Home About us Contact
|
Home About us Contact | ||
|
|
||
Tissue Resorption (tissue + resorption)
Selected AbstractsChange in supporting tissue following loss of a permanent maxillary incisor in childrenDENTAL TRAUMATOLOGY, Issue 6 2007Helen D. Rodd Abstract,,, Alveolar bone resorption is an inevitable consequence of tooth loss and may be detrimental to long-term dental aesthetics and function. The aim of the present study was to quantify the degree of tissue resorption following the loss of a permanent incisor in a young population. The study group comprised 11 boys and five girls who all required the extraction of a permanent maxillary central incisor due to trauma-related sequelae. Mean age at tooth loss was 10.8 years. Upper alginate impressions were taken at regular intervals following tooth loss and were cast in yellow dental stone. Study models were sectioned longitudinally through the mid-point of both the maxillary incisor socket and the contra-lateral incisor to provide a thin plaster section. Digital photographs were acquired of the edentulous (A1) and dentate (A2) surfaces of this section and image analysis software was employed to quantify the surface area of both A1 and A2. At 3 months postextraction, mean A1 was 15.7% less than mean A2. By 6 months mean A1 had further reduced and was 25.3% less than that of the corresponding dentate alveolus. However, at subsequent time intervals following tooth extraction (>6 months), tissue loss appeared to stabilise with an overall reduction in tissue area remaining at 22%. This reduction in supporting tissue area was found to be highly statistically significant (P = 0.002, anova). Furthermore, girls appeared to have an overall greater degree of tissue loss than boys (P = 0.015). Further research is indicated to explore factors influencing the degree of tissue loss following incisor extraction and the benefit of therapeutic interventions in limiting this resorption. [source] Hypothermic insult to the periodontium: a model for the study of aseptic tooth resorptionDENTAL TRAUMATOLOGY, Issue 1 2000C. W. Dreyer Abstract , The aim of the current investigation was to define an animal model for the study of hard tissue resorption by examining the responses of the periodontal ligament (PDL) to both single and multiple episodes of hypothermic injury to the crowns of rat teeth. A group of 12 male rats weighing 200,250 g were anesthetized, and pellets of dry ice (CO2) were applied once to the crowns of the right first maxillary molars for continuous periods of 10 or 20 min. Animals were sacrificed at 2, 7, 14 and 28 days and tissues were processed for routine histological examination. A second group of eight animals and a third group of 12 animals were subjected to three applications of dry ice over a period of 1 week and sacrificed at 2 and 14 days respectively after the final application. In addition to thermal insult, the periodontium of teeth from a fourth group of six rats was subjected to mechanical trauma. Examination of the sections from the group undergoing a single freezing episode revealed that, by 1 week, shallow resorption lacunae had appeared on the root surface. These became more extensive after 14 days. At the same time hyaline degeneration was evident in the PDL. Within this group, teeth subjected to the longer 20-min application times generally showed more extensive injuries. By 28 days, evidence of repair was observed with reparative cementum beginning to line the resorption lacunae in the root dentin. Sections from animals subjected to multiple episodes of thermal trauma and those subjected to additional mechanical insult showed more extensive external root resorption than those from single-injury animals. It was concluded that low temperature stimuli applied to the crowns of rat molars were capable of eliciting a sterile degenerative response in the PDL which, in turn, resulted in external root resorption. Furthermore, the degree of this tissue injury was commensurate with the duration and number of exposures to the trauma. The results also indicated that progression of the resorptive process required periodic exposure to the injury, in the absence of which repair to the damaged root occurred. [source] Activity of the matrix metalloproteinase-9 promoter in human normal and tumor cellsJOURNAL OF CELLULAR PHYSIOLOGY, Issue 1 2004Cristina Morelli Matrix metalloproteinases (MMPs) belong to a family of proteins essential for those processes involving extracellular matrix degradation, such as embryonic development, morphogenesis, and tissue resorption and remodeling. Some members of this family play a crucial role also in tumor invasion. Most notably, MMP-9 is expressed in invasive tumors, and represents a key protein in brain tumor progression, whereas it is not expressed in adult normal tissues. The expression of the MMP-9, like other members of the family, is transcriptionally regulated. We, therefore, postulated that the MMP-9 promoter could be useful in driving selective expression of exogenous genes in tumor cells. This represents a key feature for gene therapy applications, since currently employed viral promoters induce severe organ toxicity, limiting the clinical benefits. In this study, we investigated the activity of the MMP-9 promoter in driving exogenous gene expression in human cell lines. High levels of reporter gene expression were detected in tumor derived cell lines, whereas the MMP-9 promoter activity in non-tumor cells was negligible. Furthermore, we show that tumor necrosis factor alpha (TNF,) is able to enhance considerably the MMP-9 promoter activity only in tumor cells. Since recent studies have indicated that MMP-9 enzymatic activity is detectable in the blood, it would be possible to screen potential responsive patients for a tumor gene therapy approach based on the MMP-9 promoter. Taken together these data suggest that MMP-9 promoter has the characteristics for transcritpionally targeted and inducible gene therapy applications. J. Cell. Physiol. 199: 126,133, 2004© 2003 Wiley-Liss, Inc. [source] Differentiation and functions of osteoclasts and odontoclasts in mineralized tissue resorptionMICROSCOPY RESEARCH AND TECHNIQUE, Issue 6 2003Takahisa Sasaki Abstract The differentiation and functions of osteoclasts (OC) are regulated by osteoblast-derived factors such as receptor activator of NFKB ligand (RANKL) that stimulates OC formation, and a novel secreted member of the TNF receptor superfamily, osteoprotegerin (OPG), that negatively regulates osteoclastogenesis. In examination of the preosteoclast (pOC) culture, pOCs formed without any additives expressed tartrate-resistant acid phosphatase (TRAP), but showed little resorptive activity. pOC treated with RANKL became TRAP-positive OC, which expressed intense vacuolar-type H+ -ATPase and exhibited prominent resorptive activity. Such effects of RANKL on pOC were completely inhibited by addition of OPG. OPG inhibited ruffled border formation in mature OC and reduced their resorptive activity, and also induced apoptosis of some OC. Although OPG administration significantly reduced trabecular bone loss in the femurs of ovariectomized (OVX) mice, the number of TRAP-positive OC in OPG-administered OVX mice was not significantly decreased. Rather, OPG administration caused the disappearance of ruffled borders and decreased H+ -ATPase expression in most OC. OPG deficiency causes severe osteoporosis. We also examined RANKL localization and OC induction in periodontal ligament (PDL) during experimental movement of incisors in OPG-deficient mice. Compared to wild-type OPG (+/+) littermates, after force application, TRAP-positive OC were markedly increased in the PDL and alveolar bone was severely destroyed in OPG-deficient mice. In both wild-type and OPG-deficient mice, RANKL expression in osteoblasts and fibroblasts became stronger by force application. These in vitro and in vivo studies suggest that RANKL and OPG are important regulators of not only the terminal differentiation of OC but also their resorptive function. To determine resorptive functions of OC, we further examined the effects of specific inhibitors of H+ -ATPase, bafilomycin A1, and lysosomal cysteine proteinases (cathepsins), E-64, on the ultrastructure, expression of these enzymes and resorptive functions of cultured OC. In bafilomycin A1-treated cultures, OC lacked ruffled borders, and H+ -ATPase expression and resorptive activity were significantly diminished. E-64 treatment did not affect the ultrastructure and the expression of enzyme molecules in OC, but significantly reduced resorption lacuna formation, by inhibition of cathepsin activity. Lastly, we examined the expression of H+ -ATPase, cathepsin K, and matrix metalloproteinase-9 in odontoclasts (OdC) during physiological root resorption in human deciduous teeth, and found that there were no differences in the expression of these molecules between OC and OdC. RANKL was also detected in stromal cells located on resorbing dentine surfaces. This suggests that there is a common mechanism in cellular resorption of mineralized tissues such as bone and teeth. Microsc. Res. Tech. 61:483,495, 2003. © 2003 Wiley-Liss, Inc. [source] | ||||||||||