Continuous Compressive Force Research Articles

Comparison of fracture resistance of teeth with prepared protaper next, protaper gold, and hyflex CM rotary files

Preparation of the root canal system is a crucial step in root canal treatment. Endodontically treated teeth differ structurally from healthy, untreated teeth. This can lead to root cracking by creating pressure on the canal wall, reducing the fracture resistance of the tooth. Different designs, including cross-sectional shape, tip, taper, flute, radial land, helix angle, rake angle, and pitch, can influence the outcome of the root canal preparation and the risk of root fracture. The purpose of this study was to evaluate the fracture resistance of teeth after root canal preparation using three different NiTi rotary files: ProTaper Next (PN), ProTaper Gold (PG), and HyFlex CM (HC). Thirty premolars with a single and straight root canal were decoronated at the cementoenamel junction, leaving 14 mm of the root. The subjects were divided into 3 groups. Group 1 (n = 10) was prepared using PN, group 2 (n = 10) was prepared using PG, and group 3 (n = 10) was prepared using HC. After instrumentation and irrigation, the specimens were subjected to a continuous vertical compressive force (crosshead-speed of 2.28 mm/sec) in order to record the force (in newtons) until root fracture. To describe the surface characteristic of the dentinal root after the preparation, a section fragment from the apical third of the specimens was observed using a scanning electron microscope (SEM) at 2500x magnification. The micrographs were analyzed according to the Hulsman’s method. The results demonstrated that there was a statistically significant difference in root fracture resistance among the three groups. (p = 0.043). The LSD post hoc test indicated that HC showed a higher root fracture resistance (p < 0.05) compared to both PN and PG. In conclusion, the different file systems of PN, PG, and HC instruments generate different root fracture resistance of teeth. In comparison to PN and PG, HC instruments tend to result in increased fracture resistance.

Flexible nanogenerator based on sponge-shaped piezoelectric composite

With the rapid development of Internet of Things technology, the huge network connected by sensors has blend into every corner of the society. Exploring an appropriate power source to drive these sensors is an essential demand. Piezoelectric nanogenerators (PENGs) is considered as a promising approach, which can be employed to convert mechanical energy generated by small-scale physical deformation into electrical output. Herein, we proposed a flexible PENG based on sponge-shaped piezoelectric composite. The open-circuit voltage, short-circuit current and power density of the developed device achieved 33 V, 0.7 μA and 3 mW m−2, respectively. This PENG successfully charged a 10 μF capacitor to 1.8 V in 280 s under the condition that the vibrator applies a continuous compressive force. In addition, experimental measurements to evaluate its actual output performance were well carried out. Resulting from its porous properties, this sponge-shaped PENG possesses higher flexibility and higher output capacity, which provides a promising potential in a variety of applications including energy harvesting and self-powered sensing.

Loading history changes the morphology and compressive force-induced expression of receptor activator of nuclear factor kappa B ligand/osteoprotegerin in MLO-Y4 osteocytes.

BackgroundIn this study, we investigated the effect of the mechanical loading history on the expression of receptor activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG) in MLO-Y4 osteocyte-like cells.MethodsThree hours after MLO-Y4 osteocytes were seeded, a continuous compressive force (CCF) of 31 dynes/cm2 with or without additional CCF (32 dynes/cm2) was loaded onto the osteocytes. After 36 h, the additional CCF (loading history) was removed for a recovery period of 10 h. The expression of RANKL, OPG, RANKL/OPG ratio, cell numbers, viability and morphology were time-dependently examined at 0, 3, 6 and 10 h. Then, the same additional CCF was applied again for 1 h to all osteocytes with or without the gap junction inhibitor to examine the expression of RANKL, OPG, the RANKL/OPG ratio and other genes that essential to characterize the phenotype of MLO-Y4 cells. Fluorescence recovery after photobleaching technique was also applied to test the differences of gap-junctional intercellular communications (GJIC) among MLO-Y4 cells.ResultsThe expression of RANKL and OPG by MLO-Y4 osteocytes without a loading history was dramatically decreased and increased, respectively, in response to the 1-h loading of additional weight. However, the expression of RANKL, OPG and the RANKL/OPG ratio were maintained at the same level as in the control group in the MLO-Y4 osteocytes with a loading history but without gap junction inhibitor treatment. Treatment of loading history significantly changed the capacity of GJIC and protein expression of connexin 43 (Cx43) but not the mRNA expression of Cx43. No significant difference was observed in the cell number or viability between the MLO-Y4 osteocyte-like cells with and without a loading history or among different time checkpoints during the recovery period. The cell morphology showed significant changes and was correlated with the expression of OPG, Gja1 and Dmp1 during the recovery period.ConclusionOur findings indicated that the compressive force-induced changes in the RANKL/OPG expression could be habituated within at least 11 h by 36-h CCF exposure. GJIC and cell morphology may play roles in response to loading history in MLO-Y4 osteocyte-like cells.

The expression and regulation of Wnt1 in tooth movement–initiated mechanotransduction

The Wnt signaling pathway acts as a key regulator of skeletal development and its homeostasis. However, the potential role of Wnt1 in the mechanotransduction machinery of orthodontic tooth movement-initiated bone remodeling is still unclear. Hence, this study focused on the regulatory dynamics of the Wnt1 expression in both the periodontal ligament (PDL) and osteocytes invivo and invitro. The Wnt1 expression in the orthodontically moved maxillary first molar in mice was assessed at 0, 1, and 5days, on both the compression and tension sides. Primary isolated human PDL (hPDL) fibroblasts, as well as murine long-bone osteocyte-Y4 (MLO-Y4) cells, were exposed to continuous compressive force and static tensile force. The relative quantification of immunodetection showed that orthodontic tooth movement significantly stimulated the Wnt1 expression in both the PDL and alveolar osteocytes on the tension side on day 5, whereas the expression on the compression side did not change. This increase in the Wnt1 expression, shown invivo, was also noted after the application of 12% static tensile force in isolated hPDL fibroblasts and 20% in MLO-Y4 cells. In contrast, a compressive force led to the attenuation of the Wnt1 gene expression in both hPDL fibroblasts and MLO-Y4 cells in a force-dependent manner. In the osteocyte-PDL coculture system, recombinant sclerostin attenuated Wnt1 in PDL, whereas the antisclerostin antibody upregulated its gene expression, indicating that mechanically-driven Wnt1 signaling in PDL might be regulated by osteocytic sclerostin. Our findings provide that Wnt1 signaling plays a vital role in tooth movement-initiated bone remodeling via innovative mechanotransduction approaches.

Effect of continuous compressive force on the expression of RANKL, OPG, and VEGF in osteocytes.

The present study aimed to investigate the effect of a compressive force (CF) on the expression of receptor activator of nuclear factor kappa-B ligand (RANKL), osteoprotegerin (OPG), and vascular endothelial growth factor (VEGF) in murine osteocytes (MLO-Y4) as well as animal study. After application of a CF for 1, 3, 6, and 12 h, gene and protein expression of RANKL, OPG, and VEGF in MLO-Y4 cells were determined by real-time PCR and enzyme-linked immunosorbent assay (ELISA). Furthermore, the effect of a stretch-activated (S-A) channel was examined by gadolinium (Gd3+) administration. In an animal experiment, the expression of these factors in osteocytes of alveolar bone was examined after experimental tooth movement in rats. After CF application, significant increases in RANKL, VEGF and RANKL/OPG ratio were shown. The upregulated gene and protein levels of these factors were reduced by Gd3+ administration. After tooth movement, upregulated RANKL and VEGF were imunohistochemically shown in osteocytes of alveolar bone. These findings suggest that CF application on osteocytes elevates expression of osteoclast-inducing factor and angiogenesis factor in vivo and vitro.

Research progress on migration and accretion of Nadanhada terrane

The Nadanhada terrane is the most developed area of Mesozoic marine strata in eastern China. The migration process of the Nadanhada terrane is restored from two aspects of Palaeomagnetism and biopalaeogeography. It is concluded that the subduction of the oceanic plate to the continental margin of East Asia is accompanied by the strong deformation of the sedimentary cover during the growth of the Nadanhada terrane. Under the continuous compressive force generated by the subduction of the oceanic plate to the continental margin of East Asia, accretionary wedges continue to form in the direction of oceanic basin. At the same time, large detachment planes gradually form between accretionary complex and the basement of the Jiamusi massif. The evolution history of the Nadanhada terrane can be divided into five stages: the drift stage, the accretion stage of the continental margin, the bending stage of the terrane structural line, the compression stage of the terrane and the anticlockwise rotation stage of the terrane. Bijin terrane can be seen as the extension of Nadanhada terrane in NNE direction.

Intermittent compressive force promotes osteogenic differentiation in human periodontal ligament cells by regulating the transforming growth factor-\u03b2 pathway

Mechanical force regulates periodontal ligament cell (PDL) behavior. However, different force types lead to distinct PDL responses. Here, we report that pretreatment with an intermittent compressive force (ICF), but not a continuous compressive force (CCF), promoted human PDL (hPDL) osteogenic differentiation as determined by osteogenic marker gene expression and mineral deposition in vitro. ICF-induced osterix (OSX) expression was inhibited by cycloheximide and monensin. Although CCF and ICF significantly increased extracellular adenosine triphosphate (ATP) levels, pretreatment with exogenous ATP did not affect hPDL osteogenic differentiation. Gene-expression profiling of hPDLs subjected to CCF or ICF revealed that extracellular matrix (ECM)-receptor interaction, focal adhesion, and transforming growth factor beta (TGF-β) signaling pathway genes were commonly upregulated, while calcium signaling pathway genes were downregulated in both CCF- and ICF-treated hPDLs. The TGFB1 mRNA level was significantly increased, while those of TGFB2 and TGFB3 were decreased by ICF treatment. In contrast, CCF did not modify TGFB1 expression. Inhibiting TGF-β receptor type I or adding a TGF-β1 neutralizing antibody attenuated the ICF-induced OSX expression. Exogenous TGF-β1 pretreatment promoted hPDL osteogenic marker gene expression and mineral deposition. Additionally, pretreatment with ICF in the presence of TGF-β receptor type I inhibitor attenuated the ICF-induced mineralization. In conclusion, this study reveals the effects of ICF on osteogenic differentiation in hPDLs and implicates TGF-β signaling as one of its regulatory mechanisms.

Continuous Compressive Force Induces Differentiation of Osteoclasts with High Levels of Inorganic Dissolution.

BackgroundOsteoclast precursor cells are constitutively differentiated into mature osteoclasts on bone tissues. We previously reported that the continuous stimulation of RAW264.7 precursor cells with compressive force induces the formation of multinucleated giant cells via receptor activator of nuclear factor κB (RANK)-RANK ligand (RANKL) signaling. Here, we examined the bone resorptive function of multinucleated osteoclasts induced by continuous compressive force.Material/MethodsCells were continuously stimulated with 0.3, 0.6, and 1.1 g/cm2 compressive force created by increasing the amount of the culture solution in the presence of RANKL. Actin ring organization was evaluated by fluorescence microscopy. mRNA expression of genes encoding osteoclastic bone resorption-related enzymes was examined by quantitative real-time reverse transcription-polymerase chain reaction. Mineral resorption was evaluated using calcium phosphate-coated plates.ResultsMultinucleated osteoclast-like cells with actin rings were observed for all three magnitudes of compressive force, and the area of actin rings increased as a function of the applied force. Carbonic anhydrase II expression as well as calcium elution from the calcium phosphate plate was markedly higher after stimulation with 0.6 and 1.1 g/cm2 force than 0.3 g/cm2. Matrix metalloproteinase-9 expression decreased and cathepsin K expression increased slightly by the continuous application of compressive force.ConclusionsOur study demonstrated that multinucleated osteoclast-like cells induced by the stimulation of RAW264.7 cells with continuous compressive force exhibit high dissolution of the inorganic phase of bone by upregulating carbonic anhydrase II expression and actin ring formation. These findings improve our understanding of the role of mechanical load in bone remodeling.

Suture compression induced midpalatal suture chondrocyte apoptosis with increased caspase-3, caspase-9, Bad, Bak, Bax and Bid expression

ObjectivePrevious studies found bone resorption and chondrocytes loss in mouse models of mid-palatal suture when given continuous compressive force, although chondrocytes response remained unknown. Herein, we design this study to determine how continuous compression force induces chondrocytes apoptosis. MethodsThirty C57BL/6 male mice (aged 6 weeks) were randomly assigned into controls (not ligated to a spring), blank controls (ligated with no compression) and the compression group (ligated with 20-g compression). After 4 d, palatal tissues were sampled and stained by TB and safranin-O. Tunel staining measured the percentage of apoptotic chondrocytes, and immunohistochemistry was performed to label apoptosis-associated proteins (e.g., Bcl-2, Bcl-xl, Bax, Bak, Bid, Bad, caspase-3, caspase-8 and caspase-9). Intergroup comparison was made by the rank sum test, and P < 0.05 was defined as statistical significance. ResultsAfter 7d of induction, TB and safranin-O staining revealed that the cartilage area in the compression group was significantly decreased, while the control group remained largely unaltered. Tunel staining showed that apoptotic cell numbers in the mid-palatal suture were significantly higher than the control group. Immunohistochemistry showed that mice in the compression group had significantly increased expression of caspase-3, caspase-9, Bad, Bak, Bax and Bid; However, caspase-8 remained unaltered. No expression of Bcl-2 and Bcl-xl was detected. ConclusionsContinuous compression force induces chondrocytes apoptosis in the mid-palatal suture. This process might be associated with the mitochondrial pathway.

A new intramedullary sustained dynamic compression nail for the treatment of long bone fractures: a biomechanical study.

We developed a new intramedullary interlocking nail (sustained dynamic compressive nail; SDCN) which can sustain a continuous dynamic compressive force on the fracture edges to overcome implant failure, screw loosening and nonunion complications encountered in the traditionally used static intramedullary nailing (SIMN). Six pairs of composite femurs were fixed with SIMN and SDCN. The axial compression, bending, torsional stiffness, and strain values were analyzed. The mean axial compression stiffness values were 427.1 N/mm for the SDCN and 217.8 N/mm for SIMN, indicating a statistically significant difference (p=0.006). The mean stiffness values of rotation were 1.42 Nm/° for the SDCN and 0.89 Nm/° for SIMN. Anteroposterior bending tests were carried out. The mean results of stiffness were measured as 218 N/mm for the SDCN and 182.7 N/mm for the SIMN. The mean strain measurements in compression were 2454.5 µ-strain for the SDCN and 1123.8 µ-strain for the SIMN. Biomechanically, the intramedullary SDCN is more stable than the SIMN system and it provides good abutment of the nail to the bone. Also, SDCN increases the stability by producing continuous compression and increasing the contact pressure of the fracture ends.

Effect of compressive force on human osteoblast-like cells and bone remodelling: An in vitro study

ObjectiveThe aim of this study was to determine the effect of continuous compressive force (CF) on expression by human alveolar bone-derived osteoblasts (HOBs) of some specific molecules involved in bone remodelling. DesignHOBs were cultured with or without CF (control, 2.0, 4.0gcm−2) for 1, 3 and 7 days. Expression of alkaline phosphatase (ALP), type I collagen (Col I), osteopontin (OPN), osteocalcin (OCN), transcription factor Runx2, receptor activator of nuclear factor κB ligand (RANKL), osteoprotegerin (OPG) and prostaglandin E2 (PGE2) was analysed by real-time-polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA) and/or immunostaining. ResultsThe results revealed that CF upregulated ALP and Col I expression at both messenger RNA (mRNA) and protein levels but did not affect expression of OPN and OCN mRNA. Runx2 mRNA was inhibited by CF, which also altered the expression of molecules involved in osteoclastogenesis, by enhancing RANKL expression and suppressing OPG expression. At 4.0gcm−2 of CF, the expression of RANKL and PGE2 was significantly upregulated. ConclusionThe results suggest that initial application of CF on HOBs can simultaneously affect expression of markers related to both osteogenesis and osteoclastogenesis.

The fracture resistance of teeth restored with different adhesive dowels

Objective. Fiber-reinforced composite dowels are suggested to be a better alternative to metal dowels. This in vitro study evaluated the fracture resistance and fracture modes of teeth restored with nine different dowel systems. Materials and methods. Ninety mandibular pre-molar teeth were decoronated and nine homogenous groups were composed. Root canal and dowel canal preparations were made and nine different dowel systems were used to fabricate restorations. Core build-ups were made with a composite resin core material. Specimens were mounted in acrylic resin blocks and continuous compressive force was applied until fracture occurred. Fracture resistance and fracture mode data were collected. One-sample Kolmogorov-Smirnov and one-way ANOVA tests were performed for the fracture resistance data of the groups. Results. There were no significant differences among the fracture resistances of the groups. All specimens of the pre-fabricated stainless steel dowel group fractured catastrophically. However, even in the worst-case, five specimens of the fiber-reinforced composite groups had favorable fracture modes. Conclusions. The teeth restored with fiber reinforced composite dowels were as resistant to fracture as teeth restored with stainless steel dowels. Fracture modes of teeth restored with fiber reinforced composite dowels were more advantageous than teeth restored with pre-fabricated stainless steel dowels.

Initial responses of osteoblasts derived from human alveolar bone to various compressive forces

Mechanical stress generated by orthodontic force is recognized as a major factor in the modulation of alveolar bone remodeling. During this process, osteoblasts play a crucial role, not only by participating in bone formation but also by promoting osteoclastogenesis. The aim of this study was to investigate how continuous compressive force (CF) affects human primary osteoblasts (HOBs) in terms of cell proliferation, apoptosis, and expression of interleukin-6 (IL-6) and chemokine CXC ligand 8 (CXCL8). Human primary osteoblasts, isolated from human mandibular bone pieces, were cultured with or without CF (1-4 g cm(-2)) for up to 72 h. Cell viability and proliferation were evaluated using the MTT assay. RT-PCR was used to determine the levels of expression of KI67 (a proliferation marker), BAX (a pro-apoptotic marker), BCL2 (an apoptotic inhibitor), IL6, and CXCL8 mRNAs, while a multiplexed bead immunoassay was used to measure the release of IL-6 and CXCL8. The results revealed that CF decreased cell viability and proliferation in a time- and force-dependent manner. After applying CF for 24 h, the mRNA expression of KI67 was markedly inhibited, whereas the mRNA expression of BAX and BCL2 was unaltered. In addition, CF enhanced the levels of IL6 and CXCL8 mRNAs in a force-dependent manner, whereas the levels of the corresponding proteins were reduced in the compressed HOBs.

Alterations in intermediate filaments expression in disc cells from the rat temporomandibular joint following exposure to continuous compressive force

The articular disc in the temporomandibular joint (TMJ) that serves in load relief and stabilizing in jaw movements is a dense collagenous tissue consisting of extracellular matrices and disc cells. The various morphological configurations of the disc cells have given us diverse names, such as fibroblasts, chondrocyte-like cells and fibrochondrocytes; however, the characteristics of these cells have remained to be elucidated in detail. The disc cells have been reported to exhibit heterogeneous immunoreaction patterns for intermediate filaments including glial fibrillary acidic protein (GFAP), nestin and vimentin in the adult rat TMJ. Because these intermediate filaments accumulate in the disc cells as tooth eruption proceeds during postnatal development, it might be surmised that the expression of these intermediate filaments in the disc cells closely relates to mechanical stress. The present study was therefore undertaken to examine the effect of a continuous compressive force on the immunoexpression of these intermediate filaments and an additional intermediate filament - muscle-specific desmin - in the disc cells of the TMJ disc using a rat experimental model. The rats wore an appliance that exerts a continuous compressive load on the TMJ. The experimental period with the appliance was 5 days as determined by previous studies, after which some experimental animals were allowed to survive another 5 days after removal of the appliance. Histological observations demonstrated that the compressive force provoked a remarkable acellular region and a decrease in the thickness of the condylar cartilage of the mandible, and a sparse collagen fiber distribution in the articular disc. The articular disc showed a significant increase in the number of desmin-positive cells as compared with the controls. In contrast, immunopositive cells for GFAP, nestin and vimentin remained unchanged in number as well as intensity. At 5 days after removal of the appliance, both the disc and cartilage exhibited immunohistological and histological features in a recovery process. These findings indicate that the mature articular cells are capable of producing desmin instead of the other intermediate filaments against mechanical stress. The desmin-positive disc cells lacked α-smooth muscle actin (α-SMA) in this study, even though desmin usually co-exists with α-SMA in the vascular smooth muscle cells or pericytes. Because the precursor of a pericyte has such an immunoexpression pattern during angiogenesis, there is a further possibility that the formation of new vessels commenced in response to the extraordinary compressive force.

Mechanisms involved in regulation of osteoclastic differentiation by mechanical stress-loaded osteoblasts

Mechanical stress is known to be important for regulation of bone turnover, though the detailed mechanisms are not fully understood. In the present study, we examined the effect of mechanical stress on osteoblasts using a novel compression model. Mouse osteoblastic MC3T3-E1 cells were embedded in three-dimensional (3D) gels and cultured with continuous compressive force (0-10.0 g/cm(2)) for 48 h, and the conditioned medium were collected. RAW264.7 cells were then incubated with the conditioned medium for various times in the presence of receptor activator of nuclear factor-κB ligand (RANKL). Conditioned medium was found to inhibit the differentiation of RAW264.7 cells into osteoclasts induced by RANKL via down-regulation of the expression of tumor necrosis factor receptor-associated factor 6 (TRAF6), phosphorylation of IκBα, and nuclear translocation of p50 and p65. Interestingly, the conditioned medium also had a high level of binding activity to RANKL and blocked the binding of RANK to RANKL. Furthermore, the binding activity of conditioned medium to RANKL was reduced when the 3D gel was supplemented with KN-93, an inhibitor of non-canonical Wnt/Ca(2+) pathway. In addition, expression level of osteoprotegerin (OPG) mRNA was increased in time- and force-dependent manners, and remarkably suppressed by KN-93. These results indicate that osteoblastic cells subjected to mechanical stress produce OPG, which binds to RANKL. Furthermore, this binding activity strongly inhibited osteoclastogenesis through suppression of TRAF6 and the nuclear factor-kappa B (NF-κB) signaling pathway, suggesting that enhancement of OPG expression induced by mechanical stress is dependent on non-canonical Wnt/Ca(2+) pathway.

Compressive force stimulates the gene expression of IL-17s and their receptors in MC3T3-E1 cells

During orthodontic tooth movement, cytokines released from periodontal ligament fibroblasts and alveolar bone osteoblasts can alter the process of bone remodeling. Recently, interleukin-17 (IL-17) was found to stimulate osteoclastic resorption through osteoblasts by inducing receptor activator of nuclear factor κB ligand (RANKL) expression. However, the relationship between mechanical stress and IL-17 production by osteoblasts is not clear. Therefore, we examined the effect of compressive force on the expressions of IL-17A, IL-17B, IL-17C, IL-17D, IL-17E, IL-17F, and their receptors (IL-17RA, IL-17RB, IL-17RC, IL-17RD, and IL‐17RE) using MC3T3-E1 cells as osteoblast-like cells. We also examined the effect of IL‐17A on the expression of IL-17Rs, RANKL, macrophage colony-stimulating factor (M-CSF), and osteoprotegerin (OPG). The cells were cultured with or without continuous compressive force (1.0 and 2.0 g/cm2) for up to 24 hr. The cells were also cultured with or without IL-17A (0.1, 1.0, or 10 ng/ml) for up to 72 hr. The mRNA expressions of IL‐17s and their receptors were estimated by real-time polymerase chain reaction. The expression levels of IL‐17s and their receptors increased depending on the compressive force. The addition of IL-17A increased the expression of IL-17RA, IL-17RB, IL-17RC, IL-17RE, RANKL, and M-CSF, whereas it decreased OPG expression. These results indicate that compressive force induces the expression of IL-17s and their receptors in osteoblast-like cells and that IL-17s and their receptors produced in response to compressive force may affect osteoclastogenesis through the expression of RANKL, M-CSF, and OPG.

Effect of compressive force on the expression of inflammatory cytokines and their receptors in osteoblastic Saos-2 cells

Objective In orthodontic tooth movement, some cytokines released from periodontal ligament fibroblasts and alveolar bone osteoblasts on the pressure side can alter the normal processes of bone remodelling, resulting in physiological bone resorption. We examined the effect of compressive force and interleukin (IL)-1 type I receptor antagonist (IL-1ra) on the expression of inflammatory cytokines that promote osteoclast formation, as well as on their receptors, in osteoblastic Saos-2 cells. Design The cells were cultured in Dulbecco's modified Eagle medium containing 10% fetal bovine serum with or without continuous compressive force (0.5–3.0 g/cm 2) and/or IL-1ra for up to 24 h. The gene expression levels of the cytokines and their receptors were estimated by determining mRNA levels using real-time PCR; the protein levels were determined using ELISA or immunohistochemical staining. Results The expression of IL-1β, IL-1 receptor, IL-6, IL-6 receptor, IL-8 receptor, IL-11 and tumor necrosis factor-α (TNFα) increased depending on the strength and duration of the compressive force, whereas the expression of IL-8, IL-11 receptor and TNFα receptor did not change with the application of compressive force. The expression of cytokines and their receptors produced by 3.0 g/cm 2 of compressive force decreased with the simultaneous addition of IL-1ra and the decrease was remarkable in IL-8 receptor, IL-11 and TNFα. Conclusion These results indicate that mechanical stress induces the production of inflammatory cytokines and their receptors in osteoblasts and the phenomenon is enhanced by the autocrine action of IL-1β, which is increased in amount by mechanical stress.

Compressive force stimulates the expression of osteogenesis-related transcription factors in ROS 17/2.8 cells

Objective To determine how compressive force affects the expression of osteogenesis-related transcription factors in osteoblasts. Design Cells of ROS 17/2.8, a typical osteoblastic cell line, were cultured with or without continuous compressive force (0.5–2.0 g/cm 2). Expression of mRNA encoding the osteogenesis-related transcription factors Runx2, Osterix, Msx2, Dlx5 and AJ18 was measured using real-time polymerase chain reaction. Protein expression of these transcription factors was determined by Western blotting. Results A compressive force of 1.0 g/cm 2 significantly increased mRNA and protein expression of Runx2, Osterix, Msx2 and Dlx5, which are critical for osteoblast differentiation. In contrast, mRNA and protein expression of AJ18, which downregulates osteoblast differentiation, were decreased with 1.0 g/cm 2 of compressive force. Conclusions A compressive force of 1.0 g/cm 2, which was considered optimal for bone formation under the present experimental conditions, stimulates osteoblastic differentiation via the modulation of osteogenesis-related transcription factors.

Mechanical Stress Induces Osteopontin Expression in Human Periodontal Ligament Cells Through Rho Kinase

Mechanical stress such as orthodontic forces can produce mechanical damage and inflammatory reaction in the periodontium. Osteopontin (OPN) is a multifunctional cytokine that has been correlated with periodontal disease progression. Because the periodontal ligament (PDL) can be affected by stress and PDL cells are involved in periodontal destruction and remodeling, we aimed to study the influence of mechanical stress on the expression and regulation of OPN in human PDL (HPDL) cells. The mechanical stress was generated by continuous compressive force, and the expression of OPN was examined by reverse transcription-polymerase chain reaction and Western analysis. The application of inhibitors was used to examine the mechanism involved. Both mRNA and protein expression of OPN significantly increased in a force-dependent manner. Increase of receptor activator of nuclear factor-kappa B ligand (RANKL) was also observed. Interestingly, application of indomethacin could abolish the induction of RANKL but not that of OPN, suggesting the cyclooxygenase-independent mechanism for stress-induced OPN expression. In addition, the upregulation of OPN was diminished by Rho kinase inhibitor but not by cytochalasin B. Mechanical stress affects OPN expression in HPDL cells through the Rho kinase pathway. Because OPN participates in bone resorption and remodeling induced by mechanical and biologic signals, these results suggest the significance of stress-induced OPN in HPDL cells in alveolar bone resorption and remodeling.

Differential Gene Expression of Periodontal Ligament Cells After Loading of Static Compressive Force

Compressive force is an important mechanical stimulus on the periodontal ligament (PDL) and is closely related to therapeutic tooth movement. In this study, early or late response genes related to the compressive stress in PDL cells were evaluated. Particularly, the expression of interleukin (IL)-6, IL-8, and alkaline phosphatase (ALP) was studied. The primary cultured cells from PDL were grown in a three-dimensional collagen gel, and received a continuous static compressive force (1.76 g/cm(2)). The expressed genes were screened by cDNA microarray assays for 2 or 12 hours after the initiation of the mechanical force application. The genes of interest that showed significant changes in expression in the cDNA microarray assay were analyzed further by quantitative reverse transcriptase polymerase chain reaction (RT-PCR), enzyme-linked immunoabsorbent assays (ELISA), and ALP assays. ALP, IL-6, and IL-8 were selected among the genes that significantly changed expression (/M/ >0.7) and subsequently were confirmed by quantitative RT-PCR. The secreted protein concentrations for IL-6, IL-8, and ALP activity were measured at 72 hours after application of continuous static compressive force. The protein level of IL-6 was significantly increased at 72 hours (P <0.001), but there was no significant change in IL-8 (P >0.05). ALP activity was decreased approximately 41.5% compared to the control (P = 0.015). Considering that IL-6 is a potent osteoclast activator and the compressive side of PDL during orthodontic tooth movement shows the resorption of calcified tissue, the changed expression of IL-6 and ALP in response to the static compressive force in PDL cells may contribute to the orthodontic tooth movement or alveolar bone remodeling.