Numerical simulation of the biomechanical behaviour of multi-rooted teeth.
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The elastic properties of the periodontal ligament (PDL) in eight multi-rooted teeth were examined in a combined experimental and numerical study in six minipigs. The initial tooth movement of the mandibular primary molars surrounded by the periodontium was registered three-dimensionally (3D) in an optomechanical measuring system. The dissections were then embedded in resin and cut in transverse sections. Based on these sections, 3D finite element (FE) models were constructed and numerically loaded with the same force systems as used in the experiment. The material behaviour of the PDL registered in the experiment was non-linear and could be approximated with a bilinear parameter set consisting of two Young's moduli, E1 and E2, and one ultimate strain, epsilon12, separating both elastic regimes. When a deficient congruence existed between the experimental and numerical force/deflection curves the material parameters were varied to obtain a satisfactory congruence. The material behaviour determined for these specimens delivered mean values of E1 = 0.05 MPa, E2 = 0.18 MPa and epsilon12 = 6.4 per cent for the elastic behaviour of the multi-rooted minipig teeth. There was no significant difference in the material parameters determined for specimens with two, four or six roots. The results were in close agreement with the material parameters of the PDL, determined in previous investigations of single-rooted human and pig teeth. (+info)
Differential effect of the cytolethal distending toxin of Actinobacillus actinomycetemcomitans on co-cultures of human oral cells.
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The periodontal pathogen Actinobacillus actinomycetemcomitans expresses a cytolethal distending toxin (CDT) that typically arrests the growth of eukaryotic cells at either the G0/G1 or G2/M phase of the cell cycle. It was previously found that CDT failed to arrest the growth of human periodontal ligament fibroblasts (HPLFs) when grown in pure culture. In contrast, proliferation of an oral epithelial cell line was rapidly inhibited by the toxin. In this study, the feasibility of using mixed-cell cultures and cell-specific markers to evaluate the response of oral cells, when in heterogeneous populations, to CDT was established. Proliferation of epithelial cells was rapidly inhibited and the cells were selectively eliminated in co-culture with HPLFs or cementoblasts by 24-48 h post-intoxication. Epithelial cells and HPLFs were detected and counted in co-cultures following cell-specific immunolabelling with antibodies against simian virus 40 large T antigen and the Ab-1 surface antigen, respectively. These results demonstrated that the activities of potential virulence factors, such as CDT, from periodontal pathogens can be successfully examined in mixed-cell cultures. This approach is especially relevant to infectious diseases that affect tissues with a diverse cellular composition, such as the periodontium. (+info)
Resistance of human periodontal ligament fibroblasts to the cytolethal distending toxin of Actinobacillus actinomycetemcomitans.
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BACKGROUND: The cytolethal distending toxin (CDT) of Actinobacillus actinomycetemcomitans is a typical member of this Gram-negative bacterium holotoxin family that targets a wide spectrum of eukarytotic cells, typically causing cell cycle arrest at either the G(1) or G(2)/M phase of the cell cycle. In view of the possible role of the CDT as a prominent A. actinomycetemcomitans virulence factor in periodontal diseases, we have examined the effects of the toxin on primary cultures of human periodontal ligament fibroblasts (HPLF). METHODS: HPLF and an immortalized human gingival epithelial cell line, GMSM-K, were exposed to recombinant A. actinomycetemcomitans CDT. Effects of the toxin on cell proliferation and cell cycle were assessed by a cell viability assay and flow cytometry, respectively. Double-strand DNA damage was detected by pulsed field gel electrophoresis. Binding of the toxin and its individual subunits to HPLF was examined by immunofluorescence microscopy. RESULTS: Viability of HPLF was not reduced following prolonged exposure to the CDT. There was no indication of cell cycle arrest or double-strand DNA damage. GMSM-K cells exhibited morphological alterations and a rapid decrease in cell viability within 6 and 12 hours, respectively, following exposure to the toxin for 5 minutes. These effects were dependent on toxin dose and age of the cultures and occurred more rapidly compared to CDT-treated HeLa cells. CDT-treated GMSM-K cells displayed cell cycle arrest at the S phase of growth and double-strand DNA damage was observed by 6 hours post-intoxication. Holotoxin and the CdtA subunit were detected on the surface of both HPLF and epithelial cells. CONCLUSIONS: These results demonstrate that HPLF are resistant to the cytotoxic effects of the A. actinomycetemcomitans CDT. The mechanism of resistance is not known but may be related to the inability of the toxin to cause DNA damage. The difference in sensitivities of HPLF and oral epithelial cells to the CDT has important implications for the role of this putative microbial virulence factor in periodontal pathogenesis. (+info)
In vitro time-dependent response of periodontal ligament to mechanical loading.
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This study examined the time-dependent response of bovine periodontal ligament (PDL). Applying linear viscoelastic theory, the objective was 1) to examine the linearity of the PDL's response in terms of its scaling and superposition property and 2) to generate the phase lag-vs.-frequency spectrum graph. PDL specimens were tested under three separate straining conditions: 1) tension ramp tests conducted at different strain rates, 2) pulling step-straining to 0.3 in discrete tests and to 0.3 and 0.6 in one continuous run, and 3) tension-compression sinusoidal oscillations. To this effect, bar-shaped specimens of bovine roots that comprised portions of dentin, PDL tissue, and alveolar bone were produced and strained in a microtensile machine. The experimental data demonstrated that neither the scaling nor the superposition properties were verified and that the viscoelastic response of the PDL was nonlinear. The PDL's elastic response was essentially stiffening, and its viscous component was pseudoplastic. The tangent of the PDL's strain-stress phase lag was in the 0-0.1 range in the tensile direction and in the 0.35-0.45 range in the compressive direction. In line with other biological tissues, the phase lag was largely independent of frequency. By use of the data generated, a mathematical model is outlined that reproduces both the elastic stiffening and viscous thinning of the PDL's response. (+info)
Influence of apical patency and filling material on healing process of dogs' teeth with vital pulp after root canal therapy.
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The purpose of this study was to investigate the periapical healing process of dogs' teeth with or without apical patency and after root canal filling with two types of sealers. Forty roots of premolars and incisors were utilized. The root canals were over-instrumented and dressed with a corticosteroid-antibiotic solution for 7 days to obtain ingrowth of periapical connective tissue into the canals. After this period, the tissue was removed in half of the specimens (groups with patency) and preserved in the other half (groups without patency). Canals were filled by lateral condensation technique with gutta-percha points and either a calcium hydroxide-based sealer (Sealer Plus) or a Grossman's cement (Fill Canal). The animals were killed by anesthetic overdose 60 days after the endodontic treatment and anatomic pieces were obtained and prepared for histologic examination. Data were evaluated in a blind analysis on the basis of several histomorphologic parameters. The groups without patency had better results (p=0.01) than those in which the ingrown connective tissue was removed. Comparing the sealers, Sealer Plus had significantly better results (p=0.01) than Fill Canal. In conclusion, both the apical patency (presence or absence) and the type of root canal filling material influenced the periapical healing process in dogs' teeth with vital pulp after root canal treatment. The use of a calcium hydroxide-based sealer in teeth without apical patency yielded the best results among the experimental conditions proposed. (+info)
Preparation of recombinant human bone morphogenetic protein-2 loaded dextran-based microspheres and their characteristics.
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AIM: To prepare new pharmaceutical forms with sustained delivery properties of recombinant human bone morphogenetic protein-2 (rhBMP2) for tissue engineering and guided tissue regeneration (GTR) use. METHODS: rhBMP2-loaded dextran-based hydrogel microspheres (rhBMP2-MPs), which aimed to keep rhBMP2 bioactivity and to achieve long-term sustained release of rhBMP2, were prepared by double-phase emulsified condensation polymerization. The physical, chemical performances and biological characteristics of those microspheres were studied both in vitro and in vivo. RESULTS: The microspheres' average diameter was 30.33+/-4.32 microm with 75.4% ranging from 20 microm to 40 microm and the drug loading and encapsulation efficiency were 7.82% and 82.25%, respectively. The rhBMP2-releasing profiles in vitro showed that rhBMP2 release could be maintained more than 10 d. The rhBMP2-MPs, with good swelling and biodegradation behavior, could be kept for 6 months at below 4 degree without significant characteristic change or bioactivity loss. Cytology studies showed that rhBMP2-MPs could promote the proliferation of periodontal ligament cells (PDLCs) approximately 10 d, while the bioactivity of concentrated rhBMP2 solution could keep no more than 3 d. Scanning electron microscope showed that rhBMP2-MPs could be enchased into the porous structure of calcium phosphate ceremic (CPC) and the eugonic growth of PDLCs in CPC/rhBMP2-MPs scaffolds. Animal experiments indicated that using CPC/rhBMP2-MPs scaffolds could gain more periodontal tissue regeneration than using rhBMP2 compound firsthand with CPC (CPC/rhBMP2). CONCLUSION: By encapsulating rhBMP2 into dextran-based microspheres, a small quantity of rhBMP2 could achieve equivalent effects to the concentrated rhBMP2 solution and at the same time, could prolong rhBMP2 retention both in vitro and in vivo. (+info)
Changes in fluoride sensitivity during in vitro senescence of normal human oral cells.
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We have previously reported that sodium fluoride (NaF) showed slightly higher cytotoxicity against human oral tumor cell lines than normal human oral cells. Possible changes in the NaF sensitivity of three normal human oral cell types (gingival fibroblast HGF, pulp cell HPC, periodontal ligament fibroblast HPLF) during in vitro ageing were investigated in the present study. When these cells were subcultured at 1:4 split ratio every week, their saturation density declined with increasing population doubling level (PDL), and they ceased to divide when they reached 20 PDL. Mitochondrial function, evaluated by MTT stainability per cell basis, was elevated at the terminal phase. NaF dose-dependently reduced the viable cell number, but did not show any beneficial (growth promoting) effect (so-called "hormesis") at lower concentrations. NaF produced large DNA fragments, without induction of internucleosomal DNA fragmentation, possibly due to weak activation of caspases -3, -8 and -9. Higher concentrations of NaF were required to reduce the number of viable senescent cells than younger cells, indicating that cells become resistant to cytotoxicity of NaF with in vitro ageing. (+info)
Cell transplantation in wounded mixed connective tissues.
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Direct transplantation of multipotent precursor cells into the periodontium could provide a therapeutic approach for restoring periodontal tissues destroyed by periodontitis or trauma. To improve the understanding of cell migration, proliferation, and differentiation, we used a rodent model combining orthodontic tooth movement and transplantation of Lac-Z-positive murine-cultured periodontal ligament (PL) or femur-derived bone marrow precursor cells into a defined mandibular wound site, thus promoting tissue regeneration in wounded periodontium. Our results show that in orthodontically traumatized tissues, transplanted PL and bone marrow cells migrated systemically, contributing to the repopulation of sites with reduced cell/matrix density. The transplanted PL cells proliferated in adjacent alveolar bone marrow spaces, thus migrating to vascular tissues in the PL. The capillary walls in the PL serve as delivery sites for these cells and other marrow-derived hematopoietic cells, including monocytes. The transplanted marrow cells, extracted from femur of transgenic (TgR) mice exhibited similar behavior to those of transplanted PL cells, showing high proliferative activity in alveolar marrow as well as intensive repopulating capacity in wounded periodontium. On the other hand, the buccal skin fibroblasts failed to migrate and home effectively and thus the transplantation of these cells had no effect on periodontium regeneration. Based on these results, we conclude that the transplanted PL and bone marrow cells migrate systemically and following a cyclical process of growth and development and differentiate into PL fibroblasts, osteoblasts, and cementoblasts, thereby contributing to periodontal regeneration. (+info)