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Review Article
Laser Teeth Bleaching: Evaluation of Eventual Side Effects on
Enamel and the Pulp and the Efficiency In Vitro and In Vivo
Roeland Jozef Gentil De Moor,1Jeroen Verheyen,1,2 Peter Verheyen,3Andrii Diachuk,1
Maarten August Meire,1Peter Jozef De Coster,1MiekeDeBruyne,
1and Filip Keulemans1
1Department of Restorative Dentistry and Endodontology, Ghent Dental Laser Centre, Ghent Dental Photonics Research Cluster,
Ghent University, Ghent University Hospital, Dental School, De Pintelaan 185-P8, 9000 Gent, Belgium
2Department of Clinical Neurosciences, John van Geest Centre for Brain Repair and Wellcome Trust-Medical Research Council
Stem Cell Institute, University of Cambridge, Cliord Allbutt Building, Cambridge Biosciences Campus, Cambridge, CB2 0QH, UK
3SOLA Academy, Bernhard Gottlieb University Clinic of Dentistry, Sensengasse 2A, 1090 Vienna, Austria
Correspondence should be addressed to Roeland Jozef Gentil De Moor; roeland.demoor@ugent.be
Received August ; Revised November ; Accepted November
Academic Editor: Toni Zeinoun
Copyright © Roeland Jozef Gentil De Moor et al. is is an open access article distributed under the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.
Light and heat increase the reactivity of hydrogen peroxide. ere is no evidence that light activation (power bleaching with high-
intensity light) results in a more eective bleaching with a longer lasting eect with high concentrated hydrogen peroxide bleaching
gels. Laser light diers from conventional light as it requires a laser-target interaction. e interaction takes place in the rst instance
in the bleaching gel. e second interaction has to be induced in the tooth, more specically in the dentine. ere is evidence
that interaction exists with the bleaching gel: photothermal, photocatalytical, and photochemical interactions are described. e
reactivity of the gel is increased by adding photocatalyst of photosensitizers. Direct and eective photobleaching, that is, a direct
interaction with the colour molecules in the dentine, however, is only possible with the argon ( and nm) and KTP laser
( nm). A number of risks have been described such as heat generation. Nd:YAG and especially high power diode lasers present a
risk with intrapulpal temperature elevation up to ∘C. Hypersensitivity is regularly encountered, being it of temporary occurrence
except for a number of diode wavelengths and the Nd:YAG. e tooth surface remains intact aer laser bleaching. At present, KTP
laser is the most ecient dental bleaching wavelength.
1. Introduction
Heating hydrogen peroxide (HP) results in an acceleration
of its decomposition and oxidant-free radical formation [].
erefore, the dental bleaching process can be accelerated
by additional heat activation. One of the activation methods
resultinginanincreaseofthetemperatureinthebleaching
gel is power bleaching with high-intensity light [].
e eectiveness of this method for vital tooth bleaching
has been demonstrated in animal studies, clinical studies and
reports, and a number of reviews [–]. Side eects for the
tooth, that is, alteration of the enamel surface, posttreatment,
andpulpsensitivity,havebeensuggestedandinvestigated[,
,,].
Potential adverse eects on enamel were primarily inves-
tigatedinvitrousingextractedhumanandbovineteeth.
Reports on the eects of light-activated systems were diver-
gent, which was also the case for conventional in-oce
bleaching techniques. On the one hand, changes in micro-
hardness, the presence of porosities, changes in surface
roughness, a reduction in fracture toughness, alteration of
the calcium/phosphate ratio, erosion, decrease in abrasion
resistance, and the formation of depressions were reported.
e enamel surface changes varied mostly with the bleaching
products used, especially high concentrations of hydrogen
peroxide; that is, –% (w/w) and % (w/w) carbamide
peroxide (CPO) (-% HP) could have a damaging eect,
whereas low concentrations % or % CPO (w/w) (–%
HP) had no eect []. On the other hand, rehardening of
porous enamel as a result of saliva ion reprecipitation has
been described. Although remineralisation due to the saliva
Hindawi Publishing Corporation
e Scientific World Journal
Volume 2015, Article ID 835405, 12 pages
http://dx.doi.org/10.1155/2015/835405
e Scientic World Journal
may be responsible for a gradual mineral rebuild-up, full
repair of the enamel is not established due to a degradation
of the organic matrix []. To date, nevertheless, no clinical
adverseeectsofpowerbleachingonenamelhavebeen
reported.
Sensitivity aer bleaching is higher when HP is combined
with thermal activation [–]. Diverging results once again
have been published regarding the eect of power bleaching
on the pulp [–]. Also for this topic there is a lack of in vivo
studies and there are no studies evaluating long-term eects
of HP exposure on dental pulp.
An intrapulpal temperature increase of .∘Cisnowa-
days regarded as the threshold value, which should not
be exceeded to avoid irreversible pulp damage []. It
appears that temperature during light-activated bleaching is
in general under control, especially due to the presence of a
bleaching [,].
2. Aim
At present, there is no review on the eciency of laser
activated bleaching and its eect on the tooth (enamel and
pulp).eaimofthisreviewisthereforetoevaluatethe
inuence of the temperature rise during laser bleaching on
the pulp, the postoperative sensitivity, and eventual enamel
alterations. e eciency is evaluated on the basis of the
colour change in vitro and in vivo.
3. Methods and Materials
e electronic literature search included the databases
PubMed and Web of Science for manuscripts published with
full journal reference from January to November .
All languages were accepted provided there was an abstract
in English. e following MeSH terms and key words were
used: “lasers” AND “tooth bleaching,” “lasers” AND “tooth
discoloration,” “tooth bleaching” OR “teeth bleaching” AND
(argon laser OR diode laser OR KTP laser OR Nd:YAG laser
OR Er:YAG laser OR Er, Cr:YSGG laser OR carbon dioxide
laser). Two reviewers (AD and BV) independently assessed
abstracts and full-text articles. First the reviewers considered
the abstracts as potentially relevant. Abstracts dealing with
this topic but without access to full journal article were not
taken into consideration. Case reports were included only
when they exclusively reported observations which were not
described in other publications. en full articles were read.
Both reviewers selected independently the same full-text
articles; that is, Cohen’s kappa = ..
4. Results
4.1. Temperature Rise in the Pulp. Taking into account the
subject of the present review both power intensity and
wavelength of the light used during the bleaching procedure
mustbetakenintoconsideration[]. An overview of the
changes in temperature in the pulp during laser dental
bleaching is given in Table .
4.1.1. CO2Laser (10,600 nm). Luk et al. []reportedthat
the use of a CO2laser (, nm) on teeth for bleaching
purposes led to a temperature increase of . to .∘Cwith
gel at the enamel surface and . to .∘Catthepulpalside
of the dentine. Due to a lack of controlled clinical studies
this wavelength was not approved for bleaching by the ADA
[]. At present this wavelength is no longer used for dental
bleaching.
4.1.2. Nd:YAG (1,064 nm). Next to the CO2laser, the highest
temperature elevations in the pulp were registered with the
Nd:YAG laser (,nm) irrespective of the use of coloured
bleaching gels (blue, red, and transparent) [,].
4.1.3. Diode Lasers. High power diode lasers (– nm)
are also known to be able to rise the pulpal temperature
andshouldbeusedincombinationwithableachinggel.An
overview of the reported data is given in Table .
Laser activation with a nm diode laser ( s, W)
without bleaching gel may result in a temperature increase of
∘Cinthepulpchamber;whenapplyingthegelduringlaser
activation only .∘C temperature increase was recorded [].
With a nm diode laser, there was an increase of
temperature with .∘CatW-sand.
∘Cat.W-
s [].Inthesamestudytemperaturerisewasloweraer
application of a bleaching gel; the decrease was product
related: By White gel (By Dental, Pistoia, Italy) at W resulted
in a rise of .∘Candat.Wof.
∘CwithWhiteness
HP (FGM Produtos Odontol´
ogicos, Joinville, Brazil) it was
+.∘CatWand+.
∘Cat.W.ebleachinggelthus
acts as a selective absorber near the dental surface, preventing
light penetration into the internal tooth structure. Apparently
the composition of the gel is also important as the gel layer
was mm thick in both investigations.
An increase of .∘Cwithadiode laser ( nm) ( W,
s) and .∘CwithanEr:YAG(,nm)(mJ,Hz,
s) was registered by Sari et al. []. e temperature in the
gel, however, was .∘Cforthediodeand.
∘CforEr:YAG.
e increase in the pulp chamber temperature with a
diode laser ( nm) used at W- s is below the critical
temperatureincreaseof.
∘C that is nowadays regarded as
the threshold value and which should not be exceeded to
prevent irreversible pulp damage []. In the same study the
diode laser at W- s resulted in a temperature increase
up to .∘Cand.
∘C with W- s; the importance of use
of the gel with appropriate thickness was emphasized by
measurements of the temperature at the surface: W resulted
in ∘C, W in .∘C, and W in .∘C.
Similar ndings were registered by Fornaini et al. []
where an nm diode at W during × s resulted in
heating of the gel up to .∘CandatW-× s up to .∘C.
A temperature increase of –∘Cand–
∘Cwas
observed when a nm diode laser was used to activate
Opalescence Xtra (Ultradent Products, South Jordan, UT,
USA) and Opus White (Opus Dent, London, UK) for . W-
sandW-s[].
A mean increase of .∘Cinthepulpwasseenwithan
nm diode used at W- s [].
With a hydrogen peroxide bleaching agent, the mean
maximum pulpal temperature rise was .∘CforaLED,
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T : Increase in temperature (∘C) in the pulp (without or with gel application) aer exposure to laser light.
Authors Wavelength Settings Bleaching gel Result/temperature
Luketal.,[] , nm (CO)
mW
× sec/ sec
interval
GT: mm
𝐷:tomm
Opalescence Extra
Quick White
Star Brite
Nypro Gold
Pulp without and with gel
+. +.
+. +.
+. +.
+. +.
Michida et al., [] , nm (Nd:YAG)
mJ, Hz (. W)
sec
GT: . to mm
𝐷:mm
Whiteness HP Pulp with gel
+.
Dominguez et al., []
, nm (Nd:YAG)
mJ, Hz
× sec
GT: mm
𝐷:mm
Ena White Power
Opalescence Endo
QWhite
Pulp with gel
+.
+.
+.
, nm (Er :YAG)
mJ, Hz
× sec
GT: mm
𝐷:mm
Ena White Power
Opalescence Endo
QWhite
Pulp with gel
+.
nm (diode)
. mJ, Hz
× sec
GT: mm
𝐷:mm
Ena White Power
Opalescence Endo
QWhite
Pulp with gel
+.
nm (diode)
mW
× sec
GT: mm
𝐷:mm
Ena White Power
Opalescence Endo
QWhite
Pulp with gel
+.
+.
+.
Klaric et al., [] nm (femtosecond
diode)
mW, min
Unfo cused
GT: ?
𝐷:?
Without gel
ZOOM
Boost
Vivastyle
Vivastyle
Vivastyle
Enamel surface Pulp
+. +.
+. +.
+. +.
+. +.
+. +.
+. +.
mW, min
Focused
GT: ?
𝐷:?
Without gel
ZOOM
Boost
Vivastyle
Vivastyle
Vivastyle
Enamel surface Pulp
+. +.
+. +.
+. +.
+. +.
+. +.
+. +.
Sulieman et al., a [] nm (diode)
W, sec
GT: mm
𝐷:justabovethe
surface of the gel
Opus Mix bleaching
powder + % HP
liquid
Pulp without and with gel
+ +.
Kivanc¸etal.,[] nm (diode)
W, sec
GT: mm
𝐷:mm By White (BW)
Whiteness HP
(WHP)
Pulp without and with gel
+. BW +
WPH +.
. W, sec
GT: mm
𝐷:mm
Pulp without and with gel
+. BW +.
WPH +
Sari et al. [], Epub
nm (diode)
W,sec
GT:
𝐷:Whiteness HP
Pulp with gel
+.
nm (Nd:YAG)
mJ, Hz, sec
GT:
𝐷:
Pulp with gel
+.
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T : C o nti nue d .
Authors Wavelength Settings Bleaching gel Result/temperature
Sulieman et al., [] nm (diode)
sec
W
W
W
GT: mm
𝐷:justabovethe
surface of the gel
Opus Mix bleaching
powder + % HP
liquid
Surface Pulp without and
with gel
. +. +.
. +. +.
+. +.
Fornaini et al., []
nm (diode)
× sec—rest time
min
W
W
GT:
𝐷:gHPsolution+
g carbopol (HP
concentration to
%)
Peak gel temperature
.
.
nm (KTP)
× sec—rest time
min
W
W
GT:
𝐷:
Peak gel temperature
.
Wetter et al., [,] nm (diode)
. W, sec
GT: ?
𝐷:mm Opalescence Xtra
(OPX)
Opus White (OW)
Pulp with gel
OPX +
OW comparable ()
W,sec
GT: ?
𝐷:mm
Pulp with gel
OPX +
OW comparable ()
Eldeniz et al., [] nm (diode)
W, sec
GT: OPX?—QS: mm
𝐷:?
Opalescence Xtra
(OPX)
Quasar Brite (QS)
Pulp with gel
+.
Zhangetal.,[] nm (diode)
. W, sec
GT: mm
𝐷:mm Hi Lite
Pulp with gel
+.
nm (KTP)
W,sec
GT: mm
𝐷:mm
Pulp with gel
.
Verheyen et al., [] nm (diode)
W,sec
GT: ?
𝐷:?
Opus White (OW)
Ti-O gel (TO)
Pulp with gel
OW
TO
Goharkhay et al., [] nm (diode)
W,sec
W,sec
GT: ?
𝐷:mm
Opalescence Xtra
Boost
Pulp without and with gel
+
+. +.
Pleen et al., [] nm (dio de)
mW, × s ec
GT: ?
𝐷:mm
% experimental HP
gel
In the gel Pulp with gel
+. +.
Carrasco et al., []LED-laser
/ nm
mW, × sec
GT: mm
𝐷:mm
Whiteness HP Pulp without and with gel
+. +.
Torres et al., []LED-laser
/ nm
mW
× secc
GT: mm
𝐷:mm
Whiteform Perox Red Critical temperature rise of .∘C
not reached
Coutinho et al., []
LED/laser
/ nm
LED/laser
/ nm
mW, × sec
mW, × sec Whiteness HP
Pulp with gel
Incisor +.
Canine +.
Premolar +.
Incisor +.
Canine +.
Premolar +.
GT: gel thickness; 𝐷: distance between light source and the bleaching gel.
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.∘C for a KTP laser ( W- s), and .∘Cforanm
diode laser (. W- s) [].
WithanoutputpowerofW-sofannmdiode laser,
pulpaltemperatureincreasewasshowntobeapproximately
∘C with the Opus White gel (Opus Dent), whereas a TiO2
emulsion showed almost no temperature changes in the pulp
[].
A treatment protocol with intermittent irradiation of six
times for s, with breaks in between, at a power setting
of less than W, with a nm diode laser excluded thermal
damage to the pulp, whereas the temperature at the surface
was ∘C. Irradiation at W with the same protocol resulted
in a temperature elevation of .∘C at the surface and .∘Cin
the pulp chamber [].
e addition of colorants mayhelptoprovideabetter
absorption of high power diode laser light in the bleaching
gel and less transmission towards the pulp chamber. Pleen
et al. [] demonstrated that a low-intensity red diode laser
( nm) ( mW- × s) with a green-coloured bleach gel
resulted in not more than a .∘C temperature elevation in the
pulp chamber.
It is clear that power and type (wavelength) of the light
source inuence temperature variation. Studies have shown
that near-infrared lasers could improve the inammatory
response of the pulpal tissue, reducing pulp damage and
relieving pain aer the bleaching process []. Its use would
diminish patients’ sensitivity complaints aer the procedure.
In this respect LED devices were associated with diode lasers
emitting in the near-infrared. According to Carrasco et al.
[] / nm ( mW- × s) temperature is under con-
trol. Other studies also demonstrated negligible temperature
changes: / nm ( mW- × s) [], / nm
( mW- × s), and / nm ( mW/ × s []).
Moreover it appears that these combination types of light
sources with low power density are not powerful enough to
provide a better bleaching ecacy as compared to other light
sources [,,].
A comparison between dierent laser wavelengths by
Dominguez et al. [] used as follows: that is, three bleaching
gels (transparent, with blue dye, with red dye, composition of
dye mentioned) exposed during times for sec to the light
source with a min interval and an overall contact time of the
gel with the tooth surface during min, demonstrated the
following temperature eects in decreasing order: Nd:YAG
( nm) (rise of .∘Cinthepulpchamber)>halogen
lamp ( nm) >low power diode ( nm) >low power LED
(– nm) >2𝜔Nd:YAG ( nm) >Er:YAG ( nm).
ese ndings coincided with the ndings of Torres et al. []
(halogen versus diode / nm) and Carrasco et al. []
(halogen versus diode / nm versus LED).
In a study of Klaric et al. [] a comparison was
made between ZOOM (– nm) during min, LED
( nm) during min, OLED (organic light emitting
diode) (– nm) during min, and a femtosecond laser
( nm) (Millenia, Spectra Physics, USA) during min:
ZOOM resulted in high temperature elevations (+.∘C)
in the pulp whereas elevations were +.∘Cwithoutuseof
bleaching gel; the femtosecond laser focused: +.∘Cwithout
gel and +.∘C with gel; the femtosecond laser unfocused:
+.∘Cwithoutgeland+.
∘Cunfocused.Inthisrespect
it has also to be mentioned that the mechanism of heat
conversion depends directly on the tissue constituents and
the irradiation wavelength used. It is known that the tooth
absorption coecient is lower for the wavelength range
<𝜆< nm; thus scattering predominates over absorption
at these wavelengths.
Er:YAG (2,940 nm). In a study of Kivanc¸etal.[]tem-
perature increase in the pulp was neglectable. A very low
temperature rise of .∘C was registered by Sari et al. [].
KTP (532 nm). Using the green light of the KTP to irradiate a
red coloured bleaching gel resulted in a temperature of ∘C
at W during sec and .∘CatWduringsec[].
With a hydrogen peroxide bleaching agent, the mean
maximum pulpal temperature rise was .∘CforaLED,
.∘C for a KTP laser, and .∘Cforadiodelaser[].
4.2. Inuence on the Characteristics and Material Properties of
the Teeth. eaimofableachingprocedureistobleachthe
tooth without morphological and chemical changes. How-
ever, side eects aer power bleaching in the enamel such as
changes in microhardness, the presence of porosities, changes
in surface roughness, a reduction in fracture toughness,
alteration of the calcium/phosphate ratio, erosion, decrease
in abrasion resistance, and the formation of depressions were
reported. Weakening of enamel structure by oxidation of
organic or inorganic elements is considered to be the main
cause [].
4.2.1. Morphological Analysis. Morphological analysis
showed slight changes with the diode laser ( nm) and
the LED/laser ( nm/ nm) []. Surface eects were
unrelated to the pH of the high concentration HP bleaching
gels with laser activation and referred more to a better
or lesser absorption of the laser light by the bleaching
gel. Chromophores and the use of TiO2appeared to be
favourable for the maintenance of an intact tooth surface
[]. No signicant eects on the morphology of the enamel
surface aer laser bleaching with diode laser, KTP, Nd:YAG,
and Er:YAG were observed by Dominguez et al. [].
4.2.2. Mineral Content. FT-RS results showed a decreased
mineral content aer bleaching procedures with and without
light activation and with % HP-based bleaching agents.
e use of a LED/laser ( nm/– nm) resulted in
comparable calcium loss as compared to the non-light-
activated bleach gels for of brands. Exposing Pola Oce
(Southern Dental Industries, Sao Paulo, SP, Brazil) to the
LED/laser did not result in a signicant calcium loss []. An
explanation for this dierence was not given.
No signicant dierences in levels of calcium and phos-
phorus were seen aer / nm LED/laser bleaching [].
In a study of Cesar et al. []with%HP-basedbleach-
ing agents activated with a LED/laser (. nm/ nm),
FT-Raman spectroscopy data showed no signicant chem-
ical changes in the inorganic components for the tested
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groups. Carbonate and phosphate area peaks were not signif-
icantly changed. Whiteness HP Maxx (FGM Produtos Odon-
tol´
ogicos Ltda., Santa Catarina, Brazil) and Opalescence Xtra
(Ultradent Products) were also tested in the study of Berger
et al. []. ere was a signicant reduction of the dental
organics associated with type I collagen vibration only in
the group of Whiteform-Perox Red gel (Formula & Acao,
Sao Paulo, SP, Brazil). is means that there is a dierence
between both studies. Total contact time of the gels was
identical, that is, consecutive gel applications for min.
Irradiation protocols, however, diered: in Berger et al. [],
there was a bleaching gel le on third molars undisturbed
for min and then irradiated for min; the light irradiation
was repeated times with a min interval between radiations;
in Cesar et al. [] there was photoactivation of the gel
for sec for a total of min of application on bovine
teeth. Moreover, similar dierences in ndings were also
observed with non-light-activated high concentration HP
bleaching gels. Whether the dierences found for the present
two studies are related just to the bleaching protocol is not
clear yet; in fact dierences in oxidizing potential (stronger),
stronger concentrations, longer treatment times, and lower
pH of bleaching gels could be responsible for the changes
found in the studies [].
Inastudywithbovineteethusingalowpowerdiodelaser
( nm, mW power) it was seen that the enamel crys-
tallinity was dramatically decreased by a bleaching treatment
without laser irradiation. However, crystallinity increased
as laser irradiation time increased. It was concluded that
professional bleaching treatment with HP combined with a
diode laser irradiation not only improves the bleaching eect
but also protects against the change of enamel structure com-
pared with the bleaching treatment without laser irradiation
[].
TEM analysis showed the formation of a new phase 𝜇m
thicklayer.eassumptionwasalsomadethatthechemical
property of the bleaching gel could have been changed
through exposure to laser irradiation. It can also be that this
phenomenon accounts for bovine teeth where the enamel
contains signicantly more interprismatic organic material
compared to human enamel even though its structure and
compositions are very similar to those of human enamel.
4.2.3. Microhardness. e microhardness test is suitable for
determining small changes in surface that demonstrated the
eectofbleachingproductsonenamel[].
A comparison between argon laser ( nm, mW,
sec irradiation and -minute intervals during min) and
halogenlamp-basedphotopolymerizer(minandmW,
and -minute intervals during min) did not result in
dierences with the control group using % and % CP
[].
Zhang et al. [] showed no dierences between the
control (% HP) and KTP (W, sec, energy density (ED)
. J/cm2), diode nm (.W, sec, ED: . J/cm2),
and blue LED composite curing lamp ( nm, s, ED:
. J/cm2) experimental groups. Diode laser ( nm) irra-
diation ( times, sec irradiation at . W of newly placed)
ofthe%HPgelassociatedornotwithACPdidnotinterfere
with microhardness [].
Reduction in microhardness was found aer bleaching
with a LED/laser (/ nm, light intensity of mW,
min laser activation of the gel, followed by -minute rest; this
procedure was repeated times), which recovered to baseline
values aer week of immersion in articial saliva [].
4.2.4. Enamel Permeability. Higher permeability of the
enamel surface aer a bleaching procedure with a LED/laser
(– nm) and QTH light as compared to a control
(% HP) was reported; there were no signicant dierences
between the two bleach protocols [].
Bleaching with a / nm LED/laser did not show
anystatisticaldierencewithbaselinewithregardtodye
penetration [].
4.2.5. Caries Susceptibility of Bleached Enamel. In-oce laser
bleaching with a LED/laser ( nm) does not result in a
higher susceptibility for caries lesions [].
4.2.6. Fracture Strength. Araujo et al. []showedthata
LED/laser (. nm/ nm) did not inuence the fracture
strength of enamel aer light-activated bleaching.
4.2.7. Bonding to Bleached Enamel. Bonding to intracoronally
light-activated bleached dentine should be performed at
least days aer a bleaching procedure with a LED/laser
(. nm/ nm) []. A time interval of to weeks was
advocated for applying silorane-based composite restorations
of methacrylate based composites aer bleaching with an
nm diode laser []. A week interval aer bleaching
with an nm diode and – nm blue LED showed
statisticallysignicantlylowershearbondvaluesascompared
to the control and bleaching with QTH light (– nm)
[].efailuremodeinthislatterstudywasadhesivefor
the diode laser (%) and the LED (%); for both the
control group and the QTH lamp the failure mode was mixed
(adhesive and cohesive) (%).
4.3. Hypersensitivity
4.3.1. Diodes and LED/Lasers (Diodes). Sensitivity is
described by some as common with the diode laser.
Bleaching with a diode laser ( nm, % HP) just reached
the level that can be tolerated by the patient []. Comparing
a diode laser ( nm, % HP) with PAC activation (–
nm, % HP), LED activation (– nm, % HP)
and no light activation (% HP) resulted in the lowest
sensitivity for the diode laser [].
In the study of Kossatz et al. [] .% of the participants
had sensitivity even hours aer laser bleaching with a
LED/laser unit ( nm/ nm, % HP) with a protocol
of gel activation during min, leaving the gel undisturbed
during min and repeating this protocol times and the
in-oce bleaching agent was refreshed every minutes
during a -minute application period. Immediate sensitivity
was also scored in the study of Mondelli et al. []witha
LED/laser ( nm/ nm, % HP). Sensitivity decreased
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aer hours to return to normal aer days. ere were
no dierences between in-oce gels (light- and non-light-
activated).
An increased expression of substance P was seen when a
LED laser ( nm, % HP) was used [].
More recent studies demonstrated that sensitivity was
generated independently of the light sources used: Almeida
et al. [] with a LED/laser at –/ nm, Martin et al.
[] with a LED/laser at / nm, and Moncada et al.
[] with a LED/laser at –/– nm. e latter
two studies demonstrated a higher impact of the increase
in concentration of bleaching agents on tooth sensitivity;
treatment with carbamide peroxide generated also lower
sensitivity than treatment with HP independently of the light
sources.
A comparison between all these studies is dicult and
impossible because each investigation is dierent, that is,
dierent protocols. Moreover, complete basic information,
that is, power settings, gel thickness, distance between gel,
and light source, is not provided in the listed studies.
4.3.2. Nd:YAG. When using the Nd:YAG laser (, nm,
% HP) for laser bleaching at W, Hz, 𝜇spulsedura-
tion, and an energy density of . J/cm2in association with
a red coloured gel, no enhancement of the bleaching success
was found []. ere was no reduction in hypersensitivity,
ascanbeseenwhenNd:YAGisusedforthetreatmentof
dentinal hypersensitivity. Only % of the patients in this
study had a pain-free treatment with the Nd:YAG laser. e
remaining patients felt the development of warmth to the
point of pain, even a few days aer laser treatment. e
authors concluded to query the appliance of Nd:YAG laser
irradiation for in-oce bleaching.
4.4. Laser Bleaching: Tooth Colour Change and Eciency
4.4.1. Colour Change In Vitro. A comparison based on
analysis of photoreectance spectra between the use of an
argon laser ( nm) and halogen lamp with % and %
CPO gave better results for the % CPO gel. Halogen was
as eective as argon laser with % CPO; argon was more
eective than halogen for the % CPO []. A compari-
son between LED/diode laser (– nm/ nm), argon
( nm), PAC (– nm), and halogen (– nm)
showed better results for a % HP than for % CBP.
A decrease in reectance values was seen aer days;
no dierence was observed in bleaching eciency between
activated and nonactivated bleaching gels with high HP
concentrations [].
In a study comparing KTP ( nm, % HP) with a
diodelaser(nm,%HP,%HP,and%HP)[]
improved changes in brightness of up to ten steps on the
Vitapan classical shade guide were detected. Prerequisites,
however, were a perfect match of the chosen wavelength and
the bleaching gel. A neutral and basic pH of the bleaching
gel is also advantageous. e higher bleaching power of KTP
as compared to an nm diode laser was conrmed by
Fornaini et al. [].
Diode laser activation ( nm, % HP) of the bleaching
agent was not more eective than the halogen lamp for
bleaching root canal treated primary molars [], safer for T∘
development. Activation of a % HP bleaching gel by diode
laser ( nm, % HP) as well as a xenon halogen light, a
plasma arc lamp, and halogen light did not dier in result
from the use of the same gel without light activation [].
A comparison between a nm diode laser and a xenon
arc lamp (– nm) used with a % HP bleaching gel
showed that there was an increase in colour saturation (Δ𝐶∗)
of –% and a change in whiteness (Δ𝐿∗)of –% []. e
highest ecacy was achieved with the diode laser at W, the
lowest with the diode laser at .W. However, due to the risk
of higher temperature development, the authors considered
the xenon lamp as the safest. A comparison between a diode
laser ( nm) and LED (nm) demonstrated signicant
comparable change in chroma for the two % HP bleach gels
investigatedandthelightsources.erewasalsoasignicant
change in lightness for all test conditions, but the diode scored
signicantly best with the Whiteness HP bleaching agents
(FGM Produtos Odontol´
ogicos, Joinville, Brazil) than with
Opalescence Xtra (Ultradent Products) [].
A comparison between dierent laser wavelengths by
Dominguez et al. [] demonstrated that the source of irradi-
ation was more relevant than the bleaching agent for ecient
tooth bleaching. ey exposed three % HP bleaching gels
(transparent, with blue dye, and with red dye, composition of
dye mentioned) during times for sec to the light source
with a min interval; contact time of the gel with the tooth
surface was min. LED (– nm, low power), halogen
lamp ( nm), and diode ( nm, low power) produced
greatercolourchangesthantherestofthelightsources:
Nd:YAG ( nm), Er:YAG ( nm), and 𝜔Nd:YAG
( nm). e mean improvement in tooth whiteness with
the latter three wavelengths is in the same order as without
photoactivation. It is thus the question if these wavelengths
arereallysuitedforbleachinggelactivation.esendings
dier from other studies where the eect of an Nd:YAG was
comparable with a halogen light [], and the eect of KTP
was better as compared to diode (nm) and blue LED
( nm) [], but these chromophores were chosen as a
function of the wavelength used (Nd:YAG: Q-switch dye with
maximum absorption at nm) (KTP: sulphorhodamine B
with maximum absorption at . nm).
4.4.2. Clinical Ecacy. When the Nd:YAG laser (% HP)
was used for bleaching, Strobl et al. [] found no supportive
inuence of the laser radiation on the bleaching. e authors
registered a change in the colour of the bleach gel aer
laser activation, being a result of the increased formation of
chemicals radicals, but could not explain why this does not
translateinimprovedclinicalresult.
e use of a low-intensity red diode laser ( nm, %
HP) with a green-coloured bleach gel resulted in a change of
colour (Δ𝐸 wasincreasedfrom.to.aerweek)[].
Overall shade change values recorded by spectropho-
tometer reading expressed as Δ𝐿,Δ𝑎,Δ𝑏,andΔ𝐸 were sig-
nicantly higher for diode laser ( nm, % HP) bleaching
than PAC activation (– nm, % HP), LED activation
e Scientic World Journal
(– nm, % HP), and no light activation (% HP),
although shade guide evaluations did not exhibit any dier-
ences []. One session of min of in-oce bleaching with
or LED ( nm, % HP) ( min irradiation to each group of
teeth) or diode laser ( nm, % HP) ( sec irradiation
pertooth)asinitiatorfollowedby%CPhome-bleaching
during days was not more eective than % CP home-
bleaching alone during days [].Bleachingwithannm
diode laser and % HP showed greater shade improvement
for teeth with hue A shade than those with hue C and D. e
bleaching process is better in younger patients and gender is
not a factor that aects the bleaching process [].
LED/laser at nm (one wavelength mentioned) did not
show any improvement in bleaching result for the treatment
of vital teeth as compared to halogen light, LED, and non-
light-activated % HP. All treatments resulted in an increase
of Δ𝐸 (best score for the non-light-activated protocol), which
was maintained for month and then dropped at months
(from on average at month to . at months for the
light-activated systems and from . to . for the non-
light-activated group) []butalsomeaningthattherewas
only a slight colour rebound. LED/laser (nm/ nm)
did not improve the in-oce bleaching results with % HP
as compared to QTH (quartz-tungsten-halogen) light and at
home bleaching with % CPO []. A change in colour was
registered for all protocols, which was maintained over a -
month period []. In another investigation LED/laser (–
nm/ nm, % HP) did not improve the bleaching
eectiveness during any phase of the study []ascompared
totwodierentLEDs(–nmatmWand–
nmatmW,with%HP)andahalogenlamp(–
nm at mW, % HP) and additional sessions did not
improve the results obtained in the rst session. Change of
color was registered for all systems. In a study by Mondelli
et al. []in-ocebleaching(%and%HP)withand
without activation with a LED/laser ( nm/ nm) was
compared with home bleaching (% CPO). All techniques
and bleaching agents were eective. ere was no dier-
ence in Δ𝐸 between non-light- and light-activated in-oce
treatment. e initial increase in Δ𝐸 decreased over a time
period of months (from on average . to for the high
concentration HP, from . to . for the home bleaching
procedure with % CPO).
Visible green light KTP laser ( nm, % HP) com-
bined with sulphorhodamine B-photosensitizer bleaching
gel activated for sec at W provided a clinically useful
improvement in tooth shade in teeth with tetracycline discol-
orations [,]. KTP was more ecient than a nm diode
laser for the removal of discolourations due to red fruits,
tea, and coee []. KTP is more ecient for tetracycline
discolouration than a high powered green LED for the
bleaching of tetracycline-stained dentine [].
5. Discussion
Light sources are marketed with the idea that light plays a
signicant role in tooth bleaching as catalyst for the ioniza-
tion of HP in the bleaching gel and increasing the bleaching
eect. Studies on light sources with incoherent light sources
have produced contradictory results, but the following con-
clusions were drawn on the basis of a systematic review: ()
both light-activated and non-light-activated systems showed
similar immediate and short-term bleaching eects when
high concentrations of HP (–%) were used as bleaching
gel; () there is limited evidence that a light-activated system
produced better immediate bleaching ecacy than when
non-light-activated systems with a lower concentration of HP
(–%) were used [].
Two key factors determining overall tooth bleaching
ecacy from peroxide containing gels are the concentration
of the HP and the duration of application.
For as far as the specic topic of laser activated bleaching
is concerned, contradictory results are found as was also seen
with conventional bleaching procedure using high hydrogen
peroxide concentrations. In addition, the number of laser
activated bleaching studies is limited as compared to the
literature on light-activated bleaching. Comparisons between
the eects of dierent wavelengths are dicult to make: ()
for laser bleaching absorption in the bleaching gel is aimed
to drive the ionization of the HP; this depends on the specic
wavelength needed to directly photolyze or photooxidate the
chromophores in the dentine; () the chosen wavelength
has to coincide with the absorption peak of chromophores
or photocatalysers in the bleaching gel (if present) in order
to catalyse the ionisation of the hydrogen peroxide and to
drive the photolysis; () there is the heterogeneity of the
heating temperature of the gel, that is, the photothermal eect
which is even so inuenced not only by the wavelength,
but also by the specic power settings; () because of the
previously mentioned heterogeneity of the laser settings, seen
when a specic laser wavelength is considered, the bleaching
gel must be developed taking into account the specic
laser wavelength; () in addition, power density or energy
density (uence) of the laser beam is important; temporal
characteristics of the laser beam are to be considered such
as continuous versus pulsed delivery and consequently the
pulserateandthepulseduration;othervariablesthatrelateto
dierences in the method of energy transfer such as contact
versus noncontact delivery mode, focused versus unfocused,
andbeamdiameterhavealsotobeconsidered.Lastbutnot
least there are the dierences in the exposure time of the gel
to the laser light and the specic bleaching protocol (e.g., one
exposure or consecutive exposures of a fresh bleaching gel do
also contribute to the heterogeneous data).
In general, laser bleaching is performed with a hand
piece or a bre in noncontact mode, unfocused, and with
continuous emission. Regarding the power or energy, high
power lasers are generally used, except when bleaching is
performed with the argon laser ( or . nm) or with a
, , or nm diode laser.
All studies selected for this survey on laser bleaching have
in common the fact that a high HP concentrated bleaching
gel is used ( to % HP and or % CP, i.e., to %
HP). None of the clinical studies used low concentrations
of HP. For HP concentrations of %, it is known that light
activation produced better immediate bleaching eects [].
e EU Council Directive //EU of September ,
[], restricts the use of bleaching and bleaching products:
e Scientic World Journal
onlydentistsmayuseproductsfortoothbleachingandonly
bleaching products that contain or release between .% and
% HP and products for tooth bleaching and bleaching that
contain or release up to .% HP are available as over-the-
counter products. Products with HP concentrations over
% are prohibited as cosmetics. is clearly means () that
products containing or releasing more than % are prohibited
for dental bleaching and () that dental bleaching is not
considered as a medical action but only as cosmetical and
hence nonhealing procedure. Information on laser activation
ofbleachingproductsupto%withlasershasnotbeen
published.
A number of wavelengths can be considered as not rec-
ommended for laser bleaching: Nd:YAG (, nm), Er:YAG
(, nm), and CO2(, nm). e eect of these laser
wavelengths is purely based on heating of the bleaching gel
(Nd:YAG) or should only be restricted to heating of the
bleaching gel (Er:YAG and CO2: care has to be taken not to
remove tooth substance with Er:YAG and CO2because both
wavelengths are well absorbed by water and hydroxylapatite
which might result in supercial ablation of tooth substance).
Although the CO2-laser received an FDA approval for
bleaching, the ADA soon aer recommended not to use this
wavelength for bleaching.
From all bleaching wavelengths the diode wavelengths
have been most extensively investigated. A large range of
diode wavelengths are used as laser bleaching wavelengths.
ese near-infrared lasers are used at low power or at high
power. Both low power and high power diode lasers do not
result in an enhanced bleaching ecacy when compared to
non-light-activated bleaching with high HP concentrations.
e question is even if low power diodes aid in the activation
of the bleaching gel. Care, however, has to be taken with the
high power diodes so as not to heat the bleaching gel at a level
at which thermal damage of the pulp might occur.
Another key factor to increase the rate of the chemical
reaction is to increase the temperature, where a rise of ∘C
can double the reaction rate. On the one hand the thickness
of the bleaching gel layer is important to ensure that the
laser light can pass through this layer. e distance between
thehandpieceorbreendandthegelisimportantwhen
the energy is considered. Laser interaction is not limited to
the gel alone and laser light has also to interact with the
discolouration in the tooth.
Adding chromophores, chosen in accordance to the
absorption peak of the gel, acts as a selective absorber near the
dental surface, preventing light penetration into the internal
toothstructure.ecolourofthegelisimportantasit
inuences the nal temperature, since dierent light sources
have dierent emission wavelengths and the absorption peak
changes following gel colour. Also here the question is if the
dyes added for photoactivation of the gel with diode lasers
are helpful in activating the bleaching gel. With high power
diode lasers, irrespective of the thickness of the bleaching gel,
care has to be taken still so as not to extensively dehydrate the
enamelduetothetemperatureeect.
Recently LED devices were associated with diode lasers
emitting in the near-infrared, which, with appropriate energy
density, are being used to desensitize the teeth under
bleaching [,]. ese studies demonstrated that near-
infraredlaserscouldreducetheinammatoryresponseofthe
pulpal tissue, reducing pulp damage and relieving pain aer
the bleaching process. e use of these devices (so-called LED
lasers), however, did not result in any increased bleaching
ecacy. us the question is to what extent these low power
diodes are of help in the bleaching process.
Light-activated systems were found to increase the occur-
rence of severity of tooth sensitivity []. e light source
itself can increase pulpal temperature leading to increased
tooth sensitivity []. e latter was also encountered with
diode lasers [,] and Nd:YAG [,,]. For both
wavelengths laser light is transmitted through the bleaching
gel in combination with a heating of the gel, irrespective of
the thickness of the gel leading to tooth sensitivity [,,
,]. An additional explanation is also that laser activated
bleaching may increase the expression of substance P in the
human dental pulp [,].
Taking into account all dierent wavelengths used for
laser activated bleaching, the KTP laser when used at
appropriate settings and combined with the red coloured
bleaching gels (Smart Bleach, SBI) has been shown to be
one of the best options for photoactivated dental bleaching.
Wals h [ ] demonstrated a higher bleaching eect with KTP
than with a diode laser based on DOTCAM analysis, a
result which was also conrmed in other studies [,,
]. Its ecacy was also demonstrated for the bleaching of
tetracycline discoloured teeth []. Temperature elevation in
the pulp chamber was also under control when appropriate
settings were used in conjunction with a red coloured gel
(containing sulphorhodamine B as a chromophore) [,
]. e safety of the procedure was demonstrated by an
unaltered enamel surface aer KTP laser bleaching []; no
signicant dierences in the enamel microhardness pre- and
posttreatment [] and no changes in the compositional
structure of dentin surfaces were found []. Occasional mild
postoperative sensitivity was seen during the h following
theprocedureasradicalsareneutralizedbycatalaseandother
pulpal enzymes [,]. Catalase had been found to protect the
dentalpulpduringvitalbleachingprocedures[]. A catalase
application was demonstrated to eliminate residual hydrogen
peroxide during non-vital bleaching procedures [].
6. Conclusions
() It is dicult to draw conclusions for laser bleaching
on eciency and ecacy from the present-day lit-
erature because of the dierence in concentrations
in hydrogen peroxide used, the dierence in wave-
lengths of lasers (especially the diodes) used, the
dierence in laser settings and protocols used, and
dierences in bleaching gels used with or without
photocatalyst.
() Comparative studies evaluating bleaching techniques
with high concentrations of hydrogen peroxide and
with or without the use of light activation resulted in
enhanced lightening. Most oen comparable results
were found irrespective of light exposure.
e Scientic World Journal
() No long-term evaluations for laser enhanced bleach-
ing procedures are available.
() Based on the limited number of investigations, at
present, only one particular wavelength appears to be
abletoperformdirectphotobleaching(orphotooxi-
dation), that is, KTP ( nm). When KTP is used in
combination with a bleaching gel containing a chro-
mophore(sulphorhodamine)allowingtheabsorption
of the laser light, photodynamic reactions can be
induced (photochemical activation of the gel with
limited photothermal activation). is combination
of wavelength and specically dyed bleaching gel also
allows for safe bleaching (no damage of the enamel,
no heating of the pulp) when the guidelines of the
manufacturer are followed.
()Atpresentanumberofwavelengthsarenotrecom-
mended for laser bleaching: Nd:YAG, Er:YAG, and
CO2. Combination devices consisting of LED-diode
laser do not result in enhanced lightening and are in
fact not eective. When using high power diode lasers
for bleaching care has to be taken so as not to overheat
the pulp. Also diode lasers are not really advocated
for laser bleaching except when the wavelength is
used in combination with a bleaching gel containing
wavelength specic absorbers.
() With the exception of KTP used in combination with
agelwithaspecicallyredcolouredlightabsorber
(sulphorhodamine B) for the green light ( nm),
laseractivatedbleachingissolelybasedonheatingof
the bleaching gel.
() All studies have been conducted with high concen-
trated hydrogen peroxide gels. is means that the
so tissues have to be thoroughly protected during the
in-oce power bleaching procedure. No studies were
conducted to investigate the safety of laser bleaching
procedures on the so tissues adjacent to the laser
activated bleaching gel.
7. Recommendations for Future Investigations
ree factors are to be considered when using a light source
and should be mentioned in the studies: light intensity,
spectral distribution, and irradiation time. Since the total
energy depends on light intensity and irradiation time, light
curing units with high intensity may allow a reduction in
irradiation time. Second generation LEDs present higher
power than rst generation LEDs. Further research is needed
to evaluate if high power (narrow band) LEDs can be used for
light-activated bleaching. With the price of a number of laser
devices in mind, this technology might be of interest for the
activation of bleaching gels.
An important relationship exists among gel colour, laser
wavelength, thermal transmission, and clinical ecacy, but
not between gel temperature, shade change, and HP concen-
tration. In this respect the use of absorbing substances to
increase the radiation absorption (and the temperature in the
gel) is known. With the use of TiO2it has been demonstrated
that there is another way to improve dental bleaching without
the risk of damaging the pulp. Hence the composition of
the gel with the absorbers and additional compounds (agents
enabling to catalyse the redox reaction) should also be given
in detail.
Conflict of Interests
e authors declare that there is no conict of interests
regarding the publication of this paper.
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