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The effects of light on bleaching and tooth sensitivityduring in-office vital bleaching: A systematic reviewand meta-analysis
Li-Bang He a, Mei-Ying Shao a, Ke Tan b, Xin Xu a, Ji-Yao Li a,*aState Key Laboratory of Oral Diseases, Sichuan University, Chengdu, Chinab Sichuan Center for Disease Control and Prevention, Chengdu, China
j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 6 4 4 – 6 5 3
a r t i c l e i n f o
Article history:
Received 24 October 2011
Received in revised form
11 April 2012
Accepted 14 April 2012
Keywords:
In-office bleaching
Light-activation
Tooth colour
Tooth sensitivity
Systematic review
Meta-analysis
a b s t r a c t
Objective: To evaluate the influence of light on bleaching efficacy and tooth sensitivity
during in-office vital bleaching.
Data sources: We performed a literature search using Medline, EMBASE and Cochrane
Central up to September 2011.
Study selection: All randomised controlled trials (RCTs) or quasi-RCTs comparing the light-
activated bleaching system with non-activation bleaching system were included. Reports
without clinical data concerning bleaching efficacy or tooth sensitivity were excluded.
Results: Eleven studies were included in the meta-analysis. A light-activated system pro-
duced better immediate bleaching effects than a non-light system when lower concentra-
tions of hydrogen peroxide (15–20% HP) were used (mean difference [MD], �1.78; 95%
confidence interval [CI]: [�2.30, �1.26]; P < 0.00001). When high concentrations of HP (25–
35%) were employed, there was no difference in the immediate bleaching effect (MD, �0.39;
95% CI: [�1.15, 0.37]; P = 0.32) or short-term bleaching effect (MD, 0.25; 95% CI: [�0.47, 0.96];
P = 0.50) between the light-activated system and the non-light system. However, the light-
activated system produced a higher percentage of tooth sensitivity (odds ratio [OR], 3.53; 95%
CI: [1.37, 9.10]; P = 0.009) than the non-light system during in-office bleaching.
Conclusions: Light increases the risk of tooth sensitivity during in-office bleaching, and light
may not improve the bleaching effect when high concentrations of HP (25–35%) are employed.
Therefore, dentists should use the light-activated system with great caution or avoid its use
altogether. Further rigorous studies are, however, needed to explore the advantages of this
light-activated system when lower concentrations of HP (15–20%) are used.
# 2012 Elsevier Ltd. All rights reserved.
Available online at www.sciencedirect.com
journal homepage: www.intl.elsevierhealth.com/journals/jden
1. Introduction
In recent years, tooth discolouration has become a common
cosmetic complaint.1,2 A growing number of patients
request dental treatment for tooth whitening procedures,
fuelled by their health-related and aesthetic demands.
* Corresponding author at: Department of Operative Dentistry, West CSouth Road, Chengdu 610041, China. Tel.: +86 28 85501439; fax: +86 2
E-mail address: jiyao_li@yahoo.com.cn (J.-Y. Li).
0300-5712/$ – see front matter # 2012 Elsevier Ltd. All rights reservehttp://dx.doi.org/10.1016/j.jdent.2012.04.010
In-office bleaching and dentist-prescribed, home-applied
bleaching are the two most commonly utilised whitening
procedures. Compared with home bleaching, however, in-
office bleaching has advantages in terms of clinician
control, quick whitening results, reduced treatment time,
and avoidance of material ingestion and discomfort from
wearing trays.3,4
hina College of Stomatology, Sichuan University, No. 14 Ren Min8 85582167.
d.
j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 6 4 4 – 6 5 3 645
In-office bleaching uses different concentrations of a
hydrogen peroxide (15–38% HP) formulation directly on the
tooth surface.5,6 The in-office bleaching can result in signifi-
cant bleaching results after only one treatment, but may
require longer application time or multiple treatment to obtain
optimum results.7,8 However, longer application time or
multiple treatment will increase the risk of tooth sensitivity.9
Therefore, researchers have attempted to reduce bleaching
time by accelerating HP decomposition so that faster bleach-
ing effects, reduced tooth sensitivity and better patient
compliance could be achieved.8 The most common way to
dissociate HP is to apply a physical activation technique such
as light or heat, which provides energy for the reaction.5,10
Early techniques employed both heat and light, with an
empirical acceptance that using heat as a catalyst would speed
up the decomposition of the peroxide, thereby brightening
teeth more rapidly. This method, however, always increased
tooth temperature and sensitivity.11,12 Subsequently, new
systems have been developed that utilise light [e.g., halogen
curing lights, xenon–halogen lights, plasma arcs, light-
emitting diodes (LEDs), LED plus lasers, and lasers] to speed
up the whitening process while generating less heat.13
Manufacturers have claimed that light-activated bleaching
systems could lighten tooth colour by eight shades or more in
just one visit.14 Media outlets have also highlighted the magical
effect of such bleaching systems using light activation.
However, scientific studies on the validity of adjunct lights in
tooth bleaching have proven controversial. Some studies have
shown the positive effects of light-activated bleaching
agents,15–17 while others have demonstrated little-to-no con-
tributions.9,18,19 In addition, there has been increasing focus on
tooth sensitivity during light-activated bleaching.4
At present, several reviews of light-activated bleaching are
available in the literature.5,13,20 However, no reviews have
conducted quantitative assessments of the original studies.
Thus, the volume of information makes it difficult to draw
valid conclusions regarding the effects of supplementary light
during bleaching. Therefore, the objectives of this study were
to systematically review the literature regarding light-activat-
ed bleaching and to quantitatively assess the influence of light
on bleaching efficacy and tooth sensitivity.
2. Materials and methods
2.1. Data sources
To identify all studies reporting on the association between
adjunct lights and tooth whitening, we conducted a system-
atic search of the literature to September 2011 using Medline,
EMBASE (1966–2012), and Cochrane Central Register of
Controlled Trials. No restrictions were placed on the publica-
tion date or languages, and all relevant studies were translated
and reviewed. The main terms used in the search were:
(bleaching or whitening or brightening or colour) and (light or
lamp or activation or heat or radiation or laser or UV or
ultraviolet) and (tooth or teeth). The search strategy was
appropriately modified for each database by consulting with
experts in the field. The reference lists of all located studies
were also hand-searched for additional relevant publications.
2.2. Selection criteria
2.2.1. Types of studiesAll randomised controlled trials (RCTs) or quasi-RCTs com-
paring the light-activated bleaching system with the non-
activation bleaching system were included. Reports without
clinical data regarding bleaching efficacy or tooth sensitivity
were excluded; such abstracts were also excluded. Only
parallel or split design clinical human trials were considered.
2.2.2. Types of participantsThis review included studies involving subjects aged 18 years or
older. Teeth tested in the studies were free of severe stains (e.g.,
tetracycline stains, fluorosis, or discoloration secondary to
endodontic treatment). All participants were characterised by
the absence of previous bleaching treatments. Subjects with
systemic diseases or developmental conditions were also
excluded.
2.2.3. Types of interventionOnly vital in-office bleaching systems were included. The light-
activation method could involve any kind of light lamp (e.g.,
halogen, plasma arc, LED, LED plus lasers or laser alone). In each
specified study, both the light-activated system and the non-
light system employed identical bleaching gels and time
sequences.
2.3. Outcome measures
Bleaching outcome was evaluated by visual colour matching
and/or instrumental measurement. (1) The visual measure-
ment of whiteness was obtained using a shade guide (Vita
Classical Shade Guide, Bad Sackingen, Germany). The 16 tabs
of the shade guide were arranged in sequence, and each shade
tab was assigned a numerical value ranging from 1 to 16 (B1,
A1, B2, D2, A2, C1, C2, D4, A3, D3, B3, A3.5, B4, C3, A4, C4).
(2) The instrumental measurement used a digital imaging
device/spectrophotometer (e.g., Vita Easyshade, Vita Zahnfabrik)
to evaluate the degree of whiteness. The overall colour change
value (Delta E) was computed or extracted from the studies.
Tooth sensitivity was assessed using a visual analogue
scale (VAS), a verbal scale or as a percentage of patients with
tooth sensitivity.
2.4. Data extraction and quality assessment
Two reviewers independently examined and coded the list of
titles and abstracts for inclusion in our meta-analysis. Data
involving the authors, year of publication, light source, sample
size, bleaching agents, bleaching results, and tooth sensitivity
were extracted from each study (Table 1). The reviewers also
grouped the bleaching results from all of the included
publications according to different post-bleaching time:
immediately (within one day), short-term follow-up (1
week–4 weeks), and median-term follow-up (12 weeks–24
weeks). Due to the great variations in the desensitising
procedures provided after tooth bleaching, data associated
with tooth sensitivity were obtained only pertaining to
sensitivity observed immediately after bleaching. The authors
of five of the included studies were contacted to obtain the
Table 1 – Summary of main characteristics of included trials.
Firstauthor(year)
Light source Samplesize
Bleachinggel/time
Bleaching outcomes Toothsensitivity
Risk ofbias
Type Spectrum(nm)
Power Visualmeasurement(Dshade guide)
Instrumentalmeasurement (DE)
ImmediateKossatz
(2011)4LED/laser 470, 830 200 mW/cm2 15 35% HP,
15 min� 3 twosessions
1.11 � 0.6 n.r. 15 (15) Low
Non light 15 35% HP,15 min� 3 twosessions
1.34 � 0.7 n.r. 13 (15)
ImmediateCalatayud
(2011)19LED 380–530 n.r. 21 35% HP,
10 min � 22.9 � 3.3 n.r. n.r. Low
Non light 21 35% HP,10 min � 2
2.4 � 2.8 n.r. n.r.
2 wk 6 wk 14 wk 2 wk 6 wk 14 wkBernardon
(2010)18LED/laser n.r. n.r. 30 35% HP,
15 min� 3 twosessions
2.26 � 1.37 2.32 � 1.38 2.45 � 1.34 8.76 � 3.40 8.61 � 3.48 8.37 � 3.08 NA Moderate
Non light 30 35% HP,15 min� 3 twosessions
2.26 � 1.30 2.35 � 1.38 2.59 � 1.45 8.41 � 3.14 7.96 � 3.26 8.03 � 3.08 NA
Immediate 1 moAlomari
(2010)22Halogenlight
n.r. n.r. 10 35% HP,20 min � 3
2.0 � 1.9 4.5 � 2.1 0.80 � 0.4 Moderate
LED n.r. n.r. 10 35% HP,20 min � 3
4.3 � 2.0 6.4 � 2.0 1.00 � 0.0
Metalhalidelight
n.r. n.r. 10 35% HP,20 min � 3
3.0 � 1.3 5.2 � 1.8 0.80 � 0.4
Non light 10 35% HP,20 min � 3
4.4 � 1.8 5.2 � 1.9 0.30 � 0.5
Immediate ImmediateStrobl
(2010)23(Nd:YAG)laser
1064 4 W 20 35% HP,3.5 min � 2
4.53 � 3.52 5.39 � 3.00 NA High
two sessionsNon light 20 35% HP,
3.5 min � 24.53 � 3.52 5.83 � 3.17
two sessions NA1 wk 1 wk
Ontiveros(2009)24
Halidelamp
350–600 25 W 20 25% HP,15 min � 3
6.1 � 3.1 6.0 � 2.6 2.8 � 3.0 Low
Non light 20 25% HP,15 min � 3
4.5 � 3.0 4.7 � 2.2 1.4 � 1.6
Kugel(2009)25
Metalhalidelight
n.r. n.r. 11 25% HP,20 min � 3
NA NA 10 (11) Moderate
Non light 11 25% HP,20 min � 3
NA NA 6 (11)
j o
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e n
t i
s t
r y
4
0 (
2 0
1 2
) 6
4 4
– 6
5 3
64
6
Marson(2008)9
Halogenlight
400–500 n.r. 10 35% HP,15 min� 3 twosessions
NA NA 5 (10) Moderate
LED 450–500 n.r. 10 35% HP,15 min� 3 twosessions
NA NA 8 (10)
LED laser 470 n.r. 10 35% HP,15 min� 3 twosessions
NA NA 6 (10)
Non light 10 35% HP,15 min� 3 twosessions
NA NA 6 (10)
Immediate 1 wk 4 wkZiemba
(2005)17Metalhalidelight
365–500 n.r. 25 20% HP,15 min � 3
2.9 � 1.6 3.3 � 1.9 3.5 � 2.1 n.r. 0.7 � 1.4 Low
Non light 25 20% HP,15 min � 3
4.2 � 1.7 4.5 � 1.8 4.9 � 1.9 n.r. 0.4 � 0.9
Immediate 3 mo 6 moTavares
(2003)15Short-arcplasmalight
400–505 130–160mW/cm2
29 15% HP,20 min � 3
1.72 � 0.20 2.35 � 0.23 2.89 � 0.34 NA 14 (29) Low
Non light 29 15% HP,20 min � 3
3.65 � 0.31 4.03 � 0.33 4.04 � 0.33 NA 4 (29)
24 hrPapathanasiou
(2002)26Halogenlight
n.r. n.r. 20 35% HP,20 min
6.85 � 1.46 n.r. NA High
Non light 20 35% HP,20 min
6.25 � 1.55 n.r. NA
n.r. – not reported, N.A. – not applicable, hr = hour, wk = week, mo = month.
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t i
s t
r y
4
0 (
2 0
1 2
) 6
4 4
– 6
5 3
6
47
j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 6 4 4 – 6 5 3648
missing data. Four responded, and one author provided
numerical data that had only been shown graphically in the
original text.19
Quality assessments of the included trials were evaluated
using the Cochrane risk of bias criteria.21 The assessment
criteria contained six items: sequence generation, allocation
concealment, blinding of the outcome assessors, incomplete
outcome data, selective outcome reporting, and other possible
sources of bias.
During data extraction and quality assessment, any
disagreements between the reviewers were resolved through
discussion, and if needed, by consulting a third reviewer.
2.5. Statistical analysis
To summarise bleaching efficacy and tooth sensitivity for each
outcome, we calculated the mean difference (MD) for the
continuous data and risk estimates (odds ratio: OR) for the
Fig. 1 – Flow diagram of the l
dichotomous data with a 95% confidence interval (CI). The
random effects models were employed for each pooled
analysis.
Heterogeneity was assessed using the Cochran Q test and I2
statistics, with significance set at P < 0.1. If heterogeneity was
significant, a sensitivity analysis was performed to explore the
influence of the low quality studies.
All analyses were conducted using RevMan (Review
Manager) version 5.0 software (Cochrane Collaboration,
Copenhagen, The Netherlands).
3. Results
3.1. Study characteristics
The searches yielded 301 citations, including 70 duplicates.
Among the 231 remaining publications, 11 studies (nine RCTs
iterature search process.
Fig. 2 – Immediate bleaching efficacy in light-activated treatment versus non-light treatment.
j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 6 4 4 – 6 5 3 649
and two controlled clinical trials) qualified for this meta-
analysis (Fig. 1).4,9,15,17–19,22–26 Among these studies, all 11
studies compared bleaching efficacy, 4,9,15,17–19,22–26 and seven
studies compared tooth sensitivity.4,9,15,17,22,24,25
Quality assessments showed that five out of the nine RCTs
had low risk of bias,4,15,17,19,24 whereas the remaining four
RCTs had a moderate quality risk of bias.9,18,22,23 Six RCTs
adequately described the method of randomisation.4,15,17–19,24
Three of the studies used flipping a coin,4,18,24 and the other
three used a random table or random keys.15,17,19 The
allocation concealment was adequate in three RCTs.15,17,22
All RCTs except for one adopted assessor blinding.4,9,15,18,19,22–
26 The reporting of dropouts was considered adequate in seven
RCTs.4,9,15,17,19,24,25 Two controlled clinical trials had a high
risk of bias.23,26 The main characteristics and methodological
quality of the included trials are summarised in Table 1.
3.2. Bleaching efficacy
3.2.1. Immediate effect (within one day)As shown in Fig. 2, seven studies reported the immediate
bleaching efficacy.4,15,17,19,22,23,26 All of the studies adopted
Table 2 – Summary of main results of meta-analysis.
MD
Bleaching efficacy
Immediate effect High concentration HP 0.39
Low concentration HP �1.7
Short-term effect High concentration HPa 0.25
High concentration HPb 0.87
Tooth sensitivity
Incidence of tooth sensitivity 3.53
Intensity of tooth sensitivity 0.57
a Visual measurements of tooth colour.b Instrumental measurements of tooth colour.c OR.y P value for heterogeneity.
visual measurements of colour change. Two studies showed a
more favourable effect of the light-activated system,15,17
whereas the others did not.4,19,22,23,26 The pooled meta-analysis
of all seven studies showed significant heterogeneity (x2 = 81.45,
P < 0.00001, I2 = 93%). Sensitivity analysis detected two trials
using lower concentrations of HP (15–20% HP)15,17 that were
mainly responsible for the heterogeneity. Hence, subgroup
analysis was conducted according to different bleaching
concentrations of HP (low concentration: 15–20% and high
concentration: 25–35%), thereby avoiding heterogeneity.
A subgroup analysis of three studies using high concentra-
tions of HP showed no significant difference between the light-
activated system and the non-light system (MD, �0.39; 95% CI:
[�1.15, 0.37]; Z = 1.00; P = 0.32).4,19,22 In addition, sensitivity
analysis also detected two controlled clinical trials with a high
risk of bias.23,26 Because these two trials did not influence the
overall effect of the pooled data, they were not included in the
final meta-analysis. In the two studies that used lower
concentrations of HP (15–20% HP),15,17 the subgroup analysis
favoured the use of a light-activated system to produce better
bleaching efficacy (MD, �1.78; 95% CI: [�2.30, �1.26]; Z = 6.72;
P < 0.00001) (Fig. 2 and Table 2).
Light-activation vs. non-light
[95% CI] P I2 Py
[�1.15, 0.37] 0.32 36% 0.21
8 [�2.30, �1.26] <0.00001 44% 0.18
[�0.47, 0.96] 0.50 18% 0.30
[�0.23, 1.98] 0.12 0% 0.40
c [1.37, 9.10] 0.009 12% 0.33
[0.21, 0.92] 0.002 16% 0.30
Fig. 3 – Short-term bleaching efficacy in light-activated treatment versus non-light treatment, as measured using the visual
method.
j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 6 4 4 – 6 5 3650
3.2.2. Short-term effect (1 week–4 weeks)Four studies assessed short-term bleaching effects using
visual measurements.17,18,22,24 Ziemba et al.17 reported signifi-
cantly greater shade changes with the light-activated system
than with the non-light system. Heterogeneity was observed
between different trials. A sensitivity analysis determined that
the study by Ziemba et al.17 used lower concentration of HP
(20% HP) than all the other trials.18,22,24 Further subgroup
analysis showed no significant differences between the light-
activated system and the non-light system using high
concentrations of HP (MD, 0.25; 95% CI: [�0.47, 0.96];
Z = 0.68; P = 0.50) (Fig. 3 and Table 2).
Three studies reported on instrumental measurements of
tooth colour in both light-activated and non-light systems.18,23,24
All such studies employed high concentrations of HP. One
controlled clinical trial was excluded because of its high risk of
bias.23 No significant heterogeneity was noted in the pooled
analysis. Meta-analysis revealed no significant differences
between the light-activated and the non-light system (MD,
0.87; 95% CI: [�0.23, 1.98]; Z = 1.55; P = 0.12) (Fig. 4 and Table 2).
3.2.3. Median-term effect (12 weeks–24 weeks)Two studies could be included in this group.15,18 Tavares and
colleagues15 reported that the light-activated system had
significantly better results than the non-light system, even
Fig. 4 – Short-term bleaching efficacy in light-activated treatme
instrumental method.
after 24 weeks of follow-up, when a low concentration HP was
used (15%). Bernardon and colleagues,18 however, revealed no
significant differences between the two groups 14 weeks post-
bleaching in cases where a high concentration of HP (35%) was
utilised. Because of significant heterogeneity and a sample
size that was too small in these two studies, meta-analysis
was not conducted.
3.3. Tooth sensitivity
3.3.1. Likelihood of tooth sensitivityFour studies compared tooth sensitivity using dichotomous
data.4,9,15,25 Heterogeneity was not observed between the
studies. Meta-analysis demonstrated a significantly higher
likelihood of tooth sensitivity with the light-activated system
than with the non-light system (OR, 3.53; 95% CI: [1.37, 9.10];
Z = 2.61; P = 0.009) (Fig. 5 and Table 2).
3.3.2. Intensity of tooth sensitivityThree studies compared tooth sensitivity using continuous
data.17,22,24 Heterogeneity between the studies was not
significant. A subsequent meta-analysis favoured the use of
non-light systems because they were associated with less
tooth sensitivity (MD, 0.57; 95% CI: [0.21, 0.92]; Z = 3.12;
P = 0.002) (Fig. 6 and Table 2).
nt versus non-light treatment, as measured using the
Fig. 6 – Intensity of tooth sensitivity for light-activated treatment versus non-light treatment.
Fig. 5 – Incidence of tooth sensitivity for light-activated treatment versus non-light treatment.
j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 6 4 4 – 6 5 3 651
4. Discussion
Because of the hypothesis that light plays a significant role in
tooth bleaching, several studies have sought to determine the
influence of light on bleaching efficacy.9,17–19,22,23 However,
these studies assessing the association between adjunct lights
and tooth whitening have produced contradictory results. By
and large, our systematic review revealed that both light-
activated and non-light systems showed similar immediate
and short-term bleaching effects when high concentrations of
HP (25–35%) were employed as the bleaching gel. There is
limited evidence, however, that a light-activated system
produced better immediate bleaching efficacy than non-light
system when a lower concentration of HP (15–20%) was used.
In terms of peroxide chemistry, there are two viewpoints
on the beneficial effects of light enhancement for HP. Some
studies have suggested that light could increase the tempera-
ture of HP and thereby speed up bleaching.19,27 While others
have insisted that an increased release of radicals from HP via
photolysis may be an important pathway, in which the
photolysis of HP can be activated by wavelengths of 365 nm or
less.13,28 Nevertheless, in teeth, the effective temperature
needed to accelerate bleaching (52–60 8C) is within the range
that could cause irreversible pulpal damage.17,29,30 Addition-
ally, at present, the majority of whitening lamps used in
clinical practice provide emissions in the visible spectrum
(400–700 nm).13 Because of these limitations, the magnitude of
the effects associated with whitening lamps should be re-
evaluated.
Regardless of heat or photolysis mechanism, the dehydra-
tion effect has been frequently mentioned as an important
factor in light-activated systems.4,20,24 Tooth dehydration
leads to an immediate increase in tooth brightness rather
than a decrease in tooth colorisation.31 This dehydration is
most likely caused by the heat produced by light, the method
of tooth isolation and the bleach itself.20
Because a high concentration HP (25–35%) is used during in-
office bleaching, light may not contribute much to the
bleaching results, especially considering the following rea-
sons. The high concentration of bleach itself can quickly
produce enough radicals that react with pigments.4 From the
patient’s perspective, every tooth has a set limit on how
quickly it can change colour and how bright it can become.32
Once this limit is reached, tooth colour will not change
regardless of whether light is used to accelerate the bleaching
process.
When lower concentrations of HP (15–20%) were used
during the in-office bleaching, light indeed produced better
immediate bleaching effects according to our data analysis.
Possible reasons are that the light facilitated HP photolysis,
whereby increments of hydroxyl radicals compensated for the
low concentrations of HP.4 Furthermore, light-induced dehy-
dration may have played an important role in immediate
bleaching efficacy. Because limited data support this observa-
tion, however, no consolidated conclusion could be drawn in
this meta-analysis. Further studies are warranted on the
efficacy of lower concentrations of HP on tooth bleaching.
In this meta-analysis, both visual and instrumental mea-
surements of tooth colour were used. They showed similar
statistical results during the short-term follow-up period.
Among the included studies, all but one evaluated tooth colour
with the Vita classical shadeguide.4,9,15,17–19,22–24,26 Seven studies
employed two or three trained examiners for their visual
measurements.4,9,18,19,22,24,26 Consistent light conditions for
colour matching were also mentioned in six of the studies.9,17–
19,22,24 While four studies employed a spectrophotometer or
chromameter for the instrumental measurement, one study
used digital photography and image analysis software. The
studies also demonstrated that a spectrophotometer had the
j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 6 4 4 – 6 5 3652
same measurement scale as a Vita Shade Guide.24,33 It may be
wise to use multiple methods to evaluate the effectiveness of
tooth bleaching products 34–36 which is also recommended by the
American Dental Association.24,37
Tooth sensitivity is the most frequently reported side-effect
after vital tooth bleaching.38,39 Our pooled analysis suggests
that a light-activated system is likely to increase the occurrence
or severity of tooth sensitivity. Three studies demonstrated that
more severe sensitivity was observed with light-activated
systems.4,23,25 Kugel et al.25 even reported that three partici-
pants in the light-activated group discontinued the 60-min
treatment because of severe sensitivity. This sensitivity may be
explained by the fact that light sources can increase pulpal
temperatures, leading to increased tooth sensitivity.40 More-
over, the light may have accelerated the permeability of the
enamel and dentine, subsequently resulting in the easy passage
of the peroxide through the enamel and dentine to the pulp.41–43
This process may take 5–15 min.44 When the duration of light-
activated bleaching was prolonged, a higher degree of sensitivi-
ty was noted.9 An additional explanation is that laser-activated
bleaching systems increase the expression of substance P in
human dental pulp.45 Substance P is closely related to
neurogenic inflammatory reactions in pulp tissue. Kossatz
et al.4 and Strobl et al.23 have also reported on increased tooth
sensitivity when an LED/laser was used.
Because light increases the risk of sensitivity during in-office
bleaching, clinicians may need to reconsider the rational
application of bleaching lamps. Furthermore, when light-
activated bleaching procedures are conducted, dentists should
follow the manufacturer’s instructions to limit the duration of
light activation, especially to minimise undesired pulpal
responses.20
This systematic review performed an analysis of immedi-
ate bleaching efficacy and tooth sensitivity of light-activated
systems. Insufficient data regarding median-term effect or
long-term follow-up were included in this analysis. The
methodological quality of assessed studies was generally
moderate, based on the Cochrane risk of bias criteria. The two
controlled clinical trials were not included in the final meta-
analysis because of their high risk of bias.23,26 Because only a
small number of studies compared the bleaching efficacy and
tooth sensitivity of light-activated system with non-light
system when lower concentrations of HP (15–20%) were used,
a convincing conclusion cannot be drawn at present.
Therefore, more well-designed RCTs are needed to further
confirm the robustness of our findings.
5. Conclusions
Light may not improve bleaching efficacy when high con-
centrations of hydrogen peroxide (25–35%) are employed
during in-office bleaching. Because the light-activated system
increases the risk of tooth sensitivity, dentists should use this
system with great caution or avoid its use altogether. When
lower concentrations of hydrogen peroxide (15–20%) are
applied, there is limited evidence that light is able to produce
better immediate bleaching effects. Therefore, more large-
scale, rigorous studies are still needed to explore the
advantages of this light-activated system.
Acknowledgements
We thank the authors of the studies included in this meta-
analysis for providing evidence of associations between
adjunct lights and tooth whitening. We thank Professor
Guan-Jian Liu in particular for his help in the correction of
the statistical methods. None of the authors have any conflicts
of interest in relation to this study.
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