. Specific mutations in genes for different FGF receptor molecules have been identified for achondroplasia and Crouzon's syndrome, and in a regulatory gene (Msx2) for one type of craniosynostosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Hyperfibers and vesicles in dentin matrix in dentinogenesis imperfecta (DI) associated with osteogenesis imperfecta (OI)

Dentin matrix of deciduous teeth from two patients affected by dentinogenesis imperfecta (DI) associated with types IB and IVB osteogenesis imperfecta (OI) displayed previously undescribed structures in transmission electron microscopic examination. Vesicles were seen in dentin of both patients, and abnormally thick collagen fibers (hyperfibers) were found in dentin of the patient with the rare type IB OI. Both vesicles and hyperfibers were situated in abnormal, atubular areas of dentin. Matrix vesicles, which have normally been identified in mantle dentin only, were abundant in selected areas of the affected dentin, thereby supporting the concept that dentin matrix in OI is elaborated by successive cell generations. The hyperfibers, not previously described in either normal or abnormal human dentin, have possibly been formed by fusion of several collagen fibers. Further ultrastructural studies of dentin in DI with OI may help to clarify the marked clinical variation in teeth of patients affected by OI.

ED-A region-containing isoform of cellular fibronectin is present in dentin matrix in dentinogenesis imperfecta associated with osteogenesis imperfecta

To elucidate the defective dentin formation in osteogenesis imperfecta (OI), we analyzed the expression of selected fibronectin (FN) isoforms in the dentin matrix of a patient with dentinogenesis imperfecta (DI) associated with OI, and in normal teeth. Frozen tooth sections were immunostained with three monoclonal antibodies (MAbs). The MAb recognizing the major cell-binding region (f-33), shared by plasma FN (pFN) and cellular FN (cFN), stained the pulp of normal adult permanent teeth intensely, while no reactivity was present in predentin, (demineralized) dentin, or dental cementum. The periodontal ligament stained unevenly. The dentin matrix of the patient with OI displayed reactive zones, alternating layerwise or concentrically with non-reactive ones. Staining throughout the connective tissue of adult oral mucosa, analyzed for the form of FN present, was intense, and in dermis, which was also studied, it was moderate. Reactivities in dental tissues with the MAb specific for the ED-A region (IST-9), included in cFN but not pFN, were similar to those with MAb f-33. The mucosal connective tissue stained weakly and dermis was negative, except that nerves and endothelia of some large blood vessels stained clearly. The MAb specific for the ED-B segment (BC-1), also included in cFN only, did not stain any of the tissues analyzed. The results suggest that, unlike mucosal and dermal FNs, FNs in the dental tissues are largely cellular, and also that dentin formation in OI may be completed by successive generations of pulpal fibroblasts differentiated into hard-tissue-forming cells.