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.

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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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n a

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f d

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.

j o

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n a

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f d

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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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