Periodontal Tissue Remodeling Research Articles

Assessment of tumor necrosis factor alpha (TNFα) and interleukin 6 level in gingival crevicular fluid during orthodontic tooth movement: a randomized split-mouth clinical trial

BackgroundOrthodontic tooth movement (OTM) is based on induction of periodontal tissue remodeling. Mechanical tooth stimulation results in the release of pro-inflammatory mediators. These mediators cause bone resorption and deposition at the pressure and tension sites and play a role in OTM. Thus, assessment of chemical biomarkers can help determine the exact amount of load and its duration of application required for each tooth and select the most efficient treatment plan with minimal complications.ObjectiveThis study aimed to determine the level of tumor necrosis factor alpha (TNFα) and interleukin 6 (IL-6) in gingival crevicular fluid (GCF) during OTM.MethodsThis randomized split-mouth clinical trial (parallel) was performed on 10 patients who were presenting to the Orthodontic Department of Qazvin University of Medical Sciences from November 2015 to June 2016. A canine tooth was randomly selected as the study group and subjected to distalization force while the contralateral canine tooth served as control. Using paper strip, GCF was collected from the study and control teeth prior to orthodontic force application (T0), one hour after (T1) and 28 days after force application (T2), then the level of TNFα and IL-6 was measured using ELISA. Data were analyzed using SPSS version 20 via Friedman and Wilcoxon test, and considering the significance level at p<0.05.ResultsThe level of TNFα (p=0.0799) and IL-6 (p=0.678) at both sides of study teeth was higher than both side of control teeth at T1. Also, the level of IL-6 (p=0.515) and TNFα (p=0.508) were higher at the tension side compared to the pressure side; but the difference was not statistically significant.ConclusionDue to the free circulation of GCF in gingival sulcus, the level of mediators in the GCF collected from the mesial and distal areas alone cannot serve as a suitable index for assessment of activity at the tension and pressure sites.Trial registrationThe trial was registered at the Iranian Registry of Clinical Trials with the IRCT ID: IRCT2017030632903N2.FundingThe present study was supported by a grant from the Research Council, Qazvin University of Medical Sciences, Qazvin, Iran (thesis no.: 40).

Effects of LL-37 on Gingival Fibroblasts: A Role in Periodontal Tissue Remodeling?

Mounting evidence suggests that the host defence peptide, LL-37, plays a role in both inflammation and in wound healing; however, the role of this peptide in the remodeling and maintenance of oral tissues is not yet fully understood. Fibroblasts are the most abundant cell type within the periodontal tissues, and gingival fibroblasts play an important role in maintaining and repairing the gingival tissues which are constantly exposed to external insults. In this study we examined the direct effects of LL-37 treatment on gingival fibroblasts and found that LL-37 significantly increased secretion of both interleukin 8 (IL-8) and IL-6 from these cells. LL-37 tended to decrease matrix metalloproteinase (MMP) activity in gingival fibroblasts, but this decrease did not reach statistical significance. LL-37 significantly increased tissue inhibitor of metalloproteinase-1 (TIMP-1) production by gingival fibroblasts, but had no significant effect on TIMP-2 levels. LL-37 was also shown to significantly increase production of basic fibroblast growth factor (bFGF), hepatocyte growth factor (HGF), and keratinocyte growth factor (KGF) in gingival fibroblasts. Taken together, these results suggest an important role for the host defence peptide, LL-37, in modulating the fibroblast response to remodeling in periodontal tissues.

Expression pattern of YAP and TAZ during orthodontic tooth movement in rats.

Orthodontic tooth movement (OTM) is a periodontal tissue remodeling and regeneration process that is caused by bio-mechanical stimulation. This mechanical-chemical transduction process involves a variety of biological factors and signaling pathways. It has been shown that the Hippo-YAP/TAZ signaling pathway plays a pivotal role in the mechanical-chemical signal transduction process. Moreover, YAP and TAZ proteins interact with RUNX family proteins via different mechanisms. To explore the regulation of the Hippo signaling pathway during periodontal tissue remodeling, we examined the upper first molar OTM model in rats. We examined YAP, TAZ and RUNX2 expression at 12 hours, 24 hours, 2 days (2d), 4 days, 7 days (7d) and 14 days (14d) after force application. Haemotoxylin and eosin staining, immunohistochemical staining and western blot analysis were used to examine the expression level and localization of these proteins. We found that YAP, TAZ and RUNX2 expression started increasing at 2d, YAP and TAZ expression was proportional to the orthodontic force applied until peaking at 7d, and at 14d the expression started to decrease. YAP and TAZ were observed in osteocytes, bone matrix and periodontal ligament cells during OTM. Furthermore, using double labeling immunofluorescence staining, we found that the increase in TAZ expression was associated with RUNX2 expression, however, YAP and RUNX2 showed different expression patterns. These results suggest that the Hippo-YAP/TAZ signaling pathway participates in periodontal tissue remodeling through various mechanisms; TAZ may adjust bone tissue remodeling through RUNX2 during OTM, while YAP may regulate periodontal cell proliferation and differentiation.

Ipriflavone promotes proliferation and osteogenic differentiation of periodontal ligament cells by activating GPR30/PI3K/AKT signaling pathway.

ObjectivesThis study was performed to investigate the effects and mechanism of ipriflavone (IP) on the proliferation and osteoblastic differentiation of periodontal ligament cells in vitro and periodontal tissue remodeling following orthodontic tooth movement (OTM) in vivo.Materials and methodsHuman periodontal ligament cells (hPDLCs) were cultured in vitro and cell counting kit-8, alkaline phosphatase (ALP) activity assay, plate clone formation assay, and alizarin red staining were used to test proliferation and osteogenic differentiation of hPDLCs. What is more, the expression of ALP, Runx2, and GPR30 was examined by real-time polymerase chain reaction and Western blot. To find out if PI3K/AKT signaling pathway was involved in the process, AKT and p-AKT were examined by Western blot. LY294002 (PI3K signaling pathway inhibitor) and small interfering RNA targeting GPR30 mRNA (siGPR30) were used to verify the function of GPR30-mediated PI3K/AKT pathway in this process. Twenty-four male Wistar rats were randomized into 2 groups, the control group with force application and the IP group with force application plus IP. Morphological changes in the periodontal tissue between roots of teeth were investigated using hematoxylin and eosin (HE) staining and bone morphogenetic protein-2 was detected to assess bone remodeling by immunohistochemical staining.ResultsIn vitro, 10−7 M IP was selected significantly promoting proliferation, ALP activity, colony forming efficiency, and mineral deposition (P<0.05) on hPDLCs. Gene expressions of ALP, Runx2, GPR30, and p-AKT were all upregulated than the control group (P<0.05). According to the mechanism, promotion of ALP and Runx2 interdicted by LY294002 and siGPR30 reduced the activation of PI3K/AKT signaling pathway. In addition, HE staining and immunohistochemical staining results showed that the IP group had more new bone formation in the periodontal tissue compared to the control group in vivo.ConclusionIP can promote the expression of ALP and Runx2 which was probably related to the GPR30-mediated PI3K/AKT signaling pathway. Moreover, IP coordination seemed to have the potential to prevent relapsing following OTM.

Expression and regulation of the ERK1/2 and p38 MAPK signaling pathways in periodontal tissue remodeling of orthodontic tooth movement.

The present study aimed to investigate the expression and regulation of extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase (MAPK) signaling pathways in periodontal tissue remodeling of orthodontic tooth movement. Sprague Dawley rats with orthodontic tooth movement were generated. After tension stress for 1, 3, 5, 7 and 14 days, the protein and mRNA expression levels of ERK1/2 and p38 in periodontal tissue were determined by western blotting and reverse transcription-quantitative polymerase chain reaction (RT-qPCR), respectively. Primary human periodontal ligament cells (hPDLCs) were separated and characterized. Following exposure to centrifugal force for 1, 2, 6, 8 and 12 h, the protein expression levels of ERK1/2 and p38 MAPK, and the mRNA expression levels of ERK1/2, p38 and osteogenesis associated-genes [including alkaline phosphatase (ALP), osteopontin (OPN), collagen I (Col I), osteocalcin (OCN) and bone sialoprotein (BSP)] were measured. The protein expression levels of ERK1/2 and p38 MAPK in periodontal tissue and hPDLCs treated with stress were similar to those in the control groups. However, compared with the control, the phosphorylation and mRNA expression levels of the genes encoding ERK1/2 and p38 MAPK in orthodontic periodontal tissue and forced hPDLCs were elevated. These increases reached a peak at 5 days for orthodontic periodontal tissue and at 6 h for forced hPDLCs. In forced hPDLCs, the mRNA expression levels of ALP, OPN, Col I, OCN and BSP were notably and continuously upregulated in a time-dependent manner. In addition, hPDLCs were treated with the ERK1/2 inhibitor, PD098059, and the p38 MAPK inhibitor, SB203580, and the mRNA expression levels of the osteogenesis associated-genes were then measured using RT-qPCR. Following treatment with the ERK1/2 inhibitor and p38 MAPK inhibitor, the mRNA expression levels of ALP, OPN, Col I, OCN and BSP were significantly downregulated. In conclusion, ERK1/2 and p38 MAPK signaling pathways may be positively and closely associated with periodontal tissue remodeling of orthodontic tooth movement.

Hydrogen sulfide regulates bone remodeling and promotes orthodontic tooth movement.

Hydrogen sulfide (H2S) is a gas signaling molecule that has multiple influences on physiological and pathological processes in the mammalian body, including vasodilation, neurotransmission, inflammation, hypoxia sensing and bone remodeling. Our previous studies suggested that H2S might be involved in the periodontal tissue remodeling during the orthodontic tooth movement (OTM) via increasing periodontal ligament cell differentiation, tissue mineralization, bone formation and collagen synthesis. The aim of the present study was to investigate the effects of H2S on alveolar bone remodeling that is associated with tooth movement. Experiments were performed in an OTM mouse model. Sodium hydrosulfide (NaHS), which is a donor of H2S and DL-propargylglycine (PAG) and a cystathionine-γ-lyase (CSE) inhibitor, which could also decrease H2S expression, were administered intraperitoneally and respectively. A total of 60 male C57BL6/J mice were divided into 4 groups; Control, NaHS, PAG and combination (PAG+NaHS). The rate of OTM and the bone mineral density (BMD) of alveolar bone were scanned and measured by micro-computed tomography (micro-CT). The number of osteoclasts and expression of the tumor necrosis factor ligand superfamily member-11 (RANKL), alkaline phosphatase (ALP), osteocalcin (OCN) and osteoprotegerin (OPG) in alveolar bone were accessed to evaluate the osteoclastic activity and osteogenesis with histochemistry of tartrate-resistant acid phosphatase staining, immunohistochemistry and reverse transcription-quantitative polymerase chain reaction. In the alveolar bone, NaHS increased the OTM and decreased the BMD, respectively. PAG significantly decrease OTM and increased the BMD. NaHS combined with PAG rescued the PAG-induced changes in the OTM and the BMD. Additionally, the number of osteoclasts, the expression of RANKL, ALP, OCN and the ratio of RANKL/OPG were significantly up-regulated in the NaHS group. In contrast, PAG down-regulated the number of osteoclasts, the expression of RANKL, ALP, OCN and the ratio of RANKL/OPG. These findings suggested that H2S might facilitate the OTM by enhancing alveolar bone remodeling as a result of an increased osteoclastic activity and osteogenesis.

Efficacy of horse chestnut leaf extract ALH-L1005 as a matrix metalloproteinase inhibitor in ligature-induced periodontitis in canine model.

Matrix metalloproteinases (MMPs) are the main proteinases associated with periodontal tissue destruction and remodeling. Therefore, inhibition of host-derived MMPs has a key role in the prevention and reduction of periodontitis progression. Horse chestnut (Aesculus hippocastanum L.) extracts have been used as treatments for inflammatory disease, traditionally. This study assessed the clinical effect as a MMP inhibitor of horse chestnut leaf extract ALH-L1005 on periodontitis. ALH-L1005 was obtained from horse chestnut leaf and its MMP inhibitory activities estimated. Periodontitis was induced in beagles assigned to 4 groups and medicated for 6 weeks: low dose test (LT; ALH-L1005, 100 mg/kg/day), high dose test (HT; ALH-L1005, 200 mg/kg/day), positive control (PC; doxycycline, 10 mg/kg/day), or negative control (NC; placebo). Before and after administration, clinical indices of the teeth and MMP quantity in gingival tissues using zymography were measured. Clinical conditions of the LT, HT, and PC groups were significantly improved after 6 weeks. In zymographic evaluations, gelatinolytic and caseinolytic activities were suppressed in LT, HT, and PC groups but not in the NC group. The results suggest that ALH-L1005 could be an effective agent for clinical prevention and treatment of periodontitis by inhibiting the gelatinase and collagenase activities, which can detach periodontal ligaments from alveolar bone.

Effects of soy isoflavone genistein on orthodontic tooth movement in guinea pigs

Background: Osteoblast and osteoclast are the important factor in periodontal tissue remodeling for the orthodontic treatment success. Resorption process takes place in compression area by osteoclast and apposition in the tension area by osteoblast. In general hormone condition and age affect remodeling process. Estrogen has a high contribution in remodelling process and decreased in elderly individual such as menopausal women. Soybean contains isoflavone genistein which has similar structure and activity to estrogen. Many researchers indicate that isoflavone genistein not only has an inhibitor effect in osteoporosis but also has estrogenic and antiestrogenic effect as well. Purpose: The study aimed to investigate the effect of soybean isoflavone genistein administration on osteoblast and osteoclast cells number in orthodontic tooth movement of young and old guinea pigs. Method: The research was quasi-experimental study with post test only with control design. The experimental animals were 24 male guinea pigs that divided into: young guinea pigs (±4 months old) and old guinea pigs (±2.5 years old). Each group was divided into 4 subgroups for receiving the treatment namely; control, orthodontic treatment, genistein treatment and orthodontic+genistein treatment. All of the subjects were sacrificed at day 7 and the specimens were histologically analyzed using tartrate resistance acid phosphatase (TRAP) and hematoxylin eosin (HE) staining and observed using microscope that connected to obtilab and an image raster program. Result: U Mann-Whitney statistical analysis showed there were significant differences in osteoblast cell numbers; between orthodontic treatment and orthodontic+genistein treatment in the old guinea pigs (p=0.004); between orthodontic treatment in the young guinea pig and orthodontic+genistein treatment in the old guinea pig (p=0.016); between orthodontics treatment and orthodontic+genistein treatment in the young guinea pigs (p=0.025). U Mann-Whitney statistical analysis showed there were significant differences in osteoclast cell numbers: between the orthodontic treatment in the old guinea pig and orthodontics+genistein treatment in the young guinea pigs (p=0.007); between orthodontic treatment group in the young guinea pigs and orthodontics+genistein treatment in the old guinea pigs; between orthodontic treatment and orthodontic+ genistein treatment in the young guinea pigs (p=0.007). All groups administered by genistein the numbers of osteoblast in the surrounding of the tension sites increased, while in the surrounding of the compression sites had less osteoclasts; even, there were no osteoclasts found in some samples. Conclusion: Soybean isoflavone genistein administration on orthodontic tooth movement increased osteoblast numbers in the tension sides and decreased osteoclast numbers in the compression sides.

Effects of hydrogen sulfide on the expression of alkaline phosphatase, osteocalcin and collagen type I in human periodontal ligament cells induced by tension force stimulation.

Periodontal ligament cells (PDLCs) are important in homeostasis and remodeling in the mechanically‑stimulated periodontium. The aim of the present study was to investigate the effects of hydrogen sulfide (H2S) on periodontal tissue remodeling by examining the mRNA and protein expression levels of alkaline phosphatase (ALP), osteocalcin (OCN) and collagen type I (COL‑1) in human (h)PDLCs induced by tension force application. Cultured hPDLCs were treated with H2S for 24h, followed by application of a tension force for 1, 3 and 6h. Cell proliferation and apoptosis were determined using a Cell Counting Kit 8 assay and flow cytometric analysis, respectively. The mRNA expression levels of ALP, OCN and COL‑1 were quantified using reverse transcription‑quantitative polymerase chain reaction analysis, and western blot analysis was used to detect the protein levels of ALP, OCN and COL‑1. The results demonstrated that the mRNA and protein expression levels of ALP, OCN and COL‑1 increased with H2S treatment in a concentration‑dependent manner, which was enhanced by the application of tension force in a relatively short period of time. These findings suggested that H2S may be important in periodontal tissue remodeling during orthodontic tooth movement via increasing hPDLC differentiation, tissue mineralization, bone formation and collagen synthesis.

Hydrogen sulfide promotes osteogenic differentiation of human periodontal ligament cells via p38-MAPK signaling pathway under proper tension stimulation

ObjectiveHydrogen sulfide (H2S), one of endogenous gaseous signalling molecules, can be induced by mechanical force stimulation on human periodontal ligament cells (hPDLCs). Little is known about the mechanism of H2S on the osteogenic differentiation although previous studies have demonstrated that H2S stimulated or inhibited osteoclastic differentiation. The present study was to investigate whether H2S played a regulatory role in osteogenic differentiation of the periodontal tissue remodeling and the involvement of mitogen-activated protein kinase (MAPK) signaling in this process. DesignhPDLCs were applied with cycle tension force for 6h, 12h, 24h or 48h to select the optimal time for force application. Then the effects of H2S on hPDLCs osteogenic differentiation were investigated. Signal-regulated kinases p38-MAPK and ERK activities with H2S treatment were measured. Finally, specific MAPK inhibitors SB203580 and U0126 were employed to investigate the involvement of the two kinases in hPDLCs osteogenic differentiation with H2S pre-treatment. ResultsTension stimulation promoted mRNA and protein expression of ALP, OCN and Runx2 in hPDLCs. The expression of ALP, OCN and Runx2 increased in a concentration-dependent manner with H2S pre-treatment. Importantly, p38-MAPK and ERK were activated in different ways upon induction by H2S. Furthermore, expression of Runx2, ALP and OCN, the osteogenic regulators, was reversed by SB203580 and U0126. ConclusionsH2S could promote osteogenic differentiation of hPDLCs by activating p38-MAPK and ERK signaling pathways.

Mechanical stress regulates osteogenic differentiation and RANKL/OPG ratio in periodontal ligament stem cells by the Wnt/β-catenin pathway

BackgroundThe balance between osteoblastic and osteoclastic activity is critical in orthodontic tooth movement (OTM). Mesenchymal stem cells (MSCs) play an important role in maintaining bone homeostasis, and periodontal ligament stem cells (PDLSCs) are tissue-specific MSCs in the periodontal ligament. However, whether PDLSCs are required for periodontal tissue remodeling during OTM is not fully understood. MethodsHere, we used PDGFRα and Nestin to trace PDLSCs during OTM in rats. We treat human PDLSCs with 100kpa static pressure for 1h or 12h in vitro, and examined the phenotypic changes and expression of RANKL and OPG in these cells. ResultsIn vivo, we found that positive signals of PDGFRα and Nestin in the PDL gradually increased and then decreased on the pressure side to which pressure was applied. In vitro, the osteogenic differentiation of PDLSCs was significantly increased after force treatment for 1h relative to 12h. In contrast, the expression ratio of RANKL/OPG was reduced at 1h and significantly increased at 12h. Furthermore, we found that the Wnt/β-catenin pathway was dynamically activated in the PDL and in PDLSCs after mechanical stimulation. Importantly, the canonical Wnt pathway inhibitor DKK1 blocked the osteogenesis effect and rescued the ratio of RANKL/OPG in PDLSCs under force treatment for 1h. ConclusionsOur findings reveal that PDLSCs participate in OTM and that the Wnt/β-catenin pathway maintains bone homeostasis during tooth movement by regulating the balance between osteoblastic and osteoclastic activity. General significanceWe describe a novel potential mechanism related to tooth movement.

The effect of calcitriol on high mobility group box 1 expression in periodontal ligament cells during orthodontic tooth movement in rats.

High mobility group box 1 (HMGB1) is a late inflammatory cytokine that plays an important role in periodontal tissue remodeling during orthodontic tooth movement. Calcitriol (1,25-dihydroxyvitamin D3 [1α,25 (OH)2D3]) is a systemic calcium-regulating hormone shown to downregulate expression of multiple proinflammatory cytokines in human periodontal ligament cells in response to orthodontic force. The purpose of this study was to investigate the effect of 1α,25(OH)2D3 on the expression of HMGB1 in periodontal ligament (PDL) cells during orthodontic tooth movement. Seven-week-old male Wistar rats were used for experimentation. Tooth movement was assessed using a nickel-titanium coil spring to apply mechanical loading to the tooth for 5 days. This was followed by administration of either 1α,25(OH)2D3 or normal saline by gavage every other day for up to 28 days. Immunohistochemistry was used to analyze the expression of tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6 and HMGB1. After discontinuation of orthodontic force, expression of the early inflammatory cytokines IL-6 and TNF-α were time-dependently reduced in the 1α,25(OH)2D3 group compared with the control group at each time point. Similarly, expression of HMGB1 was decreased over time in both the 1α,25(OH)2D3 and normal saline groups, and 1α,25(OH)2D3 administration enhanced this decline. These findings indicate that administration of 1α,25(OH)2D3 might provide a favorable microenvironment for orthodontic tooth movement by downregulating expression of HMGB1 in PDL cells.

Expression of Wnt3a, Wnt10b, β-catenin and DKK1 in periodontium during orthodontic tooth movement in rats

Objective: To investigate the expression of Wnt3a, Wnt10b, β-catenin and DKK1 in the periodontal ligament (PDL) during orthodontic tooth movement (OTM) in rats. Materials and methods: Nickel-titanium closed-coil springs were used to deliver an initial 50 g mesial force to the left maxillary first molars in 30 rats. The force was kept constant for 1, 3, 5, 7, 10 and 14 days until the animals were sacrificed. The right maxillary molars without force application served as control. Paraffin-embedded sections of the upper jaws were prepared for histological and immunohistochemical analyses to detect Wnt3a, Wnt10b, β-catenin and DKK1 expression in PDL. Results: Wnt3a, Wnt10b, β-catenin and DKK1 were expressed on both the ipsilateral and contralateral sides of PDL in each group. After the application of orthodontic force, the expression of β-catenin and DKK1 was initially increased and then decreased on both sides, with maximal levels of expression at day 7 and day 10, respectively. On the compression side, Wnt3a and Wnt10b levels started to increase at day 5, while on the tension side, these two molecules began to increase at day 1. Furthermore, the expression levels of Wnt3a, Wnt10b, and β-catenin were much stronger on the tension side than on the compression side at any of the observation points, while DKK1 level was much higher on the compression side. Conclusion: Wnt3a, Wnt10b, β-catenin and DKK1 expression may be related to the periodontal tissue remodeling following the application of an orthodontic force in rats. These observations suggest that the Wnt/β-catenin signaling pathway may play a crucial role in periodontal tissue remodeling during OTM.

CCR5-CCL Axis in PDL during Orthodontic Biophysical Force Application

Tooth movement by application of orthodontic biophysical force primarily reflects the role of soluble molecules released from the periodontal ligament (PDL). Thus far, many factors have been reported to be involved in orthodontic tooth movement (OTM), but key molecules that orchestrate responses of periodontal tissues to biophysical force are still enigmatic. In this in vivo study, in which the upper first molars in rats were moved, differential display–polymerase chain reaction revealed that CC chemokine receptor 5 (CCR5) level was differentially increased during OTM. Strong immunoreactivity for CCR5 was found in the PDL undergoing force application. Moreover, the in vitro compression or tension force application to primary cultured human PDL cells increased the expression of CCR5 and CCR5 ligands. In vitro tension force on human PDL cells did not induce RANKL, an osteoclastogenesis-inducing factor, but did induce the upregulation of IL12, an osteoclast inhibitory factor, and osteoblast differentiation factors, including Runx2, which was attenuated under tension by CCR5 gene silencing whereas augmented with CCR5 ligands. In contrast, in vitro compression force did not induce the expression of osteoprotegerin, a decoy receptor for RANKL and Runx2, but did induce the upregulation of RANKL, which was attenuated under compression by CCR5 gene silencing. These results suggest that the CCR5–CCR5 ligands axis in PDL cells may play a crucial role in the remodeling of periodontal tissues and can be a therapeutic target for achieving efficient OTM.

Scleraxis and osterix antagonistically regulate tensile force-responsive remodeling of the periodontal ligament and alveolar bone.

The periodontal ligament (PDL) is a mechanosensitive noncalcified fibrous tissue connecting the cementum of the tooth and the alveolar bone. Here, we report that scleraxis (Scx) and osterix (Osx) antagonistically regulate tensile force-responsive PDL fibrogenesis and osteogenesis. In the developing PDL, Scx was induced during tooth eruption and co-expressed with Osx. Scx was highly expressed in elongated fibroblastic cells aligned along collagen fibers, whereas Osx was highly expressed in the perialveolar/apical osteogenic cells. In an experimental model of tooth movement, Scx and Osx expression was significantly upregulated in parallel with the activation of bone morphogenetic protein (BMP) signaling on the tension side, in which bone formation compensates for the widened PDL space away from the bone under tensile force by tooth movement. Scx was strongly expressed in Scx(+)/Osx(+) and Scx(+)/Osx(-) fibroblastic cells of the PDL that does not calcify; however, Scx(-)/Osx(+) osteogenic cells were dominant in the perialveolar osteogenic region. Upon BMP6-driven osteoinduction, osteocalcin, a marker for bone formation was downregulated and upregulated by Scx overexpression and knockdown of endogenous Scx in PDL cells, respectively. In addition, mineralization by osteoinduction was significantly inhibited by Scx overexpression in PDL cells without affecting Osx upregulation, suggesting that Scx counteracts the osteogenic activity regulated by Osx in the PDL. Thus, Scx(+)/Osx(-), Scx(+)/Osx(+) and Scx(-)/Osx(+) cell populations participate in the regulation of tensile force-induced remodeling of periodontal tissues in a position-specific manner.

Expression of OPG, RANKL, and RUNX2 in rabbit periodontium under orthodontic force.

This study aims to investigate the expression changes of RANKL, RUNX2, and OPG in rabbit periodontal tissues under orthodontic force and explore its effect on the remodeling of periodontal tissues. A total of 16 specific pathogen-free rabbits were used in this study. The maxillary appliance was worn on the right (experimental) side, and the appliance-free left side was used as the control. Rabbits were sacrificed after 3, 5, 7, and 14 days of treatment. Changes in the expression levels of OPG, RANKL, and RUNX2 in the periodontium were detected using real-time PCR and western blotting methods. The OPG expression levels decreased after 3 to 14 days of treatment, while the expression levels of RANKL and RUNX2 increased after 3 to 14 days. The OPG expression levels decreased while those of RANKL and RUNX2 increased during orthodontic tooth movement, which suggested that they play a role in the osteogenesis process and the reconstruction of periodontal tissue.

Periodontal Biological Events Associated with Orthodontic Tooth Movement: The Biomechanics of the Cytoskeleton and the Extracellular Matrix.

The mechanical stimuli generated by orthodontic forces cause deformation of extracellular matrices and cells, vascular changes, inflammation, and the release of active biological agents generating a complex multifactorial sequence of biological events culminating in bone remodelling enabling orthodontic tooth movement. Orthodontic forces on the teeth generate stresses in periodontal tissues according to a number of variables including the type (continuous, interrupted, or intermittent), magnitude, direction, and frequency of the applied load. Whether the strain is compressive or tensile determines whether bone deposition or bone resorption will occur. The mechanically induced strains mediate structural changes in extracellular matrices and in cells, consequently affecting cellular gene expression and function. In the extracellular matrix, mechanosensing molecules integrated into the structure of various proteins can be activated upon load-induced protein unfolding. These specialized molecules have the capacity to sense and then to convert microenvironmental biomechanical stimuli into intracellular biochemical signals that interact to generate a coordinated tissue response. It is also possible that the applied force may directly cause nuclear deformation with configurational changes in chromatin, thus influencing gene expression. In this review article we summarize the current general concepts of mechanotransduction influencing the remodelling of periodontal tissues thus enabling tooth movement in response to applied orthodontic loads.

Expression of HMGB1 in the periodontal tissue subjected to orthodontic force application by Waldo's method in mice.

Recent studies indicate that high mobility group box protein 1 (HMGB1) originating from periodontal ligament (PDL) cells can be a potential regulator in the process of orthodontic tooth movement and periodontal tissue remodeling. The aim of this study is to investigate HMGB1 expression in periodontal tissue during orthodontic tooth movement in mice according to Waldo's method. Six 7-week-old C57BL6 mice were used in these experiments. The elastic band was inserted into the teeth space between the right first and second maxillary molars. After 3 days of mechanical loading, mice were fixed with transcardial perfusion of 4 % paraformaldehyde in 0.1 M phosphate buffer (pH 7.4), and the maxillary was extracted for histochemical analyses. The histological examination revealed local PDL tear at the tension side and the formation of extensive cell-free hyaline zones at the compression side. The immunolocalization of HMGB1 was significantly presented at tension side of PDL, apical area and dental pulp, whereas at the compression side of PDL, the labeling of HMGB1 was almost undetectable as the presence of hyaline zone. Taken together, we concluded that the orthodontic tooth movement by Waldo's method leads to histological changes and HMGB1 expression pattern that differ from those of coil spring method, including PDL tear and extensive hyaline zone which may severely destroy periodontal tissue and in turn impede tooth movement.

Upregulation of relaxin receptors in the PDL by biophysical force.

We have previously reported that relaxin (Rln) expression from the ovary is upregulated by orthodontic tooth movement. This study was performed to test the hypothesis that Rln family peptides (Rxfps), the G-protein-coupled Rln receptor, is induced in periodontal ligament (PDL) cells to modulate the molecules involved in periodontal tissue remodeling while applying biophysical force. Rats were implanted with orthodontic appliances to investigate changes to Rxfps in vivo. An in vitro biophysical force analysis was performed to measure the level of Rxfp 1 messenger RNA (mRNA) in primary human PDL cells. The levels of Rxfp 2 transcription and translation increased in a time-dependent manner during tooth movement. Rxfp 2 was localized in the PDL by immunofluorescence. In vitro analyses revealed that the level of Rxfp 1 mRNA in PDL cells increased significantly with both compression and tension force. The levels of matrix metalloproteinase (MMP)-1, MMP-2, interleukin-6, and vascular endothelial growth factor mRNA, which are important for periodontal tissue remodeling, also changed under force application and Rln treatment. PDL cells responded to Rln to modulate effector molecules for periodontal tissue remodeling by upregulating Rxfps expression under a biophysical force. Rln and Rxfps may serve as a PDL turnover molecule complex to control orthodontic tooth movement.

Mechanical vibration may be a novel adjuvant approach to promoting stability and retention following orthodontic treatment

Introduction: Orthodontic tooth movement occurs as a consequence of paradental tissue remodeling in response to applied mechanical forces. Retention is a necessary procedure to prevent relapse when orthodontic appliances are removed. Developing new methods to promote stability and retention following orthodontic treatment has always been desired. Recent studies have demonstrated the favorable effects of low magnitude, high frequency (LMHF) mechanical vibration on bone homeostasis through an ability to stimulate cell metabolism and to enhance osteoblast proliferation, osteoblastic gene expression and bone formation. The Hypothesis: In this paper, we propose that LMHF mechanical vibration is a viable adjuvant method to accelerate bone and periodontal tissue remodeling, thereby promoting stability and shortening retention time. Evaluation of the Hypothesis: Much effort has been made to explore therapies to prevent relapse and shorten orthodontic retention time with limited success. LMHF mechanical vibration may be a promising approach to accelerate alveolar bone remodeling, ultimately promote stability and shorten retention time.