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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.
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.
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.
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)
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The effect of localized x-radiation on the growth of mandibular bone and molar eruption was evaluated by morphometric methods. A dose of 20 Gy of x-radiation was given to the molar zone of growing rats. The animals were then killed in groups at 30 and 60 days postirradiation. Two groups of nonirradiated, age-matched rats were used as controls. Parameters related to molar eruption, mandibular length, and mandibular height were measured on lateral radiographs. The results obtained showed that the values of the biometric parameters were lower in experimental than in control animals. Odontoblastic atrophy, alveolodentary ankylosis, and meager or no root formation were the most conspicuous histologic findings. Osteodentin was found between canaliculary dentin and bone in cases of ankylosis. The morphometric data presented confirm the probability of alterations in mandibular growth and tooth eruption following x-radiation and suggest that this be considered in planning radiotherapy in children.
Electron-dense granules within cells of the dental follicle and stellate reticulum of rat mandibular molars can be isolated; their major components are 167 and 200 kDa proteins. Injecting these granule proteins into postnatal rats results in a delay of incisor eruption and eyelid separation. These inhibitory effects were most pronounced with the 167 kDa protein (a delay of 3 days in incisor eruption and of 2 days in eyelid opening) and were opposite to the stimulatory effects of epidermal growth factor. Thus, these granules may play an inhibitory part in tooth eruption.
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Increases in the distance from the cemento-enamel junction to the alveolar crest (CEJ-AC) have often been attributed to senile atrophy of the bone or to the effects of periodontitis, without reference to the condition of the alveolar crest. This study investigated the relationship between CEJ-AC distance, tooth wear, gender, site of the CEJ-AC measurements, and age in 161 pre-white-contact Australian aboriginal skulls. Individual teeth were included in the study when there was no evidence of dehiscence, periodontitis, or abscess cavity formation in the supporting alveolar bone. The CEJ-AC distances increased as the severity of attrition increased; in male skulls, CEJ-AC distances were greater than in female skulls for all categories of tooth wear. In general, CEJ-AC distances measured on the mesial aspects of teeth were greater than those recorded distally; lingual distances generally exceeded buccal recordings. The best explanation of these findings and similar reports in the anthropological literature is that continuous tooth eruption occurred without the concomitant coronal movement of alveolar bone. This conclusion has significant ramifications for anthropological, epidemiological, and clinical studies which use the CEJ and AC as reference points when measuring periodontal attachment loss (periodontitis).
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