Download A clinical investigation of the efficacy of low level laser

A clinical investigation of the efficacy of low level laser
therapy in reducing orthodontic postadjustment pain
Hong-Meng Lim BDS, MDS Orthodontics, MORTH RCS (Edin), Kenneth K.K. Lew MDS
Orthodontics,
BDS,
FDSRCS
(Edin)
and
David
K.L.
Tay
BDS,
MS.
Singapore, Available online 31 October 2005.
Abstract : Low level laser therapy (LLLT) has been shown to produce analgesic effects in
many clinical applications. The aim of this clinical study was to test the efficacy of LLLT in
controlling orthodontic postadjustment pain. Thirty-nine volunteers were selected for this
study that used a double-blind design with placebo control. Elastomeric separators were
placed at the proximal contacts of one premolar in each quadrant of the dentition to induce
orthodontic pain. The tip of a 30 mW gallium-arsenide-aluminium (830 nm) diode laser
probe was then placed at the buccal gingiva and directed at the middle third of the root.
Three different treatment durations of 15, 30, and 60 seconds and one placebo treatment of
30 seconds were tested within each subject. The study was conducted over 5 days, and the
visual analogue scale (VAS) was used to quantify the pain experienced by the subjects before
and after laser applications for each day. Analysis of the VAS median scores showed that
teeth exposed to laser treatment had lower levels of pain as compared with those with the
placebo treatment. However, nonparametric statistical analysis of the data showed that the
differences between treatments and placebo within each subject were not statistically
significant.
(AM
J
ORTHOD
DENTOFAC
ORTHOP
1995;108:614-22.)
INTRODUCTION
It is a well-known clinical observation that after an application of force there will be an initial
period of discomfort or pain lasting about 2 to 4 days.1, 2, 3, 4 and 5 Severe pain was linked to the
application of excessive force.3,
6, 7 and 8
According to Proffit,3 light forces are the key to
avoiding pain concomitant with orthodontic treatment. Burstone6 also noted that the
duration of pain was increased with increased force levels used. It has been postulated by the
proponents of the traditional pain-force relationship that, on the basis of the findings of the
classical histologic studies,7, 9, 10 and 11 heavier forces would cause greater compression of the
periodontal ligament with more tissue damages and, correspondingly, would result in more
severe pain responses. However, pain or discomfort was still experienced by most patients
even when supposedly physiologic and light forces were used.2 Clinical studies by several
investigators could not find a relationship between pain severity and force level. 1, 12, 13, 14, 15 and
16
In summary, the relationship between pain and force levels is still controversial. Owing to
the wide individual variation, the presence of pain does not mean that there is underlying
irreversible tissue damage, whereas tissue damage may not always be accompanied by pain.
Many patients have avoided orthodontic treatment because of the fear of pain,17 and 18 and it
has been proposed that pain from orthodontic treatment could have prevented the patients
from achieving effective plaque control.19 The use of pharmacologic analgesics has its
attendant side effects and is contraindicated in patients who are allergic to those drugs. It has
been suggested that tooth movement could be affected in patients taking nonsteroidal
antiinflammatory drugs (NSAID).20 As yet, there is no clinically proven, noninvasive,
nonpharmacologic method to alleviate pain experienced by the orthodontic patients except
for chewing a stick of gum or a plastic wafer immediately after orthodontic activation or
adjustment.3 and 21 However, gum chewing must be instituted before the pain sets in, that is,
within the first 8 hours after activation.3 This method would be ineffective when the teeth
become too tender for repetitive chewing, on gum or on a plastic wafer, to be tolerated.
Low level laser has been shown by many investigators to produce analgesic effects in various
therapeutic and clinical applications.22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35 and 36 Depending on the
energy output and focus, laser can be classified into high, medium, or low power laser.
Terminology for the low power laser included soft laser, mid laser, low energy laser, as well as cold
laser. Low level laser therapy (LLLT) is the new internationally accepted designation 32 and is
defined as laser treatment in which the energy output is low enough so as not to cause a rise
in the temperature of the treated tissue above 36.5° C or normal body temperature. Because
of its lower energy output and intensity, its effects are mainly nonthermal and
biostimulatory. The biostimulatory effects of LLLT have been reported by several
investigators.37 The mechanisms of laser analgesia have not been established, but it has been
attributed to its antiinflammatory and neuronal effects.38 It was proposed by Harris38 that
low level laser irradiation has a benign stimulatory influence on depressed neuronal and
lymphocyte respiration. Other neuronal effects include stabilization of membrane potential
and release of neurotransmitters.39, 40, 41 and 42 The transmission of laser through tissue is highly
wavelength specific and is most optimal in the optical window of 500 to 1200 nm.38 The 830
nm wavelength of the gallium-arsenide-aluminium (Ga-As-Al) diode laser lies in this optical
window and it has been shown to have the greatest tissue penetration when compared with
the other laser system.43
The main objective of this clinical investigation was therefore to determine the clinical
efficacy of the low level laser therapy with the Ga-As-AI diode laser as a method to reduce
orthodontic postadjustment pain. Specifically, we wanted (1) to determine whether low level
laser therapy could provide immediate relief for orthodontic postadjustment pain, (2) to
determine whether low level laser therapy could alter the time course of the intensity of
orthodontic post-adjustment pain, and (3) if pain relief could be achieved by laser
application, to determine the shortest duration of laser application needed to achieve that
effect.
Materials and methods
The study employed a within-subject experimental design44 with each subject being exposed
to four treatment parameters (15, 30, and 60 seconds of laser treatment and 30 seconds of
placebo application). Within each subject, a multigroup pretest-posttest design with placebo
control45 was used. One premolar in each quadrant of the dentition constituted the basic
experimental unit. Two factors were considered separately: (1) the immediate pain relieving
effect of the different treatment parameters and (2) the effect of the different treatment
parameters on the time course of pain intensity over 5 days. To exclude experimenter's
biases and placebo effect in the subjects, the study was conducted double blind. The
sequence of application of the four treatment parameters were randomized among the
subjects by the Latin Square method.46 and 47 The purpose of this procedure was to control for
the site variability in the different quadrants of the dentition. Any effects that are not due to
the treatment but are due to the inherent differences between treatment sites would be
canceled out by this randomization .
Thirty-nine volunteer dental students (aged 21 to 24 years) were chosen for the study. Each
subject had to fulfill the following criteria: (l) intact upper and lower dental arches with no
open interproximal contacts and at least one premolar in each quadrant of the dentition, and
(2) the teeth must also be free from any acute or chronic pathologic conditions.
The laser unit used was a Class 3B48 Ga-As-Al diode laser probe by P-laser System (P-Laser
System International, Egedalsvej, Vekso) (Fig. 1) with a wavelength of 830 nm.
Display Full Size version of this image (9K)
Fig.
1. P-Laser
system
laser
probe.
The laser beam emitted in a constant wave with mean output of 30 mW. The intensity of
this laser beam was worked out to be 59.7 mW/cm2. Other similar low level laser systems
used in other investigations include the Panalas-4000 (Japan Medical Laser Laboratory and
Matsushita Electric Co., Tokyo, Japan) and Proton Plus (RONVIG Instruments, Daugaard,
Denmark).
In America, the Food and Drug Administration (FDA)49 has only approved the use of a
dental laser for soft tissue procedures (oral soft tissue surgery) and polymerization of dental
restorative materials. With regard to the use of the laser in pain relief, the most frequently
used low level lasers in the United States are the infrared (830 nm) gallium-aluminiumarsenide lasers and the visible (633 nm) helium neon lasers.37 As the use of laser in pain relief
is still experimental, informed consent was obtained from all subjects to comply with the
“Guidelines for the use of human subjects in dental research (Council on Dental
Research).”50 The students were aware that they could withdraw from the study at any time
without giving any reason.
The visual analogue scale (VAS)51 was used in this study to quantify the pain levels (Fig. 2).
Display Full Size version of this image (94K)
Fig.
2. Visual
Analogue
Scale
(VAS)
score
card
used
in
this
study.
The subjects were instructed to mark with an “X” on the scale corresponding to the pain
that they were experiencing. The VAS score is defined as the distance in centimetres (up to
one decimal place) from the left extreme of the line to the “X” marked by the subjects.
Unitek Alastik TM Quik Stik S-2 separators (Unitek Corp./3M, Monrovia, Calif.) were used
to induce orthodontic pain by causing separation of the teeth. The Alastik force module
separator plier was used to apply the separators onto the proximal contacts. The separators
were placed at the mesial and distal proximal contacts of one premolar in each quadrant of
the dentition. Before this, a preseparation VAS score was taken to exclude any pre-existing
painful conditions. Five minutes after the placement of separators, the pretreatment VAS
scores were recorded. The laser probe was then applied onto the buccal mucosa of the
premolar overlying the middle third of the root and the posttreatment scores for each
premolar were recorded immediately after the laser exposure. The separators were left in situ
for 5 days. On the second, third, fourth, and fifth days, the subjects were again instructed to
record the pretreatment and the posttreatment scores. As the intensity of orthodontic
postadjustment pain was found to peak around 18 to 36 hours,4 the duration of the study
would cover this period adequately.
In accordance with our objectives, two null hypotheses were tested. The first null hypothesis
stated that there was no therapeutic immediate pain relieving effect from the low level laser
therapy. The second null hypothesis stated that there was no difference in the time course of
pain intensity between the treatment groups and the placebo group. The Friedman two-way
analysis of variance of ranks52 and 53 was used as the main test for statistical inference. It is the
nonparametric equivalent to the parametric one-way analysis of variance (ANOVA) and
therefore the two factors were tested separately with the Friedman's test. The procedure of
the Friedman's test was described in detail by Siegel52 and Glantz.53 The formula for
calculating the Friedman's test statistic based on the rank sum for statistical significance is as
follows:
where Rt denotes sum of ranks for treatment t ∑denotes the sum over all the treatments k is
the number of treatments n is the number of subjects
The smaller the value of X2r, the less of a pattern there is relating the ranks within each
subject to the treatment. The calculated X2r values were then compared with the values in the
table for Chi-square (X2r) distribution.44
In a pretest-posttest experimental design, one of the appropriate methods of statistical
analysis of the data is to take the differences between the pretreatment and posttreatment
scores (gain scores) as the basic data rather than to use the absolute VAS scores for
comparisons.45 The computation of the data by the Friedman's test was done by the Statview
II computer statistical analysis program.
Results
The medium VAS scores for each of the four treatment parameters on each day are
tabulated
in
Table
Display Full Size version of this image (33K)
I.
The time course of the VAS pain scores over the 5 days is represented by the composite
plots
of
all
the
median
VAS
scores
over
5
days
in
Fig.
3.
Display Full Size version of this image (47K)
Fig. 3. Time course of pretreatment and posttreatment VAS median scores for each of four
treatment
groups
recorded
over
5
days.
The histogram provides an descriptive trend of the pretreatment and posttreatment median
scores of each treatment group for each of the 5 days. It could be seen that the pretreatment
scores of the placebo group were the highest among the four groups on the second and third
day, whereas the pretreatment scores of the 30- and 60-second treatment groups were the
lowest. Another point to note was that the posttreatment scores were generally lower than
the pretreatment scores. It must be pointed out that this apparent immediate pain relieving
effect was also noted in the placebo group.
The results of the statistical comparisons are shown in Table II and Table III.
Display Full Size version of this image (37K)
Display Full Size version of this image (36K)
Table II shows the rank sums of the differences (gain scores) between the pretreatment and
posttreatment scores of each treatment group for each day. These scores allow a comparison
of the immediate pain relieving effect of the four treatment parameters. The lower the rank
sum, the better the effect. No trend in the rank sums was noted. The computed Friedman
statistics (X2r) of the gain scores for each day are also listed at the bottom of the table. The
X2r values were corrected for ties (which occurred when there were two or more equal
values), to give more representative X2r values. Comparisons of the X2r values of the gain
scores between pretreatment and posttreatment scores for each day, with the critical X2r
value (X2r crit) at the chance probability level of p = 0.05 with 3 df (X2r crit = 7.815), showed
that there was no overall statistically significant differences between the treatment groups
and placebo group, except for that between the pretreatment and posttreatment scores of
the fourth day (X2r = 8.468). However, analysis of the mean ranks and rank sums of the gain
scores for the fourth day showed that the placebo group had the lowest values (mean rank of
2.141 and rank sum of 83.5). The mean ranks and rank sums of the three treatment groups
were very close in values. This observation would not be expected if the laser therapy had
any immediate pain relieving effect. Therefore the differences noted here were also probably
due to chance.
Table III shows the rank sum of the gain scores between the pretreatment scores of each
subsequent day and the baseline postseparation pain scores (pretreatment scores of first day).
These allowed comparison of the time course of pain intensity among the four groups. A
weak trend was noted on day 2 and day 3 with the 30- and 60-second treatment groups
showing lower rank sums. The rank sums of the gain scores between the pretreatment scores
of day 2 and day 1 of the 30-and 60-second treatment groups were 90.5 and 96.5,
respectively, compared with 98 and 105 for the placebo and 15-second treatment groups,
respectively. The rank sums of the gain scores between the pretreatment scores of day 3 and
day 1 of the 30- and 60-second treatment groups were both 89.5, compared with 97.5 and
93.5 for the placebo group and 15-second treatment group, respectively. This trend could
mean that the increase in pain levels was lesser for the treatment groups of 30 and 60
seconds when compared with the 15-second treatment group and placebo group on day 2
and day 3. However, as in Table II, comparisons of the Friedman's X2r values of the gain
scores for the between day pretreatment scores with the same critical value (p = 0.05, 3 df,
X2r crit = 7.815) showed that there was no statistically significant overall difference between
all the gain scores for each of the between-day pretreatment scores comparison.
Discussion
Visual analogue scale as a method of pain measurement has been reviewed extensively and
was found to be a reliable method.5, 54, 55, 56, 57, 58, 59 and 60
The measurements of the marking “X” were made with a millimeter ruler to an accuracy of
±0.05 cm. Any measurement errors within ±0.05 cm would probably not be clinically
significant in reflecting the pain responses within each subject. Sampling error could arise in
this study because the subjects constituted an experimentally accessible population. Subjects
were not selected at random but enrolled on a voluntary basis. In addition, being dental
students, they are from a highly defined population group with regard to their dental
experiences and attitudes to dental pain and fear. Although the use of the dental students
reduced somewhat the emotive and attitudinal variables of pain responses and thus provided
a more objective assessment of the treatment, the conclusions drawn from this sample might
not fully apply to the general orthodontic patient population. Even among the dental
students, the voluntary nature of the enrollment of subjects could have excluded those
subjects with lower pain thresholds and different attitudes to dental treatment.
The results of this study were validated by the various features of the experimental design
such as within-subject design,44 double blindness, latin square method of randomisation,46 and
47
and placebo control. Within-subject design served very well in this study to control for
confounding factors. Experiments with such design are very sensitive to how the treatment
affects each person. With between-subject design, the changes due to treatment may be
masked by the variability in pain responses between subjects. A weakness of the withinsubject design is that it assumed that there was no appreciable between site interaction
through the systemic (crossover) effect of the low level laser therapy. Multiple treatment
interference through systemic effect in this study could have invalidated the placebo control
as it would be under the indirect influence of treatment as well.
The pain scores were highly subjective and should be treated as ordinal data. The statistical
fallacy of using the mean to describe ordinal data and its distribution was discussed by Lee”'
and Health.62 Median is preferable to the mean as a measure of central tendency of a sample
when the data do not follow a normal distribution or when the measurements are on an
ordinal scale. The mean is very sensitive to a skewed distribution, the presence of outliers,
and it assumes that the scores are equidistant. Nonequivalence is a general condition in all
ordinal subjective data. Since the data from the visual analogue scale (VAS) would be best
analyzed on the ordinal scale, a nonparametric version of the repeated measure analysis of
variance suitable for within-subject experimental design (Friedman's test) was used.
No trend was noted for the gain scores between pretreatment and posttreatment scores for
each day (Table II). From the data, it appeared that the low level laser therapy with 15-, 30-,
and 60-second exposures could not provide immediate therapeutic pain relief as both
descriptive data and statistical tests did not reveal any trend between treatment and placebo.
The apparent immediate pain relieving effect of the treatment as evidenced by the lower
posttreatment pain scores as compared with the pretreatment pain scores (Table I, Fig. 3)
was most probably due to the Hawthorne's effect.45 Hawthorne's effect refers to two
phenomena: (1) The subjects' knowledge that they were participating in a clinical trial of the
analgesic efficacy of the low level laser could have induced them to report lower pain scores
after laser application. This is known as the perceived demand characteristics of the
experiment by the subjects. (2) There could be the true placebo effect due to the genuine
belief that the treatment had an effect.
From the gain scores of the pretreatment scores of between-day comparisons (Table III),
there was a weak trend of lower ranks for the 30- and 60-second treatment groups in the day
2-day 1 and day 3-day 1 comparisons. Although the trend was only noted on the second and
third day and the differences were small and not statistically significant (at p < 0.05), it could
be that the treatment effects were small and only managed to show a weak trend on the
second and third day when orthodontic pain normally peaked in intensity.4 and 5 These smaller
gain scores for the 30- and 60-second treatment groups reflected lower pain intensities for
these two treatment groups on the second and third day. Thus, it was possible that one or
two applications of the low level laser (Ga-As-Al) could have some therapeutic effects on the
time course of the intensity of orthodontic pain.
From clinical observations, the placement of separators is known to cause considerable pain
although there is much individual variation with some patients reporting no pain at all. The
method of orthodontic pain simulation using separators could have produced highly variable
pain responses and pain with a magnitude that was not sufficiently high enough to allow the
treatment effect to be felt. This could have resulted in the nonsignificant findings. However,
Roth and Thrash4 used the same method of pain induction to test the efficacy of
transcutaneous electrical nerve stimulation (TENS) as a method of pain control and found
that TENS could significantly provide relief of orthodontic pain. A point to note is that the
authors used parametric analysis of the VAS data, which should have been treated as ordinal
data.
One of the problems in the planning of this study was the determination of the size of the
treatment effect that we would like to detect and consider clinically significant. This was
because pain responses are highly subjective and variable. It must be noted that the lack of
statistical significance did not equate that there was no clinical effect. We should be looking
more at the general trend of the pain scores rather than the statistical significance of the
differences in determining whether there is a potential clinical application for low level laser
therapy in orthodontics.
Orthodontic pain has been related to the acute inflammatory responses of the periodontal
ligament to orthodontic forces.63 and 64 Kess et al.65 showed that prostaglandins level increased
and peaked at 24 hours after the application of orthodontic forces, whereas Kamogashira et
al.66 showed that the level of substance P increased and peaked at 36 hours after separation
of incisors by orthodontic forces. Prostaglandins has been suggested by Ferreira67 and Higg68
to sensitize pain receptors resulting in increased pain sensitivity to hyperalgesic inflammatory
mediators, such as histamine or bradykinin. The mechanisms of laser analgesia have been
suggested to be due to the direct effect of the laser on the nerve fibers, by stabilizing its
depolarizing potential, or to its effects on the cellular and biochemical processes of the
inflammatory responses.38 As no immediate therapeutic pain relief was noted in this study
and the treatment effect took about 24 to 48 hours to become apparent, the results of this
study tended to support the hypothesis that laser analgesia was due mainly to the effect of
laser treatment on the inflammatory processes.
Laser analgesia is a new treatment modality and has the advantages of being noninvasive,
easy to administer, and having no known adverse tissue reactions. It is worthwhile to look
into its potential applications in orthodontics. The apparent lack of significant treatment
effect in this study could be due to several reasons. First, it could be that the low level laser
therapy did not actually have any therapeutic effect. Second, it could be because the
treatment effect was too small and was masked by the placebo effect. Finally, it could be due
to the multiple treatment interference through systemic effect that invalidated the placebo
control. Therefore future investigations should look into increasing the size of the
experimental effect by changing the treatment parameters, increasing the magnitude of pain
induction, and providing a no treatment control group. The laser energy in joules (J)
delivered to the target tissue was worked out to be 0.45 J, 0.95 J, and 1.8 J for the 15, 30, and
60 seconds beam durations, respectively. These dosages were well within the range of 0.5 to
10 J per treatment point recommended by Kert and Rose.32 Thus there may be room for
increasing the dosage per treatment point by increasing the treatment duration.
Conclusions
1. A weak trend of lower pain scores and lower increases in pain intensity in the 30- and 60second treatment groups, on the second and third day, was observed when compared with
the placebo group.
2. However, the two null hypotheses of no treatment effect for the two factors considered in
this study could not be rejected statistically.
3. Although low level laser was found to be unable to provide immediate pain relief, it could
have a potential in reducing the intensity of pain during its time course with just one or two
applications. Further investigations into the potential of low level laser therapy, using
different treatment protocols and treatment parameters in controlled double blind clinical
trials, are warranted.
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American
Journal
of
Orthodontics
and
Volume 108, Issue 6, December 1995, Pages 614-622
Dentofacial
Orthopedics