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The tracing errors associated with the structures used in Björk's method of mandibular superimposition are investigated using multiple tracings of fifty lateral cephalometric radiographs. The horizontal error levels were much less than the vertical, midline structures more reliable than bilateral structures, and the lower third molar tooth germ more reliable than the inferior dental canal.
The dental casts and cephalometric radiographs of 46 patients, treated with mandibular second premolar extraction and edgewise orthodontic mechanotherapy, were evaluated for changes over a minimum 10-year postretention period. The sample was divided into two groups: early (mixed dentition) extraction of mandibular second premolars and late (permanent dentition) extraction of mandibular second premolars. Results showed no difference in long-term stability between the two groups. Arch length and arch width decreased with time and incisor irregularity increased throughout the postretention period. No predictors or associations could be found to help the clinician in determining the long-term prognosis in terms of stability. The sample was regrouped according to the postretention degree of incisor irregularity. Statistically significant differences in cephalometric measurements were found between the minimally crowded group and the moderately to severely crowded group.
It has been reported in the literature that some rural populations of Sub-Saharan and Eastern Africa and other isolated areas around the world, practise gouging or enucleation of primary tooth buds to cure childhood illnesses. The unerupted primary canine tooth bud is believed to be the cause of febrile illness, diarrhoea, and vomiting; prevalent in infants in these areas of the world. Tooth bud gouging has implications for the developing dentition, and is a potential risk to the health and life of the child. Reported prevalence ranges from 22%-90%. From the information in this case report, the practise of tooth bud gouging is no longer confined to rural areas and may well be performed by communities that have emigrated to the UK. The three sisters described, now resident in the UK, suffered tooth gouging in a city clinic in Uganda. The damage caused to the primary and permanent dentition is described and treatment planning and options are suggested for each case to restore structure and function. Appropriate provision of healthcare and education could avoid the potential long-term damage to the health of the child and their developing dentition by the practise of tooth bud gouging, whether it occurs in the developing or developed world.
Tooth germs of upper first molars of 1, 3, and 5-d-old rats, fixed in formaldehyde, were stained for the detection of apoptosis by the TUNEL method, and by the azo-dye method for the demonstration of acid phosphatase. For conventional light and electron microscopy the specimens were fixed in glutaraldehyde-formaldehyde and embedded in glycol methacrylate and Araldite. Results showed that macrophages, present in the stellate reticulum, contained basophilic bodies and TUNEL-positive globules, i.e. apoptotic bodies, in their interior. Macrophages also possessed strong acid phosphatase activity. Electron microscopy showed the presence of large vacuoles inside the macrophages containing dense fragmented material. Taken together these results suggest that the intra-epithelial macrophages of the stellate reticulum engulf apoptotic bodies.
Lingual nerve damage is one of the most common complications of lower third molar removal. However evaluation of the factor involved in these lesions is difficult since most previous series are heterogeneous. The purpose of this prospective randomized study was to ascertain the impact of lingual nerve protection in a homogeneous series including only patients undergoing third molar germectomy (i.e. removal of the developmental bud prior to anchoring of the roots in the jaw). Data from a total of 300 germectomy procedures were included in this study. All procedures were performed by the same experienced surgeon randomly with or without lingual nerve protection. No lingual nerve injury was observed after third molar germectomy regardless of whether or not lingual nerve protection was used. Lingual nerve protection is unnecessary for lower third molar germectomy.
Purpose: The purpose of this study was to observe developing teeth in a lengthened mandible after distraction. Material: Ten mongrel dogs with deciduous dentitions were used. Methods: A corticotomy was carefully made around a tooth bud and the external distractor (Orthofix M-100((R))) was connected. After a 5-day latent period, distraction was started at a rate of 0.75 mm per day for 10 consecutive days. Then, the lower jaw was stabilized by an external fixation to allow ossification. While the operation was performed on the left side (Distraction group), the contralateral side was studied for comparison (Control). In addition, a corticotomy, artificial fracture and external fixation were carried out to confirm the influence of the operation (Fracture group). Then macroscopic, radiographic and histological evaluations were carried out. Results: In the Distraction group, the space between the wall of the dental follicle and the crown expanded as distraction began. The end of the calcified root became wider and irregular during the distraction period, and finally, the apex closed. In the Fracture group, the teeth erupted although slight alterations of the root shape were observed in association with the operation period. Conclusion: The root became irregular, but the teeth erupted within the distraction area. Copyright 2001 European Association for Cranio-Maxillofacial Surgery.
The alveolar bone is a suitable in vivo physiological model for the study of apoptosis and interactions of bone cells because it undergoes continuous, rapid and intense resorption/remodelling, during a long period of time, to accommodate the growing tooth germs. The intensity of alveolar bone resorption greatly enhances the chances of observing images of the extremely rapid events of apoptosis of bone cells and also of images of interactions between osteoclasts and osteocytes/osteoblasts/bone lining cells. To find such images, we have therefore examined the alveolar bone of young rats using light microscopy, the TUNEL method for apoptosis, and electron microscopy. Fragments of alveolar bone from young rats were fixed in Bouin and formaldehyde for morphology and for the TUNEL method. Glutaraldehyde-formaldehyde fixed specimens were processed for transmission electron microscopy. Results showed TUNEL positive round/ovoid structures on the bone surface and inside osteocytic lacunae. These structures--also stained by hematoxylin--were therefore interpreted, respectively, as osteoblasts/lining cells and osteocytes undergoing apoptosis. Osteoclasts also exhibited TUNEL positive apoptotic bodies inside large vacuoles; the nuclei of osteoclasts, however, were always TUNEL negative. Ultrathin sections revealed typical apoptotic images--round/ ovoid bodies with dense crescent-like chromatin--on the bone surface, corresponding therefore to apoptotic osteoblasts/lining cells. Osteocytes also showed images compatible with apoptosis. Large osteoclast vacuoles often contained fragmented cellular material. Our results provide further support for the idea that osteoclasts internalize dying bone cells; we were however, unable to find images of osteoclasts in apoptosis.
To identify novel marker molecules associated with chondro-osteogenic differentiation, we have set up a differential screening system based on a cDNA library subtraction in organ cultures of prenatal mouse mandibular condyles. Differential screening of a cDNA library constructed from in vitro cultured condyles allowed the isolation of a novel gene, named E25. Full-length E25 cDNA is predicted to encode a type II integral membrane protein of 263 amino acid residues. In situ hybridization experiments show that E25 is expressed in the outer perichondrial rim of the postnatal mandibular condyle, which contains the proliferating progenitor cells, but not in the deeper layers of the condyle containing the more differentiated chondroblasts and chondrocytes. Other cartilagenous tissues and their perichondrium were negative. Strong in situ hybridization signals were also detected on bone trabeculae of mature bone in tooth germs and in hair follicles. Northern blot analysis showed strong expression in osteogenic tissues, such as neonatal mouse calvaria, paws, tail, and in skin. This expression profile suggests that E25 could be a useful marker for chondro-osteogenic differentiation. Homology searches of DNA databanks showed that E25 belongs to a novel multigene family, containing three members both in man and mouse. The mouse E25 gene locus (Itm2) was mapped to the X chromosome.
Cell adhesion molecules are involved in a number of biological functions, such as cell survival, cell differentiation, tissue repair, and development. A novel molecule, POEM (preosteoblast epidermal growth factor-like repeat protein with meprin, A5 protein, and receptor protein-tyrosine phosphatase mu domain), was isolated by reverse transcription-polymerase chain reaction using a set of degenerate primers designed after other known epidermal growth factor (EGF)-like motifs. From its structure, POEM was suggested to be a novel adhesion molecule with five EGF-like domains, an Arg-Gly-Asp (RGD) cell binding motif, and a meprin, A5 protein, and receptor protein-tyrosine phosphatase mu (MAM) domain. By in situ hybridization using embryonic day 16.5 (E16.5) mouse embryos, strong expression of POEM mRNA was observed in developing kidney renal tubules, parathyroid and thyroid glands, developing bone, tooth germ, and endocrine organs of the brain. The inner ear, skeletal muscle, smooth muscle (except for the vascular system), and skin were also positive for POEM expression. Bacterial recombinant POEM protein containing the RGD sequence and MAM domain showed strong cell adhesion, spreading, and survival-promoting activities. By mutating the RGD sequence to RGE, the cell spreading and survival activities were significantly decreased, but the MAM domain was shown to contribute only to cell adhesion and not to cell spreading and survival-promoting activities. The distribution of POEM in several tissues was close to that of alpha(8)beta(1) integrin. Therefore, we conducted cell adhesion assays using KA8 cells, a K562 leukemia clone stably expressing alpha(8) integrin. Parental K562 cells, which expressed alpha(5)beta(1) integrin, bound to fibronectin but not to POEM. On the other hand, KA8 cells showed strong binding and spreading on both fibronectin and POEM. These results suggest that POEM is a novel ligand for alpha(8)beta(1) integrin and that POEM may be involved in the development and function of various tissues, such as kidney, bone, muscles, and endocrine organs.
The formation of dentin provides one well accepted paradigm for studying mineralized tissue formation. For the assembly of dentin, several cellular signaling pathways cooperate to provide neural crest-derived mesenchymal cells with positional information. Further, "cross-talk" between signaling pathways from the mesenchymal derived odontoblast cells and the epithelially derived ameloblasts during development is responsible for the formation of functional odontoblasts. These intercellular signals are tightly regulated, both temporally and spatially. When isolated from the developing tooth germ, odontoblasts quickly lose their potential to maintain the odontoblast-specific phenotype. Therefore, generation of an odontoblast cell line would be a valuable reproducible tool for studying the modulatory effects involved in odontoblast differentiation as well as the molecular events involved in mineralized dentin formation. In this study an immortalized odontoblast cell line, which has the required biochemical machinery to produce mineralized tissue in vitro, has been generated. These cells were implanted into animal models to determine their in vivo effects on dentin formation. After implantation, we observed a multistep, programmed cascade of gene expression in the exogenous odontoblasts as the dentin formed de novo. Some of the genes expressed include the dentin matrix proteins 1, 2, and 3, which are extracellular matrix molecules responsible for the ultimate formation of mineralized dentin. The biological response was also examined by histology and radiography and confirmed for mineral deposition by von Kossa staining. Thus, a transformed odontoblast cell line was created with high proliferative capacity that might ultimately be used for the regeneration and repair of dentin in vivo.
The fixation sites of two antibodies, HNK-1-anti-leu 7 and anti- HNK-1/N-CAM, were studied during visceral cephalogenesis in the rat. The labelling patterns of both antibodies were different. Anti-leu 7 staining was restricted to trunk neural crest cells, the peripheral nervous system, myotomes and premuscular cells, the eye rudiment and the olfactory vesicle. On the other hand, anti- HNK-1/N-CAM extended to the otocyst, several epithelia (including tooth germs) and precartilages. Anti-HNK-1/N-CAM staining of somites and cranial nerve ganglia was more precocious than anti-leu 7 labelling. We conclude that both antibodies, despite several common sites labelling, display quite different immunological properties, and that the expression "HNK-1" positive has no absolute significance.
The neural cell adhesion molecule (NCAM) is a molecule that mediates calcium-independent cell-cell adhesion, and is expressed during development in a variety of tissues including nonneuronal ones. Expression of NCAM during molar tooth development was analyzed in this present study. In the enamel organ, NCAM expression was detected from the embryonic day 13 onward in restricted areas, including a part of the stratum intermedium of the tooth germ at the bell stage. Mesenchymal cells also expressed NCAM from the bud stage of the first molar onward. In addition to the strong expression in the dental follicle, weak and transient expression was detected in the dental papilla. The second and the third molars appeared to initiate their development by the interaction between the epithelial cells and NCAM-expressing mesenchymal cells. Comparison of the expression patterns of NCAM and transcription factor Barx1 revealed a possibility that Barx1 negatively regulates NCAM expression.
To address the molecular mechanisms of cementogenesis, we have isolated dental follicle cells and examined them to see if they contain cementoblast progenitors. Dental follicle tissue was dissected from the root surface of bovine tooth germ and cells were released by digestion with bacterial collagenase. The released cells were maintained as a bovine dental follicle cells (BDFC). To elucidate the differentiation capacity of BDFC, they were transplanted into severe combined immunodeficiency (SCID) mice for 4 weeks. Transplanted BDFC formed cementumlike matrix; in contrast, bovine alveolar osteoblast (BAOB) transplants formed bonelike matrix, and bovine periodontal ligament cells (BPDL) formed a small amount of the cementumlike matrix. Immunohistochemical analysis showed that cementumlike matrix was positive for anti-cementum attachment protein monoclonal antibody, whereas bone-like matrix was negative. These results indicated that the BDFC contained cementoblast progenitors that were able to differentiate to cementoblasts in vivo. They also indicated that the BDFC are phenotypically distinct from BAOB and BPDL, and provide a useful model for investigating molecular mechanisms of cementogenesis.
Amelogenins are the major protein species synthesized by secretory ameloblasts and are believed to be involved in enamel mineralization. During enamel formation, amelogenins are progressively degraded into smaller fragments by protease activity. These amelogenin fragments are removed from the enamel extracellular space, thereby enabling full mineralization of the dental enamel. Enamel from fluorotic teeth is porous and contains more proteins and less mineral than sound enamel. In this study we examined the hypothesis that fluoride (F-) is capable of inhibiting the proteolysis of amelogenins in enamel being formed in organ culture. Hamster molar tooth germs in stages of secretory amelogenesis were pulse labeled in vitro with [3H]- or [14C] proline and subsequently pulse chased. The explants were exposed to F- at different days of chase (i.e., during secretory amelogenesis early after labeling, later after labeling or at stages just beyond secretory amelogenesis). Exposure of secretory stage explants to F- enhanced the release of radiolabeled fragments when F- was applied early after labeling but progressively less if applied later. In contrast, F- had no such effect in stages beyond secretion. The enhanced release of radiolabeled fragments in secretory stages was associated with a reduction of radioactivity in the soft tissue enamel organ indicating that fragmentation of enamel matrix proteins (mainly amelogenins) occurred intracellularly. Analysis by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that the fluorotic enamel contained less radiolabeled parent amelogenins (M(r) 28 kD and 26 kD) but more low-molecular-mass fragments than enamel from control explants. Our data indicate that F- promotes intracellular degradation of the newly synthesized parent amelogenins during secretory stage. Our in vitro data do not support the concept that F- impairs extracellular proteolysis of amelogenins, either in the secretory phase or in the stage just beyond the secretory phase.
This is the first report on the stratum intermedium in vertebrates other than mammals. The aim of this study is to elucidate the fine structure and cytochemical features of the stratum intermedium during the stages of enameloid formation in Lepisosteus. Inner dental epithelium, stratum intermedium, stellate reticulum, and outer dental epithelium are consistently present in the tooth germs of Lepisosteus. The stratum intermedium cells are oval in shape, contain elliptical nuclei, and extend many small processes. It is implied that the structure of the enamel organ is different among actinopterygians, and that constitution of the enamel organ in Lepisosteus resembles that in higher vertebrates. Marked Ca-ATPase activity is observed at the cell membrane of the stratum intermedium cells, suggesting that the cells are involved in calcium transport during the stages of enameloid formation.
The size and shape characteristics of permanent mandibular first molars were compared in a group of young males with Down syndrome (DS) and a control group of normal males. Generalized size was quantified by the log transforms of five intercusp distances and shape by a principal component analysis of the log distances scaled to constant size. On average the DS molars were smaller than the controls by 8%, the most marked reduction being in the distance between the distal and distolingual cusps. The scores on two of the four components of shape also differed between the DS and control teeth. These two shape components, which accounted for over 41% of the total shape variation, were determined specially by the occlusal morphology of the distal crown region. Discriminant function analyses also indicated the importance of the distal regions in discriminating between control and DS molars. Evidence suggests that trisomy 21 is associated with a general retardation in growth. The observed features of DS molars were consistent with decreased cellular activity in the developing tooth germs, producing morphological changes that were more pronounced in the later-forming crown regions.
Type I collagen is expressed in a variety of connective tissue cells and its transcriptional regulation is highly complex because of the influence of numerous developmental, environmental, and hormonal factors. To investigate the molecular basis for one aspect of this complex regulation, the expression of alpha 1(I) collagen (COL1A1) gene in osseous tissues, we fused a 3.6-kb DNA fragment between bases -3,521 and +115 of the rat COL1A1 promoter, and three deletion mutants, to the chloramphenicol acetyltransferase (CAT) marker gene. The expression of these ColCAT transgenes was measured in stably transfected osteoblastic cell lines ROS 17/2.8, Py-la, and MC3T3-E1 and three fibroblastic lines NIH-3T3, Rat-1, and EL2. Deletion of the distal 1.2-kb fragment of the full-length ColCAT 3.6 construct reduced the promoter activity 7- to 30-fold in the osteoblastic cell lines, twofold in EL2 and had no effect in NIH-3T3 and Rat-1 cells. To begin to assess the function of COL1A1 upstream regulatory elements in intact animals, we established transgenic mouse lines and examined the activity of the ColCAT3.6 construct in various tissues of newborn animals. The expression of this construct followed the expected distribution between the high and low collagen-producing tissues: high levels of CAT activity in calvarial bone, tooth, and tendon, a low level in skin, and no detectable activity in liver and brain. Furthermore, CAT activity in calvarial bone was three- to fourfold higher than that in the adjacent periosteal layer. Immunostaining for CAT protein in calvaria and developing tooth germ of ColCAT3.6 mice also confirmed the preferred expression of the transgene in differentiated osteoblasts and odontoblasts compared to fibroblast-like cells of periosteum and dental papilla. This study suggests that the 3.6-kb DNA fragment confers the strong expression of COL1A1 gene in high collagen producing tissues of intact animals and that the 5' flanking promoter sequence between -3,521 and -2,295 bp contains one or more stimulatory elements which are preferentially active in osteoblastic cells.
The purpose of this study was to investigate the prognosis of 50 consecutively autotransplanted teeth to the maxillary incisor region. Thirty-five were transplanted in cases of traumatic injuries, eleven in cases of agenesis and four in cases with impaction of maxillary canines. The average follow-up time was 7 years and 6 months (range 4-17 years). The transplants were examined clinically in respect of tooth vitality and radiographically in respect of root canal obliteration, periradicular changes, root formation, and root length. The results show a success rate of 82 per cent. It is concluded that the procedure of tooth transplantation has the advantage of maintaining or restoring alveolar bone volume and gives the opportunity to replace a missing tooth without involvement of neighbouring teeth as prosthetic abutments.