Compressive force induces VEGF production in periodontal tissues

Computational Insights into the Interplay of Mechanical Forces in Angiogenesis

This study employs a meshless computational model to investigate the impacts of compression and traction on angiogenesis, exploring their effects on vascular endothelial growth factor (VEGF) diffusion and subsequent capillary network formation. Three distinct initial domain geometries were defined to simulate variations in endothelial cell sprouting and VEGF release. Compression and traction were applied, and the ensuing effects on VEGF diffusion coefficients were analysed. Compression promoted angiogenesis, increasing capillary network density. The reduction in the VEGF diffusion coefficient under compression altered VEGF concentration, impacting endothelial cell migration patterns. The findings were consistent across diverse simulation scenarios, demonstrating the robust influence of compression on angiogenesis. This computational study enhances our understanding of the intricate interplay between mechanical forces and angiogenesis. Compression emerges as an effective mediator of angiogenesis, influencing VEGF diffusion and vascular pattern. These insights may contribute to innovative therapeutic strategies for angiogenesis-related disorders, fostering tissue regeneration and addressing diseases where angiogenesis is crucial.

Angiogenic potential in periodontal stem cells from upper and lower jaw: A pilot study

BACKGROUND

Teeth and supporting oral tissues are attractive and accessible sources of stem cells. Periodontal ligament stem cells (PDLSC) are readily isolated from extracted third molars, and exhibit the ability to self-renew and differentiate into multiple mesodermal cell fates. Clinical experience suggests that the exact location of periodontal defects affects the oral bone remodeling and wound healing. Compared to the mandible, the maxilla heals quicker and more efficiently. Angiogenesis is key in tissue regeneration including dental tissues, yet few studies focus on the angiogenic potential of PDLSC, none of which considered the differences between upper and lower jaw PDLSC (u-PDLSC and l-PDLSC, respectively).

METHODS

Here we studied the angiogenic potential of u-PDLSC and l-PDLSC and compared the results to well-established mesenchymal stem cells (MSC). Cells were characterized in terms of surface markers, proliferation, and vascular endothelial growth factor (VEGF) secretion, and angiogenic assays were performed. Newly formed capillaries were stained with CD31, and their expression of platelet endothelial cell adhesion molecule (PECAM-1), angiopoietin 2 (ANGPT2), and vascular endothelial growth factor receptor 1 and 2 (VEGFR-1, VEGFR-2) were measured.

RESULTS

Periodontal stem cells from the upper jaw showed a higher proliferation capacity, secreted more VEGF, and formed capillary networks faster and denser than l-PDLSC. Gene expression of angiogenesis-related genes was significantly higher in u-PDLSC than in l-PDLSC or MSC, given that culture conditions were suitable.

CONCLUSION

The oral cavity is a valuable source of stem cells, particularly PDLSC, which are promising for oral tissue engineering due to their robust growth, lifelong accessibility, low immunogenicity, and strong differentiation potential. Notably, u-PDLSC exhibit higher VEGF secretion and accelerate capillary formation compared to l-PDLSC or MSC. This study suggests a potential molecular mechanism in capillary formation, emphasizing the significance of precise location isolation of PDLSC.

A narrative review of the effects of vitamin D3 on orthodontic tooth movement: Focus on molecular and cellular mechanisms

Orthodontic tooth movement (OTM) is a critical process in dental alignment, driven by the application of calibrated orthodontic forces. This study delves into the intricate molecular and cellular mechanisms by which vitamin D3 influences OTM. Vitamin D3 is identified as a critical regulator in bone metabolism, enhancing osteoblast activity and bone formation while also modulating osteoclast quantity and RANKL expression, essential for the remodeling of the alveolar bone. The precise mechanisms through which vitamin D3 facilitates these processes are explored, highlighting its potential in accelerating bone remodeling and, consequently, tooth alignment. This comprehensive review underscores vitamin D3's anabolic impact on bone metabolism and its pivotal role in the synthesis and mineralization processes governed by osteoblasts. The findings illuminate vitamin D3's promise in augmenting orthodontic therapy, suggesting its utility in improving treatment efficiency and reducing duration. However, the need for further research into the optimal application of vitamin D3 in orthodontics is emphasized, particularly concerning dosage, timing, and delivery methods.

The Influence of Orthodontic Treatment on Periodontal Health between Challenge and Synergy: A Narrative Review

By correctly repositioning teeth, orthodontic therapy improves both the function and appearance of an occlusion. The relationship between teeth and the tissues that surround and support them significantly influences these alterations. With ever more adults seeking orthodontic care, orthodontists are increasingly seeing patients with periodontal issues. Concerns about the patient's appearance, such as uneven gingival margins or functional issues caused by inflammatory periodontal diseases, should be accounted for when designing orthodontic treatment plans. Furthermore, orthodontics may increase the chances of saving and recovering a degraded dentition in cases of severe periodontitis. Today, general dentists, dontists, and orthodontists play integrative roles that enable them to achieve the best possible results for their patients. This review will improve the results of interdisciplinary treatments and increase cooperation between dental specialists by drawing attention to the essential connection between orthodontics and periodontics in regular clinical practice.

Pathogenesis of non-infection related inflammatory root resorption in permanent teeth: A narrative review

BACKGROUND

The mechanism of action of root resorption in a permanent tooth can be classified as infection-related (e.g., microbial infection) or non-infection-related (e.g., sterile damage). Infection induced root resorption occurs due to bacterial invasion. Non-infection-related root resorption stimulates the immune system through a different mechanism.

OBJECTIVES

The aim of this narrative review is to describe the pathophysiologic process of non-infection-related inflammatory processes involved in root resorption of permanent teeth.

METHODS

A literature search on root resorption was conducted using Scopus (PubMed and Medline) and Google Scholar databases to highlight the pathophysiology of bone and root resorption in non-infection-related situations. The search included key words covering the relevant category. It included in vitro and in vivo studies, systematic reviews, case series, reviews, and textbooks in English. Conference proceedings, lectures and letters to the editor were excluded.

RESULTS

Three types of root resorption are related to the non-infection mechanism of action, which includes surface resorption due to either trauma or excessive orthodontic forces, external replacement resorption and external cervical resorption. The triggers are usually damage associated molecular patterns and hypoxia conditions. During this phase macrophages and clastic cells act to eliminate the damaged tissue and bone, eventually enabling root resorption and bone repair as part of wound healing.

DISCUSSION

The resorption of the root occurs during the inflammatory phase of wound healing. In this phase, damaged tissues are recognized by macrophages and neutrophiles that secrete interlaukines such as TNF-α, IL-1, IL-6, IL-8. Together with the hypoxia condition that accelarates the secretion of growth factors, the repair of the damaged perioduntiom, including damaged bone, is initiated. If the precementum and cementoblast are injured, root resorption can occur.

CONCLUSIONS

Wound healing exhibits different patterns of action that involves immune stimulation in a bio-physiological activity, that occurs in the proper sequence, with overlapping phases. Two pathologic conditions, DAMPs and hypoxia, can activate the immune cells including clastic cells, eliminating damaged tissue and bone. Under certain conditions, root resorption occurs as a side effect.

Effect of genetic polymorphisms rs2301113 and rs2057482 in the expression of HIF-1α protein in periodontal ligament fibroblasts subjected to compressive force

OBJECTIVE

Many genes and signaling molecules are involved in orthodontic tooth movement, with mechanically and hypoxically stabilized HIF-1α having been shown to play a decisive role in periodontal ligament signaling during orthodontic tooth movement. Thus, this in vitro study aimed to investigate if genetic polymorphisms in HIF1A (Hypoxia-inducible factor α-subunits) influence the expression pattern of HIF-1α protein during simulated orthodontic compressive pressure.

METHODOLOGY

Samples from human periodontal ligament fibroblasts were used and their DNA was genotyped using real time Polymerase chain reaction for the genetic polymorphisms rs2301113 and rs2057482 in HIF1A . For cell culture and protein expression experiments, six human periodontal ligament fibroblast cell lines were selected based on the patients' genotype. To simulate orthodontic compressive pressure in fibroblasts, a 2 g/cm2 force was applied under cell culture conditions for 48 hours. Protein expression was evaluated by Western Blot. Paired t-tests were used to compare HIF-1α expression with and without compressive pressure application and unpaired t-tests were used to compare expression between the genotypes in rs2057482 and rs2301113 (p<0.05).

RESULTS

The expression of HIF-1α protein was significantly enhanced by compressive pressure application regardless of the genotype (p<0.0001). The genotypes in the genetic polymorphisms rs2301113 and rs2057482 were not associated with HIF-1α protein expression (p>0.05).

CONCLUSIONS

Our study confirms that compressive pressure application enhances HIF-1α protein expression. We could not prove that the genetic polymorphisms in HIF1A affect HIF-1α protein expression by periodontal ligament fibroblasts during simulated orthodontic compressive force.

Potential Use of Hyperbaric Oxygen Therapy in Orthodontic Treatment: A Systematic Review of Animal Studies

Understanding the fundamental principles of tooth movement could reduce the duration of treatment and achieve a stable outcome, resulting in patient satisfaction. Hyperbaric oxygen therapy was a modality in which a patient inhaled 100% O₂ while subjected to high atmospheric pressure. Hyperbaric oxygen therapy facilitated the supply of oxygen to the human body's organs and tissues and served a variety of applications, including patient care and wound treatment. This review article aimed to describe animal studies of the potential effects of hyperbaric oxygen therapy in orthodontic therapy. It was conducted using a systematic literature review method, including searching PubMed and Google Scholar for publications relevant to the research topics. The search was filtered to include only research on orthodontic treatment and hyperbaric oxygen therapy and was published in any year. Articles that did not specify biological components of orthodontic tooth movement (OTM) were excluded. The Preferred Reporting Items identified the papers for the Systematic Reviews and Meta-Analyses (PRISMA) strategy, which resulted in the selection of 11 publications. Hyperbaric oxygen therapy affected parameters of biomarkers representing the clinical, molecular, and cellular biology of bone formation and resorption in periodontal tissues in responding to orthodontic physical forces, including alkaline phosphatase, collagen synthesis, osteoblast, osteoclast, osteocyte, type I collagen, vascular endothelial growth factor, osteocalcin, fibroblast, matrix metalloproteinase-8, transforming growth factor-β, partial pressure of oxygen, partial pressure of carbon dioxide, trabecular bone density, and tooth mobility. Hyperbaric oxygen therapy induced an inflammatory response to follow OTM events during active orthodontic therapy. Hyperbaric oxygen therapy might play a role in the tissue healing process during passive treatment. Nonetheless, additional research should be conducted to establish the efficacy of hyperbaric oxygen therapy in orthodontics.

Extracellular adenosine triphosphate induces IDO and IFNγ expression of human periodontal ligament cells through P2 X7 receptor signaling

BACKGROUND

Mechanical stimuli induce the release of adenosine triphosphate into the extracellular environment by human periodontal ligament cells (hPDLCs). Extracellular adenosine triphosphate (eATP) plays the role in both inflammation and osteogenic differentiation. eATP involves in immunosuppressive action by increasing immunosuppressive molecules IDO and IFNγ expression on immune cells. However, the role of eATP on the immunomodulation of hPDLCs remains unclear. This study aimed to examine the effects of eATP on the IDO and IFNγ expression of hPDLCs and the participation of purinergic P₂ receptors in this phenomenon.

METHODS

hPDLCs were treated with eATP. The mRNA and protein expression of indoleamine-pyrrole 2,3-dioxygenase (IDO) and interferon-gamma (IFNγ) were determined. The role of the purinergic P₂ receptor was determined using calcium chelator (EGTA) and PKC inhibitor (PKCi). Chemical inhibitors (KN62 and BBG), small interfering RNA (siRNA), and P₂ X₇ receptor agonist (BzATP) were used to confirm the involvement of P₂ X₇ receptors on IDO and IFNγ induction by hPDLCs.

RESULTS

eATP significantly enhanced mRNA expression of IDO and IFNγ. Moreover, eATP increased kynurenine which is the active metabolite of tryptophan breakdown catalyzed by the IDO enzyme and significantly induced IFNγ protein expression. EGTA and PKCi reduced eATP-induced IDO and IFNγ expressions by hPDLCs, confirming the role of calcium signaling. Chemical P₂ X₇ inhibitors (KN62 and BBG) and siRNA targeting the P₂ X₇ receptor significantly inhibited the eATP-induced IDO and IFNγ production. Correspondingly, BzATP markedly increased IDO and IFNγ expression.

CONCLUSION

eATP induced immunosuppressive function of hPDLCs by promoting IDO and IFNγ production via P₂ X₇ receptor signaling. eATP may become a promising target for periodontal regeneration by modulating immune response and further triggering tissue healing.

An Evaluation of Different 3D Cultivation Models on Expression Profiles of Human Periodontal Ligament Fibroblasts with Compressive Strain

The effects of compressive strain during orthodontic treatment on gene expression profiles of periodontal ligament fibroblasts (PDLFs) have mostly been studied in 2D cell culture. However, cells behave differently in many aspects in 3D culture. Therefore, the effect of pressure application on PDLFs in different 3D structures was investigated. PDLFs were either conventionally seeded or embedded into different 3D structures (spheroids, Mebiol^® gel, 3D scaffolds) and exposed to compressive force or incubated without pressure. For one 3D scaffold (POR), we also tested the effect of different compressive forces and application times. Expression of an angiogenic gene (VEGF), a gene involved in extracellular matrix synthesis (COL1A2), inflammatory genes (IL6, PTGS2), and genes involved in bone remodelling (OPG, RANKL) were investigated by RT-qPCR. Depending on the used 3D cell culture model, we detected different effects of compressive strain on expression profiles of PDLFs. COL1A2 was downregulated in all investigated 3D culture models. Angiogenetic and proinflammatory genes were regulated differentially between models. In 3D scaffolds, regulation of bone-remodelling genes upon compressive force was contrary to that observed in 3D gels. 3D cell culture models provide better approximations to in vivo physiology, compared with conventional 2D models. However, it is crucial which 3D structures are used, as these showed diverse effects on the expression profiles of PDLFs during mechanical strain.

BBS7-SHH Signaling Activity Regulates Primary Cilia for Periodontal Homeostasis

Objectives: Mechanical stimuli are essential for the maintenance of periodontal ligament (PDL) homeostasis. Although there are several studies on atrophic changes in PDL due to occlusal hypofunction, the underlying mechanism is still unknown. Here, we aimed to explore the changes of gene expression in occlusal hypofunctional PDL and elucidate the related role in maintaining the PDL homeostasis.

Methods: To investigate the transcriptomic difference between control and hypofunctional PDL tissue from patients, RNA sequencing was performed on 34 human teeth. The atrophic changes in PDL were evaluated by histological analysis. The effect of the Bardet-Biedl syndrome 7 (BBS7) knockdown was evaluated by the RT-qPCR, Western blot, wound healing, and tubule formation assay.

Results: We detected that the expression of BBS7 was downregulated in occlusal hypofunctional PDL through RNA sequencing. Dynamic changes, including the number of periodontal ligament cells, alignment of collagen fibers, diameter of blood vessels, appearance of primary cilia, and torturous oxytalan fibers, were observed following occlusal hypofunction. Furthermore, Sonic hedgehog signaling (Shh) activity was closely associated with BBS7 expression in PDL cells. In addition, the cell migration and angiogenesis were also suppressed by BBS7 knockdown in vitro.

Conclusion: We suggest that BBS7 plays an essential role in maintaining Shh signaling activity for PDL homeostasis.

Development of a new evaluation method for orthodontic forces generated in individual patients

Numerous experimental studies have examined how much orthodontic force is needed to move teeth more smoothly; however, no reports have examined this clinically in individual, living subjects. We aimed to develop a method for quantifying the force exerted on individual teeth by an orthodontic wire to measure how loads placed on crowded teeth change dynamically over time. Accordingly, we fabricated a series of dental casts of patients undergoing orthodontic treatment (using optical impressions and a three-dimensional printer), fitted these models with nickel-titanium wire, and subjected them to bending load tests. During leveling, nickel-titanium wire is generally considered to exert a weak force due to its low elastic modulus, with a weak orthodontic force applied over a long period of time due to its superelasticity; however, we found that the actual energy exerted by nickel-titanium wire is also largely affected by other factors (e.g., amount of crowding).

Compression loading of osteoclasts attenuated microRNA-146a-5p expression, which promotes angiogenesis by targeting adiponectin

Osteoclastogenesis in alveolar bone induced by compression stress triggers orthodontic tooth movement. Compression stress also stimulates angiogenesis, which is essential for osteoclastogenesis. However, the effects of osteoclastogenesis induced by compression on angiogenesis are poorly understood. In vivo, we found the markers of angiogenesis increased during orthodontic bone remodeling. In vitro, osteoclast-derived exosomes increased proliferation, migration, and tube formation of human umbilical vein endothelial cells (HUVECs), as well as expression of vascular endothelial growth factor and CD31. The promotive effects of exosomes derived from compressed osteoclasts were greater than those derived from osteoclasts without compression. Next, we analyzed changes in the microRNA transcriptome after compression stress and focused on microRNA146a-5p (miR-146a), which was significantly decreased by compression. Transfection of an inhibitor of miR-146a stimulated angiogenesis of HUVECs while miR-146a mimics repressed angiogenesis. Adiponectin (ADP) was confirmed to be a target of miR-146a by dual luciferase reporter assay. In HUVECs treated with exosomes, we detected increased ADP which promoted angiogenesis. Knockdown of ADP in HUVECs reduced the promotive effects of exosomes. Our results demonstrate that the decreased miR-146a observed in osteoclasts after compression promotes angiogenesis by targeting ADP, suggesting a novel method to interfere with bone remodeling induced by compression stress.

Role and Regulation of Mechanotransductive HIF-1α Stabilisation in Periodontal Ligament Fibroblasts

Orthodontic tooth movement (OTM) creates compressive and tensile strain in the periodontal ligament, causing circulation disorders. Hypoxia-inducible factor 1α (HIF-1α) has been shown to be primarily stabilised by compression, but not hypoxia in periodontal ligament fibroblasts (PDLF) during mechanical strain, which are key regulators of OTM. This study aimed to elucidate the role of heparan sulfate integrin interaction and downstream kinase phosphorylation for HIF-1α stabilisation under compressive and tensile strain and to which extent downstream synthesis of VEGF and prostaglandins is HIF-1α-dependent in a model of simulated OTM in PDLF. PDLF were subjected to compressive or tensile strain for 48 h. In various setups HIF-1α was experimentally stabilised (DMOG) or destabilised (YC-1) and mechanotransduction was inhibited by surfen and genistein. We found that HIF-1α was not stabilised by tensile, but rather by compressive strain. HIF-1α stabilisation had an inductive effect on prostaglandin and VEGF synthesis. As expected, HIF-1α destabilisation reduced VEGF expression, whereas prostaglandin synthesis was increased. Inhibition of integrin mechanotransduction via surfen or genistein prevented stabilisation of HIF-1α. A decrease in VEGF expression was observed, but not in prostaglandin synthesis. Stabilisation of HIF-1α via integrin mechanotransduction and downstream phosphorylation of kinases seems to be essential for the induction of VEGF, but not prostaglandin synthesis by PDLF during compressive (but not tensile) orthodontic strain.

Effects of sodium chloride on the gene expression profile of periodontal ligament fibroblasts during tensile strain

Purpose

During orthodontic tooth movement, pressure and tension zones develop in the periodontal ligament, and periodontal ligament fibroblasts (PDLF) become exposed to mechanical strain. Enhanced salt (NaCl) concentrations are known to modulate responses of PDLF and immune cells to different stimuli like mechanical strain. Here, we investigated the impact of tensile strain on the gene expression profile of PDLF under normal (NS) and high salt (HS) conditions.

Methods

After preincubation under NS or HS (+40 mM NaCl in medium) conditions for 24 h, PDLF were stretched 16% for 48 h using custom-made spherical cap silicone stamps using an established and published setup. After determination of cell number and cytotoxicity, we analyzed expression of genes involved in extracellular matrix reorganization, angiogenesis, bone remodeling, and inflammation by quantitative real-time polymerase chain reaction (RT-qPCR).

Results

Tensile strain did not affect the expression of genes involved in angiogenesis or extracellular matrix reorganization by PDLF, which however modulate inflammatory responses and bone remodeling in reaction to 16% static tensile strain. Salt (NaCl) treatment triggered enhanced extracellular matrix formation, expression of cyclooxygenase 2 and bone metabolism in PDLF during tensile strain.

Conclusions

Salt (NaCl) consumption may influence orthodontic tooth movement and periodontal bone loss via modulation of extracellular matrix and bone metabolism. Excessive salt intake during orthodontic therapy may cause adverse effects regarding periodontal inflammation and bone resorption.

Effects of Compressive and Tensile Strain on Macrophages during Simulated Orthodontic Tooth Movement

During orthodontic tooth movement (OTM) to therapeutically correct the position of misaligned teeth, thus improving oral health and quality of life, fibroblasts, macrophages, and other immune cells within the periodontal ligament (PDL), which connects a tooth to its surrounding bone, are exposed to compressive and tensile strain. While it is known that PDL fibroblasts are critically involved in the biological regulation of OTM by a mechanotransductively triggered release of cytokines, it is unclear whether macrophages also react to pressure and tension in a similar manner thus impacting on or mediating OTM. RAW264.7 macrophages were seeded onto conventional 6-well cell culture plates for pressure or on Bioflex plates for tension assays and preincubated for 24 h. For in vitro simulation of physiological orthodontic compressive or tensile strain for 2 h, 4 h, 24 h, and 48 h, glass discs (2 g/cm²) were placed or adherent macrophages isotropically stretched for 16%, respectively. We determined cell number, cytotoxicity, and gene/protein expression of Vegf-a/VEGF-A (macrophage-mediated angiogenesis), Mmp-8/9 (extracellular matrix reorganization), and Cox-2/PG-E2, Il-6/IL-6, and Tnf-α/TNF-α (proinflammatory mediators) by RT-qPCR and ELISA. Compressive but not tensile strain resulted in a significant reduction in cell number after only 2 h. Mmp-8 and Mmp-9 expression was significantly enhanced within 24 h of compressive and in part tensile strain. Significantly increased Vegf-a/VEGF-A expression was detected within 4 h of pressure, but not during application of tensile strain. Expression of proinflammatory mediators Cox-2/PG-E2, Il-6/IL-6, and Tnf-α/TNF-α was significantly increased as early as 2-4 h after application of compressive or tensile strain. Our results indicate that macrophages respond early on to compressive and tensile strain occurring during OTM with an enhanced gene expression of proinflammatory cytokines, which could affect PDL fibroblasts, osteoblasts, and immune cells triggering or enhancing the biological mechanisms and osteoclastogenesis underlying OTM.

Asperosaponin VI Injection Enhances Orthodontic Tooth Movement in Rats

Background

This study was performed to investigate the effect of local injection of asperosaponin VI (ASA VI) on the orthodontic tooth movement in rats.

Material/Methods

A total of 64 healthy female Sprague-Dawley rats were selected and divided into 2 groups randomly: the ASA VI group and the control group. For the ASA VI group, 10 mg/kg ASA VI solution was injected into buccal submucoperiosteal of bilaterally first maxillary molars, and the same volume of normal saline was given to the control group. The orthodontic force was applied to the maxillary first molars. All rats were sacrificed on days 3, 7, or 14. Tooth movement effects on the periodontium were analyzed through hematoxylin and eosin (H&E) staining, tartrate-resistant acid phosphatase (TRAP) staining and immunohistochemistry analysis. Tooth movement measurements and alveolar bone volumetric changes were analyzed using a micro-computed tomography (CT) scan. Molecular changes were evaluated by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot.

Results

The ASA VI group presented with a significant increase of tooth movement, osteoclast number, and the expression of osteoclast differentiation factor (ODF) compared with the control group. ASA VI also induced a significant decrease in bone volume and density and an increase in trabecular spacing and RANKL (receptor activator of nuclear factor kappa-B ligand) expression at the compression side. Furthermore, ASA VI stimulated bone formation on the tension side by enhancing OCN (osteocalcin) expression and RUNX2 (runt-related transcription factor 2) expression, increasing bone volume and density and decreasing in trabecular spacing.

Conclusions

Injection of ASA VI may accelerate tooth movement via increasing the activity of osteoclasts, stimulating bone resorption at the compression side. Furthermore, ASA VI has a positive effect on bone formation at the tension side.

The role of mechanotransduction versus hypoxia during simulated orthodontic compressive strain-an in vitro study of human periodontal ligament fibroblasts

During orthodontic tooth movement (OTM) mechanical forces trigger pseudo-inflammatory, osteoclastogenic and remodelling processes in the periodontal ligament (PDL) that are mediated by PDL fibroblasts via the expression of various signalling molecules. Thus far, it is unknown whether these processes are mainly induced by mechanical cellular deformation (mechanotransduction) or by concomitant hypoxic conditions via the compression of periodontal blood vessels. Human primary PDL fibroblasts were randomly seeded in conventional six-well cell culture plates with O₂-impermeable polystyrene membranes and in special plates with gas-permeable membranes (Lumox®, Sarstedt), enabling the experimental separation of mechanotransducive and hypoxic effects that occur concomitantly during OTM. To simulate physiological orthodontic compressive forces, PDL fibroblasts were stimulated mechanically at 2 g·cm⁻² for 48 h after 24 h of pre-incubation. We quantified the cell viability by MTT assay, gene expression by quantitative real-time polymerase chain reaction (RT-qPCR) and protein expression by western blot/enzyme-linked immunosorbent assays (ELISA). In addition, PDL-fibroblast-mediated osteoclastogenesis (TRAP⁺ cells) was measured in a 72-h coculture with RAW264.7 cells. The expression of HIF-1α, COX-2, PGE2, VEGF, COL1A2, collagen and ALPL, and the RANKL/OPG ratios at the mRNA/protein levels during PDL-fibroblast-mediated osteoclastogenesis were significantly elevated by mechanical loading irrespective of the oxygen supply, whereas hypoxic conditions had no significant additional effects. The cellular–molecular mediation of OTM by PDL fibroblasts via the expression of various signalling molecules is expected to be predominantly controlled by the application of force (mechanotransduction), whereas hypoxic effects seem to play only a minor role. In the context of OTM, the hypoxic marker HIF-1α does not appear to be primarily stabilized by a reduced O₂ supply but is rather stabilised mechanically.

Synergistic alveolar bone resorption by diabetic advanced glycation end products and mechanical forces

BACKGROUND

The association between diabetes mellitus (DM) and bone diseases is acknowledged. However, the mechanistic pathways leading to the alveolar bone (AB) destruction remain unclear. This study aims to elucidate the mechanical forces (MF)-induced AB destruction in DM and its underlying mechanism.

METHODS

In vivo periodontal tissue responses to MF were evaluated in rats with diabetes. In vitro human periodontal ligament (PDL) cells were either treated with advanced glycation end products (AGEs) alone or with AGEs and MF.

RESULTS

In vivo, the transcription of VEGF-A, colony stimulating factor-1 (CSF-1), and Ager was upregulated in diabetes, whereas changes in DDOST and Glo1 mRNAs were negligible. DM induced VEGF-A protein in the vascular cells of the PDL and subsequent angiogenesis, but DM itself did not induce osteoclastogenesis. MF-induced AB resorption was augmented in DM, and such augmentation was morphologically substantiated by the occasional undermining resorption as well as the frontal resorption of the AB by osteoclasts. The mRNA levels of CSF-1 and vascular endothelial growth factor (VEGF) during MF application were highly elevated in diabetes, compared with those of the normal counterparts. In vitro, AGEs treatment elevated Glut-1 and CSF-1 mRNA levels via the p38 and JNK pathways, whereas OGT and VEGF levels remained unchanged. Compressive MF especially caused upregulation of VEGF, CSF-1, and Glut-1 levels, and such upregulation was further enhanced by AGEs treatment.

CONCLUSIONS

Overloaded MF and AGEs metabolites may synergistically aggravate AB destruction by upregulating CSF-1 and VEGF. Therefore, regulating the compressive overloading of teeth, as well as the levels of diabetic AGEs, may prove to be an effective therapeutic modality for managing DM-induced AB destruction.

Dental hypofunction alters subgingival microorganisms: a pilot study

BACKGROUND

The aim of this study was to evaluate dental plaque compositions, vascular endothelial growth factor (VEGF) and hypoxia-inducible factor (HIF) 1-alpha levels in gingival crevicular fluid (GCF) at hypofunctional and normofunctional teeth in healthy individuals and chronic periodontitis patients.

METHODS

Sixty systemically healthy individuals were enrolled. Study groups were: group 1 hypofunctional healthy group (group 1, N.=15); group 2 hypofunctional periodontitis group (group 2, N.=15); group 3 normofunctional healthy group (group 3, N.=15); and group 4 normofunctional periodontitis group (group 4, N.=15). Clinical periodontal measurements (plaque index, gingival index and clinical attachment level) were recorded. Dental plaque and GCF samples were taken. VEGF and HIF 1-alpha levels in GCF were determined. Subgingival plaque samples were evaluated for 11 different bacterial species as, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola, Prevotella intermedia, Peptostreptococcus micros, Fusobacterium nucleatum, Campylobacter rectus, Eubacterium nodatum, Eikenella corrodens and Capnocytophaga species.

RESULTS

Tannerella forsythia, Peptostreptococcus micros, Eubacterium nodatum levels decreased in hypofunctional healthy and periodontitis groups (P<0.05). Porphyromonas gingivalis levels increased in hypofunctional healthy group and decreased in hypofunctional periodontitis group (P<0.05). There was also a decrease in Eikenella corrodens levels in hypofunctional periodontitis group (P<0.05). There were no difference regarding the Aggregatibacter actinomycetemcomitans, Capnocytophaga spp., Prevotella intermedia and Fusobacterium nucleatum levels among the groups (P>0.05). VEGF and HIF-1α levels in both GCF and serum samples were also similar (P>0.05).

CONCLUSIONS

Within the limits of this study, the authors found that the levels of four significant bacterial strains were decreased in both hypofunctional healthy and hypofunctional periodontitis groups compared to normofunctional equivalents. Though not evaluated in this study, this situation could be due to periodontal ligament atrophy and related physiological alterations.

Sodium-chloride-induced effects on the expression profile of human periodontal ligament fibroblasts with focus on simulated orthodontic tooth movement

Increased salt (NaCl) consumption triggers chronic diseases such as hypertension or osteopenia. Its impact on orthodontic tooth movement and periodontitis, however, has not been investigated, although both processes are related to the immune system, with periodontal ligament fibroblasts (PDLFs) playing a key mediating role. Here, we investigated the impact of NaCl on the expression pattern of PDLFs in a model of simulated compressive orthodontic strain. Periodontal ligament fibroblasts were preincubated for 24 h with additional 0 or 40 mM NaCl and concurrently treated for another 48 h with or without compressive strain of 2 g cm^-2 . We analyzed the expression of genes and proteins involved in orthodontic tooth movement by reverse transcription quantitative polymerase chain reaction (RT-qPCR), ELISA, and immunoblot. Co-culture experiments were performed to observe PDLF-mediated osteoclastogenesis. A higher (40 mM) concentration of NaCl in the culture medium resulted in increased secretion of prostaglandin, expression of alkaline phosphatase, and expression of genes involved in extracellular matrix remodeling, but decreased compression-induced expression of the interleukin-6 (IL6) gene. The 40 mM concentration of NaCl also enhanced receptor activator of nuclear factor kappa-B ligand (RANKL) but reduced that of osteoprotegerin (OPG), resulting in upregulated PDLF-mediated osteoclastogenesis. A high NaCl concentration in the periodontal ligament, corresponding to a high-salt diet in vivo, may influence orthodontic tooth movement and periodontitis through increased secretion of prostaglandins by PDLFs and upregulated PDLF-mediated osteoclastogenesis, possibly accelerating orthodontic tooth movement and propagating periodontitis and periodontal bone loss.

Effects of ethanol on human periodontal ligament fibroblasts subjected to static compressive force

Consumption of toxic substances such as alcohol is widespread in the general population and thus also in patients receiving orthodontic treatment. Since human periodontal ligament (hPDL) fibroblasts play a key role in orthodontic tooth movement (OTM) by expressing cytokines and chemokines, we wanted to clarify whether ethanol modulates the physiological activity and expression pattern of hPDL fibroblasts during static compressive force application. We pre-incubated hPDL fibroblasts for 24 h with different ethanol concentrations, corresponding to casual (0.041% blood alcohol concentration [BAC], % by volume) and excessive (0.179%) alcohol consumption. At each ethanol concentration, we incubated the cells for another 48 h with and without an additional physiological compressive force of 2 g/cm² occurring during orthodontic tooth movement in compression areas of the periodontal ligament. Thereafter, we analyzed expression and secretion of genes and proteins involved in OTM regulation by RT-qPCR and ELISA. We also performed co-culture experiments to observe hPDL-fibroblast-mediated osteoclastogenesis. We observed no effects of ethanol on cytotoxicity or cell viability of hPDL fibroblasts in the applied concentrations. Ethanol showed an enhancing effect on angiogenesis and activity of alkaline phosphatase. Simultaneously, ethanol reduced the induction of IL-6 and increased prostaglandin E₂ synthesis as well as hPDL-fibroblast-mediated osteoclastogenesis without affecting the RANK-L/OPG-system. hPDL fibroblasts thus seem to be a cell type quite resistant to ethanol, as no cytotoxic effects or influence on cell viability were detected. High ethanol concentrations, however, seem to promote bone formation and angiogenesis. Ethanol at 0.179% also enhanced hPDL-induced osteoclastogenesis, indicating increased bone resorption and thus tooth movement velocity to be expected during orthodontic therapy.

Alveolar Bone Osteoclast Profile in the Periodontitis Wistar Rats Model with the Snail Slime (Achatina Fulica) Application

BACKGROUND

Bone damage is a result of periodontal disease that occurs due to changes in osteoclast and osteoblast activity in response to local inflammation. The bacteria Aggregatibacter actinomycetemcomitans produces Lipopolysaccharide (LPS), which can increase osteoclast activity.

AIM

This study aimed to analyse the decrease in alveolar bone osteoclasts in periodontitis rats' model with the application of snail slime.

METHODS

Wistar rats (27) with periodontitis divided into three groups, namely the control group (debridement), P1 group (debridement and application of oral snail slime) 300 Mg/Kg Body weight, P2 group (debridement, application of topical snail slime) 0.1 Mg. Osteoclast profile analysis was carried out by HE staining procedure to determine the histological feature of osteoclasts. The statistical significance was determined using the Shapiro-Wilk Test, One Way ANOVA, and Post Hoc test (p < 0.05).

RESULTS

Osteoclast profile in rats with periodontitis applied with snail slime significantly decreased the number of osteoclasts with both oral and topical administration, there were significant differences in the number of osteoclasts between groups (one way ANOVA, p < 0.05) and there were no significant differences between groups P1 and P2 (Post Hoc, p > 0.05).

CONCLUSION

In this study, there was a decrease in the number of osteoclasts which were slipped by snail slime in Wistar rats with periodontitis; this indicates a periodontitis healing process.

Hypoxia-induced upregulation of angiogenic factors in immortalized human periodontal ligament fibroblasts

Hypoxia induces complex cellular responses that are mediated by a key transcription factor, hypoxia-inducible factor-1 (HIF-1). HIF-1 promotes production of cytokines and angiogenic factors and contributes to recovery of injured tissues. In the present study, expressions of angiogenin (ANG) and vascular endothelial growth factor (VEGF), which are potent angiogenic factors in mammalian tissues, were examined in immortalized fibroblasts exposed to hypoxia. After 24 h of exposure to hypoxia, ANG and VEGF mRNAs expressions were significantly elevated in periodontal ligament (PDL) fibroblasts but not in embryonic fibroblasts. Hypoxia also increased productions of ANG and VEGF proteins in PDL fibroblasts. HIF-1α mRNA expression was not affected by hypoxia in either fibroblast, although HIF-1α protein expression was enhanced after exposure to hypoxia. Treatment of PDL fibroblasts with dimethyloxaloylglycine, a prolyl hydroxylase inhibitor that stabilizes the HIF-1α protein, significantly increased expressions of ANG and VEGF mRNAs under normoxia. This suggests that stabilization of HIF-1α is crucial for upregulation of ANG and VEGF in PDL fibroblasts. These results indicate that, under hypoxic conditions, HIF-1α upregulates synthesis of ANG and VEGF in PDL fibroblasts and promotes angiogenesis.

Extracellular Matrix Component Remodeling in Respiratory Diseases: What Has Been Found in Clinical and Experimental Studies?

Changes in extracellular matrix (ECM) components in the lungs are associated with the progression of respiratory diseases, such as asthma, chronic obstructive pulmonary disease (COPD), and acute respiratory distress syndrome (ARDS). Experimental and clinical studies have revealed that structural changes in ECM components occur under chronic inflammatory conditions, and these changes are associated with impaired lung function. In bronchial asthma, elastic and collagen fiber remodeling, mostly in the airway walls, is associated with an increase in mucus secretion, leading to airway hyperreactivity. In COPD, changes in collagen subtypes I and III and elastin, interfere with the mechanical properties of the lungs, and are believed to play a pivotal role in decreased lung elasticity, during emphysema progression. In ARDS, interstitial edema is often accompanied by excessive deposition of fibronectin and collagen subtypes I and III, which can lead to respiratory failure in the intensive care unit. This review uses experimental models and human studies to describe how inflammatory conditions and ECM remodeling contribute to the loss of lung function in these respiratory diseases.

Periostin plays role in force-induced stem cell potential by periodontal ligament stem cells

Mechanical stimuli have been shown to play an important role in directing stem cell fate and maintenance of tissue homeostasis. One of the functions of the mechanoresponsive tissue periodontal ligament (PDL) is to withstand the functional forces within the oral cavity. Periodontal ligament stem cells (PDLSCs) derived from periodontal tissue have been demonstrated to be able to respond directly to mechanical forces. However, the mechanisms of action of mechanical force on PDLSCs are not totally understood. The aim of this study was to investigate the mechanisms by which compressive force affects PDLSCs, especially their stemness properties. PDLSCs were established from extracted human third molars; their stem cell characteristics were validated by detecting the expression of stem cell markers and confirming their ability to differentiate into osteogenic and adipogenic lineages. PDLSCs were subjected to various magnitudes of static compressive force (0 [control], 0.5, 1.0, 1.5, or 2 g/cm² ). Application of 1.0 g/cm² compressive force significantly upregulated a panel of stem cell marker genes, including NANOG and OCT4. Conversely, higher force magnitudes downregulated these genes. Mechanical loading also upregulated periostin, a matrix protein that plays important roles in tissue morphogenesis. Interestingly, knockdown of periostin using siRNA abolished force-induced stem cell marker expression in PDLSCs. This study suggests a proper magnitude of compressive force could be one important factor involved in the modulation of the pluripotency of PDLSCs through the action of periostin. The precise mechanism by which periostin regulates stemness requires further detailed investigation.

Effects of the Highly COX-2-Selective Analgesic NSAID Etoricoxib on Human Periodontal Ligament Fibroblasts during Compressive Orthodontic Mechanical Strain

Human periodontal ligament (hPDL) fibroblasts play a major role during periodontitis and orthodontic tooth movement, mediating periodontal inflammation, osteoclastogenesis, and collagen synthesis. The highly COX-2-selective NSAID etoricoxib has a favorable systemic side effect profile and high analgesic efficacy, particularly for orthodontic pain. In this in vitro study, we investigated possible side effects of two clinically relevant etoricoxib concentrations on the expression pattern of mechanically strained hPDL fibroblasts and associated osteoclastogenesis in a model of simulated orthodontic compressive strain occurring during orthodontic tooth movement. hPDL fibroblasts were incubated for 72 h under physiological conditions with etoricoxib at 0 μM, 3.29 μM, and 5.49 μM, corresponding to clinically normal and subtoxic dosages, with and without mechanical strain by compression (2 g/cm²) for the final 48 h, simulating conditions during orthodontic tooth movement in compressive areas of the periodontal ligament. We then determined gene and/or protein expression of COX-2, IL-6, PG-E₂, RANK-L, OPG, ALPL, VEGF-A, P4HA1, COL1A2, and FN1 via RT-qPCR, ELISA, and Western blot analyses as well as apoptosis, necrosis, cell viability, and cytotoxicity via FACS, MTT, and LDH assays. In addition, hPDL fibroblast-mediated osteoclastogenesis was assessed by TRAP staining in coculture with RAW267.4 cells for another 72 h. Gene and protein expression of all evaluated factors was significantly induced by the mechanical compressive strain applied. Etoricoxib at 3.29 μM and 5.49 μM significantly inhibited PG-E₂ synthesis, but not COX-2 and IL-6 gene expression nor RANK-L-/OPG-mediated osteoclastogenesis or angiogenesis (VEGF-A). Extracellular matrix remodeling (COL1A2, FN1) and bone anabolism (ALPL), by contrast, were significantly stimulated particularly at 5.49 μM. In general, no adverse etoricoxib effects on hPDL fibroblasts regarding apoptosis, necrosis, cell viability, or cytotoxicity were detected. Clinically dosed etoricoxib, that is, a highly selective COX-2 inhibition, did not have substantial effects on hPDL fibroblast-mediated periodontal inflammation, extracellular matrix remodeling, RANK-L/OPG expression, and osteoclastogenesis during simulated orthodontic compressive strain.

The role of physical forces in osteoclastogenesis

The movements of life at every level from organs, tissues, cells to sub-cells, are all conducted in certain physical environments. In the human body, skeletal tissue among all connective tissues is influenced the most by physical forces. Studying the biological behavior of bone cells under different physical environments is helpful in further understanding bone homeostasis and metabolism. Among all bone cells, osteoclast (OC) and OC steered bone remodeling is one of the key points in bone metabolism. In the past few decades, people's understanding of OC was mostly limited to its involvement of bone resorption under physiological and pathological conditions. However, more and more studies started to focus on how physical forces affect the formation and differentiation of OC. This review tries to illustrate the knowledge up to date about how osteoclastogenesis is regulated by physical forces through direct and indirect ways, including fluid shear force, compressive force, and microgravity. The direct way describes the straightforward effects produced by different forces in osteoclastogenesis, whereas the indirect way describes the effects of different forces in osteoclastogenesis through regulation of other bone cells when a certain force is applied. Molecular mechanisms were analyzed and reviewed in both direct and indirect regulation by different forces. Finally, we discussed the status quo and tendency of related research, as well as other unresolved issues, and some future prospects.

Tissue Mechanical Forces and Evolutionary Developmental Changes Act Through Space and Time to Shape Tooth Morphology and Function

Efforts from diverse disciplines, including evolutionary studies and biomechanical experiments, have yielded new insights into the genetic, signaling, and mechanical control of tooth formation and functions. Evidence from fossils and non-model organisms has revealed that a common set of genes underlie tooth-forming potential of epithelia, and changes in signaling environments subsequently result in specialized dentitions, maintenance of dental stem cells, and other phenotypic adaptations. In addition to chemical signaling, tissue forces generated through epithelial contraction, differential growth, and skeletal constraints act in parallel to shape the tooth throughout development. Here recent advances in understanding dental development from these studies are reviewed and important gaps that can be filled through continued application of evolutionary and biomechanical approaches are discussed.

Prevalence of gingival recession after orthodontic treatment of infraversion and open bite

Purpose

Aim of the present study was to investigate the prevalence of gingival recession and related factors in teeth with low occlusal function (open bite and infraversion) after orthodontic treatment.

Methods

From January 2014 to December 2017, 403 patients received orthodontic treatment. Their gingival recession and related factors before and after treatment were retrospectively analyzed.

Results

The prevalence of gingival recession in patients with infraversion and open bite after orthodontic treatment were 80.6 and 75.0%, respectively; these values were 43.4 and 47.5% before treatment, respectively. Notably, the Miller index of gingival recession increased after orthodontic treatment (P < 0.05). The risk of gingival recession in patients with infraversion or open bite after orthodontic treatment was remarkably higher than the risk in other patients (odds ratio [OR] = 16.712 and 5.073, respectively); the gingival recession rate was related to treatment with tooth extraction (OR = 2.043), as well as gingival biotype (OR = 0.341) and gingival index (GI) before orthodontic treatment (OR = 97.404; P < 0.05).

Conclusions

Patients with these two types of low occlusal function are more likely to exhibit gingival recession after orthodontic treatment. Moreover, the prevalence of gingival recession after orthodontic treatment is higher among patients who have undergone tooth extraction during orthodontic treatment, and among those who exhibit thin gingival biotype and high gingival index before orthodontic treatment.

Expression of biological mediators during orthodontic tooth movement: A systematic review

OBJECTIVES

The aim of the present systematic review was to offer a timeline of the events taking place during orthodontic tooth movement(OTM).

MATERIALS AND METHODS

Electronic databases PubMed, Web of Science and EMBASE were searched up to November 2017. All studies describing the expression of signaling proteins in the periodontal ligament(PDL) of teeth subjected to OTM or describing the expression of signaling proteins in human cells of the periodontal structures subjected to static mechanical loading were considered eligible for inclusion for respectively the in-vivo or the in-vitro part. Risk of bias assessment was conducted according to the validated SYRCLE's RoB tool for animal studies and guideline for assessing quality of in-vitro studies for in-vitro studies.

RESULTS

We retrieved 7583 articles in the initial electronic search, from which 79 and 51 were finally analyzed. From the 139 protein investigated, only the inflammatory proteins interleukin(IL)-1β, cyclooxygenase(COX)-2 and prostaglandin(PG)-E2, osteoblast markers osteocalcin and runt-related transcription factor(RUNX)2, receptor activator of nuclear factor kappa-B ligand(RANKL) and osteoprotegerin(OPG) and extracellular signal-regulated kinases(ERK)1/2 are investigated in 10 or more studies.

CONCLUSION

The investigated proteins were presented in a theoretical model of OTM. We can conclude that the cell activation and differentiation and recruitment of osteoclasts is mediated by osteocytes, osteoblasts and PDL cells, but that the osteogenic differentiation is only seen in stem cell present in the PDL. In addition, the recently discovered Ephrin/Ephs seem to play an role parallel with the thoroughly investigated RANKL/OPG system in mediating bone resorption during OTM.

Expression kinetics of human periodontal ligament fibroblasts in the early phases of orthodontic tooth movement

PURPOSE

Human periodontal ligament (hPDL) fibroblasts play a crucial mediating role in orthodontic tooth movement (OTM). In this study, we investigated the expression kinetics of genes associated with OTM in its early phase to obtain better insight into the timing and regulation of molecular and cellular signalling and transformation processes occurring in compressive areas of the periodontal ligament during OTM.

METHODS

Adherent hPDL fibroblasts were stimulated with physiological orthodontic compressive forces of 2 g/cm² for 24, 48, 72, and 96 h under cell culture conditions. At each time point, we quantified relative gene expression of genes involved in bone remodelling (ALPL), inflammation (COX2, IL-6), extracellular matrix reorganization (COL1A2, P4HA1, FN1, MMP8) and angiogenesis (VEGF-A) by means of RT-qPCR as well as protein expression of osteoclastogenesis-regulating RANK-L and OPG relative to pressure-untreated controls incubated for corresponding time periods. In addition, coculture experiments with osteoclast precursor cells were performed to determine the extent of hPDL-fibroblast-mediated osteoclastogenesis (TRAP staining).

RESULTS

As primary response to compressive forces within 24 h, we observed an induction of genes associated with angiogenesis, inflammation, osteoblastogenesis, and the remodelling of the extracellular matrix, with RANK-L expression at first slightly inhibited and only increased after 48 h. Major hPDL-mediated osteoclastogenesis was observed after 72 h with minor, non-RANK-L-dependent osteoclastogenesis occurring as early as 24 h after compressive force application.

CONCLUSIONS

hPDL fibroblasts seem to play a major mediating role in the early phase of OTM with a differentiated, time-dependent regulation and expression pattern of cytokines and other mediators.

ClC-3 Promotes Osteogenic Differentiation in MC3T3-E1 Cell After Dynamic Compression

ClC-3 chloride channel has been proved to have a relationship with the expression of osteogenic markers during osteogenesis, persistent static compression can upregulate the expression of ClC-3 and regulate osteodifferentiation in osteoblasts. However, there was no study about the relationship between the expression of ClC-3 and osteodifferentiation after dynamic compression. In this study, we applied dynamic compression on MC3T3-E1 cells to detect the expression of ClC-3, runt-related transcription factor 2 (Runx2), bone morphogenic protein-2 (BMP-2), osteopontin (OPN), nuclear-associated antigen Ki67 (Ki67), and proliferating cell nuclear antigen (PCNA) in biopress system, then we investigated the expression of these genes after dynamic compression with Chlorotoxin (specific ClC-3 chloride channel inhibitor) added. Under transmission electron microscopy, there were more cell surface protrusions, rough surfaced endoplasmic reticulum, mitochondria, Golgi apparatus, abundant glycogen, and lysosomes scattered in the cytoplasm in MC3T3-E1 cells after dynamic compression. The nucleolus was more obvious. We found that ClC-3 was significantly up-regulated after dynamic compression. The compressive force also up-regulated Runx2, BMP-2, and OPN after dynamic compression for 2, 4 and 8 h. The proliferation gene Ki67 and PCNA did not show significantly change after dynamic compression for 8 h. Chlorotoxin did not change the expression of ClC-3 but reduced the expression of Runx2, BMP-2, and OPN after dynamic compression compared with the group without Cltx added. The data from the current study suggested that ClC-3 may promotes osteogenic differentiation in MC3T3-E1 cell after dynamic compression. J. Cell. Biochem. 118: 1606-1613, 2017. © 2016 Wiley Periodicals, Inc.

Contribution of biomechanical forces to inflammation-induced bone resorption

AIM

This study aimed to evaluate the contribution of biomechanical loading to inflammation-induced tissue destruction.

MATERIALS AND METHODS

A total of 144 adult Holtzman rats were randomly assigned into four experimental groups: control (C), ligature-induced periodontal disease (P), orthodontic movement (OM), and combination group (OMP). On days 1, 3, 7, and 15, following baseline, nine animals from each experimental group were killed. Bone volume fraction (BVF) and bone mineral density (BMD) were measured using micro-computed tomography. Expression and synthesis profile of cytokines and receptors of inflammation in gingival tissues were evaluated by PCR array assay and multiplex immunoassay.

RESULTS

At 15 days, the OMP group presented a significantly (p < 0.05) lower BVF and BMD levels when compared to all the other groups. The OMP group presented the highest number of upregulated protein targets in comparison to the other groups. Furthermore, the gene expression and protein levels of CCL2, CCL3, IL-1β, IL1-α, IL-18, TNF-α, and VEGF were significantly (p < 0.05) higher in the OMP group when compared to the P group.

CONCLUSIONS

In summary, mechanical loading modulates the inflammatory response of periodontal tissues to periodontal disease by increasing the expression of several pro-inflammatory mediators and receptors, which leads to increased bone resorption.

Bone Response of Loaded Periodontal Ligament

The tooth-periodontal ligament-alveolar bone complex acts symbiotically to dissipate the mechanical loads incurred during mastication and/or orthodontic tooth movement. The periodontal ligament functions both in the tension and compression. At the molecular and celleular levels, the loads in the periodontal ligament trigger mechanobiological events in the alveolar bone, which leads to bone modeling and remodeling. The current review focuses on the bone response to mechanical loading of the periodontal ligament on the tension and pressure sides. Understanding the bone response has major implications for dentistry, including a better understanding of the different types of orthodontic tooth movement.

Intermittent Hypoxia Influences Alveolar Bone Proper Microstructure via Hypoxia-Inducible Factor and VEGF Expression in Periodontal Ligaments of Growing Rats

Intermittent hypoxia (IH) recapitulates morphological changes in the maxillofacial bones in children with obstructive sleep apnea (OSA). Recently, we found that IH increased bone mineral density (BMD) in the inter-radicular alveolar bone (reflecting enhanced osteogenesis) in the mandibular first molar (M1) region in the growing rats, but the underlying mechanism remains unknown. In this study, we focused on the hypoxia-inducible factor (HIF) pathway to assess the effect of IH by testing the null hypothesis of no significant differences in the mRNA-expression levels of relevant factors associated with the HIF pathway, between control rats and growing rats with IH. To test the null hypothesis, we investigated how IH enhances mandibular osteogenesis in the alveolar bone proper with respect to HIF-1α and vascular endothelial growth factor (VEGF) in periodontal ligament (PDL) tissues. Seven-week-old male Sprague-Dawley rats were exposed to IH for 3 weeks. The microstructure and BMD in the alveolar bone proper of the distal root of the mandibular M1 were evaluated using micro-computed tomography (micro-CT). Expression of HIF-1α and VEGF mRNA in PDL tissues were measured, whereas osteogenesis was evaluated by measuring mRNA levels for alkaline phosphatase (ALP) and bone morphogenetic protein-2 (BMP-2). The null hypothesis was rejected: we found an increase in the expression of all of these markers after IH exposure. The results provided the first indication that IH enhanced osteogenesis of the mandibular M1 region in association with PDL angiogenesis during growth via HIF-1α in an animal model.

The Effect of An Angiogenic Cytokine on Orthodontically Induced Inflammatory Root Resorption

Objective

Orthodontically induced inflammatory root resorption (OIIRR) is an undesirable sequel of tooth movement after sterile necrosis that takes place in periodontal ligament due to blockage of blood vessels following exertion of orthodontic force. This study sought to assess the effect of an angiogenic cytokine on OIIRR in rat model.

Materials and Methods

In this experimental animal study, 50 rats were randomly divided into 5 groups of 10 each: E10, E100 and E1000 receiving an injection of 10, 100 and 1000 ng of basic fibroblast growth factor (bFGF), respectively, positive control group (CP) receiving an orthodontic appliance and injection of phosphate buffered saline (PBS) and the negative control group (CN) receiving only the anesthetic agent. A nickel titanium coil spring was placed between the first molar and the incisor on the right side of maxilla. Twenty-one days later, the rats were sacrificed. Histopathological sections were made to assess the number and area of resorption lacunae, number of blood vessels, osteoclasts and Howship’s lacunae. Data were statistically analyzed using ANOVA and Tukey’s honest significant difference (HSD) test.

Results

Number of resorption lacunae and area of resorption lacunae in E1000 (0.97 ± 0.80 and 1. 27 ± 0.01×10^-3, respectively) were significantly lower than in CP (4.17 ± 0.90 and 2.77 ± 0.01×10-3, respectively, P=0.000). Number of blood vessels, osteoclasts and Howship’s lacunae were significantly higher in E1000 compared to CP (P<0.05).

Conclusion

Tooth movement as the outcome of bone remodeling is concomitant with the formation of sterile necrosis in the periodontal ligament following blocked blood supply. Thus, bFGF can significantly decrease the risk of root resorption by providing more oxygen and angiogenesis.

Effects of vascular endothelial growth factor on osteoblasts and osteoclasts

INTRODUCTION

Bone remodeling is crucial to the success of many dental procedures and is tightly regulated. Vascular endothelial growth factor (VEGF), a key cytokine for angiogenesis, is also an important regulator of bone remodeling. We aimed to examine the mechanisms by which VEGF induces bone remodeling by studying its effects on cultured osteoblasts and osteoclasts.

METHODS

Preosteoblastic MC3T3-E1 cells were treated with vehicle or VEGF-A165. Cell proliferation, migration, and invasion potentials were assessed. Preosteoclastic RAW264.7 cells were treated with vehicle or VEGF with or without the receptor activator of nuclear factor kappa-B ligand (RANKL), and osteoclast formation was measured with tartrate-resistant acid phosphatase staining. Conditioned media from vehicle-treated or VEGF-treated MC3T3-E1 cells were tested for the levels of RANKL and osteoprotegerin (OPG) and were used to treat RAW264.7 cells to observe osteoclast formation.

RESULTS

VEGF significantly induced MC3T3-E1 cell proliferation, migration, and invasion. VEGF did not directly induce osteoclastogenesis but significantly increased the RANKL/OPG ratio in the conditioned media from the MC3T3-E1 cultures; this significantly increased osteoclast formation.

CONCLUSIONS

VEGF stimulates osteoclast differentiation by increasing the osteoblastic RANKL/OPG ratio but has no direct effect on osteoclast precursor cells, and it induces osteoblast proliferation, migration, and invasion potentials in vitro.

The effects of fluid shear stress on proliferation and osteogenesis of human periodontal ligament cells

Shear stress is one of the main stress type produced by speech, mastication or tooth movement. The mechano-response of human periodontal ligament (PDL) cells by shear stress and the mechanism are largely unknown. In our study, we investigated the effects of fluid shear stress on proliferation, migration and osteogenic potential of human PDL cells. 6dyn/cm(2) of fluid shear stress was produced in a parallel plate flow chamber. Our results demonstrated that fluid shear stress rearranged the orientation of human PDL cells. In addition, fluid shear stress inhibited human PDL cell proliferation and migration, but increased the osteogenic potential and expression of several growth factors and cytokines. Our study suggested that shear stress is involved in homeostasis regulation in human PDL cells. Inhibiting proliferation and migration potentially induce PDL cells to respond to mechanical stimuli in order to undergo osteogenic differentiation.

The effect of hypoxia on the formation of mouse incisor enamel

OBJECTIVE

The permanently growing mouse incisors exhibit all stages of tooth development along their inciso-apical axis at any time. Any disturbance or injury of the ameloblasts during enamel formation or maturation may result in permanent defects in the finished enamel since the enamel does not undergo repair or remodeling after formation. In order to increase our understanding of how hypoxia affects enamel formation, we induced severe acute hypoxia in adult mice and observed its effects on the enamel in incisors.

DESIGN

Incisors from hypoxic mice were obtained 5 and 49 days after the hypoxic insult. Hypoxic and control incisors were dissected out and observed by scanning electron microscopy (SEM). Incisors were subsequently ground longitudinally or transversely, etched, and observed again by SEM. The nature and position of defects were considered in relation to the configuration and dynamics of the incisors.

RESULTS

The effect of hypoxia varied considerably, among mice, among incisors, and among ameloblasts. Affected enamel showed hypoplasia with hypomineralization or hypomineralization without hypoplasia. Vascular endothelial growth factor (VEGF) showed considerably stronger labeling in hypoxic compared to control ameloblasts.

CONCLUSIONS

The present study demonstrates quantitative and qualitative defects in the enamel reflecting the vulnerability of ameloblasts toward severe acute hypoxia in mouse incisors.

Biological Events in Periodontal Ligament and Alveolar Bone Associated with Application of Orthodontic Forces

Orthodontic force-induced stresses cause dynamic alterations within the extracellular matrix and within the cytoskeleton of cells in the periodontal ligament and alveolar bone, mediating bone remodelling, ultimately enabling orthodontic tooth movement. In the periodontal ligament and alveolar bone, the mechanically induced tensile strains upregulate the expression of osteogenic genes resulting in bone formation, while mechanically induced compressive strains mediate predominantly catabolic tissue changes and bone resorption. In this review article we summarize some of the currently known biological events occurring in the periodontal ligament and in the alveolar bone in response to application of orthodontic forces and how these facilitate tooth movement.

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.

Immunolocalization of FGF-2 and VEGF in rat periodontal ligament during experimental tooth movement

Objective

This article aimed at identifying the expression of fibroblast growth factor-2 (FGF-2) and vascular endothelial growth factor (VEGF) in the tension and pressure areas of rat periodontal ligament, in different periods of experimental orthodontic tooth movement.

Methods

An orthodontic force of 0.5 N was applied to the upper right first molar of 18 male Wistar rats for periods of 3 (group I), 7 (group II) and 14 days (group III). The counter-side first molar was used as a control. The animals were euthanized at the aforementioned time periods, and their maxillary bone was removed and fixed. After demineralization, the specimens were histologically processed and embedded in paraffin. FGF-2 and VEGF expressions were studied through immunohistochemistry and morphological analysis.

Results

The experimental side showed a higher expression of both FGF-2 and VEGF in all groups, when compared with the control side (P < 0.05). Statistically significant differences were also found between the tension and pressure areas in the experimental side.

Conclusion

Both FGF-2 and VEGF are expressed in rat periodontal tissue. Additionally, these growth factors are upregulated when orthodontic forces are applied, thereby suggesting that they play an important role in changes that occur in periodontal tissue during orthodontic movement.

Biomechanical force induces the growth factor production in human periodontal ligament-derived cells

Although many reports have been published on the functional roles of periodontal ligament (PDL) cells, the mechanisms involved in the maintenance and homeostasis of PDL have not been determined. We investigated the effects of biomechanical force on growth factor production, phosphorylation of MAPKs, and intracellular transduction pathways for growth factor production in human periodontal ligament (hPDL) cells using MAPK inhibitors. hPDL cells were exposed to mechanical force (6 MPa) using a hydrostatic pressure apparatus. The levels of growth factor mRNA and protein were examined by real-time RT-PCR and ELISA. The phosphorylation of MAPKs was measured using BD™ CBA Flex Set. In addition, MAPKs inhibitors were used to identify specific signal transduction pathways. Application of biomechanical force (equivalent to occlusal force) increased the synthesis of VEGF-A, FGF-2, and NGF. The application of biomechanical force increased the expression levels of phosphorylated ERK and p38, but not of JNK. Furthermore, the levels of VEGF-A and NGF expression were suppressed by ERK or p38 inhibitor. The growth factors induced by biomechanical force may play a role in the mechanisms of homeostasis of PDL.

Osteoimmunology in orthodontic tooth movement

The skeletal and immune systems share a multitude of regulatory molecules, including cytokines, receptors, signaling molecules, and signaling transducers, thereby mutually influencing each other. In recent years, several novel insights have been attained that have enhanced our current understanding of the detailed mechanisms of osteoimmunology. In orthodontic tooth movement, immune responses mediated by periodontal tissue under mechanical force induce the generation of inflammatory responses with consequent alveolar bone resorption, and many regulators are involved in this process. In this review, we take a closer look at the cellular/molecular mechanisms and signaling involved in osteoimmunology and at relevant research progress in the context of the field of orthodontic tooth movement.

Involvement of TSP1 and MMP9/NGAL in angiogenesis during orthodontic periodontal remodeling

In the present study the aim was to measure the levels of Thrombospondin-1 (TSP1) and Lipocalin-2/matrix metalloproteinase 9 (MMP9/NGAL) complex in gingival crevicular fluid (GCF) at different time points of orthodontic treatment, to determine the relationship between these values and those of total-matrix metalloproteinase 9 (MMP9) and theirs implication in angiogenesis balance, in the situation of a good control of the bacterial plaque, emphasizing the role of TSP1 and MMP9/NGAL complex. GCF samples were collected from 16 young orthodontic patients requiring upper canine distalization (test tooth) with first premolar extraction. The contralateral canine (control tooth) was free from orthodontic force. For the orthodontic appliance, brackets Roth 0.018 inch with 0.012 inch NiTi archwire and a laceback were used. TSP1, MMP9/NGAL, and MMP9 increased from 1 hour before activation of orthodontic appliance to a maximum at 8 hours for MMP9 and 72 hours for MMP9/NGAL and TSP1. The results show a change in time of TSP1, MMP9/NGAL, and MMP9 levels in GCF of patients with this method of orthodontic treatment. The powerful correlation of MMP9/NGAL with TSP1 suggests their stronger involvement in angiogenesis processes in PDL during orthodontic periodontal remodeling, in the situation of a healthy periodontium and a good control of the bacterial plaque.

Gravity loading induces adenosine triphosphate release and phosphorylation of extracellular signal-regulated kinases in human periodontal ligament cells

AIM

The periodontal ligament (PDL) receives mechanical stress (MS) from dental occlusion or orthodontic tooth movement. Mechanical stress is thought to be a trigger for remodeling of the PDL and alveolar bone, although its signaling mechanism is still unclear. So we investigated the effect of MS on adenosine triphosphate (ATP) release and extracellular signal-regulated kinases (ERK) phosphorylation in PDL cells.

METHODS

Mechanical stress was applied to human PDL cells as centrifugation-mediated gravity loading. Apyrase, Ca(2+)-free medium and purinergic receptor agonists and antagonists were utilized to analyze the contribution of purinergic receptors to ERK phosphorylation.

RESULTS

Gravity loading and ATP increased ERK phosphorylation by 5 and 2.5 times, respectively. Gravity loading induced ATP release from PDL cells by tenfold. Apyrase and suramin diminished ERK phosphorylation induced by both gravity loading and ATP. Under Ca(2+)-free conditions the phosphorylation by gravity loading was partially decreased, whereas ATP-induced phosphorylation was unaffected. Receptors P2Y4 and P2Y6 were prominently expressed in the PDL cells.

CONCLUSION

Gravity loading induced ATP release and ERK phosphorylation in PDL fibroblasts, and ATP signaling via P2Y receptors was partially involved in this phosphorylation, which in turn would enhance gene expression for the remodeling of PDL tissue during orthodontic tooth movement.

Biomarkers of periodontal tissue remodeling during orthodontic tooth movement in mice and men: overview and clinical relevance

Biologically active substances are expressed by cells within the periodontium in response to mechanical stimuli from orthodontic appliances. Several possible biomarkers representing biological modifications during specific phenomena as simile-inflammatory process, bone resorption and formation, periodontal ligament changes, and vascular and neural responses are proposed. Citations to potentially published trials were conducted by searching PubMed, Cochrane databases, and scientific textbooks. Additionally, hand searching and contact with experts in the area were undertaken to identify potentially relevant published and unpublished studies. Selection criteria were as follows: animal models involving only mice and rats undergoing orthodontic treatment; collection of gingival crevicular fluid (GCF) as a noninvasively procedure for humans; no other simultaneous treatment that could affect experimental orthodontic movement. The data suggest that knowledge of the remodeling process occurring in periodontal tissues during orthodontic and orthopedic therapies may be a clinical usefulness procedure leading to proper choice of mechanical stress to improve and to shorten the period of treatment, avoiding adverse consequences. The relevance for clinicians of evaluating the rate of some substances as valid biomarkers of periodontal effects during orthodontic movement, by means of two models of study, mice and men, is underlined.