Download Inflammation and Tooth Movement

Inflammation and Tooth Movement: The Role
of Cytokines, Chemokines, and Growth
Factors
Ildeu Andrade Jr, Silvana R. A. Taddei, and Paulo E. A. Souza
When an orthodontic force is applied, the periodontal tissues express extensive macroscopic and microscopic changes, leading to alterations in 5
microenvironments: extracellular matrix, cell membrane, cytoskeleton, nuclear protein matrix, and genome. Capability of adaptive reaction to applied
mechanical loading relies in the DNA of periodontal ligament (PDL) and
alveolar bone cells. However, an inflammatory process is a precondition for
these modifications to occur, which will lead to orthodontic tooth movement (OTM). PDL’s vascularity and blood flow changes, as well as mechanical alterations in the cytoskeleton of PDL and bone cells, will result in local
synthesis and release of various key mediators, such as chemokines, cytokines, and growth factors. These molecules will induce many cellular responses by various cell types in the periodontium, providing a favorable
microenvironment for bone resorption or deposition and, consequently, for
OTM. In these inflammation and tissue remodeling sites, cells may also
communicate with one another through the interaction of cytokines and other
related molecules. The aim of this review is to bring focus on the role of these
important local inflammatory mediators that are closely related to the mechanotransduction involved in OTM. (Semin Orthod 2012;18:257-269.) © 2012
Elsevier Inc. All rights reserved.
M
echanotransduction induced by orthodontic force occurs when external strain
induces mechanosensing (the cell senses structural changes in the extracellular matrix, caused
by external mechanical loading), transduction,
Associate Professor, Department of Orthodontics, Faculty of Dentistry, Pontifícia Universidade Católica de Minas Gerais (PUC
Minas), Belo Horizonte, Minas Gerais, Brazil; Immunopharmacology, Department of Biochemistry and Immunology, Instituto de
Ciências Biológicas, Universidade Federal de Minas Gerais, Belo
Horizonte, Minas Gerais, Brazil; Associate Professor, Department of
Oral Pathology, Faculty of Dentistry, Pontifícia Universidade
Católica de Minas Gerais (PUC Minas), Belo Horizonte, Minas
Gerais, Brazil.
Address correspondence to Ildeu Andrade Jr, DDS, MS, PhD,
Department of Orthodontics, Faculty of Dentistry, Pontifical
Catholic University of Minas Gerais (PUC Minas), Av. Dom José
Gaspar 500, CEP 31.270-901, Belo Horizonte, Minas Gerais,
Brazil. E-mail: [email protected]
© 2012 Elsevier Inc. All rights reserved.
1073-8746/12/1804-0$30.00/0
http://dx.doi.org/10.1053/j.sodo.2012.06.004
and cellular response in several paradental tissues. This process leads to vasculature and extracellular matrix remodeling in the periodontal
ligament (PDL), gingiva, and alveolar bone.
This remodeling is facilitated by proliferation,
differentiation, and apoptosis of local periodontal cells, bone cell precursors, and leukocyte
migration from the microvascular compartment.1,2 In this context, an aseptic acute inflammatory response is occurring in the early phase
of orthodontic tooth movement (OTM), followed by an aseptic and transitory chronic inflammation. As orthodontic forces (continuous,
interrupted, or intermittent) are not uniform
throughout the applied region, areas of tension
or compression are developed leading to varied
inflammatory processes resulting in different tissue remodeling responses.1,3
This sequence of events leads to an increase
in the number of monocytes and polymorphonuclear leukocytes, which exit from the micro-
Seminars in Orthodontics, Vol 18, No 4 (December), 2012: pp 257-269
257
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Andrade Jr, Taddei, and Souza
vasculature into the extravascular space.1 These
migratory cells produce various inflammatory
mediators, which interact directly or indirectly
with the entire population of native paradental
cells. These molecules, such as chemokines, cytokines, and growth factors (GFs), mediate and
maintain the vascular and cellular changes in an
autocrine or paracrine way, stimulating or inhibiting cellular activity.1 Such mediators are believed to activate tissue remodeling, characterized by selective bone resorption or deposition
in compression and tension sites of the PDL,
respectively.1,3
This article reviews the current biomedical
literature on inflammation in OTM. It seeks to
summarize the role of chemokines, cytokines,
and GFs and to explore their clinical implications in routine orthodontic practice. It does not
propose a complete picture (as the research is as
yet incomplete in the current scenario), but orients the reader to the role that these mediators
play in the inflammatory periodontal tissue reactions, in response to orthodontic force application.
Cytokines and Tooth Movement
Cytokines are extracellular signaling proteins directly involved in the bone remodeling and inflammatory process during OTM, which act directly or indirectly, to facilitate bone and PDL
cells differentiation, activation, and apoptosis.1,3
Investigations of their mechanisms of action
have identified their effector (proinflammatory)
and suppressive (anti-inflammatory) functions
during OTM.
The receptor activator of nuclear factor-!B
ligand (RANKL) and macrophage colony-stimulating factor (M-CSF) expressed by osteoblast and
apoptotic osteocyte are the most important proinflammatory cytokines responsible for recruitment,
differentiation, activation, and survival of osteoclasts.4 These cytokines bind to their respective
receptors, RANK and c-Fms, expressed in osteoclast precursors and mature osteoclasts, to produce these events through osteoclast– osteoblast
communication.2,4 By contrast, osteoblasts also express osteoprotegerin (OPG), a decoy receptor of
RANKL, which inhibits the RANK/RANKL interaction, preventing osteoclastogenesis and accelerating mature osteoclast apoptosis.1,4
When subjected to continuous (0.5-3.0 g/cm2)
or intermittent (2.0 or 5.0 g/cm2) mechanical–
compressive force, PDL cells induce osteoclastogenesis in vitro through downregulation of OPG
expression and upregulation of RANKL expression, via prostaglandin E2 (PGE2) and interleukin
(IL)-1" synthesis.5,6 In accordance, mice research
also demonstrated that osteoclastogenesis appears to be primarily regulated through M-CSF
and RANKL signaling by PDL cells in the compression side in the first week of orthodontic
force application.7,8 In the compression sites
during human OTM (250 g), the same standard
of RANKL and OPG expression is observed in
gingival crevicular fluid (GCF) after 24 hours.9
By contrast, in vitro cyclic tensile strain increases
OPG levels and decreases RANKL synthesis in
cultured osteoblasts and PDL cells in a force
magnitude-dependent way.10
Furthermore, RANKL gene transfer or M-CSF
administration to the periodontal tissue induces
osteoclastogenesis and accelerates experimental
OTM in rodents,11 whereas local OPG gene
transfer has opposite results.12 Therefore, local
MCSF/RANKL or OPG treatment might be a
useful tool for shortening the duration of orthodontic treatment or improving orthodontic anchorage, respectively, but their clinical applications are still far off. Currently, alveolar
decortication has been the most frequently applied clinical alternative to accelerate orthodontic
treatment in humans.13 Animal studies have
shown that alveolar corticotomy increases the expression of M-CSF and RANKL in PDL, enhancing
the rate of OTM during the initial tooth-displacement phase.14 In addition, a previous study reported that OPG levels were greater than
RANKL levels under physiological conditions in
human GCF.15 However, an increased RANKL/
OPG ratio was observed in patients with severe
root resorption under orthodontic treatment
that could be related to a greater bone resorption. Therefore, a local OPG treatment might be
a future tool to prevent or paralyze root resorption during OTM.
Tumor necrosis factor (TNF)-# is another
proinflammatory cytokine that has been investigated in OTM and is involved in bone resorption
and acute as well as chronic inflammation.
TNF-# is produced primarily by activated monocytes and macrophages, but also by osteoblasts,
epithelial cells, and endothelial cells.16 In vitro
Inflammation and Tooth Movement
studies have demonstrated that in bone, TNF-#
can directly and indirectly induce osteoclastogenesis by binding to its p55 receptor on osteoclast precursors and by upregulating expression of RANKL, M-CSF, and other chemokines
on osteoblasts.17-19 TNF-# is also an apoptotic
factor for osteocytes, which could be the signal
for osteoclast recruitment to resorb bone in the
PDL pressure side, at the same time inhibiting
osteoblasts.20
The real role of TNF-# in bone resorption,
upregulating and increasing the amount of
OTM, was shown in rodent models with TNF-#
receptor impairment.21,22 A recent in vitro study
suggested that PDL fibroblasts secrete higher
levels of TNF-# at the PDL compression side
than at the tension side.23 This imbalance leads
to RANKL expression by activating CD4! T
cells, thereby facilitating bone resorption during
OTM. Taken together, local TNF-# treatment or
stimulation of cells that produce this proinflammatory protein might be a future alternative to
accelerate OTM. Moreover, local TNF-#-antibody injection might be a useful tool to improve
the anchorage site during OTM, as a previous
study has demonstrated its clinical application
by inhibiting bone resorption in rheumatoid arthritis.24
Like TNF-#, IL-1 (alpha and beta) is a proinflammatory cytokine that is highly expressed on
the PDL pressure side of humans and animals
and the adjacent alveolar bone in the early
stages of OTM.6,25-28 Its role in OTM has been
the focus of previous human studies25,27,28 that
demonstrated an increase in osteoclast activity
and survival, while at the same time inducing
bone marrow cells and osteoblasts to produce
RANKL in the early phase of OTM.29,30 Moreover, IL-1 can induce osteoclast formation directly from osteoclast precursors under TNF
stimulation in vitro.31
Other in vitro studies have also demonstrated
that IL-1 strongly promotes osteoclast formation
by increasing M-CSF and PGE2 production and
decreased OPG production by osteoblasts.26,32
Under 24 hours of continuous compressive
forces in vitro (3.0 g/cm2), osteoblastic cells
respond by expressing IL-1", IL-6, IL-11, TNF-#,
and receptors for IL-1, IL-6, and IL-8, suggesting
an osteoblastic autocrine mechanism induced by
mechanical stress.33 Indeed, animal studies with
absence of IL-1" and/or TNF-# signaling dem-
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onstrated impaired tooth movement,21,22 but
the mechanisms behind this finding remain unknown.
Polymorphisms in IL-1 gene, which determines the degree of alteration in the amount of
cytokines secreted, have been studied in OTM.34
The allele 1 at the IL-1 gene, known to decrease
the production of IL-1 cytokine in vivo, significantly increases the risk of external apical root
resorption in patients during OTM. The clinical
implication is that potential orthodontic patients can be screened for the IL-1" genotype by
analyzing the DNA from a simple cheek swab or
mouth wash taken during the initial examination, to identify those who carry 2 copies of the
high-risk allele. It would then be possible to
inform patients about their predispositions before starting treatment, and closely monitor
those at risk, by periodic radiographs. Moreover,
a recent study has shown that IL-1" (!3954)
genotype was associated with faster tooth movement in humans.35
In addition, IL-1 receptor antagonist (IL-1Ra)
competitively blocks the interactions of IL-1 with
IL-1 receptors, inhibiting its activity. IL-1Ra has
been used as a therapeutic tool in conditions
related to bone resorption, such as rheumatoid
arthritis.36 Moreover, a decreased physiological
IL-1Ra expression in GCF has been shown to
correlate with faster OTM in humans.35 We speculated that in the future, IL-1Ra can be clinically
used to modulate the amount and side effects of
OTM.
Other cytokines, such as IL-6, IL-8, and IL-11,
also stimulate alveolar bone resorption during
OTM by acting early in the inflammatory response.37-39 These cytokines can be enhanced
by, or can act synergistically with, TNF-# and
IL-1.40 By contrast, IL-11 can have anabolic effects, alone or in association with bone morphogenetic protein-2 (BMP-2), inducing osteoblastic
differentiation in mouse mesenchymal cells.41
Different anti-inflammatory cytokines play inhibitory effects, controlling inflammation and
bone resorption. IL-18 and IL-10 are also expressed in the PDL during OTM, and both inhibit
osteoclastogenesis and bone resorption.42,43 Furthermore, IL-10 inhibits the production of IL-1,
IL-6, and TNF-#, and its expression is higher in
PDL tension than in compression sites.25,44
From a clinical standpoint, analysis of cytokine levels in GCF during OTM may, in the
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Andrade Jr, Taddei, and Souza
future, reveal the rate of OTM and determine
the optimum force level that should be applied
by orthodontic devices. Analysis of cytokine levels in GCF may also be helpful in monitoring the
biological activities in the periodontium during
the retention period, which could provide information about possible relapse.
Chemokines and Tooth Movement
Chemokines belong to the superfamily of small
heparin-binding cytokines.45 The ability to induce cell migration is the common feature that
distinguishes this group of cytokines.46 Structurally, the chemokines are classified in 4 subfamilies based on the position of 2 highly conserved
cysteine residues at the N-terminus: C, CC, CXC,
and CX3C. To mediate their cellular effects,
these molecules bind to selective 7-transmembrane domain receptors, which are coupled to
heterotrimeric G proteins, differentiating also
from other cytokines. The chemokine receptors
are named according to their ligand family, such
as CCR for receptors of CC ligands and CXCR
for CXC ligands.45 The chemokine system is
promiscuous or redundant, as different chemokines can bind to a given chemokine receptor,
and a given chemokine may bind to different
chemokine receptors.45,46 However, binding of
chemokines to their respective receptors does
not necessarily achieve the same functions in
vivo.46 Chemokines present different biological
outcomes in different tissues, which are controlled by geography and timing.45,46 They play a
central role in trafficking and homing of leukocytes, immune cells, and stromal cells, during
physiological (homeostatic chemokines) and inflammatory conditions (inflammatory chemokines).46 In addition, chemokines induce other
biological processes, such as angiogenesis, cell
proliferation, and apoptosis.45
In inflammatory sites, cellular recruitment begins when local cytokines, pathogens, GFs,
chemokines themselves, and mechanical stress
trigger off the production of inflammatory
chemokines by several cell types.45 These locally
produced chemokines bind to the cell surface of
the vascular endothelium and/or to the extracellular matrix, formatting gradients of chemokines, and, consequently, directing cell recruitment to inflammation sites.47 Therefore,
recruited and activated macrophages, neutro-
phils, and lymphocytes will respond to the tissue
factors and secrete several mediators that will act
together, leading to bone and PDL remodeling
during OTM.
In addition to leukocytes, the chemokines
provide key signals for trafficking, differentiation, and activity of bone cells,17,48 playing an
important role in bone remodeling and bone
inflammatory disease. In this context, some researchers have investigated how a given chemokine or chemokine receptor can regulate this process. Previous studies in vitro have demonstrated
that CC-chemokine ligand 3 (CCL3), CCL2,
CCL5, and CXC-chemokine ligand (CXCL9)
chemokines promote chemotaxis of osteoclasts
when binding to their respective CC receptors
(CCR1, CCR2, CCR3, CCR5, and CXCR3), which
are expressed by osteoclast precursors.17,48,49,50
Others have shown that CCL5, CCL7, CCL2,
CCL3, CXCL12, and IL-8 (CXCL8) promote
RANKL-induced differentiation of osteoclast
precursors.48,51-55 Chemokines also stimulate activity of osteoclasts, such as CCL2, CCL3, and
IL-8,51,52,55 and prolong osteoclast survival, such
as CCL3 and CCL9 (ligands CCR1).48,51 Moreover, RANKL induces osteoclast production of
CCL2, CCL3, and CCL5, which suggests an autocrine and paracrine signalization during osteoclastogenesis, and an increase of bone resorption.48,49
Chemokines can also induce recruitment,
proliferation, and survival of osteoblasts. Osteoblasts express chemokine receptors, such as
CXCR1, CXCR3, CXCR4, CXCR5, CCR1, CCR3,
CCR4, and CCR5.17 CCL5, a ligand of CCR1,
CCR3, CCR5, and CCR4, can induce osteoblast
recruitment and avoid apoptosis of this cell.17
The chemokine CXCL10 induces osteoblast proliferation and release of alkaline phosphatase
and "-acetylhexosaminidase, while CXCL12 and
CXCL13 induce both proliferation and collagen
type I mRNA expression in osteoblasts.56
The osteoblast– osteoclast communication
through RANK/RANKL/OPG system is essential
in the regulation of bone remodeling, as previously described.4 This interaction between osteoclast and osteoblast can also be mediated by
chemokines through paracrine signalization. In
inflammation sites, this process is initiated when
the proinflammatory cytokines IL-1 and TNF-#
promote the production of CCL2, CCL3, and
CCL5 by the osteoblast.46,48 The release of these
Inflammation and Tooth Movement
chemokines by osteoblasts can significantly contribute to recruitment and development of osteoclasts at osteolysis sites, thereby exacerbating
bone loss.17,48 Furthermore, CCL3 is also indirectly involved with osteoclast differentiation, as
this chemokine stimulates increased expression
of RANKL by osteoblasts53 and induces cell– cell
adhesion between osteoclasts and osteoblasts.52
Because chemokines play an important role
in bone remodeling, several studies have investigated the levels of these proteins in OTM.
CCL2, CCL3, CCL5, IL-8 (CXCL8), and CXCL12
expression were greatly increased in periodontal
tissues of murines and humans submitted to
orthodontic force.22,56-58 A recent study in
Wistar rats has demonstrated that IL-8 and CCL2
may facilitate the process of root resorption after
7 days of excessive mechanical loading (50 g).58
Although the expression of these chemokines
has been observed in periodontium submitted
to orthodontic force, their functional role in
OTM is yet to be known. The authors of the
present article demonstrated that the axis TNF#/p55 induces expression of CCL5 after 12
hours of continuous force (10 g) in the PDL of
mice during OTM.22 As CCL5 is a ligand of
CCR5 receptor, we have investigated the role
of this chemokine receptor after the application of orthodontic force.56 The results demonstrated that the amount of tooth movement and
the number of osteoclasts were increased in
CCR5-deficient mice (CCR5"/") after 12 days of
mechanical loading (10 g). The data also revealed that the mRNA levels of osteoclastogenesis and osteoclast activity markers (Cathepsin K,
RANKL, and matrix metalloproteinase-13(MMP13)) were higher in CCR5"/" mice after 3 days.
Moreover, osteoblast differentiation markers
(runt-related transcription factor 2 [RUNX2]
and osteocalcin [OCN]), and negative regulators of bone resorption (OPG and IL-10) were
decreased in CCR5"/" mice after 3 and 7 days.
Taken together, these results suggested that diminished osteoblast differentiation in CCR5"/"
led to a reduction of inhibitory signals for osteoclasts, resulting in increased bone resorption
and greater OTM. Therefore, CCR5 might be a
downregulator of bone resorption during OTM,
as this receptor indirectly inhibits osteoclast recruitment and reduces this cell activity.56 Further studies are now required to confirm the
role of other chemokines/chemokine receptors
261
involved in osteoclast and osteoblast recruitment, differentiation and activity during OTM,
and their possible impact in clinical orthodontics.
In summary, the chemokines interfere directly and indirectly in osteoclast and osteoblast
recruitment, differentiation, and consequent
bone resorption and formation. Therefore, the
development of strategies that are capable to locally and selectively modulate the chemokine pathways might contribute to a better control of the
rate of OTM, as well as the stabilization of the
orthodontic results. Drugs such as met-RANTES
and P8A are currently used for blockage of specific
chemokine receptors, leading to a diminished
bone resorption in rheumatoid arthritis.59,60 In
the future, the local administration of these present and upcoming drugs could be useful to increase biological anchorage at specific sites and
stability of the final results.
Growth Factors and Tooth Movement
GF are substances that bind to specific receptors
on the surface of their target cells, stimulating
cell proliferation, migration, and differentiation. Moreover, they display important roles in
hematopoiesis, the inflammatory process, angiogenesis, and tissue healing.61 GF may also act
locally to modulate bone remodeling, and consequently, OTM.27,61
Vascular endothelial growth factor (VEGF) is
an essential mediator of angiogenesis and increased vascular permeability.61 As osteoblast
and osteoclast express VEGF receptor-1, some
studies have investigated the effect of VEGF
on bone remodeling under mechanical loading.62,63 In vitro studies have shown that PDL
cells and apoptotic osteocytes increase VEGF
production after compressive force application.62,63 VEGF can modulate the recruitment,
differentiation, and activation of osteoclast precursors, increasing bone resorption.64 Moreover, VEGF can also indirectly induce bone resorption, as it promotes angiogenesis in vitro,
allowing new capillaries to assist the recruitment
of osteoclast precursors to the bone surface close
to the resorption site.63 In accordance, VEGF
enhances osteoclast recruitment and increases
the rate of experimental OTM in vivo,65 which
are both inhibited by anti-VEGF polyclonal antibody treatment.66 The expression of VEGF was
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Andrade Jr, Taddei, and Souza
also detected in osteoblasts, osteocytes, and fibroblasts in PDL tension sites after 10 days of
OTM in C57BL/6J mice.65 Taken together, it is
reasonable to conclude that VEGF plays an important role in bone remodeling at both compression and tension sites of the PDL during
OTM.
The transforming growth factor (TGF)-" superfamily (TGF-"1 to -"3) is another important
GF related to bone and PDL tissue remodeling
during OTM. Under mechanical loading, the
cyclic tensile force upregulates TGF-" expression in osteoblasts and also in PDL cells in
vitro.67 Furthermore, TGF-" stimulates OPG
production and downregulates IL-6 expression,
which inhibits the osteoclastogenesis-supporting
activity of these cells.67 In accordance, increased
levels of OPG and TGF-"1 mRNA are observed
in osteoblasts and other PDL cells in the tension
sites after 2 days of OTM in Wistar rats, simultaneously with a decreased number of osteoclasts
in this area.68 In humans, the level of TGF-"1 is
enhanced in GCF and in PDL tissue a few days
after continuous orthodontic force application
for rapid maxillary expansion and canine distal
movement (force of 2-2.5 N), respectively.27
However, there are no differences in the level of
this GF between tension and pressure sites.25 As
it is clear that TGF-" plays an important role in
the tension site during OTM, further studies
should now investigate the TGF-" effect on pressure sites after orthodontic force application because it is an essential factor for RANKL-induced
osteoclastogenesis and, consequently, OTM.
Bone morphogenetic proteins (BMPs) are multifunctional GFs that belong to the TGF-" superfamily and play an important role in upregulating
various transcription factors involved in osteoblastic differentiation, and consequently, in bone formation.69 To date, more than 20 BMPs have been
discovered, but BMP-2, BMP-6, BMP-7, and BMP-9
seem to have the most potent osteogenic activity.69,70 Studies have shown that under tensile
strain, human PDL cells in culture increase
BMP-2 and BMP-6 expression, suggesting that
these BMPs might play an important role in PDL
tensile sites during OTM.70,71 However, there is
a lack of information on the actual role of BMPs
in OTM.
Insulin-like growth factors (IGFs) are involved in bone formation by inducing proliferation, differentiation, and apoptosis of osteo-
blasts.72 The IGFs effect is regulated by growth
hormone, parathyroid hormone, vitamin D3,
corticosteroids, TGF-", IL-1, and platelet-derived growth factor. Studies have shown that
under continuous tensile mechanical loading,
rat tibiae osteocytes and calvaria osteoblasts increase IGF-I synthesis, which stimulates bone formation.73,74 In PDL tissues, IGF also acts as antiapoptotic and proliferative factor for fibroblasts
and osteoblasts in vitro.75 Accordingly, an in vivo
study using Wistar rats demonstrated that 4
hours of a continuous tensile force (0.1-0.5 N)
applied to a tooth induces increased expression
of IGF-I and IGF-I receptor in PDL cells in tension sites, but a decreased expression in compression sites.76 Therefore, a local increase of
IGF-I appears to provide a link between the mechanical loading and tissue remodeling in the
tensile site during OTM.
Fibroblast growth factors (FGFs) belong to a
family of 23 members that bind to 4 structurally
related high-affinity receptors.77 Among FGFs,
FGF-2 can regulate bone remodeling by stimulating osteoblast-like cell proliferation and differentiation in vitro, and by increasing osteoclast
formation and activity.78 An in vitro study demonstrated that compressive forces induce production of FGF-2 by human PDL cells, which stimulates RANKL expression.79 Moreover, there is an
increased expression of this GF in the compression
site of PDL tissues after 1 day of mechanical loading in humans in vivo.39 The results suggest that
FGF-2 can be involved in bone resorption during
OTM.39,79 However, whether FGF-2 plays an important role in the tensile site after mechanical
loading is yet to be elucidated. As FGF-6, FGF-8,
FGF-9, FGF-18, and FGF-23 are also known as
regulators of bone cell functions, they should be
tested following application of the orthodontic
force.39,77-79
A further GF showing increased levels in GCF
after the first 24 hours of OTM in humans is the
epidermal growth factor (EGF).27 A recent study
has shown that the administration of EGF–liposome in the mucosa adjacent to the tooth in
Holtzman rats was able to stimulate the expression of RANKL, leading to an increased number
of osteoclasts in the PDL compression sites, and
consequently, to enhancement of tooth movement under a continuous force (20 g).80 In addition, the expression of both EGF and EGFR in
osteoblasts and PDL fibroblasts is increased at
Inflammation and Tooth Movement
PDL tensile sites in rats and cats.80,81 Taken
together, these data suggest that EGF is involved
in remodeling of mineralized and nonmineralized extracellular matrix in both tensile and
compressive sites during OTM.
Taken together, the current knowledge indicates that mechanical loading stimulates local expression of many GF involved in bone
and PDL remodeling in the early stages of
OTM in both tensile and compressive sites. In
the future, local injection of a single GF or a
263
combination of multiple GFs in the periodontal tissues might modulate the rate of OTM or
help to improve the stability of the orthodontic results.
Inflammation in OTM
When an orthodontic force is applied to a
tooth, immediate changes are observed in
periodontal tissues (Fig 1). Compression sites
Figure 1. In compression sites, the orthodontic force induces local hypoxia and mechanotransduction. The
local hypoxia increases the expression of interleukin (IL)-1", IL-6, IL-8, tumor necrosis factor (TNF)-#, and
vascular endothelial growth factor (VEGF) in periodontal ligament (PDL) fibroblasts. The physical strain also
stimulates the PDL cells to produce growth factors, prostaglandin E2 (PGE2), and chemokines (mechanotransduction). Moreover, stressed PDL peripheral nerve fibers release vasoactive neurotransmitters, such as calcitonin
gene–related peptide and substance P. The cytokines IL-1", IL-6, IL-8, and TNF-# lead to increased expression
of adhesion molecules (VCAM-1 and ICAM-1) and chemokines, which in turn promote leukocyte adhesion and
migration. Furthermore, PGE2 and VEGF increase vascular flow and permeability, leading to plasma extravasation and leukocyte diapedesis. These alterations trigger an acute inflammatory response, which is replaced by a
chronic process that allows leukocytes and osteoclast precursors to continue their migration into the strained
paradental tissues, modulating this remodeling process. (Color version of figure is available online.)
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Andrade Jr, Taddei, and Souza
are characterized by tissue and cell damage,
reduction in the number of patent capillaries,
occlusion, and partial disintegration of blood
vessels, leading to ischemia and hypoxia.1
These alterations trigger an acute inflammatory response, featured by vasodilatation and
migration of leukocytes out of capillaries.1
This process is initiated when local hypoxia
increases the expression of IL-1", IL-6, IL-8,
TNF-#, and VEGF in PDL fibroblasts.82 At the
same time, the physical strain stimulates the
PDL production of these cytokines, as well as
of GFs and chemokines, through a process
called mechanotransduction.2 In this context,
IL-1 and TNF-# activate microvascular endothelial cells, leading to increased expression of
adhesion molecules (VCAM-1 and ICAM-1),
inducing local chemokine expression, which
in turn promotes leukocyte adhesion and migration.83 Moreover, stressed PDL peripheral
nerve fibers release vasoactive neurotransmitters, such as calcitonin gene–related peptide
and substance P.1 These neuropeptides, together with VEGF and PGE2, increase vascular
flow and permeability, leading to plasma extravasation and leukocyte diapedesis.61 These
recruited leukocytes interact directly or indirectly with the entire population of native paradental cells, increasing the production of
specific chemokines, cytokines, and GFs involved in bone resorption. In this way, the
acute phase of inflammation is replaced by a
chronic process that allows leukocytes and osteoclast precursors to continue their migration into the strained paradental tissues, modulating this remodeling process.1
Bone Resorption
Under mechanical loading, fibroblasts, osteoblasts, and other PDL cells, located at the pressure site (Fig 2), release signaling molecules,
such as PGE2, IL-1, IL-6, TNF-#, and IL-11.25,26
Among these mediators, IL-1 and TNF-# stimulate osteoblasts to produce chemokines, such as
CCL3, CCL2, and CCL5.17,26,48,56,57,83 These
chemotactic proteins, joined by others, such as
CXCL12, and cytokines (RANKL and TNF-#)
induce chemotactic recruitment of osteoclast
precursors to osteolysis sites, where these cells differentiate into mature osteoclasts through osteoblast– osteoclast communications.17,48,49,54 For the
differentiation to occur, PGE2 and cytokines, such
as IL-1, IL-6, IL-8, and TNF-#, stimulate, directly or
indirectly, osteoblast/stromal cells to produce the
main regulators of osteoclast differentiation: MCSF and RANKL.3-6 This process is achieved
when M-CSF and RANKL bind to their respective specific receptors, c-Fms and RANK, which
are both expressed on osteoclast precursors.
However, osteoclastogenesis can be downregulated when OPG, a RANKL decoy receptor produced by osteoblastic and PDL cells, binds to
RANKL, inhibiting the RANK/RANKL interaction.4 Therefore, OPG level is decreased in compression sites during OTM, enhancing osteoclastogenesis in this area.25
The mechanical loading-induced hypoxia
promotes the expression of hypoxia inducible
factor 1-#, which increases the expression of
RANKL by human PDL fibroblasts at pressure
sites, enhancing osteoclastogenesis.84 In addition to osteoblast and PDL cells, damaged osteocytes are also a source of RANKL and M-CSF. In
this context, orthodontic force causes microdamages in alveolar bone near PDL pressure
sites that compromise osteocyte integrity, physically damaging the cells by oxidative stress, or by
disruption of the blood flow and/or fluid flow in
the lacunar– canalicular system.63 This damaged
tissue, together with local TNF-# and IL-1, can
induce osteocyte apoptosis, which initiates bone
resorption close to the microdamaged sites, as it
upregulates the expression of RANKL, VEGF,
and M-CSF and, consequently, modulates the
osteoclast precursor recruitment and differentiation.63 Moreover, VEGF also indirectly induces
bone resorption, as it promotes angiogenesis,
allowing new capillaries to augment osteoclast
precursors recruitment to the bone surface close
to the resorption sites.63
Not only RANKL, but also other cytokines
(IL-", TNF-#, IL-6, IL-11), GFs (FGF-2, EGF),
and chemokines (CCL2, CCL3, CCL5, CCL7,
CCL9, IL-8) can, directly or indirectly, increase
osteoclast differentiation, survival, and activity.17,31,48,78,80 Moreover, in an amplified loop,
CCL3 increases the expression of RANKL by
osteoblasts.53 In parallel, RANKL induces production of CCL2, CCL3, and CCL5 by osteoclasts, suggesting an autocrine and paracrine
signalization during osteoclastogenesis, and an
increased bone resorption.48,49
Inflammation and Tooth Movement
265
Figure 2. In compression site, fibroblasts, osteoblasts, and other PDL cells release PGE2, IL-1, IL-6, TNF-#, and
IL-11, under mechanical loading. Among these mediators, IL-1 and TNF-# stimulate osteoblasts to produce
chemokines, such as CCL3, CCL2, and CCL5. Together with CXCL12, as well as the cytokines receptor activator
for nuclear factor-!B ligand (RANKL) and TNF-#, they induce chemotactic recruitment of osteoclast precursors
to osteolysis sites, where these cells differentiate into mature osteoclasts through osteoblast– osteoclast communications. PGE2 and cytokines (IL-1, IL-6, IL-8, and TNF-#) stimulate osteoblast/stromal cells to produce
macrophage colony-stimulating factor and RANKL, which bind to their receptors c-Fms and RANK expressed on
osteoclast precursors, respectively. Damaged osteocytes are also a source of RANKL and macrophage colonystimulating factor. Other cytokines (IL-", TNF-#, IL-6, IL-11), growth factors (fibroblast growth factor-2,
epidermal growth factor), and chemokines (CCL2, CCL3, CCL5, CCL7, CCL9, IL-8) can increase osteoclast
differentiation, survival, and activity. However, osteoclastogenesis can be downregulated when osteoprotegerin
binds to RANKL, inhibiting the RANK/RANKL interaction. (Color version of figure is available online.)
Bone Formation
In orthodontics, bone formation (Fig 3) begins
40-48 hours after force application in the PDL
tension sites.85 Osteocytes participate in the process of osteogenesis, being acutely sensitive and
responsive to applied tensile orthodontic forces.
Their cellular projections facilitate communications with neighboring osteocytes, as well as with
alveolar bone surface-lining cells and bone marrow cavity cells. Osteoblasts, which maintain direct contact with osteocytes, respond to these
signals and initiate bone apposition.86
Moreover, stretched PDL fiber bundles stimulate cell replication.1 Stem-cells (pericytes), migrated from blood vessel walls, and mesenchy-
mal stem-cells differentiate into preosteoblastic
cells 10 hours after force application.86 Chemokines, cytokines, and GFs are directly involved in
this process. CCL3, CCL5, CXCL10, CXCL12,
and CXCL13 induce osteoblast precursor recruitment, proliferation, differentiation, and
survival.17,53,57,86 Local osteoblasts and osteocytes express GFs, such as TGF-" and IGF-1, that
promote osteoblast precursors proliferation and
differentiation, and mineralization of new bone
by mature osteoblasts.73,74,85 In addition, BMP,
EGF, and IL-11 upregulate osteoblast differentiation and function.41,69,81 In PDL tension sites,
osteoblasts and PDL fibroblasts express VEGF,
which stimulates angiogenesis, an important
266
Andrade Jr, Taddei, and Souza
Figure 3. Osteoblast differentiation and bone formation occur in the tension site during orthodontic tooth
movement. Stretched PDL cells stimulate cell replication by releasing chemokines, cytokines, and growth factors.
Stem-cells (pericytes), migrated from blood vessel walls, and mesenchymal stem-cells differentiate into preosteoblastic cells after force application. The chemokines, CCL3, CCL5, CXCL10, CXCL12, and CXCL13, induce
osteoblast precursors recruitment, proliferation, differentiation, and survival. Local osteoblasts and osteocytes
express growth factors (transforming growth factor-" and insulin-like growth factor-1) that promote proliferation
and differentiation of osteoblast precursors, as well as mineralization of new bone by mature osteoblasts. In
addition, bone morphogenetic protein, epidermal growth factor, and IL-11 upregulate osteoblast differentiation
and function. Osteoblasts and PDL fibroblasts express VEGF, which stimulates angiogenesis. Meanwhile, transforming growth factor-" and insulin-like growth factor-1 stimulate proliferation and differentiation of osteoblasts
and PDL cells, as well as collagen synthesis. (Color version of figure is available online.)
process in new bone formation.61,65 Moreover,
anti-inflammatory cytokines involved in bone
formation, such as IL-10 and OPG, are produced
by osteoblasts and inhibit osteoclastogenesis.4,44
To maintain the integrity of the PDL apparatus
simultaneously with bone formation, TGF-" and
IGF-1 stimulate proliferation and differentiation
of osteoblasts and PDL cells, as well as collagen
synthesis.68,72,75
Conclusions
Chemokines, cytokines, and GFs are the main
molecules involved in bone cell recruitment, ac-
tivation, proliferation, differentiation, and survival. These molecules stimulate PDL and bone
cells to orchestrate an inflammatory response,
followed by osteoclastogenesis and bone resorption in compression sites, and by osteoblast and
new bone formation at PDL tension sites. The
research trend is now directed toward elucidating the molecular mechanisms involved in these
events. Although several studies have investigated chemokines, cytokines, and GFs in OTM,
it is difficult to establish a global vision that
illustrates the specific role and the exact moment that these molecules participate in PDL
Inflammation and Tooth Movement
and bone remodeling. Different experimental
conditions, such as animal species, time and
force magnitude, appliance design, and methods to detect the expression of these molecules,
restrain the general comprehension of the cellular and molecular mechanisms involved in
OTM. Nevertheless, current knowledge raises
the possibility of local administration of substances that are able to act on specific cytokines,
chemokines, and GF. These molecules can modulate the outcome of the application of orthodontic force, accelerating OTM, enhancing biological anchorage at specific sites, possibly
decreasing the rebound effect, and assisting in
the prevention of root resorption.
References
1. Krishnan V, Davidovitch Z: Cellular, molecular, and tissue-level reactions to orthodontic force. Am J Orthod
Dentofacial Orthop 129:469, e1-32, 2006
2. Krishnan V, Davidovitch Z: On a path to unfolding the
biological mechanisms of orthodontic tooth movement.
J Dent Res 88:597-608, 2009
3. Meikle MC: The tissue, cellular, and molecular regulation of orthodontic tooth movement: 100 years after Carl
Sandstedt. Eur J Orthod 28:221-240, 2006
4. Boyce BF, Xing L: Functions of RANKL/RANK/OPG in
bone modeling and remodeling. Arch Biochem Biophys
473:139-146, 2008
5. Kanzaki H, Chiba M, Shimizu Y, et al: Periodontal ligament cells under mechanical stress induce osteoclastogenesis by receptor activator of nuclear factor kappaB
ligand up-regulation via prostaglandin E2 synthesis.
J Bone Miner Res 17:210-220, 2002
6. Nakao K, Goto T, Gunjigake KK, et al: Intermittent force
induces high RANKL expression in human periodontal
ligament cells. J Dent Res 86:623-628, 2007
7. Oshiro T, Shiotani A, Shibasaki Y, et al: Osteoclast induction in periodontal tissue during experimental
movement of incisors in osteoprotegerin-deficient mice.
Anat Rec 266:218-225, 2002
8. Brooks PJ, Heckler AF, Wei K, et al: M-CSF accelerates
orthodontic tooth movement by targeting preosteoclasts
in mice. Angle Orthod 81:277-283, 2011
9. Nishijima Y, Yamaguchi M, Kojima T, et al: Levels of
RANKL and OPG in gingival crevicular fluid during
orthodontic tooth movement and effect of compression
force on releases from periodontal ligament cells in
vitro. Orthod Craniofac Res 9:63-70, 2006
10. Tang L, Lin Z, Li YM: Effects of different magnitudes of
mechanical strain on osteoblasts in vitro. Biochem Biophys Res Commun 344:122-128, 2006
11. Kanzaki H, Chiba M, Arai K, et al: Local RANKL gene
transfer to the periodontal tissue accelerates orthodontic tooth movement. Gene Ther 13:678-685, 2006
12. Kanzaki H, Chiba M, Takahashi I, et al: Local OPG gene
transfer to periodontal tissue inhibits orthodontic tooth
movement. J Dent Res 83:920-925, 2004
267
13. Oliveira DD, de Oliveira BF, de Araújo Brito HH, et al:
Selective alveolar corticotomy to intrude overerupted
molars. Am J Orthod Dentofacial Orthop 133:902-908,
2008
14. Baloul SS, Gerstenfeld LC, Morgan EF, et al: Mechanism
of action and morphologic changes in the alveolar bone
in response to selective alveolar decortication-facilitated
tooth movement. Am J Orthod Dentofacial Orthop 139:
83-101, 2011
15. George A, Evans CA: Detection of root resorption using
dentin and bone markers. Orthod Craniofac Res 12:229235, 2009
16. Aggarwal BB: Tumour necrosis factors receptor associated signalling molecules and their role in activation of
apoptosis, JNK and NF-kappaB. Ann Rheum Dis 59:i6-16,
2000
17. Yano S, Mentaverri R, Kanuparthi D, et al: Functional
expression of "-chemokine receptors in osteoblasts:
Role of regulated upon activation, normal T cell expressed and secreted (RANTES) in osteoblasts and regulation of its secretion by osteoblasts and osteoclasts.
Endocrinology 146:2324-2335, 2005
18. Lam J, Takeshita S, Barker JE, et al: TNF-alpha induces
osteoclastogenesis by direct stimulation of macrophages
exposed to permissive levels of RANK ligand. J Clin
Invest 106:1481-1488, 2000
19. Teitelbaum SL, Ross FP: Genetic regulation of osteoclast
development and function. Nat Rev Genet 4:638-649,
2003
20. Ahuja SS, Zhao S, Bellido T, et al: CD40 ligand blocks
apoptosis induced by tumor necrosis factor alpha, glucocorticoids, and etoposide in osteoblasts and the osteocyte-like cell line murine long bone osteocyte-Y4. Endocrinology 144:1761-1769, 2003
21. Jäger A, Zhang D, Kawarizadeh A, et al: Soluble cytokine
receptor treatment in experimental orthodontic tooth
movement in the rat. Eur J Orthod 27:1-11, 2005
22. Andrade I Jr, Silva TA, Silva GA, et al: The role of tumor
necrosis factor receptor type 1 in orthodontic tooth
movement. J Dent Res 86:1089-1094, 2007
23. Kook SH, Jang YS, Lee JC: Human periodontal ligament
fibroblasts stimulate osteoclastogenesis in response to
compression force through TNF-#-mediated activation
of CD4! T cells. J Cell Biochem 112:2891-2901, 2011
24. Weinblatt ME, Keystone EC, Furst DE, et al: Adalimumab, a fully human anti-tumor necrosis factor alpha
monoclonal antibody for the treatment of rheumatoid
arthritis in patients taking concomitant methotrexate:
The ARMADA trial. Arthritis Rheum 48:35-45, 2003
25. Garlet TP, Coelho U, Silva JS, et al: Cytokine expression
pattern in compression and tension sides of the periodontal ligament during orthodontic tooth movement
in humans. Eur J Oral Sci 115:355-362, 2007
26. Bletsa A, Berggreen E, Brudvik P: Interleukin-1alpha
and tumor necrosis factor-alpha expression during the
early phases of orthodontic tooth movement in rats. Eur
J Oral Sci 114:423-429, 2006
27. Uematsu S, Mogi M, Deguchi T: Interleukin (IL)-1 beta,
IL-6, tumor necrosis factor-alpha, epidermal growth factor, and beta 2-microglobulin levels are elevated in gingival crevicular fluid during human orthodontic tooth
movement. J Dent Res 75:562-567, 1996
268
Andrade Jr, Taddei, and Souza
28. Ren Y, Hazemeijer H, de Haan B, et al: Cytokine profiles
in crevicular fluid during orthodontic tooth movement
of short and long durations. J Periodontol 78:453-458,
2007
29. Lee YM, Fujikado N, Manaka H, et al: IL-1 plays an
important role in the bone metabolism under physiological conditions. Int Immunol 22:805-816, 2010
30. Nakamura I, Jimi E: Regulation of osteoclast differentiation and function by interleukin-1. Vitam Horm 74:357370, 2006
31. Yao Z, Xing L, Qin C, et al: Osteoclast precursor interaction with bone matrix induces osteoclast formation
directly by an interleukin-1-mediated autocrine mechanism. J Biol Chem 283:9917-9924, 2008
32. Tanabe N, Maeno M, Suzuki N, et al: IL-1 alpha stimulates the formation of osteoclast-like cells by increasing
M-CSF and PGE2 production and decreasing OPG production by osteoblasts. Life Sci 77:615-626, 2005
33. Koyama Y, Mitsui N, Suzuki N, et al: Effect of compressive force on the expression of inflammatory cytokines
and their receptors in osteoblastic Saos-2 cells. Arch Oral
Biol 53:488-496, 2008
34. Al-Qawasmi RA, Hartsfield JK Jr, Everett ET, et al: Genetic predisposition to external apical root resorption.
Am J Orthod Dentofacial Orthop 123:242-252, 2003
35. Iwasaki LR, Chandler JR, Marx DB, et al: IL-1 gene
polymorphisms, secretion in gingival crevicular fluid,
and speed of human orthodontic tooth movement. Orthod Craniofac Res 12:129-140, 2009
36. Schiff MH: Role of interleukin 1 and interleukin 1 receptor antagonist in the mediation of rheumatoid arthritis. Ann Rheum Dis 59:i103-i108, 2000
37. Lee YH, Nahm DS, Jung YH, et al: Differential gene
expression of periodontal ligament cells after loading of
static compressive force. J Periodontol 78:446-452, 2007
38. Tuncer BB, Ozmeriç N, Tuncer C, et al: Levels of interleukin-8 during tooth movement. Angle Orthod 75:631636, 2005
39. Li Y, Zheng W, Liu JS, et al: Expression of osteoclastogenesis inducers in a tissue model of periodontal ligament under compression. J Dent Res 90:115-120, 2011
40. Linkhart TA, Linkhart SG, MacCharles DC, et al: Interleukin-6 messenger RNA expression and interleukin-6
protein secretion in cells isolated from normal human
bone: Regulation by interleukin-1. J Bone Miner Res
6:1285-1294, 1991
41. Suga K, Saitoh M, Fukushima S, et al: Interleukin-11
induces osteoblast differentiation and acts synergistically
with bone morphogenetic protein-2 in C3H10T1/2
cells. J Interferon Cytokine Res 21:695-707, 2001
42. Horwood NJ, Udagawa N, Elliott J, et al: Interleukin 18
inhibits osteoclast formation via T cell production of granulocyte macrophage colony-stimulating factor. J Clin Invest
101:595-603, 1998
43. Teixeira CC, Khoo E, Tran J, et al: Cytokine expression
and accelerated tooth movement. J Dent Res 89:11351141, 2010
44. Spits H, Malefyt RW: Functional characterization of human IL-10. Arch Allergy Immunol 99:8-15, 1992
45. Silva TA, Garlet GP, Fukada SY, et al: Chemokines in oral
inflammatory diseases: Apical periodontitis and periodontal disease. J Dent Res 86:306-319, 2007
46. Schall TJ, Proudfoot AEI: Overcoming hurdles in developing successful drugs targeting chemokine receptors.
Nat Rev Immunol 11:355-363, 2011
47. Ley K, Laudanna C, Cybulsky MI, et al: Getting to the site
of inflammation: The leukocyte adhesion cascade updated. Nat Rev Immunol 7:678-689, 2007
48. Yu X, Huang Y, Collin-Osdoby P, et al: CCR1 chemokines promote the chemotactic recruitment, RANKL development, and motility of osteoclasts and are induced
by inflammatory cytokines in osteoblasts. J Bone Miner
Res 19:2065-2077, 2004
49. Binder NB, Niederreiter B, Hoffmann O, et al: Estrogendependent and C-C chemokine receptor-2-dependent
pathways determine osteoclast behavior in osteoporosis.
Nat Med 15:417-424, 2009
50. Kwak HB, Lee SW, Jin HM, et al: Monokine induced by
interferon-gamma is induced by receptor activator of
nuclear factor kappa B ligand and is involved in osteoclast adhesion and migration. Blood 105:2963-2969,
2005
51. Okamatsu Y, Kim D, Battaglino R, et al: MIP-1 gamma
promotes RANKL-induced osteoclast formation and survival. J Immunol 173:2084-2090, 2004
52. Watanabe T, Kukita T, Kukita A, et al: Direct stimulation
of osteoclastogenesis by MIP-1alpha: Evidence obtained
from studies using RAW264 cell clone highly responsive
to RANKL. J Endocrinol 180:193-201, 2004
53. Tsubaki M, Kato C, Manno M, et al: Macrophage inflammatory protein-1a (MIP-1a) enhances a receptor activator of nuclear factor KB ligand (RANKL) expression in
mouse bone marrow stromal cells and osteoblasts
through MAPK and PI3K/Akt pathways. Mol Cell
Biochem 304:53-60, 2007
54. Wright LM, Maloney W, Yu X, et al: Stromal cell-derived
factor-1 binding to its chemokine receptor CXCR4 on
precursor cells promotes the chemotactic recruitment,
development and survival of human osteoclasts. Bone
36:840-853, 2005
55. Bendre MS, Montague DC, Peery T, et al: Interleukin-8
stimulation of osteoclastogenesis and bone resorption is
a mechanism for the increased osteolysis of metastatic
bone disease. Bone 33:28-37, 2003
56. Andrade I Jr, Taddei SRA, Garlet GP, et al: CCR5 downregulates osteoclast function in orthodontic tooth movement. J Dent Res 88:1037-1041, 2009
57. Garlet TP, Coelho U, Repeke CE, et al: Differential
expression of osteoblast and osteoclastchemmoatractants in compression and tension sides during orthodontic movement. Cytokines 42:330-335, 2008
58. Asano M, Yamaguchi M, Nakajima R, et al: IL-8 and
MCP-1 induced by excessive orthodontic force mediates
odontoclastogenesis in periodontal tissues. Oral Dis 17:
489-498, 2010
59. Shaharara S, Proudfoot AEI, Woods JM, et al: Amelioration of rate adjuvant-induced arthritis by Met-RANTES.
Arthritis Rheum 52:1907-1919, 2005
60. Handel TM, Johnson Z, Rodrigues DH, et al: An engineered monomer of CCL2 has anti-inflammatory properties emphasizing the importance of oligomerization
for chemokine activity in vivo. J Leukoc Biol 84:11011108, 2008
Inflammation and Tooth Movement
61. Dai J, Rabie ABM: VEGF: An essential mediator of both
angiogenesis and endochondral ossification. J Dent Res
86:937-950, 2007
62. Miyagawa A, Chiba M, Hayashi H, et al: Compressive
force induces VEGF production in periodontal tissues. J
Dent Res 88:752-756, 2009
63. Cheung WY, Liu C, Tonelli-Zasarsky RML, et al: Osteocyte apoptosis is mechanically regulated and induces
angiogenesis in vitro. J Orthop Res 29:523-530, 2011
64. Niida BS, Kaku M, Amano H, et al: Vascular endothelial
growth factor can substitute for macrophage colonystimulating factor in the support of osteoclastic bone
resorption. J Exp Med 190:293-298, 1999
65. Kohno S, Kaku M, Tsutsui K, et al: Expression of vascular
endothelial growth factor and the effects on bone remodeling during experimental tooth movement. J Dent
Res 82:177-182, 2003
66. Kohno S, Kaku M, Kawata T, et al: Neutralizing effects of
an anti-vascular endothelial growth factor antibody on
tooth movement. Angle Orthod 75:797-804, 2005
67. Kanzaki H, Chiba M, Sato A, et al: Cyclical tensile force
on periodontal ligament cells inhibits osteoclastogenesis
through OPG induction. J Dent Res 85:457-462, 2006
68. Kobayashi Y, Hashimoto F, Miyamoto H, et al: Forceinduced osteoclast apoptosis in vivo is accompanied by
elevation in transforming growth factor beta and osteoprotegerin expression. J Bone Miner Res 15:1924-1934,
2000
69. Hogan BL: Bone morphogenetic proteins in development. Curr Opin Genet Dev 6:432-448, 1996
70. King GN, Cochran DL: Factors that modulate the effects
of bone morphogenetic protein-induced periodontal regeneration: A critical review. J Periodontol 73:925-936,
2002
71. Mitsui N, Suzuki N, Maeno M, et al: Optimal compressive force induces bone formation via increasing bone
morphogenetic proteins production and decreasing
their antagonists production by Saos-2 cells. Life Sci
78:2697-2706, 2006
72. Govoni KE, Baylink DJ, Mohan S: The multi-functional
role of insulin-like growth factor binding proteins in
bone. Pediatr Nephrol 20:261-268, 2005
73. Reijnders CM, Bravenboer N, Tromp AM, et al: Effect of
mechanical loading on insulin-like growth factor-I gene
expression in rat tibia. J Endocrinol 192:131-140, 2007
74. Hirukawa K, Miyazawa K, Maeda H, et al: Effect of tensile
force on the expression of IGF-I and IGF-I receptor in
organ-cultured rat cranial suture. Arch Oral Biol 50:367372, 2005
269
75. Han X, Amar S: IGF-1 signaling enhances cell survival in
periodontal ligament fibroblasts vs. gingival fibroblasts. J
Dent Res 82:454-459, 2003
76. Kheralla Y, Götz W, Kawarizadeh A. IGF-I, IGF-IR and
IRS1 expression as an early reaction of PDL cells to
experimental tooth movement in the rat. Arch Oral Biol
55:215-222, 2010
77. Bosetti M, Leigheb M, Brooks RA, et al: Regulation of
osteoblast and osteoclast functions by FGF-6. J Cell
Physiol 225:466-471, 2010
78. Kawaguchi H, Chikazu D, Nakamura K, et al: Direct and
indirect actions of FGF-2 on osteoclastic bone resorption
in cultures. J Bone Miner Res 15:466-473, 2000
79. Nakajima R, Yamaguchi M, Kojima T, et al: Effects of
compression force on fibroblast growth factor-2 and receptor activator of nuclear factor kappa B ligand production by periodontal ligament cells in vitro. J Periodont Res 43:168-173, 2008
80. Alves JB, Ferreira CL, Martins AF, et al: Local delivery of
EGF-liposome mediated bone modeling in orthodontic
tooth movement by increasing RANKL expression. Life
Sci 85:693-699, 2009
81. Guajardo G, Okamoto Y, Gogen H, et al: Immunohistochemical localization of epidermal growth factor in cat
paradental tissues during tooth movement. Am J Orthod
Dentofacial Orthop 118:210-219, 2000
82. Chae HS, Park HJ, Hwang HR, et al: The effect of
antioxidants on the production of pro-inflammatory cytokines and orthodontic tooth movement. Mol Cells
32:189-196, 2011
83. Kindle L, Rothe L, Kriss M, et al: Human microvascular
endothelial cell activation by IL-1 and TNF-alpha stimulates the adhesion and transendothelial migration of
circulating human CD14! monocytes that develop with
RANKL into functional osteoclasts. J Bone Miner Res
21:193-206, 2006
84. Park HJ, Baek KH, Lee HL, et al: Hypoxia inducible
factor-1# directly induces the expression of receptor
activator of nuclear factor-!B ligand in periodontal ligament fibroblasts. Mol Cells 31:573-578, 2011
85. Roberts WE, Engen DW, Schneider PM, et al: Implantanchored orthodontics for partially edentulous malocclusions in children and adults. Am J Orthod Dentofacial Orthop 126:302-304, 2004
86. Masella RS, Meister M: Current concepts in the biology
of orthodontic tooth movement. Am J Orthod Dentofacial Orthop 129:458-468, 2006