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Cyclic adenosine 3',5'-monophosphate (cAMP) concentrations and cellular distribution were studied in dental and periodontal tissues during tooth eruption in kittens. Although the mean levels of cAMP around developing teeth were similar in all the tissue samples, there were marked differences in cAMP stainability of tissues apical and occlusal to the erupting teeth.
The effect of x-radiation on erupting molars is presented. New born, 5 day old Wistar rats were locally irradiated in the molar area with doses of 20 Gy. They were killed in two groups, 30 and 60 days postirradiation respectively. Two other groups of non irradiated, age matched rats were killed at the given times. In addition a control group of 5 day old animals was also studied. Radiographic and histologic studies were performed. Odontoblastic atrophy, odontodysplasia, rootless formation, and ankylosis of tooth to bone by osteodentin formation with the resulting lack of tooth eruption were observed. The relation between the histologic alterations and tooth eruption is discussed.
Absolute and relative ages of incisor and canine eruption were recorded in 152 Holstein-Friesian and 154 Limousine X Hungarian Fleckvieh cows kept under commercial circumstances. While significant difference was found only between the emergence of the first incisor relative to the canine, a broader comparison of several breeds as published by a variety of authors put the findings within the right context. Results of a discriminant analysis suggested that the absolute ages of tooth eruption are heavily influenced by the environment. Typological inferences may be made studying tooth eruption ages relative to each other. In archaeozoology, aging based on modern toothwear analogies may be biased by these two inseparable effects.
The osteopetrotic (ia) rat was examined as an experimental model for studying the dependence of tooth eruption on bone resorption. In ia rats eruption of incisors and first molars was rare and eruption of second and third molars was reduced and delayed. Autoradiographic studies of 3H-proline incorporation showed that delayed eruption was not due to reduced tooth formation. Microscopic study revealed distortion and failure of posterior growth of the apical ends of incisors, unresorbed bone blocking the eruption pathway for molars, and ankylosis of incisors and first molars to alveolar bone. A reduction in bone resorption, known to be the primary cause of the disease in ia rats, is presumed to be the cause of the delayed or unerupted dentition. The effectiveness of attempts to increase bone resorption in ia rats at an early age by injection of vitamin A and/or parathyroid extract or by parabiotic union with a normal littermate was determined by measuring their effect on the relative size of the tibial marrow cavity. Only parabiosis had a beneficial effect on bone resorption but surgical union could not be performed in animals young enough to affect eruption of incisors and first molars in ia parabionts. These results suggest that parabiotic union of neonatal rats should allow resorption to begin early enough to test the presumed dependence of tooth eruption on bone resorption.
The monocyte chemotactic protein-1 (MCP-1) gene is expressed in the dental follicle, a loose connective tissue sac that must be present for eruption to occur. The role of MCP-1 may be to recruit mononuclear cells (monocytes) to the dental follicle, where these cells, in turn, fuse to form osteoclasts to resorb alveolar bone for the formation of an eruption pathway. Thus, it was the aim of this study to determine if MCP-1 is secreted by dental follicle cells in culture and if its secretion is enhanced by potential tooth eruption molecules. Western blotting and a two-site capture enzyme-linked immunoabsorbent assay demonstrated that MCP-1 was synthesized and secreted into the medium by the follicle cells. Incubation of the cells with either transforming growth factor-beta one (TGF-beta 1) or interleukin-one alpha (IL-1 alpha) enhanced the secretion of MCP-1 by the cells. Measurement of the chemotactic ability of the conditioned medium to attract mouse monocytes demonstrated that the chemotaxis of the medium was increased if the cells had previously been incubated in IL-1 alpha, although there appears to be a threshold concentration of MCP-1 above which chemotaxis is not enhanced. These combined results suggest that the critical initial cellular event of tooth eruption, an influx of mononuclear cells into the dental follicle at an early post-natal age, may be initiated by the secretion of MCP-1 by the dental follicle cells.
Studies of osteopetrotic rodents suggest that localized alveolar bone resorption must occur if the tooth is to erupt. To test this hypothesis directly, we injected postnatal rats with pamidronate, a bisphosphonate that reduces bone resorption by osteoclasts. The results of these experiments demonstrate that this bisphosphonate inhibits the time of tooth eruption of both rat molars and incisors. Pamidronate does not inhibit the gene expression of the putative tooth eruption molecules, colony-stimulating factor-1 and c-fos, both of which are expressed in the dental follicle, the tissue that is required for eruption to occur. Pamidronate does increase the size of the osteoclasts, including an increase in the number of nuclei, suggesting that the precursor mononuclear cells can still fuse to form osteoclasts despite the reduced ability of the osteoclasts to resorb bone. Thus, we report the discovery of an agent that inhibits tooth eruption and also show that tooth eruption requires alveolar bone resorption.
Metabolic turnover of collagen in the developing molar periodontal ligament was studied in 10, 12 and 16 days old mice by autoradiography after the administration of [3H]proline. Grain counts, in number per unit area, were made over three different zones (apical, middle and cervical) of the sections and activity time curves were drawn. Calculated regressions (log10 grain density V time) were fitted and analyses of variance to test the linearity of the regressions were carried out using the computer. Slopes +/- S.E. of the regressions, and half-lives were estimated. This study has demonstrated that collagen turnover occurred throughout the whole thickness of the ligament, from bone to cementum. Therefore, there was no evidence of a metabolically active 'intermediate plexus' in the periodontal ligament. However, the turnover rates in the apical zones of the three groups studied were significantly higher than those in the middle zones, which in turn were higher than those in the cervical zones, suggesting a differential rate of collagen turnover within the periodontal ligament. This whole sequence was significantly higher in the 12 days old compared with the 10 and 16 days old groups. Estimated half-lives confirmed this pattern of rate of collagen turnover. The molar periodontal ligament behaves and functions as a 'stimulated system' during the period 10 to 16 days, with a statistically significant rate of collagen turnover at the twelfth day, which is also the time of tooth eruption in the mouse. Thus, collagen turnover is an essential and accompanying process of tooth eruption.
In order to calibrate a precision-measuring instrument for studies of tooth eruption, a calibration device capable of repositioning an optical grating in steps accurate to at least 0.02 microns was required. At this level, piezoelectric and similar pushers encounter problems. A new calibration device based on the magnetostrictive properties of nickel was developed. Accuracy better than 0.02 microns was verified by relating its movements to the wavelength of the green line of mercury, and the device was successfully used to calibrate the instrument for establishing tooth position. Magnetostriction offers a way to calibrate precision measurement instruments for other applications.
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Previous work from our laboratories has established that eruption of the permanent mandibular premolars in dogs is dependent upon the presence of the dental follicle and that it involves resorption of alveolar bone and the roots of the deciduous predecessor above and formation of alveolar bone below the developing crown. This study illustrates the topography of the bone surfaces of the crypt by scanning electron microscopy and the ultrastructure of the cells on alveolar bone surfaces during tooth eruption. Above the developing crown where the eruption pathway forms, the bone surface is a pitted sheet, the characteristic topographic feature of bone resorption; between the crown and the mandibular canal, the bone surface has numerous interconnecting trabeculae. Transmission electron microscopy of bone cells lining the eruption pathway area of the crypt showed numerous osteoclasts with adjacent mononuclear cells. Both cell types contained specific, membrane-bound cytoplasmic vesicles shown by the work of others to be characteristic features of osteoclasts and their precursors. Basal trabeculated bone in the crypt was covered by plump osteoblasts. These data show that the metabolic events in alveolar bone associated with tooth eruption have the appropriate cellular and bony surface correlates and that the suspected control of alveolar bone resorption by the dental follicle may be mediated by its recruiting and directing to adjacent bone surfaces the mononuclear precursors of osteoclasts.
A lot of attention has been paid to the questions of how and why teeth erupt. In the past many theories were developed, all of which showed mechanistic characteristics and suggested that a certain structure exerts force on the tooth germ to initiate its eruption. The dominant theory considered the collagenous fibres or the fibroblasts within the periodontal ligament to be the primary moving force in the eruption process. However, most research was done on continuously erupting incisors of rodents or lagomorphs, an experimental model with serious drawbacks. Because dogs, like humans, have teeth with limited eruption, 25 years ago research was carried out on tooth eruption in beagles. One of the most important conclusions of this study was that the periodontal ligament is not the primary moving force in tooth eruption, as its development only begins at the end of the eruption process. In subsequent years several others have focused their research on tooth eruption in beagles. The current state of knowledge in this field can be summarized as follows: the reduced enamel epithelium and the dental follicle control bone deposition and resorption around an erupting tooth germ, enabling its occlusal movement; the periodontal ligament develops only after its emergence in the oral cavity, and is thus not important in the eruption process; the tooth itself does not play a role in the regulation of its eruption.
The structure of the alveolar bone during the tooth eruption in the young dog mandibles was investigated by microradiographic and polarized light techniques. Around the first erupting molar root a trabecular network of primary alveolar bone, less mineralized than the surrounding cortical one, was found. Numerous calcified spicules parallel one to others radiate out the spongiosa near the periodontal ligament. The collagen fiber bundles of the alveolar, woven, bone are continuous with the periodontal ligament ones. This finding indicates that the alveolar bone increases by ossification of the periodontal ligament. Therefore the latter is the forming alveolar bone substratum. The trabeculae of the occlused premolar alveolar bone are ticker and more mineralized. This modification of the occlused tooth alveolar bone could be related to the occlusal stresses.
It was the aim of this study to determine the cellular changes that occur in the enamel organ, dental follicle, and surrounding bony crypt of the rat molar prior to and during tooth eruption. By use of light microscope histochemistry to detect cells containing tartrate-resistant acid phosphatase (TRAP), it was seen that TRAP-positive mononuclear cells were present in the dental follicle prior to the onset of eruption (e.g., three days postnatal age) and then declined in number during eruption. Concurrently, TRAP-positive osteoclasts were initially present in large numbers on the surface of the bony crypts surrounding the molars (three days postnatal age) and then declined in number as eruption progressed. Electron microscopy confirmed that these were mononuclear cells and osteoclasts. The results suggest that the mononuclear cells are either precursors of the osteoclasts or perhaps release cytokines that affect osteoclast formation or activity. Staining for alkaline phosphatase (ALP) activity indicated that at an early postnatal age (secretory stage of amelogenesis), ALP was detected only in the stratum intermedium of the enamel organ, whereas at a later age (maturation phase of amelogenesis), it was present only in the ameloblasts. These results, combined with a survey of the literature, strongly suggest that ALP moves from the base of the enamel organ to the enamel itself over a period of time ranging from pre- to post-eruption. Rat molars are teeth of limited eruption, and the cellular events that occur in eruption appear comparable with what is seen in dog and human dentition, especially in terms of the cellular events seen in the dental follicle prior to and during eruption.(ABSTRACT TRUNCATED AT 250 WORDS)
The distribution of the cell adhesion molecule C-CAM was analyzed during tooth development, eruption and formation of the junctional epithelium in rat molars by immunohistochemistry and in situ hybridization. C-CAM could not be detected during odontogenesis until the late bell stage; then only the mRNA was demonstrated in the odontoblasts and ameloblasts. Prior to eruption, a local increase in C-CAM (mRNA and protein) was observed in the reduced enamel epithelium. During eruption, high C-CAM levels were seen in the fusion zone between the oral epithelium and the reduced enamel epithelium. In the adult rat, C-CAM remained strongly expressed in the junctional epithelium. Our study indicates that C-CAM may play a role in odontogenesis and during formation of the epithelial structures involved in tooth eruption and formation of the junctional epithelium.
Based on the process of tooth eruption in children of Jena during the first period of erupting permanent teeth secular changes of the dentition were investigated and the topicality of the current tables for dental age were checked. Mean age of eruption was computed for the individual types of teeth and for each sex in Jena's children and curves for eruption were constructed. On this basis population-specific standards for the dental age were calculated and the children were subdivided into "late, normal or early teether". By comparing the methods for age estimation using the number of teeth or the roentgenological method from Demirjian et al. (1973) it could be shown, that both methods lead to comparable results in the first period of permanent teeth eruption.