Download Effects of pulsed electromagnetic field vibration on

SCIENTIFIC ARTICLE
Australian Dental Journal 2007;52:(4):282-287
Effects of pulsed electromagnetic field vibration on tooth
movement induced by magnetic and mechanical forces: a
preliminary study
M Ali Darendeliler,* A Zea,† G Shen,‡ H Zoellner§
Abstract
Background: This study was designed to determine
whether or not high-frequency and low-magnitude
vibration affects orthodontic tooth movement
caused by magnetic or/and mechanical forces.
Methods: Forty-four 7-week-old Wistar rats were
randomly divided into four groups, with each group
further divided into experimental and control
subgroups. Neodymium-Iron-Boron (Nd-Fe-B)
magnets and Sentalloy closed coil springs were
placed between maxillary or mandibular first molars
and incisors to activate tooth movement. The
animals of experimental subgroups were exposed to
the vibration induced by pulsed electromagnetic
fields (PEMF) whilst the control subgroups were
under normal atmosphere. The experiment lasted
for 14 days and all of the animals were sacrificed for
examination. The changes in the space between the
molar and incisor were measured to indicate the
amount of tooth movement.
Results: The coil springs, either with sham or active
magnets, move molar much more than magnets
alone, regardless of absence or presence of PEMF
(p<0.001). Under PEMF, the coil spring moved
significantly more amount of tooth movement than
that of coil–magnet combination (p<0.01), as did the
magnets compared to sham magnets (p<0.019).
Under a non-PEMF scenario, there was no
significant difference in tooth movement between
coil spring and coil–magnets combination, nor was
there difference between magnets and sham magnets.
Conclusions: It is suggested that the PEMF-induced
vibration may enhance the effect of mechanical and
magnetic forces on tooth movement.
Key words: Tooth movement, Nd-Fe-B magnet, PEMF
vibration.
*Professor and Chair, Department of Orthodontics, Faculty of
Dentistry, The University of Sydney, New South Wales.
†Postgraduate student, Department of Orthodontics, Faculty of
Dentistry, The University of Sydney, New South Wales.
‡Associate Professor, Department of Orthodontics, Faculty of
Dentistry, The University of Sydney, New South Wales.
§Associate Professor, Department of Oral Pathology and Oral
Medicine, Faculty of Dentistry, Sydney Dental Hospital, The
University of Sydney, New South Wales.
282
Abbreviations and acronyms: ME = method analysis;
Nd-Fe-B = Neodymium-Iron-Boron; PEMF = pulsed
electromagnetic field.
(Accepted for publication 21 February 2007.)
INTRODUCTION
It has been shown that applied electrical fields can
alter the normal electrical states of bone and cartilage,
induce increased rates of cellular division and
metabolism, and thus promote increased healing of
bony and cartilaginous defects.1,2 Bassett3 proposed that
tissue integrity and function could be restored by
applying electrical and/or mechanical energy to the area
of injury. Electrical currents were applied to nonhealing fractures in animal studies4,5 and in clinical
trials6,7 and successfully helped the healing process. It
appears that electrical energy, whether applied as a
direct current or a pulsed electromagnetic field (PEMF),
has the ability to affect both the depository and
resorptive activities of bone and cartilage cells.8-10
It is believed that orthodontic tooth movement is
accompanied by site-specific bone remodelling with
inflammatory nature.11 Alveolar bone remodelling is
essential for tooth movement and is characterized by
tandem periods of osteoclastic recruitment, bone
resorption, reversal and bone formation.12 This process
involves the periodontal ligament and is dependent on
the magnitude and consistency of the force being
applied. In the area of periodontal ligament compression,
osteoclasts proliferate and initial resorption of
superficial bone occurs.13,14 In the region of periodontal
ligament tension, the periodontal fibres unwind, fibroblasts appear and osteoblasts form a non-mineralized
collagenous matrix called osteoid. The osteoid is later
mineralized, trapping some osteocytes in lacunae
within the bone.
Previous animal and clinical studies have shown that
mechanical stimulation, in particular low intensity
pulsed ultrasound, improves the rate of bone healing
via up-regulation of cartilage formation and maturation
of endochondral bone formation.15,16
Australian Dental Journal 2007;52:4.
Table 1. Experimental design and animal grouping
Experimental subgroups (with PEMF vibration)
Group
Group
Group
Group
1
2
3
4
(n=20)
(n=8)
(n=8)
(n=8)
Control subgroups (without PEMF vibration)
Left side
Right side
Left side
Right side
Sham magnet
Magnet
Sham magnet
Coil+sham magnet
Magnet
Coil+magnet
Coil+sham magnet
Coil+magnet
Sham magnet
Magnet
Sham magnet
Coil+sham magnet
Magnet
Coil+magnet
Coil+sham magnet
Coil+magnet
In addition, the results of earlier studies show that
high-frequency (30Hz), low-magnitude vibrations
induce increased anabolic activity in bone.17 Since it has
been hypothesized that there is an increase in metabolic
activity of bone, it is reasonable to assume that there
should be an increase in the rate of orthodontic tooth
movement under the influence of mechanical vibration.
Therefore, the primary aim of this study was to
determine whether or not high-frequency and lowmagnitude mechanical vibration affects orthodontic
tooth movement when it is integrated with magnetic
and/or elastic forces.
MATERIALS AND METHODS
Experimental design
Forty-four 7-week-old Wistar strain rats weighing
210–250 g were used (ethics approval: Westmead
Hospital Animal Ethics Committee protocol
no. 141.04-04). The animals were randomly divided
into four groups, with each group further divided into
the experimental and control subgroups (Table 1).
Group 1 (n=20): Demagnetized sham magnets were
bonded onto the mesial aspect of the maxillary or
mandibular left first molars and the distal aspect of the
incisors. Neodymium-Iron-Boron (Nd-Fe-B) magnets
were bonded on the contralateral side (Fig 1). Half of
the animals (n=10) were designated as experimental
subgroup (Group 1P) which were exposed to PEMF
vibration in a Helmholtz configuration eight hours a
day.18 Another half of the animals were the control
subgroup (Group 1C) which were not exposed to the
vibration. Magnets and sham magnets were bonded on
the maxillary first molars of six rats of Group 1P and
Group 1C. Subsequently, it was found that the coil
springs were more securely attached to the mandibular
teeth than maxillary teeth due to the concavity of the
maxillary teeth. Therefore, magnets and coil springs
were attached between the first molar and the incisors
of the mandible for the remaining sample groups.
Group 2 (n=8): Nd-Fe-B magnets were bonded on
the mesial aspect of the left first molars and the distal
aspect of the incisors, and the 25 g Sentalloy closed coil
springs (GAC Cat No:10-000-26) plus Nd-Fe-B
magnets were placed on the contralateral side. Half of
the animals (n=4) were exposed to PEMF eight hours a
day (Group 2P) and the other half of the animals were
not (Group 2C).
Group 3 (n=8): Demagnetized sham magnets were
bonded between left first molars and incisors, and the
Australian Dental Journal 2007;52:4.
25 g Sentalloy closed coil springs plus permanently
demagnetized sham magnets were placed on the
contralateral side. Half of the group (n=4) were
exposed to PEMF eight hours a day (Group 3P) and the
other half (n=4) were not (Group 3C).
Group 4 (n=8): 25 g Sentalloy closed coil springs
with demagnetized sham magnets were placed between
the molars and the incisors, and 25 g Sentalloy closed
coil springs with Nd-Fe-B magnets were placed on the
contralateral side. Half of the group (n=4) were
exposed to PEMF eight hours a day (Group 4P) and the
other half (n=4) were not (Group 4C).
The rats were administered an appropriate amount
of anaesthetic agent: Xylazine (10 mg/kg) and
Ketamine (90 mg/kg). Polyvinyl siloxane hydrophilic
impressions of the rat’s dentition were taken as records
(3M Imprint II Garant Quick Step Regular Body Cat
No. 9579). Then Nd-Fe-B magnets (1 mm length x
1 mm width x 0.5 mm thickness) were bonded onto the
mesial surface of the rat upper first molars in relevant
groups with 3M Transbond light cure composite resin
(Ref No. 712036) and 3M Transbond Moisture
Insensitive Primer (Ref No. 712-025). The Nd-Fe-B
Fig 1. Ne-Fe-B magnets and permanently demagnetized sham
magnets bonded on mesial surface of the maxillary first molars in a
Wistar rat.
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above via the standard analogue sound output channel.
Field strength was controlled via the amplifier power
output. Throughout this experiment, the PEMF
generated high-frequency and low-magnitude vibration
featuring 30Hz pulses, a positive duration (T) of 200
microseconds, a magnetic field (B) of 1.8 mT and a
positive rate (dB/dT) of 9 tesla/second. The magnetic
field intensity was controlled via the amplifier power
output to provide two Gauss as measured using
Holaday ELF Magnetic Field Meter (Holaday
Industries Inc., USA).
Fig 2. PEMF coils surrounding circular lexan cage produces
high-frequency and low-magnitude vibration.
magnets produced energy of 190 kilojoules/m3 with
attractive force at 1 mm of 0.5 mT (Tesla). Permanently
demagnetized sham magnets of the same dimension
were bonded onto maxillary molars on the contralateral side. The magnetization of the magnet was in
mesiodistal direction.
Sentalloy closed coil springs of 25 g (GAC Cat
No:10-000-26) were used to move the mandibular
molars forward, decreasing the length of the interdental
space between the first molar and the incisor. The
orthodontic tooth movement model was adapted from
Kobayashi et al.19 and Brudvik and Rygh.20 In
appropriate groups, Nd-Fe-B magnets and permanently
demagnetized sham magnets were bonded onto 25 g
Sentalloy closed coil springs before ligating onto the
first mandibular molars. After ligation with 3.0 silk
suture, composite resin was used to bond magnets and
sham magnets onto the mesial surface of first molars to
ensure contact with tooth structure. The springs were
then fixed anteriorly using ligature wire loops placed
around the incisal thirds of both lower incisors.
Composite resin was placed over ligature wire ends to
prevent mucosal trauma. Following recovery, the rats
were housed in circular lexan cages.
Generation of pulsed electromagnetic field (PEMF)
The electromagnetic field generating coils of internal
diameter of 40 cm which were placed above and below
the cage in the PEMF groups were arranged parallel to
each other with a separation of 20 cm (Fig 2). This
design, known as a Helmholtz configuration, produced
an even magnetic field in the space between the coils.
The principle of apparatus setup was based on the
proposal by Darendeliler et al.18 The field coil was
driven by a linear amplifier with a variable power
output of up to 800 Watts RMS (Panasonic Pty. Ltd.).
Field parameters including frequency and growth/decay
character can be precisely controlled via a computer
interface. This waveform generator comprised a
MacIntosh computer, hosting a software signal generator
(Mac the Scope, Channel D Corporation, Trenton NJ)
with the output being passed to the amplifier described
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Examination of tooth movement
The rats were sacrificed on day 14 by carbon dioxide
asphyxiation. Polyvinyl siloxane impressions of rat
dentition were taken as post-treatment records. Casts
of before and after treatment were prepared in plaster
from the impressions. Measurements were taken with
digital millimetre callipers (Orthopli Electronic Digital
Callipers Model 50001, USA) to determine the distance
between the midpoint of the incisors to the most mesial
cervical point of the first molar (interdental space). The
data were analysed with the univariate analysis of
variance and estimated marginal means, using
Statistical Package for Social Sciences program (SPSS
for Windows, version 12 SPSS Inc., Chicago, USA).
Each measurement was recorded three times on
different days to reduce error. Method error (ME)
analysis was calculated by the formula:
where d is the difference between the two registrations
of a pair and n is the number of double registrations.
Paired t tests were performed to compare the two
registrations. There was no significant difference
among the separate registrations.
RESULTS
Univariate analysis of variance was conducted to
identify the differences in amount of tooth movement
(changes in interdental spaces) between PEMF,
magnets, coil spring and coil spring combined with
magnets (Table 2). It was found that the effect of coil
spring alone, i.e., with sham magnet (Group 4,
p=0.000) was more prominent than when coil springs
were used in combination with Nd-Fe-B magnets
(Group 2, p=0.014). The effect of magnets (Group 1,
Table 2. Univariate analysis of variance testing the
effects of different modalities on tooth movement
(dependent variable: tooth movement)
Sources
Intercept
Effect of PEMF
Inter-rat differences
Effect of coil
Effect of magnet
Coil–magnet interaction
Significance (P)
0.000
0.577
0.002
0.000
0.097
0.014
Australian Dental Journal 2007;52:4.
Table 3. Univariate analysis of variance testing the
effects of different modalities on tooth movement
with presence and absence of PEMF (dependent
variable: tooth movement)
Sources
With PEMF
Without PEMF
Significance (P)
Significance (P)
0.003
0.000
0.019
0.004
0.001
0.002
0.001
0.408
0.050
0.884
Intercept
Effect of coil
Effect of magnet
Inter-rat effect
Coil–magnet interaction
p=0.097), on the other hand, was less prominent than
combination of coil spring and magnets (Group 2,
p=0.014), indicating that magnets would have
increased effect on molar tooth movement in the
presence of coil spring. It was also found that the
amount of tooth movement under the influence of
PEMF vibration (experimental subgroups) was not
significantly different from that without PEMF (control
subgroups) (p=0.577). The amount of tooth movement
between different animals with rat as a variable was
statistically significant (p=0.002).
To further examine the effects of PEMF vibration on
molar tooth movement under different force
modalities, i.e., coil spring, magnet and combined coil
spring and magnet, the univariate analysis of variance
for the presence and absence of PEMF was conducted
(Table 3). It was found that the effect of combined coil
spring and magnets under PEMF vibration was more
significant (p=0.001) than that without PEMF
(p=0.884). The effects of magnets only (p=0.019) and
coil spring only (p=0.000) under PEMF vibration were
also greater than those without PEMF (magnets
p=0.408, coils spring p=0.001). These data suggested
that the effect of magnets on tooth movement increased
when magnets were integrated with PEMF vibration.
To have a comprehensive and overall evaluation of
the differences in tooth movement between different
force modalities (magnetic, mechanic and combined
forces) under different scenarios (with and without
PEMF), a statistical plot analysis was conducted
(Fig 3). This plot revealed the following: (1) The coil
springs, either with sham or active magnets, move
molar much more than magnets alone, regardless of the
absence or presence of PEMF (p<0.001); (2) Under
PEMF, the coil spring moved significantly more amount
of tooth movement than that of coil–magnet
combination (p<0.01), as did the magnets compared to
sham magnets (p<0.019); (3) Under a non-PEMF
scenario, there was no significant difference in tooth
movement between coil spring and coil–magnets
combination, nor was there any difference between
magnets and sham magnets.
DISCUSSION
This study was designed in such a way that the NdFe-B magnet bonded onto the molar tooth of the rat
Australian Dental Journal 2007;52:4.
Fig 3. Statistical plot depicting the overall effects of Ne-Fe-B
magnets. Sentalloy coil springs and their interaction in the absence
and presence of PEMF. PCM stands for the following possible
combinations of the factors: … = Sham; ..m = magnet; .c. = coil;
.cm = coil plus magnet; p.. = PEMF; p.m = PEMF plus magnet;
pc. = PEMF plus coil; pcm = PEMF plus coil and magnet.
would interact with the PEMF, resulting in mesiodistal
vibratory stimulus to that molar. The direction of
PEMF will affect the direction of pulsating movement
of the magnet. The direction of vibration in relation to
the PEMF may have been changed, depending on the
orientation of the head. However, the variation in
PEMF direction would not cause significant bias as the
chance of being subject to this variation was even
between the animals. It was shown that Nd-Fe-B
magnets bonded onto rat molars in the presence of
PEMF vibration (Group 1P) resulted in a more
decreased interdental space than that in sham magnet
group (Group 1C) and this was statistically significant
(p=0.019) (Fig 3). This difference in interdental space
could be partly due to growth in craniofacial complex
of the animal. However, the matched control groups
could eliminate or minimize the influence of the growth
factor. The experimental duration lasted for 14 days in
this study where 7-week-old rats were used. It has been
reported that the laboratory rats grow in a pubertal
spurt between 7 and 9 weeks of age, the time suitable
for growth modification.21
It should be noted that magnets and sham magnets
were bonded on the maxillary first molars of the first
six rats of Group 1P and Group 1C, followed by the
placement moving into the mandibular counterparts.
The data from the maxillary device were still included
for statistical analysis due to the fact that the matched
controls could factor out any deviations that may
cause.
Some reports described asymmetric voltage
waveforms from mechanically deformed live bone.4,5
These changes were presumed to occur in bone during
physical activity as a result of mechanical forces.
Polarity is dependent on the direction of bending; areas
under pressure are in an electropositive state which is
usually associated with osteoclastic activity and areas
under tension are in an electronegative state which is
associated with osteoblastic activity. It is therefore
285
conceivable that under the situation of alveolar bone on
the present study with vibrating stimulus, the areas
under pressure will shortly become the areas under
tension and vice versa. It is also possible that an area of
alveolar bone is associated with both increased
osteoblastic activity and osteoclastic activity.
It was shown in this study that, influenced by Nd-FeB magnet (without coil spring) together with PEMF, the
interdental spaces increased much less than when
influenced by sham magnets (p<0.019) (Fig 3). This
indicated that the static magnetic field produced by NdFe-B magnet would have effect on tooth displacement.
The effect of magnetic field on bone healing is well
documented in the literature;22 however, the mechanism
of action is not clear. Bassett3 stated that magnetic field
could initiate increased localized calcium deposition,
which neutralizes the tissues net negative charge, allows
for subsequent vascularization and initiation of
osteogenesis. It seems that this static magnetic effect
caused by the Nd-Fe-B magnet alone could be
accentuated in the presence of PEMF which causes
vibration (Table 3).
It appeared that although the effect on tooth
movement of PEMF alone was not statistically
significant, it affected the linear measurements of the
interdental space of the experimental samples
compared with the controls (Table 3). It is well
documented in the literature that PEMF at low
frequency significantly accelerates bone fracture
healing in clinical trials6,7 and osteotomy healing in
animal studies,4,5 especially with non-unions and
delayed fracture unions. It has been suggested by Rubin
et al.4 that bone resorption which accompanies disuse
can be prevented or even reversed by the exogenous
induction of electric fields. However, the precise
mechanism of action remains unclear. Satake et al.23
found that calcium concentration in human periodontal
ligament fibroblast cells was increased in the presence
of PEMF. At the cellular level, Rodan et al.24 observed
that cyclic nucleotides and calcium vehicles carry
extracellular messages across the cell membrane.
Interactions with diffusible ions, such as Ca2+ and K+,
may convey an electric signal for DNA synthesis and
cell division.
One of the aims of this study was to evaluate
whether PEMF vibration will affect conventional
orthodontic tooth movement produced by closed coil
spring and Nd-Fe-B magnet. It was found that 25 g
Sentalloy closed coil spring moved the tooth more
when it was used alone than when combined with
magnets (Table 2), and it was especially so in the
presence of PEMF where this interaction remained
highly significant (p<0.01) (Table 3, Fig 3). This
demonstrates a possible synergistic effect of the PEMF
on the rate of tooth movement caused by the Nd-Fe-B
magnet and coil springs. In addition, it was also
interesting to note that the interdental space either
became slightly increased when magnets worked alone,
or decreased slowly when combined with coil spring,
286
regardless of the presence or absence of PEMF (Fig 3),
indicating that the magnets hinder orthodontic tooth
movement. The reasons behind the phenomenon may
be the pulsating effect of the magnet that causes the
molar tooth to remain relatively stationary. Another
explanation may lie in the fact that the attractive forces
by the magnets faded down significantly due to the
large distance between the molar and incisor, and
therefore hardly overcome the natural tendency of
molar distal drift.25
The pulsating movement caused by the interaction of
the PEMF and the Nd-Fe-B magnet could have a
greater effect than as detected because the amount
and/or direction of movement may be masked by that
produced by the coil springs. As mentioned earlier, the
Nd-Fe-B magnet alone and together with the closed coil
spring appeared to slow down the changes in decreased
interdental space. The closed coil spring, on the other
hand, moved tooth faster when exposed to PEMF than
it did without PEMF vibration (Fig 3). This phenomenon
indicates that PEMF increases the rate of tooth
movement produced by the closed coil springs. This is
in agreement with the findings of Darendeliler et al.18
They found that a combined use of PEMF with coil
springs was successful in increasing the rate of tooth
movement compared with that produced by the coil
springs alone. The mechanism of this effect has been
suggested by some researchers to involve a reduction in
“lag” phase which is common in orthodontic tooth
movement.18 We therefore postulate that the PEMF,
although it did not appear to produce much effect on
tooth movement independently (p=0.577) (Table 2),
has a synergistic effect on tooth movement when it is
applied in conjunction with coil springs (p<0.001)
(Table 3).
It is also worth noting that whilst there was no
significant difference between magnets and sham
magnets in the absence of PEMF (p=0.408) (Table 3), it
became significantly different when PEMF was
imposed where the interdental space increased much
less with magnets than with sham magnets (p=0.019)
(Table 3). This clearly demonstrated that, when taking
into consideration overcoming molar distal migration
and magnets’ long working distance, PEMF was
effective in encouraging magnets to move tooth
towards favourable direction. It is therefore safe to
contend that when combined with coil springs or
magnets, PEMF could be applied, especially at the
beginning of orthodontic treatment, to reduce the
initial “lag” phase of orthodontic tooth movement and
consequently to shorten the treatment time.
CONCLUSIONS
The effect of conventional mechanic forces, e.g., coil
springs, on orthodontic tooth movement is enhanced
with the exposure to PEMF-induced vibration. With
reasonable working distance, the magnetic forces may
be effective in enhancing tooth movement under
PEMF-induced vibration.
Australian Dental Journal 2007;52:4.
ACKNOWLEDGEMENTS
We thank the Australian Society of Orthodontics for
funding this project. We also thank Associate Professor
P Petocz of the Department of Statistics, Macquarie
University for his statistical assistance. Thanks also go
to Mr Paul Bowker, Senior Lecturer (clinical), The
University of Sydney; Ms Janice Mathews from the
Cellular and Molecular Pathology Research Unit, The
University of Sydney; all the staff of the Westmead
Animal Holding Facility and Dr. Allan Jones from the
Electron Microscopy Unit, The University of Sydney.
REFERENCES
13. Sato Y, Sakai H, Kobayashi Y, Sasaki, T. Bisphosphonate
adminstration alters subcellular localisation of vacuolar-type
H(+)-ATPase and cathepsin K in osteoclasts during experimental
movement of rat molars. Anat Rec 2000;260:72-80.
14. Sato Y, Shibasaki Y, Sasaki T. Effects of bisphosphonate
administration on root and bone resorption during experimental
movement of rat molars. In: Davidovitch Z, Mah J, eds.
Biological mechanisms of tooth movement and craniofacial
adaptation. Birmingham: EBSCO;2000:243-252.
15. Rubin C, Turner S, Bain S, Mallinckrodt C, McLeod K.
Anabolism: Low mechanical signals strengthen long bones.
Nature 2001;412:603-604.
16. Rubin C, Xu G, Judex S. The anabolic activity of bone tissue,
suppressed by disuse, is normalized by brief exposure to
extremely low-magnitude mechanical stimuli. FASEB J
2001;15:2225-2229.
1. Norton JB, Young SO, Kenner GH. Epiphyseal cartilage cAMP
changes produced by electrical and mechanical perturbations.
Clin Orthop 1977;48:915-923.
17. Nolte PA, Klein-Nulend J, Albers GH, et al. Low intensity
ultrasound stimulates endochondral ossification in vitro. J
Orthop Res 2001;19:301-307.
2. Martin RB, Gutman W. The effect of electric fields on
osteoporosis of disease. Calcif Tissue Int 1978;5:23-27.
18. Darendeliler MA, Sinclair PM, Kusy RP. The effects of samariumcobalt magnets and pulsed electromagnetic fields on tooth
movement. Am J Orthod Dentofacial Orthop 1995;107:578-588.
3. Bassett CA. Beneficial effects of electromagnetic fields. J Cell
Biochem 1993;51:387-393.
4. Rubin CT, Donahue HJ, Rubin JE, McLeod KJ. Optimisation of
electric field parameters for the control of bone remodelling:
exploitation of an indigenous mechanism for the prevention of
osteopenia. J Bone Miner Res 1993;8 Suppl 2:S573-581.
5. Yonemori K, Matsunaga S, Ishidou Y, Maeda S, Yoshida H. Early
effects of electrical stimulation on osteogenesis. Bone
1996;19:173-180.
6. Scott G, King JB. A prospective, double-blind trial of electrical
capacitive coupling in the treatment of non-union of long bones.
J Bone Joint Surg Am 1994;76:820-826.
7. Hulme J, Robinson V, DeBie R, Wells G, Judd M, Tugwell, P.
Electromagnetic fields for the treatment of osteoarthritis.
Cochrane Database Syst Rev 2002;1:CD003523.
8. Quittan M, Schuhfried O, Wiesinger GF, Fialka-Moser V.
Clinical effectiveness of magnetic field therapy – a review of the
literature. Acta Med Austraca 2002;27:61-68.
9. Ibiwoye MO, Powell KA, Grabiner MD, et al. Bone mass is
preserved in a critical-sizes osteotomy by low energy pulsed
electromagnetic fields as quantitated by in vivo micro-computed
tomography. J Orthop Res 2004;22:1086-1093.
10. Inoue N, Ohnishi I, Chen D, Deitz LW, Schwardt JD, Chao EY.
Effect of pulsed electromagnetic fields (PEMF) on late-phase
osteotomy gap healing in a canine tibial model. J Orthop Res
2002;20:1106-1114.
11. Vandevska-Radunovic V. Neural modulation of inflammatory
reactions in dental tissues incident to orthodontic tooth
movement. A review of the literature. Eur J Orthod 1999;21:231247.
12. Miyajima K, Kasai R, Kahn AJ, Hayakawa T, Iizuka T. Biological
mechanisms of tooth movement: in vitro analysis and clinical
application. In: Davidovitch Z, Mah J, eds. The biological
mechanisms of tooth movement and craniofacial adaptation.
Birmingham: EBSCO;1992:311-317.
Australian Dental Journal 2007;52:4.
19. Kobayashi Y, Hashimoto F, Miyamoto H, et al. Force-induced
osteoclast apoptosis in vivo is accompanied by elevation in
transforming growth factor beta and osteoprotegerin expression.
J Bone Miner Res 2000;15:1924-1934.
20. Brudvik P, Rygh P. The initial phase of orthodontic root
resorption incident to local compression of the periodontal
ligament. Eur J Orthod 1993;15:249-263.
21. Shen G, Hägg U, Rabie AB, Kalurachchi K. Identification of
temporal pattern of mandibular growth – A molecular and
biochemical study. Orthod Craniofacial Res 2005;8:114-122.
22. Linovitz RJ, Pathria M, Bernhardt M, et al. Combined magnetic
fields accelerate and increase spine fusion in double-blind,
randomised, placebo controlled study. Spine 2002;27:1383-1389;
discussion 1389.
23. Satake T, Yasu N, Kakai Y, et al. Effect of pulsed electromagnetic
fields on human periodontal ligament in vivo. Alterations of
intracellular Ca2+. Kanagawa Shigaku 1990;24:735-742.
24. Rodan GA, Bourret LA, Norton LA. DNA synthesis in cartilage
cells is stimulated by oscillating electric fields. Science
1978;199:690-692.
25. Roux D, Meunier C, Woda A. A biometric analysis in the rat of
the horizontal component of physiological tooth migration and
its response to altered occlusal function. Arch Oral Biol
1993;38:957-963.
Address for correspondence/reprints:
Professor M Ali Darendeliler
Department of Orthodontics
Faculty of Dentistry
The University of Sydney
Level 2, 2 Chalmers Street
Surry Hills, New South Wales 2010
Email: [email protected]
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