Orthodontic movement induces high numbers of cells expressing IFN-gamma at mRNA and protein levels

Mechanisms of Osteoclastogenesis in Orthodontic Tooth Movement and Orthodontically Induced Tooth Root Resorption

Orthodontic tooth movement (OTM) is achieved by the simultaneous activation of bone resorption by osteoclasts and bone formation by osteoblasts. When orthodontic forces are applied, osteoclast-mediated bone resorption occurs in the alveolar bone on the compression side, creating space for tooth movement. Therefore, controlling osteoclastogenesis is the fundamental tenet of orthodontic treatment. Orthodontic forces are sensed by osteoblast lineage cells such as periodontal ligament (PDL) cells and osteocytes. Of several cytokines produced by these cells, the most important cytokine promoting osteoclastogenesis is the receptor activator of nuclear factor-κB ligand (RANKL), which is mainly supplied by osteoblasts. Additionally, osteocytes embedded within the bone matrix, T lymphocytes in inflammatory conditions, and PDL cells produce RANKL. Besides RANKL, inflammatory cytokines, such as interleukin-1, tumor necrosis factor-α, and prostaglandin E2 promote osteoclastogenesis under OTM. On the downside, excessive osteoclastogenesis activation triggers orthodontically-induced external root resorption (ERR) through pro-osteoclastic inflammatory cytokines. Therefore, understanding the mechanisms of osteoclastogenesis during OTM is essential in reducing the adverse effects of orthodontic treatment. Here, we review the current concepts of the mechanisms underlying osteoclastogenesis in OTM and orthodontically induced ERR.

Impact of FGF1 on human periodontal ligament fibroblast growth, osteogenic differentiation and inflammatory reaction in vitro

PURPOSE

To investigate in vitro the impact of fibroblast growth factor 1 (FGF1) in comparison to ascorbic acid (AscA) on human periodontal ligament fibroblast (HPdLF) growth, their osteogenic differentiation, and modulation of their inflammatory reaction to mechanical stress.

METHODS

The influence of different concentrations of FGF1 (12.5-200 ng/mL) on growth and proliferation of HPdLF cells was analyzed over 20 days by counting cell numbers and the percentage of Ki67-positive cells. Quantitative expression analysis of genes encoding the osteogenic markers alkaline phosphatase (ALPL), Runt-related transcription factor 2 (RUNX2), osteocalcin (OCN), and osteopontin (OSP), as well as the fibroblast markers vimentin (VIM) and fibroblast-specific protein 1 (FSP1), was performed after 2 and 20 days of cultivation. Metabolic activity was determined by MTT assay. For comparison with AscA, 50 ng/mL FGF1 was used for stimulation for 2 and 20 days. Cell number, percentage of Ki67-positive cells, and expression of osteoblast- and fibroblast-specific genes were examined. Alkaline phosphatase activity was visualized by NBT/BCIP and calcium deposits were stained with alizarin red. Cytokine (IL‑6, IL‑8, COX2/PGE2) expression and secretion were analyzed by qPCR and ELISA in 6 h mechanically compressed HPdLF cultured for 2 days with FGF1 or ascorbic acid.

RESULTS

Higher concentrations of FGF1 promoted cell proliferation upon short-term stimulation, whereas prolonged treatment induced the expression of osteogenic markers even with low concentrations. AscA promotes cell growth more markedly than FGF1 in short-term cultures, whereas FGF1 induced osteogenic cell fate more strongly in long-term culture. Both factors induced an increased inflammatory response of HPdLF to mechanical compression.

CONCLUSION

Our data suggest that FGF1 promotes an osteogenic phenotype of HPdLF and limits inflammatory response to mechanical forces compared to AscA.

Cytokine levels in gingival crevicular fluid during orthodontic treatment with aligners compared to conventional labial fixed appliances: a 3-week clinical study

Objective: To test the hypothesis that the levels of IL-1ß and TNF-α increased more and IL-1α, IL-2, IL-6, IL-8 increased less, after 3 weeks of treatment with conventional labial fixed appliance and with aligners. Material and methods: Forty patients who were treated either with labial brackets (n = 20) or aligners (n = 20). Gingival crevicular fluid (GCF) samples were collected at baseline and after 21 days. Cytokine levels were evaluated by enzyme-linked immune sorbent assay (ELISA). Plaque index (PI), gingival index (GI), and bleeding on probing (POB) were also examined. Results: The levels of IL-1α, IL-1ß, IL-2, IL-6, IL-8 and TNF-α in the GCF were significantly increased in both groups. The levels of IL-2, IL-6, IL-8 increased more in patients treated with aligners compared to those treated by labial fixed appliances. There was a statistically significant difference in change of the mean cytokine levels of IL-1α, IL-2, IL-6, IL-8 and TNF-α compared to labial fixed appliances and aligners. Conclusions: The levels of the six studied cytokines in GCF (IL-1α, IL-1ß, IL-2, IL-6, IL-8 and TNF-α) increased after 3 weeks both after treatment with conventional labial fixed appliance and with aligners. IL-1ß and TNF-α showed a prominent increase compared to the other cytokines in the GCF of teeth by both the labial fixed appliance and aligners. However, there were only minor differences in the changes of the cytokine levels from baseline to 3 weeks between the two groups. There were no differences between the groups regarding PI, GI or POB.

Remote Corticotomy Accelerates Orthodontic Tooth Movement in a Rat Model

Introduction

With an increasing demand for orthodontic treatment for adult patients, orthodontic professionals are constantly seeking novel strategies and technologies that can accelerate tooth movement in order to shorten the treatment period. For instance, in recent years, the influences of different surgical techniques on orthodontic tooth movement in the ipsilateral side of surgery were intensively investigated. Here, we attempt to examine if corticotomy could also affect the rate of tooth movement in the contralateral side of the surgery by using a rodent model.

Materials and Methods

72 eight-week-old Sprague-Dawley rats were randomly divided into three groups as follows: the Control group (orthodontic treatment devices delivered only, no tooth movement), the orthodontic tooth movement (OTM) group (orthodontic treatment devices delivered and orthodontic treatment performed), and the Corticotomy + OTM group (remote corticotomy performed, orthodontic treatment devices delivered, followed by orthodontic treatment). The surgical procedure was conducted on the right side of the maxilla at the time of appliance placement and a force of 60 g was applied between the maxillary left first molar and maxillary incisors using nickel-titanium springs to stimulate OTM. The OTM distance and speed were tracked at 3, 7, 14, and 28 days post-surgery, followed by histological and immunohistochemical assessments.

Results

In comparison with orthodontic treatment only, the contralateral corticotomy significantly accelerated OTM. Furthermore, animals undergoing corticotomy + OTM presented with a greater number of osteoclasts on the compression side, stronger staining of the osteogenic marker on the tension side, and higher expression of an inflammatory marker than the OTM group animals.

Conclusion

Our current study demonstrates that remote corticotomy effectively accelerates alveolar bone remodeling and OTM. The study enriches our understanding of the regional acceleratory phenomenon (RAP) and offers an alternative strategy for accelerating OTM to shorten the orthodontic treatment period.

Effect of systemic delivery of Substance P on experimental tooth movement in rats

INTRODUCTION

The purpose of this study was to investigate the effect of systemic delivery of Substance P (SP) on experimental tooth movement.

METHODS

Forty-eight adult Sprague-Dawley rats were randomly divided into 2 groups and their maxillary first molars were mesially moved with the use of closed-coil springs. The experiment group received systemic injection of SP and the control group received phosphate-buffered saline solution. Transportation distances of first molars were measured. Hematoxylin and eosin staining, tartrate-resistant acid phosphatase staining, and immunohistochemistry staining were performed to evaluate alveolar bone remodeling. Then the interferon (IFN) γ and tumor necrosis factor (TNF) α concentrations in peripheral blood and local periodontal tissue were measured. Finally, the effects of SP on bone marrow-derived stem cell (BMSC) proliferation and migration were tested in vitro.

RESULTS

Systemic delivery of SP significantly increased the distance of tooth movement and stimulated both osteoclast and osteoblast activities. The concentrations of IFN-γ and TNF-α increased in peripheral blood at early phases of the experiment and decreased in periodontal tissue at late phases. In vitro, the proliferation and migration of BMSCs were promoted by SP.

CONCLUSIONS

Systemic delivery of SP can accelerate orthodontic tooth movement and promote alveolar bone remodeling potentially through immunomodulation and mobilizing endogenous mesenchymal stem cells.

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.

Probiotic consumption decreases the number of osteoclasts during orthodontic movement in mice

AIMS

The aim of the present study was to investigate the effect of probiotic (Bacillus Subtilis) supplementation on bone remodelling induced by mechanical loading.

METHODS

C57BL/6 mice were divided in two groups: (1) Probiotic and (2) Vehicle (water). The probiotic (1.5×10⁸CFU/mL) was administered orally for 14 days, starting two days before the induction of orthodontic tooth movement (OTM). OTM was determined by histomorphometric analysis by comparing the right to the left side of the maxilla. The number of osteoclasts was determined by counting TRAP-positive cells. Osteoblasts were counted on Masson's trichrome-stained slides.

RESULTS

OTM was similar between groups (with and without probiotic supplementation) (p=0.46). The number of TRAP-positive cells increased (p<0.01) on the experimental side (where the spring coil was installed) in comparison to the control side in both groups. However, the number of osteoclasts decreased (p˂0.01) in the probiotic group, in comparison to the vehicle group. There was an increase in the number of osteoblasts (p˂0.05) in both the Vehicle and Probiotic groups on the side under OTM, independent of probiotic supplementation.

CONCLUSION

Oral Supplementation with a probiotic influenced the number of osteoclasts adjacent to the tooth root during orthodontic movement in mice.

The osteoimmunology of alveolar bone loss

The mineralized structure of bone undergoes constant remodeling by the balanced actions of bone-producing osteoblasts and bone-resorbing osteoclasts (OCLs). Physiologic bone remodeling occurs in response to the body's need to respond to changes in electrolyte levels, or mechanical forces on bone. There are many pathological conditions, however, that cause an imbalance between bone production and resorption due to excessive OCL action that results in net bone loss. Situations involving chronic or acute inflammation are often associated with net bone loss, and research into understanding the mechanisms regulating this bone loss has led to the development of the field of osteoimmunology. It is now evident that the skeletal and immune systems are functionally linked and share common cells and signaling molecules. This review discusses the signaling system of immune cells and cytokines regulating aberrant OCL differentiation and activity. The role of these cells and cytokines in the bone loss occurring in periodontal disease (PD) (chronic inflammation) and orthodontic tooth movement (OTM) (acute inflammation) is then described. The review finishes with an exploration of the emerging role of Notch signaling in the development of the immune cells and OCLs that are involved in osteoimmunological bone loss and the research into Notch signaling in OTM and PD.

Biomarkers in orthodontic tooth movement

Tooth movement by orthodontic treatment is characterized by remodeling changes in the periodontal ligament, alveolar bone, and gingiva. A reflection of these phenomenons can be found in the gingival crevicular fluid (GCF) of moving teeth, with significant elevations in the concentrations of its components like, cytokines, neurotransmitters, growth Factors, and a arachidonic acid metabolites. GCF arises at the gingival margin and can be described as a transudate or an exudate. Several studies have focused on the composition of GCF and the changes that occur during orthodontic tooth movement (OTM). GCF component analysis is a non-invasive method for studying the cellular response of the underlying periodontium. Clinically, GCF can be easily collected using platinum loops, filter paper strips, gingival washings, and micropipettes. A number of GCF biomarkers involve in bone remodeling during OTM. The data suggest that knowledge of all the biomarkers present in the GCF that can be used to mark the changes in tooth that is undergoing orthodontic treatment may be of clinical usefulness leading to proper choice of mechanical stress to improve and to shorten treatment time and avoid side effects.

T Cells Are Required for Orthodontic Tooth Movement

The immune system plays a pivotal role during bone remodeling process. Orthodontic tooth movement (OTM) induces local inflammation in periodontium, but whether systemic immune response is involved in OTM remains unknown. In this study, we show that tooth movement distance was significantly reduced in T-cell-deficient immunocompromised mice compared with wild-type (WT) mice. Intravenous infusion of allogeneic T cells to the immunocompromised mice rescued the OTM distance. Correspondingly, increased numbers of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts were detected around the alveolar bone after OTM in WT mice but were barely detected in immunocompromised mice. Moreover, intravenous infusion of T cells rescued the number of TRAP-positive osteoclasts in the OTM area of the immunocompromised mice, thus suggesting T cells are required for OTM. We then reveal that OTM induced a significant elevation of type 1 T helper cell (Th1) cytokines tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) around periodontal tissue in WT but not in immunocompromised mice. Infusion of T cells could increase the levels of TNF-α and IFN-γ in periodontal tissues of immunocompromised mice. More interestingly, intraperitoneal injection of TNF-α inhibitor etanercept significantly reduced the distance of OTM in T-cell-infused immunocompromised mice. In summary, this study demonstrates a previously unrecognized mechanism that T cells are required for OTM depending on Th1-associated cytokines.

Biomarkers of Orthodontic Tooth Movement in Gingival Crevicular Fluid: A Systematic Review

BACKGROUND

The analysis of gingival crevicular fluid (GCF) may be an acceptable way to examine the ongoing biochemical processes associated with bone turnover during orthodontic tooth movement. If it is possible to biologically monitor and predict the outcome of orthodontic forces, then the management of appliances could be based on individual tissue responses, and the effectiveness of the treatment could be improved.

METHODOLOGY

A literature search was carried out in major databases, such as medline, EMBASE, cochrane library, web of science, google scholar and scopus for relevant studies. Publications in English between 2000 and 2014 which estimated GCF markers as indicators of orthodontic tooth movement were included.

RESULTS

The list of biomarkers available to date was compiled and presented in table format. Each biomarker is discussed separately based on the available evidence.

CONCLUSION

Several sensitive GCF markers are available to detect the biomechanical changes occurring during orthodontic tooth movement. Further focused research might help to analyze the sensitivity and reliability of these indicators, which in turn can lead to the development of chairside tests to assess the outcome of orthodontic therapy.

M1-like Macrophage Polarization Promotes Orthodontic Tooth Movement

Macrophages play a crucial role in inflammatory-mediated bone loss. Orthodontic tooth movement (OTM) is associated with inflammatory bone remodeling. However, whether and how macrophages contribute to mechanical force–induced OTM remains unknown. In this study, we hypothesized that polarization of M1-like macrophages may contribute to the OTM. Orthodontic nickel-titanium springs were applied to the upper first molars of rats or mice to induce OTM. The distance of OTM gradually increased after mechanical force was applied to the rats for 5 and 10 d. M1-like macrophage polarization and expression of M1 cytokine tumor necrosis factor (TNF)-α also increased after force application. More importantly, monocyte/macrophage depletion in mice by injection of clodronate liposomes decreased the distance of OTM and the number of tartrate-resistant acid phosphatase (TRAP)–positive osteoclasts and CD68+ macrophages, accompanied by reduced expressions of M1 markers TNF-α and inducible nitric oxide synthase (iNOS), whereas systemic transfusion of M1 macrophages in mice increased them. Further experiments showed that injection of recombinant TNF-α increased the distance of OTM and the number of TRAP-positive osteoclasts and CD68+ macrophages, as well as upregulated the expression of TNF-α and iNOS. Blockage of TNF-α by etanercept injection reduced the distance of OTM and the number of TRAP-positive osteoclasts and CD68+ macrophages, as well as decreased the levels of TNF-α and iNOS. These data suggest that M1-like macrophage polarization promotes alveolar bone resorption and consequent OTM after mechanical force application.

Changes of tumor necrosis factor-α, interleukin-10, and tartrate-resistant acid phosphatase5b in the crevicular fluid in relation to orthodontic movement

The aim of this study was to determine gingival crevicular fluid (GCF) expressions of tumor necrosis factor-α (TNF-α), interleukin-10 (IL-10), and tartrate-resistant acid phosphatase (TRAP) 5b in the mechanism of orthodontic tooth movement. Nine adolescents requiring canine distalization participated in the study. A canine undergoing distal movement served as the test tooth, and the contra-lateral canine served as the control. The clinical parameters were recorded and GCF samples were collected from the mesial and distal gingival crevices of teeth at baseline, 1 h, 24 h, 7 days, and 28 days following force application. GCF samples were analyzed using ELISA. The data were analyzed using three-way repeated measures analysis of variance. TNF-α and TRAP5b levels in distal and mesial sites of the test teeth were significantly higher than that at both sites of the controls. When compared with baseline values, increase was prominent at 1 h and 24 h. The IL-10 concentration decreased during experimental period at both sites of the control and test teeth. The results demonstrated that orthodontic forces evoke changes in the levels of TNF-α, IL-10, and TRAP5b during the initial stages of force application. The changes in local host response in periodontal tissues may be one of the triggers in regulating alveolar bone resorption during orthodontic tooth movement.

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.

Effect of cytokines on osteoclast formation and bone resorption during mechanical force loading of the periodontal membrane

Mechanical force loading exerts important effects on the skeleton by controlling bone mass and strength. Several in vivo experimental models evaluating the effects of mechanical loading on bone metabolism have been reported. Orthodontic tooth movement is a useful model for understanding the mechanism of bone remodeling induced by mechanical loading. In a mouse model of orthodontic tooth movement, TNF-α was expressed and osteoclasts appeared on the compressed side of the periodontal ligament. In TNF-receptor-deficient mice, there was less tooth movement and osteoclast numbers were lower than in wild-type mice. These results suggest that osteoclast formation and bone resorption caused by loading forces on the periodontal ligament depend on TNF-α. Several cytokines are expressed in the periodontal ligament during orthodontic tooth movement. Studies have found that inflammatory cytokines such as IL-12 and IFN-γ strongly inhibit osteoclast formation and tooth movement. Blocking macrophage colony-stimulating factor by using anti-c-Fms antibody also inhibited osteoclast formation and tooth movement. In this review we describe and discuss the effect of cytokines in the periodontal ligament on osteoclast formation and bone resorption during mechanical force loading.

Impact of orthodontic retainers on periodontal health status assessed by biomarkers in gingival crevicular fluid

OBJECTIVE

To evaluate whether biomarkers of inflammation and periodontal remodeling are differentially expressed in the gingival crevicular fluid (GCF) of patients wearing different types of orthodontic retainers.

MATERIALS AND METHODS

Thirty-one adult subjects (17 men and 14 women with an age range of 20 to 35 years) were allocated to three different groups. Group 1 consisted of 10 patients wearing fixed retainers, group 2 included 11 patients using lower removable retainers, and group 3 comprised 10 patients without retainers (control). Periodontal health assessment and GCF collection were carried out at two sites per subject: the lingual side of a central lower incisor and the lingual side of a lower second premolar. Aliquots from diluted GCF were screened for the presence of biomarkers using a microarray technique.

RESULTS

Group 1 patients exhibited a higher percentage of sites with visible plaque in the incisor region than the other groups (P = .03); no differences were noted in gingival bleeding and probing depths. The median concentrations (pg/mL) of interferon-gamma and interleukin-10 were significantly higher in the premolar sites of patients in group 2 (P = .01 and P = .04, respectively), whereas the concentration of matrix metalloproteinase-9 was significantly higher at the incisors of patients wearing fixed retainers (P = .02). A significant difference between the two sites was seen only in group 2.

CONCLUSIONS

The presence of different orthodontic retainers may promote specific alterations in the GCF composition. With retention periods potentially becoming longer, this finding may be of clinical significance.

Cytokine expression and accelerated tooth movement

It has been shown that inhibiting the expression of certain cytokines decreases the rate of tooth movement. Here, we hypothesized that stimulating the expression of inflammatory cytokines, through small perforations of cortical bone, increases the rate of bone remodeling and tooth movement. Forty-eight rats were divided into 4 groups: 50-cN force applied to the maxillary first molar (O), force application plus soft tissue flap (OF), force application plus flap plus 3 small perforations of the cortical plate (OFP), and a control group (C). From the 92 cytokines studied, the expression of 37 cytokines increased significantly in all experimental groups, with 21 cytokines showing the highest levels in the OFP group. After 28 days, micro-computed tomography, light and fluorescent microscopy, and immunohistochemistry demonstrated higher numbers of osteoclasts and bone remodeling activity in the OFP group, accompanied by generalized osteoporosity and increased rate of tooth movement.

Changes of caspase-1 after the application of orthodontic forces in the periodontal tissues of rats

OBJECTIVE

To investigate the changes of caspase-1 in orthodontic tooth movement and to determine whether the changes are phase-specific.

MATERIALS AND METHODS

Eighty Wistar rats were included in this study. Sentalloy closed-coil springs were placed to induce a mesial traction force on the lower right first molar. The animals were killed after 1, 3, 7, and 14 days (n = 20 at each time point). The mandibles of 10 rats were sampled for histomorphometric analysis and immunohistochemical assay, and the periodontal tissues of 10 other rats were sampled for detecting caspase-1 mRNA and protein by real-time RT-PCR and by Western blotting, respectively.

RESULTS

The inflammatory reaction was evident in paraffin sections with hematoxylin-eosin staining. The immunohistochemical assay showed that orthodontic forces significantly increased the number of caspase-1-positive cells in the periodontal ligament (PDL). Mechanical force triggered an increase of caspase-1 mRNA in periodontal tissues. The expression of caspase-1 mRNA increased from day 1, reached the peak on day 3, and then decreased. The results of Western blotting indicated that the levels of both procaspase-1 and P20 subunit significantly increased after the application of orthodontic forces, compared with those in controls (P < .05).

CONCLUSION

Caspase-1 level increases during orthodontic tooth movement and changes with different phases, which might play a significant role in orthodontic tooth movement.

Pesquisa de interferon gama em tecido periodontal de ratos submetidos à movimentação dentária induzida

INTRODUÇÃO: durante o tratamento ortodôntico, um processo inflamatório é induzido, desencadeando uma série de eventos bioquímicos que resultam na movimentação dentária. Estímulos como a hipóxia e a deformação mecânica são os principais fatores responsáveis pela quebra da homeostasia celular, resultando em estresse e liberação de diversos mediadores importantes para o movimento do dente. Para que a remodelação óssea ocorra durante o tratamento ortodôntico, fatores reguladores,como subprodutos do ácido araquidônico e citocinas,são liberados.Ao interferon gama (INF-γ , uma citocina principal liberada após a indução da resposta imune adaptativa, é atribuída a função de atrair os macrófagos, que auxiliam na remoção de restos celulares e promovem a cicatrização e reorganização das áreas com inflamação. OBJETIVO: visto que alguns aspectos biológicos que permeiam a movimentação dentária ainda não estão totalmente esclarecidos, procurou-se, neste trabalho, verificar a expressão do INF-γ por células do periodonto de ratos submetidos à movimentação ortodôntica. MÉTODOS: a amostra foi constituída por nove ratos, cujos primeiros molares superiores direitos foram movimentados com uma força de 0,5N, por 3, 7 e 14 dias. Os molares esquerdos desempenharam o papel de grupo controle. RESULTADOS: através da imunohistoquímica, foi verificada a ausência de expressão de INF-γ na quase totalidade dos tecidos estudados,tanto no lado de pressão quanto no lado de tração.

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

OBJECTIVE

In orthodontic tooth movement, some cytokines released from periodontal ligament fibroblasts and alveolar bone osteoblasts on the pressure side can alter the normal processes of bone remodelling, resulting in physiological bone resorption. We examined the effect of compressive force and interleukin (IL)-1 type I receptor antagonist (IL-1ra) on the expression of inflammatory cytokines that promote osteoclast formation, as well as on their receptors, in osteoblastic Saos-2 cells.

DESIGN

The cells were cultured in Dulbecco's modified Eagle medium containing 10% fetal bovine serum with or without continuous compressive force (0.5-3.0 g/cm(2)) and/or IL-1ra for up to 24h. The gene expression levels of the cytokines and their receptors were estimated by determining mRNA levels using real-time PCR; the protein levels were determined using ELISA or immunohistochemical staining.

RESULTS

The expression of IL-1beta, IL-1 receptor, IL-6, IL-6 receptor, IL-8 receptor, IL-11 and tumor necrosis factor-alpha (TNFalpha) increased depending on the strength and duration of the compressive force, whereas the expression of IL-8, IL-11 receptor and TNFalpha receptor did not change with the application of compressive force. The expression of cytokines and their receptors produced by 3.0 g/cm(2) of compressive force decreased with the simultaneous addition of IL-1ra and the decrease was remarkable in IL-8 receptor, IL-11 and TNFalpha.

CONCLUSION

These results indicate that mechanical stress induces the production of inflammatory cytokines and their receptors in osteoblasts and the phenomenon is enhanced by the autocrine action of IL-1beta, which is increased in amount by mechanical stress.

Cytokine expression pattern in compression and tension sides of the periodontal ligament during orthodontic tooth movement in humans

Orthodontic tooth movement is achieved by the remodeling of periodontal ligament (PDL) and alveolar bone in response to mechanical loading and is believed to be mediated by several host mediators, such as cytokines. By means of real-time polymerase chain reaction (PCR), we studied the pattern of expression of mRNA encoding several pro- and anti-inflammatory cytokines in relation to several extracellular matrix and bone remodeling markers, in tension (T) and compression (C) sides of the PDL of human teeth subjected to rapid maxillary expansion. The PDL of normal teeth was used as a control. The results showed that both T and C sides exhibited significantly higher expression of all targets when compared with controls, except for type I collagen (COL-I) and tissue inhibitor of metalloproteinase-1 (TIMP-1) on the C side. Comparing C and T sides, the C side exhibited higher expression of tumor necrosis factor-alpha (TNF-alpha), receptor activator of nuclear factor-kappaB ligand (RANKL), and matrix metalloproteinase-1 (MMP-1), whereas the T side presented higher expression of interleukin-10 (IL-10), TIMP-1, COL-I, osteoprotegerin (OPG), and osteocalcin (OCN). The expression of transforming growth factor-beta (TGF-beta) was similar in both C and T sides. Our data demonstrate a differential expression of pro- and anti-inflammatory cytokines in compressed and stretched PDL during orthodontic tooth movement.

Effects of Interferon-Gamma on Bone Remodeling during Experimental Tooth Movement

Objective: To determine the effects of interferon-gamma (IFN-γ) on bone remodeling during orthodontic tooth movement.

Materials and Methods: Thirty adult male Sprague Dawley rats were randomly categorized into five groups. IFN-γ was administered in three different doses (0.01, 0.02, and 0.05 μg/20 μL) and the remaining two groups served as control. Mandibular first molars were moved mesially by means of Ni-Ti closed coil springs in all groups. The results were evaluated histomorphometrically, and parameters of trabecular bone volume (BV/TV), trabecular bone number (Tr.N), and trabecular separation (Tr.Sep) were observed at the interradicular bone area of the mandibular first molars.

Results: Increases in BV/TV and Tr.N and decreases in Tr.Sep revealed the antiosteoclastic activity of IFN-γ.

Conclusion: IFN-γ administration may be useful clinically for anchorage control.

Cellular, molecular, and tissue-level reactions to orthodontic force

Remodeling changes in paradental tissues are considered essential in effecting orthodontic tooth movement. The force-induced tissue strain produces local alterations in vascularity, as well as cellular and extracellular matrix reorganization, leading to the synthesis and release of various neurotransmitters, cytokines, growth factors, colony-stimulating factors, and metabolites of arachidonic acid. Recent research in the biological basis of tooth movement has provided detailed insight into molecular, cellular, and tissue-level reactions to orthodontic forces. Although many studies have been reported in the orthodontic and related scientific literature, a concise convergence of all data is still lacking. Such an amalgamation of the rapidly accumulating scientific information should help orthodontic clinicians and educators understand the biological processes that underlie the phenomenon of tooth movement with mechanics (removable, fixed, or functional appliances). This review aims to achieve this goal and is organized to include all major findings from the beginning of research in the biology of tooth movement. It highlights recent developments in cellular, molecular, tissue, and genetic reactions in response to orthodontic force application. It reviews briefly the processes of bone, periodontal ligament, and gingival remodeling in response to orthodontic force. This review also provides insight into the biological background of various deleterious effects of orthodontic forces.

Mechanical loading stimulates expression of connexin 43 in alveolar bone cells in the tooth movement model

Bone osteoblasts and osteocytes express large amounts of connexin (Cx) 43, the component of gap junctions and hemichannels. Previous studies have shown that these channels play important roles in regulating biological functions in response to mechanical loading. Here, we characterized the distribution of mRNA and protein of Cx43 in mechanical loading model of tooth movement. The locations of bone formation and resorption have been well defined in this model, which provides unique experimental systems for better understanding of potential roles of Cx43 in bone formation and remodeling under mechanical stimulation. We found that mechanical loading increased Cx43 mRNA expression in osteoblasts and bone lining cells, but not in osteocytes, at both formation and resorption sites. Cx43 protein, however, increased in both osteoblasts and osteocytes in response to loading. Interestingly, the upregulation of Cx43 protein by loading was even more pronounced in osteocytes compared to other bone cells, with an appearance of punctate staining on the cell body and dendritic process. Cx45 was reported to be expressed in several bone cell lines, but here we did not detect the Cx45 protein in the alveolar bone cells. These results further suggest the potential involvement of Cx43-forming gap junctions and hemichannels in the process of mechanically induced bone formation and resorption.

Mechanical loading stimulates dentin matrix protein 1 (DMP1) expression in osteocytes in vivo

Dentin matrix protein 1 (DMP1) was originally postulated to be dentin specific. Further analysis showed that DMP1 is also expressed in mature cartilage and bone. In bone tissue, DMP1 is expressed predominantly in late osteoblasts and osteocytes. DMP1 belongs to the SIBLING (Small Integrin Binding Ligand N-linked Glycoprotein) family of cellular matrix proteins that also includes osteopontin, bone sialoprotein, dentin sialophosphoprotein, and others. In this study, we examined the effect of mechanical loading on expression of DMP1 mRNA and DMP1 protein in alveolar bone in the mouse tooth movement model by in situ hybridization and immunocytochemistry. The expression of DMP1 mRNA was determined quantitatively in mechanically loaded and control sites of dento-alveolar tissue at several time points from 6 h to 7 days after loading. The tooth movement model allows simultaneous evaluation of bone resorption and bone formation sites. Expression of DMP1 mRNA in osteocytes increased 2-fold as early as 6 h after treatment in both the bone formation and bone resorption sites. After 4 days, DMP1 expression in osteocytes increased to a maximum of 3.7-fold in the bone formation sites and 3.5-fold in the resorption sites. Osteoblasts responded in the opposite manner and showed a transient 45% decrease of DMP1 mRNA in bone formation sites and a constant decrease of DMP1 mRNA during the entire course of treatment in the bone resorption sites, with a peak inhibition of 67% at day 2. By immunocytochemistry using a C-terminal region peptide antibody to DMP1, we found that there was a transient decrease in immunoreactivity at 3 days after treatment on both the formation side and the resorption side compared with the matched contralateral control tissue. However by 7 days of loading, there was a dramatic increase in DMP1 protein immunoreactivity on both the formation side and the resorption side. These results represent changes in epitope availability using this antibody or true changes in protein levels. The observations imply that the DMP1 protein is undergoing dynamic changes in either synthesis or other protein/matrix interaction after mechanical loading of alveolar bone. The findings indicate that DMP1 is involved in the responses of osteocytes and osteoblasts to mechanical loading of bone. These results support the hypothesis that osteocytes alter their matrix microenvironment in response to mechanical loading.