The effect of low-level laser therapy during orthodontic movement: A preliminary study

Abstract

It has been emphasized that one of the most valuable treatment objectives in dental practice is to afford the patient a pain-free treatment. By the evolution of the laser applications, the dental committee aimed to achieve this goal without analgesic drugs and painful methods. Orthodontic treatment is one of these concerns, that one of the major components of patient to reject this treatment is the pain accompanied during the different treatment phases. Another great concern of the patient is not to get through prolonged periods of treatment. The aim of this study is to evaluate the effect of the low-level (GaAlAs) diode laser (809 nm, 100 mW) on the canine retraction during an orthodontic movement and to assess pain level during this treatment. A group of 15 adult patients with age ranging from 14 to 23 years attended the orthodontic department at Dental School, Damascus University. The treatment plan for these patients included extraction of the upper and lower first premolars because there was not enough space for a complete alignment or presence of biprotrusion. For each patient, this diagnosis was based on a standard orthodontic documentation with photographs, model casts, cephalometric, panorama, and superior premolar periapical radiographies. The orthodontic treatment was initiated 14 days after the premolar extraction with a standard 18 slot edgewise brackets [Rocky Mountain Company (RMO)]. The canine retraction was accomplished by using prefabricated Ricketts springs (RMO), in both upper and lower jaws. The right side of the upper and lower jaw was chosen to be irradiated with the laser, whereas the left side was considered the control without laser irradiation. The laser was applied with 0-, 3-, 7-, and 14-day intervals. The retraction spring was reactivated on day 21 for all sides. The amount of canine retraction was measured at this stage with a digital electronic caliper (Myoto, Japan) and compared each side of the relative jaw (i.e., upper left canine with upper right canine and lower left canine with lower right canine). The pain level was prompted by a patient questionnaire. The velocity of canine movement was significantly greater in the lased group than in the control group. The pain intensity was also at lower level in the lased group than in the control group throughout the retraction period. Our findings suggest that low-level laser therapy can highly accelerate tooth movement during orthodontic treatment and can also effectively reduce pain level.

Full text

ORIGINAL ARTICLE
The effect of low-level laser therapy during orthodontic
movement: a preliminary study
Mohamed Youssef & Sharif Ashkar & Eyad Hamade &
Norbert Gutknecht & Friedrich Lampert & Maziar Mir
Received: 21 September 2006 / Accepted: 22 January 2007 / Published online: 15 March 2007
#
Springer-Verlag London Limited 2007
Abstract It has been emphasized that one of the most
valuable treatment objectives in dental practice is to afford
the patient a pain-free treatment. By the evolution of the
laser applications, the dental committee aimed to achieve
this goal without analgesic drugs and painful methods.
Orthodontic treatment is one of these concerns, that one of
the major components of patient to reject this treatment is
the pain accompanied during the different treatment phases.
Another great concern of the patient is not to get through
prolonged periods of treatment. The a im of this study is to
evaluate the effect of the low-level (GaAlAs) diode laser
(809 nm, 100 mW) on the canine retraction during an
orthodontic movement and to assess pain level during this
treatment. A group of 15 adult patients with age ranging
from 14 to 23 years attended the orthodontic department at
Dental School, Damascus University. The treatment plan
for these patients included extraction of the upper and lower
first premolars because there was not enough space for a
complete alignment or presence of biprotrusion. For each
patient, this diagnosis was based on a standard orthodontic
documentation with photographs, model casts, cephalomet-
ric, panorama, and superior premolar periapical radiogra-
phies. The orthodontic treatment was initiated 14 days after
the premolar extraction with a standard 18 slot edgewise
brackets [Rocky Mountain Company (RMO)]. The canine
retraction was accomplished by using prefabricated Ricketts
springs (RMO), in both upper and lower jaws. The right
side of the upper and lower jaw was chosen to be irradiated
with the laser, whereas the left side was considered the
control without laser irradiation. The laser was applied with
0-, 3-, 7-, and 14-day intervals. The retraction spring was
reactivated on day 21 for all sides. The amount of canine
retraction was measured at this stage with a digital
electronic caliper (Myoto, Japan) and compared each side
of the relative jaw (i.e., upper left canine with upper right
canine and lower left canine with lower right canine). The
pain level was prompted by a patient questionnaire. The
velocity of canine movement was significantly greater in
the lased group than in the control group. The pain intensity
was also at lower level in the lased group than in the control
group throughout the retraction period. Our findings
suggest that low-level laser therapy can highly accelerate
tooth movement during orthodontic treatment and can also
effectively reduce pain level.
Keywords LLLT
.
Low-level laser
.
Orthodontics
.
Tooth movement
.
Pain
Introduction
Discomfort pain is a burdensome side effect accompanying
orthodontic treatment due to force application for tooth
movement. Clinical observatio n indicates that these sensa-
tions usually appear a few hours after force application [2,
27] or during the first day or first couple of days of
treatment and that pain intensity falls to normal levels after
7 days [8, 16, 29, 34].
It has been emphasized that pain reduction without
analgesic drugs is necessary in orthodontic treatment [3, 6,
8, 15, 21, 28]. Several studies showed an effective pain
Lasers Med Sci (2008) 23:27–33
DOI 10.1007/s10103-007-0449-7
M. Youssef
:
S. Ashkar
:
E. Hamade
:
M. Mir
Dental School, Damascus University,
Damascus, Syria
N. Gutknecht
:
F. Lampert
:
M. Mir (*)
Department of Dentistry, RWTH Hospital,
Pauwelsstr. 30,
52074 Aachen, Germany
e-mail: mmir@ukaachen.de

reduction after different dental treatments by using low-
level laser therapy (LLLT) [ 11, 22].
The long treatment period is another concern that makes
patients neglect to go through orthodontic treatment. Accord-
ing to the previous studies [1, 5, 7, 9, 10, 12, 13, 17, 19, 24,
26, 30, 31, 33, 35, 37–39, 41, 42], the amount of tooth
movement in response to the applied force is influenced by
several factors such as gender, status of periodontal ligament
(PDL) and, especially, the type of tooth movement, and the
magnitude of the applied force. With a healthy canine and
moderate applied force (150 g), Ricketts reported the
movement to be 1 mm at the end of activation. In general,
the mechanics applied produced canine retraction with
velocities averaging 1.27 and 0.87 mm per month for 13
and 4 kPa of stress, respectively, with minimal linear or
angular tooth movements [13, 14]. However, those studies
used different magnitudes and durations of force, and thus,
direct comparisons of their results are difficult to draw.
To avoid any confusion, we have used the same
magnitude of force (150 g) with same reactivation duration
for all our patie nts involved in the experiment.
The purpose of the present study was to determine the
differences in the velocity of movement of the canines’
retraction while applying LLLT. The other aim is to assess a
visual scale of pain level during the experiment.
Materials and methods
Patients’ selection
A group of 15 patients of both genders, with age ranging
from 14 to 23 years, attended the orthodontic department at
Dental School, Damascus University.
The treatment plan for these patients included extraction
of the upper and lower first premolars to achieve treatment
plan demands. For each patient, the diagnosis was based on
a standard orthodontic documentation with photographs,
model casts, cephalometric, and panoramic radiographics.
An additional superior and inferior premolar periapical rays
were obtained to ensure the absence of any problem that
would impede the extraction procedures.
We considered the following standards for patients’
selection:
(a) They should appear healthy.
(b) They should be free of any systemic disease.
(c) They should not be under medical treatment that
could interfere with bone metabolism (the orthodon-
tic movement mechanism) like non-steroidal anti-
inflammatory.
After clearly explaining all the risks and benefits of the
supposed treatment, the patients and each legal responsible
approved to participate in this study. This approval was
documented by a signed paper from each patient and
authorized by the dean of our dental school.
Orthodontic treatment
The orthodontic treatment was initiated 14 days after the
premolar extraction with a standard 0.018-in. slot edgewise
brackets [Rocky Mountain Company (RMO)]. The canine
retraction method chosen was Ricketts prescription by using
the prefabricated 16×16 Blue Elgiloy Ricketts Spring
(RMO). The spring was activated to deliver (150 g) force,
which was measured by Forestadent force gauge. Spring
reactivation was made every 21 days with the same force value
(150 g) and repeated till the closing of the extraction space.
The amount of tooth movement in millimeters was
prompted by measuring the distance between the following
reference points on the model casts:
1. The tip of the mesial cusp of the first molar
2. The tip of the canine cusp
The measurement was done by using a digital caliper
(Mitutoyo, Japan) before initiating the orthodontic treat-
ment and recorded.
At each reactivation interval, new impressions for each
patient of both upper and lower jaws were taken. Then a
new measurement of the previous distance was recorded.
This was maintai ned till the end of the retraction phase. All
of these measurements were organized in schedule accord-
ing to the measuring date.
On every reactivation date, the patient was asked about
the pain expe rienced during the bygone period. These
responses were ranked according to a visual pain scale and
were also organized in a schedule.
Laser irra diation
The right side of the upper and lower jaws was chosen to be
irradiated with the laser beam, whereas the left side was
considered the control without irradiation. The laser type
used was a semiconductor (GaAlAs) laser with 809-nm
Table 1 Tooth movement measurements
Lased group Control group
Days Step 1 Step 2 Step 3 Step 1 Step 2
0 DM SA Laser DM SA
3 DM Laser DM
7 DM Laser DM
14 DM Laser DM
21 DM DM
DM Distance measurement, SA spring activation
28 Lasers Med Sci (2008) 23:27–33

wavelength operated at 100-mW output according to the
manufacturer’s recommendation (Quanta, Italy).
The laser beam was delivered to the tissue by a special
handpiece. The tip of the handpiece was held in contact
with the tissue during application.
The areas chosen to be irradiated were the lingual and
buccal PDL of the canines. These areas were divided into
three:
1. Cervical
2. Middle
3. Apical
The cervical area was lased for 10 s. The middle area
was lased for 20 s. The apical area was lased for 10 s.
The total energy density (dose) at each application was
8 J (2×40 s×100 mW).
– To omit patient’s self-behavior about the pain, we have
put the tip of the handpiece not only on the right side
but also on the left side, without pressing the feet
paddle that ena bles the laser beam. In this manner, just
the red guiding light will be emitted.
– The laser regimen was applied on 0-, 3-, 7-, and 14-day
intervals after every activation.
Data collection
Tooth movement
The sequence of steps carried out during each clinical
attendance is shown in Table 1. At every 21-day interval,
the distance measurement was compared between the lased
and control group. The data were compared by two sample
t tests at P<0.05. After 6 months, the lased and control
groups’ canines’ areas were examined by periapical radio-
graphs to see if any damage developed in the adjacent
PDLs and dental tissues.
Pain questionnaire
The pain level was assessed as the shown rank values in
Table 2. Every patient was asked about the pain experi-
enced after spring activation. All these data were recorded
in a schedule.
Results
Velocity study
The velocity of the movement was obtained from the
following formulation:
V ¼ d
=
t
where V is the velocity of the canine movement, d is the
amount of canine movement in millimeters at the end of
treatment, and t is the time passed to accomplish the
movement.
Table 3 shows the mean velocity of those movements in
both lased and controlled groups. Figure 1 shows that the
velocity of tooth movement was bigger in the experiment
(lased) side than in the control side (non-lased). Figure 2
shows that the velocity of tooth movement was bigger in
the lased group in both jaws. Figure 3 shows that there
was not any significant statistical difference between the
mean velocity values of the upper and lower canines and
the jaw position did not have an effect on the velocity of
tooth movement.
Table 3 Velocity of movement of the tooth
Group Number of studied
teeth
Mean tooth movement
velocity
SD
Lased 30 2.027 0.114
Control 30 1.019 0.110
Fig. 1 The effect of laser on the amount of velocity of tooth
movement is reported by median of two experimental and control
groups (n=60)
0.092
0.025
0.095
0.024
0.00
0.05
0.10
Median
Upper Jaw Lower Jaw
Position of Jaw
Eperimental
Control
c
Fig. 2 The effect of laser on the velocity of tooth movement
regarding the jaw position is shown (n=60)
Table 2 Pain levels
Degree of pain Rank value
No pain 0
Mild pain 1
Moderate pain 2
Severe pain 3
Intolerable pain 4
Lasers Med Sci (2008) 23:27–33 29

Pain study
Figure 4 displays the pain level during different treatment
stages of lased and control groups.
To study the differences in pain levels between the lased
and control groups during combined treatment stages,
Man–Whitney U test was done. Table 4 shows mean rank
values for the degree of pain during combined treatment
stages. Table 5 shows Mann–Whitney U test results.
In Tables 4 and 5, we can observe the following:
– P≪ 0.05 at every combined treatment stage.
– There is a significant difference in the degree of pain
between the control and the experimental sides.
– Mean U values of the control side are higher than the
experimental side.
– The degree of pain is higher in the control side during
the first, second, and third stages.
Discussion
Orthodontic tooth movement involves both modeling and
remodeling activities that are modulated by systemic factors
such as nutrition, metabolic bone diseases, age, and drug
usage history [5, 7, 13, 17, 19, 26, 38, 39].
Biologically active substances, such as cytokines,
interleukins (IL-1ß, IL-1RA), and enzymes, are expres sed
by cells within the periodontium in response to mechan-
ical stress from orthodontic appliances [1, 5, 7, 9, 10, 12,
13, 17, 19, 26, 31 , 33, 35, 37–39, 41].
IL-1ß is more potent for bone resorption and the
inhibition of bone formation, and its role in orthodontic
tooth movement has been the focus of previous studies
[31, 37].
Inflammatory cytokines have been administered to
enhance orthodontically induced bone modeling. Similar
effects have bee n demonstrated wi th prostaglandin E2
(PGE2) osteocalcin administration to primates [20, 43],
and the results have been confirmed clinically [36].
However, in the clinical practice, this needs to be injected
within the mucosa, which is associated with pain and
discomforts the patients.
Strain-induced catabolic modeling at the bone PDL
interface limits the rate of tooth movement [13, 17, 26, 38].
According to several studies, LLLT is an effective tool
used to prompt bone repair and modeling post-surgery.
This has referred to the biostimulation effect of the LLLT.
This effect had been well studied in the medical field and
proven to have an enhanc ement effect o n fibroblast
growth enhancement, wound healing, and bone repair.
This enhancement can be the r esult of osteoblasts
proliferation and differentiation and intracellular changes
in these cells [ 4 , 6, 15, 18, 23 , 25, 28, 32, 40]. Shimizu et
al. studied the effects of low-power laser irradiation on
bone regeneration in midpalatal suture during expansion
in the rat and conclu ded that one-time or late irradiation
(days 4–6) had no effect. However, irradiation during
days 0–2 was most effective. Another research by
Skinner et al. showed that fibroblast procol lagen produc-
0.092
0.095
0.025
0.024
0.00
0.02
0.04
0.06
0.08
0.10
Median
Experimental Control
Upper Jaw
Lower Jaw
c
Fig. 3 The effect of jaw position on the velocity of tooth movement is
not statistically significant (P>0.05)
33.3
50.0
16.7
50.0
46.7
3.3
56.7
40.0
3.3
3.3
36.7
53.3
6.7
66.7
30.0
3.3
6.7
50.0
43.3
13.3
50.0
36.7
63.3
33.3
3.3
76.9
23.1
0
50
100
Percentage
1st 2nd 3rd 1st 2nd 3rd 4th 5th 6th
The Percentage of Pain Levels according to the studied groups and different treatment
stages
No Pain Mild Pain Moderate Pain Severe Pain Intolerable Pain
Experimental Control
Fig. 4 The pain levels during
different treatment stages are
reported (n=60)
30 Lasers Med Sci (2008) 23:27–33

tion was increased by using GaAs doses between 0.099
and 0.522 J/cm
2
.
Biostimulation effects on the bone repair are directly
dependent on the dose applied [4, 25, 40]. Different
parameters have proven to be effective for severa l different
lasers, inducing changes within cell cultures and leading to
an increased healing effect. Nevertheless, the optimal
parameters have yet to be determined [4, 40].
Luger et al. used doses of about 64 J/cm
2
during 14 days,
and although this dose could be excessive within the focused
area, the authors believe that the scattering reduces the
energy level of the laser beams to between 3 and 6% of its
original intensity. In our study, the dose of 8 J/cm
2
(the
irradiated area was about 1 cm
2
) at each of the different
points around the tooth is lower than the dose used by Luger
et al. (64 J/cm
2
), but the distribution of energy into six points
surrounding the canine teeth could be more adequate due to
a more homogeneous distribution of the energy.
Infrared radiation has a low absorption coefficient in
hemoglobin and water, and consequently, a high penetra-
tion depth in the irradiated tissue. It is well known that
infrared radiation at 750 nm can penetrate more than visible
radiation at 650 nm into soft tissues. As the objective of our
study was to stimulate bone cells, which are placed deeply
under the soft tissue (e.g., gingiva) in the PDL space, the
infrared laser was selected for our study.
Some authors have analyzed the effects of LLLT during
orthodontic treatment in animals. Saito and Shimizu [32]
studied the effects of LLLT on the expansion of midpalatal
sutures in rats, comparing the bone regeneration obtained
with and without laser treatment. Their results showed that
the therapeutic effects of laser are dependent on the total
dosage, the frequency, and the duration of the treatment.
Their laser-irradiated group showed 20–40% better results
when compared to the CG. In another study, Kawasaki and
Shimizu [18] showed that the orthodontic movement of
laser-irradiated rats’ teeth was 30% quicker than the non-
irradiated rats due to acceleration of bone formation as a
result from the cellular stimulation promoted by LLLT. Our
findings are similar to these reports. However, the ratio
lased group/control group (LG/CG) obtained in our study
was 1.98 (Table of Velocity). This ratio could be the
biostimulation factor prom oted by LLLT.
In Fig. 1, we can observe that the velocity of tooth
movement was bigger in the experi ment (lased) side than in
the contr ol side (non-lased). Also, we can see in Fig. 2 that
the velocity of tooth movement was bigger in the lased
group in both jaws. Analysis of the laser effect on the upper
and lower jaw reveals that there was not any significant
statistical difference between the mean velocity values of
the upper and lower canines and the jaw position did not
have an effect on the velocity of tooth movement (Fig. 3).
Tooth move ment is dependent on a painful, inflammatory
adaptation of the alveolar process. To relieve such pain, several
methods have been used in the literature. One of those is to use
drugs (non-steroidal anti-inflammatory drugs). Although these
drugs could be effective in relieving pain, they may also reduce
the rate of tooth movement [3, 6, 15, 21, 28]. The application
of low-energy lasers in the field of dentistry and oral surgery
has been described since the 1970s. Low-energy laser light is
supposed to reduce pain, to accelerate wound healing, and to
have a positive effect on inflammatory processes. Harazaki et
al. [11]andLimetal.[22] showed that the low-level laser
therapy is an effective tool to manage the post-adjustment
orthodontic pain. Our findings in this research confirmed the
previous findings. Figure 4 displays that, during different
treatment stages, the pain level of the lased group was less in
amount than the control group.
Table 4 Degree of pain reported in different groups (n=60)
Studied variable Combined stages Number of canines Mean rank values
Experimental Control Total Experimental Control
Degree of pain First stage 30 30 60 16.83 44.17
Second stage 30 30 60 15.83 45.17
Third stage 30 30 60 16.22 44.78
Table 5 Mann–Whitney U test results are presented
Studied variable Combined treatment stages Mann–Whitney U test value P value Significance
Pain degree First stage 40.0 0.000 Significant differences
Second stage 10.0 0.000 Significant differences
Third stage 21.5 0.000 Significant differences
Lasers Med Sci (2008) 23:27–33 31

In this study, radiographies showed no evidence of
damage in the dental and periodontal tissue promoted by
the LLLT. Further studies are required to explain the
mechanisms of laser biostimulation and clinical trials to
optimize treatment parameters and discover other effects
promoted by LLLT.
Conclusion
The (GaAlAs) low-level laser used i n this study is
considered to be an effective too l during orthodontic
treatment, as: the rate of tooth movement raised signifi-
cantly, and the pain level reduced significantly.
References
1. Alhashimi N, Frithiof L, Brudvik P, Bakhiet M (2001) Orthodontic
tooth movement and de novo sy nth esis of proinflammato ry
cytokines. Am J Orthod Dentofacial Orthop 119:307–312
2. Bergius M, Kiliaridis S, Berggren U (2000) Pain in orthodontics.
J Orofac Orthop 61:125–137
3. Bernhart MK, Southhard KA, Batterson KD, Logan HL, Baker
KA, Jakobsen JR (2001) The effect of preemptive and/or
postoperat ive ibupr ofen therapy for orthodontic pain. Am J
Orthod Dentofacial Orthop 120:20–27
4. Bolton P, Young S, Dyson M (1991) Macrophage responsiveness
to light therapy with varying power and energy densities. Laser
Therapy 3(3):105–112
5. Carvalho RS (1997) Genomic basis of orthodontic forces: role of
osteopontin in osteoblasts [dissertation]. Harvard School of Dental
Medicine, Boston
6. Dionne RA, Cooper S (1978) Evalu ation of preoperative
ibuprofen for postoperative pain after removal of third molars.
Oral Surg Oral Med Oral Pathol Oral Radiol Endod 45:851–856
7. Duan U, Inoue H, Kawakami M, Kato J, Sakuda M (1993)
Changes in bone formation during experimental tooth movement
after denervation of the rabbit inferior alveolar nerve. J Osaka
Univ Dental School 33:45–50
8. Fernandes L M, Øgaard B, Skoglund L (1998) Pain and
discomfort experienced after placement of a conventional or a
superelastic NiTi aligning archwire. J Orofac Orthop 59:331–339
9. Grieve WG III, Johanson J, Moore RN, Reinhardt RA, DuBois
LM (1994) PGE and IL-1beta levels in gingival crevicular fluid
during human orthodontic tooth movement. Am J Orthod
Dentofacial Orthop 105:369–374
10. Hall M, Masella R, Meister M (2001) PDL neuron-associated
neurotransmitters in orthodontic tooth movement: identification and
proposed mechanism of action. Todays FDA 13(2):24–25 (Feb)
11. Harazaki M, Takahashi H, Ito A, Isshiki Y (1998) Soft laser
irradiation induced pain reduction in orthodontic treatment. Bull
Tokyo Dent Coll 39:95–101
12. Insoft M, King GJ, Keeling SD (1996) The measurement of acid and
alkaline phosphatase in gingival crevicular fluid during orthodontic
tooth movement. Am J Orthod Dentofacial Orthop 109:287–296
13. Iwasaki LR, Haack JE, Nickel JC, Morton J (2000) Human tooth
movement in response to continuous stress of low magnitude. Am
J Orthod Dentofacial Orthop 117:175–183
14. Iwasaki LR, Haack JE, Nickel JC, Reinhardt RA, Petro TM (2001)
Human interleukin-1b and interleukin-1 receptor antagonist secretion
and velocity of tooth movement. Arch Oral Biol 46:185–189
15. Jackson D, Moore P, Hargreaves K (1989) Postoperative
nonsteroidal anti-inflammatory medication for the prevention of
postoperative dental pain. J Am Dent Assoc 119:641–647
16. Jones M, Chan C (1992) The pain and discomfort experienced
during orthodontic treatment. A randomized controlled trial of
two aligning a rchwires. Am J Orthod Dentofacial Orthop
102:373–381
17. Kawarizadeh A, Bourauel C, Jager A (2003) Experimental and
numerical determination of initial tooth mobility and material
properties of the periodontal ligament in rat molar specimens. Eur
J Orthod 25:569–578
18. Kawasaki K, Shimizu N (2000) Effects of low-energy laser
irradiation on bone remodeling during experimental tooth move-
ment in rats. Lasers Surg Med 26:282–291
19. King GJ, Keeling SD, Wronski TJ (1991) Histomorphometric
study of alveolar bone turnover in orthodontic tooth movement.
Bone 12:401–409
20. Kobayashi Y, Takagi H, Sakai H, Hashimoto F, Mataki S, Kobayashi
K, Kato Y (1998) Effects of local administration of osteocalcin on
experimental tooth movement. Angle Orthod 68:259–266
21. Law SLS, Southard KS, Law AS, Logan HL, Jakobsen JR (2000)
An evaluation of postoperative ibuprofen treatment of pain
associated with orthodontic separator placement. Am J Orthod
Dentofacial Orthop 118:629–635
22. Lim HM, Lew KK, Tay DK (1995) A clinical investigation of the
low level laser therapy in reducing orthodontic postadjustment
pain. Am J Orthod Dentofacial Orthop 108:614–622
23. Luger EJ, Rochkind S, Wollman Y, Kogan G, Dekel S (1998)
Effect of low-power laser irradiation on the mechanical properties
of bone fracture healing in rats. Lasers Surg Med 22:97–102
24. Mackie EJ (2003) Osteoblasts: novel roles in orchestration of
skeletal architecture. Int J Biochem Cell Biol 35:1301–1305
25. Mester E, Mester AF, Mester A (1985) The biomedical effects of
laser application. Lasers Surg Med 5:31–39
26. Middleton J, Jones ML, Wilson AN (1996) The role of the
periodontal ligament in bone modeling: the initial development of
a time dependent finite element model. Am J Orthod Dentofacial
Orthop 109:155–162
27. Ngan P, Kess B, Wilson S (1989) Perception of discomfort by
patients undergoing orthodontic treatment. Am J Orthod Dentofacial
Orthop 96:47–53
28. Ngan PW, Hägg U, Yin C (1994) The effect of ibuprofen on the
level of discomfort in patients undergoing orthodontic treatment.
Am J Orthod Dentofacial Orthop 106:88–95
29. Okeson JP (1995) Bell’s orofacial pain, 5th edn. Quintessence,
Carol Stream, Ill, pp 79 –84
30. Proffit WR, Fields HW Jr (2000) Contemporary orthodontics, 3rd
edn. Mosby, St. Louis
31. Saito M, Saito S, Ngan PW, Shanfeld J, Davidovitch Z (1991)
Interleukin-1b and prostaglandin E are involved in the response of
periodontal cells to mechanical stress in vivo and in vitro. Am J
Orthod Dentofacial Orthop 99:226–240
32. Saito S, Shimizu N (1997) Stimulatory effects of low-power
irradiation on bone regeneration in midpalatal suture during
expansion in the rat. Am J Orthod Dentofacial Orthop 111:525–532
33. Sandy JR, Farndale RW, Meikle MC (1993) Recent advances in
understanding mechanically induced bone remodeling and their
relevance to orthodontic theory and practice. Am J Orthod
Dentofacial Orthop 103:212–222
34. Scheurer P, Firestone A, Bürgin W (1996) Perception of pain as a
result of orthodontic treatment with fixed appliances. Eur J Orthod
18:349–357
32 Lasers Med Sci (2008) 23:27–33

35. Serra E, Perinetti G, D’Attillio M, Cordella C, Paolantonio M,
Festa F, Spoto G (2003) Lactate dehydrogenase activity in
gingival crevicular fluid during orthodontic treatment. Am J
Orthod Dentofacial Orthop 124:206–211
36. Shibata Y, Imai S, Tani Y, Shibasaki Y, Fukuhara T (1984)
Clinical application of prostaglandin E1 (PGE1) upon orthodontic
tooth movement. Am J Orthod 85:508–518
37. Shimizu N, Yamaguchi M, Goseki T, Ozawa Y, Saito K, Takiguchi
H, Iwasawa T, Abiko Y (1994) Cyclictension force stimulates
interleukin-1b production by human periodontal ligament cells. J
Periodontal Res 29:328–333
38. Smith RJ, Burstone CJ (1984) Mechanics of tooth movement. Am
J Orthod 85:294–307
39. Sorsa T, Ingman T, Mikkonen T, Suomalainen K, Golub LM,
Thesleft I (1992) Characterization of interstitial collagenase in
gingival crevicular fluid during orthodontic tooth movement in
man. In: Davidovitch Z (ed) The biological mechanisms of tooth
movement and craniofacial adaptation. The Ohio State University
College of Dentistry, Columbus, OH, pp 47–51
40. Van Breugel H, Bar PR (1992) Power density and exposure time
of hene laser irradiation are more important than total energy dose
in photo-biomodulation of human fibroblasts in vitro. Lasers Surg
Med 12:528
41. Vandevska-Radinovic V (1999) Neural modulation of inflamma-
tory reactions in dental tissues incident to orthodontic tooth
movement. Eur J Orthod 21:231–247
42. Winkler DG, Sutherland MK, Geoghegan JC et al (2003)
Osteocyte control of bone formation via sclerostin, a novel BMP
antagonist. EMBO J 22:6267–6276
43. Yamasaki K (1983) The role of cyclic AMP, calcium and prostaglan-
dins in the induction of osteoclastic bone resorption associated with
experimental tooth movement. J Dent Res 62:877–881
Lasers Med Sci (2008) 23:27–33 33