Tooth-Bleaching: A Review of the Efficacy and Adverse Effects of Various Tooth Whitening Products

Abstract

Tooth bleaching (whitening) is one of the most common and inexpensive method for treating discolouration of teeth. Dental aesthetics, especially tooth colour, is of great importance to majority of the people; and discolouration of even a single tooth can negatively influence the quality of life. Therefore, a review of the literature was carried out (limited to aesthetic tooth-bleaching) to provide a broad overview of the efficacy and adverse effects of various tooth whitening products on soft and hard oral tissues.

Full text

INTRODUCTION
Dental aesthetics, including tooth colour, is of great
importance for majority of the people and any
discolouration or staining can impact their quality of life
negatively. The colour of teeth reflects a combination of
its intrinsic colour and the presence of extrinsic stains
due to various factors such as smoking, intake of tannin-
rich foods and drinks (e.g. red wine), and the use of
chlorhexidine or metal salts such as tin and iron.1-3 A
number of methods can be used to remove staining like
professional cleaning and polishing, whitening tooth-
pastes, internal bleaching of non-vital teeth, external
bleaching of vital teeth, and micro-abrasion of enamel.
Severe stains can be covered with crowns or veneers,
but this is a more invasive and costly option.4,5
The increasing demand for a better appearance and
whiter smile, has made vital tooth-bleaching (also
referred to as tooth-whitening) a popular dental
procedure. It has developed into one of the fastest
growing areas of aesthetic dentistry. It provides a more
conservative treatment approach for discoloured teeth
as compared to other restorative treatment modalities
such as composite fillings, veneers or crowns.1
Commonly used methods for tooth-whitening include
in-office or power bleaching,6dentist-supervised home
bleaching or nightguard vital bleaching,7and easily
available over-the-counter (OTC) whitening products for
self-application.
METHODOLOGY
This literature review was limited to aesthetic tooth-
bleaching and aimed to provide a broad overview of
bleaching techniques, their efficacy, and adverse effects
on soft and hard tissues as well as the management of
tooth sensitivity and gingival irritation. In formulating
this review, only English-language articles available
electronically were selected. The PubMed database and
Google scholar search engine were explored with
keywords which included: tooth-whitening, tooth-
bleaching, carbamide peroxide, hydrogen peroxide,
bleaching and dentistry, home-bleaching, and vital
bleaching. Over 200 articles were initially reviewed and
82 articles were shortlisted on the basis of their
applicability to the present topic of review and then
studied in detail.
Efficacy of different types of tooth-whitening
products: Nightguard vital bleaching using 10% CP is
the most widely used and extensively researched tooth-
bleaching technique. The American Dental Association
has awarded its seal of acceptance to a number of
dentist-supervised home bleaching products containing
10% CP.8Nightguard vital bleaching techniques
have been effective for bleaching teeth stained by aging,
mild fluorosis, trauma, inherent discoloration and
tetracycline.9,10 According to the American Dental
Association guidelines for the acceptance of peroxide-
containing oral hygiene products, the clinical efficacy
may be demonstrated by a change of two value oriented
shade increments and a perceptible colour must be
maintained in 50% of the recall population at 6 months
compared to the control, to reflect the duration of
efficacy.11 In a long-term clinical trial, Leonard et al.,12
reported whitening of teeth in 98% of the participants by
10% CP and 82% of the participants retained the
whitening effect upto 47 months post-treatment. A meta-
analysis of the clinical trials from 1989-1999 on dentist-
supervised home bleaching products using 10% CP
Journal of the College of Physicians and Surgeons Pakistan 2015, Vol. 25 (12): 00 1
REVIEW ARTICLE
Tooth-Bleaching: A Review of the Efficacy and Adverse Effects
of Various Tooth Whitening Products
Abdul Majeed1, Imran Farooq2, Sias R. Grobler3and RJ Rossouw3
ABSTRACT
Tooth bleaching (whitening) is one of the most common and inexpensive method for treating discolouration of teeth. Dental
aesthetics, especially tooth colour, is of great importance to majority of the people; and discolouration of even a single
tooth can negatively influence the quality of life. Therefore, a review of the literature was carried out (limited to aesthetic
tooth-bleaching) to provide a broad overview of the efficacy and adverse effects of various tooth whitening products on
soft and hard oral tissues.
Key Words: Tooth bleaching. Whitening. Peroxide. Discolouration.
1Department of Restorative Dental Sciences / Biomedical
Dental Sciences2, College of Dentistry, University of Dammam,
Saudi Arabia.
3Oral and Dental Research Institute, Faculty of Dentistry,
University of Western Cape, South Africa.
Correspondence: Dr. Imran Farooq, Department of Biomedical
Dental Sciences, College of Dentistry, University of Dammam,
Saudi Arabia.
E-mail: drimranfarooq@gmail.com
Received: December 10, 2014; Accepted: September 03, 2015.

suggested that only 73% of the population will show a
colour change of two units or greater and 50% retain
colour at 6 months postbleaching.13 Higher CP
concentrations (15% and 20%) available for home-
bleaching may whiten teeth slightly quicker than 10% CP
during the early phase of treatment. However, the
whitening effect shows some relapse after the cessation
of active bleaching treatment before the colour is
stabilized. Teeth treated with 10% CP, stabilize in colour
for 2 weeks following the cessation of the treatment but
the higher-concentration products last much longer.14
However, it is claimed that rapid whitening shown by the
higher-concentration products is temporary and
following rebound, there will be no difference.15
HP and CP tooth-bleaching products with equivalent
peroxide concentrations demonstrate similar whitening
efficacy with few side effects.16,17
A large number of OTC whitening products, including
whitening strips or tray less whitening systems, paint-on-
gels, gels with pre-fabricated trays and whitening
toothpastes, have become increasingly popular in recent
years because of their low cost to the consumer, and
overwhelming marketing by manufacturing companies.
Whitening strips usually contain 6 - 14% HP in gel form.
An integrated clinical summary of nine randomized
clinical trials reported the efficacy of whitening strips
containing 14% HP similar to popular tray-based
bleaching systems.18 A clinical comparison of two brush-
applied whitening systems showed that a 19% sodium
percarbonate system, that dries to form an adherent film,
provided significant improvement in tooth colour
compared to 18% CP gel.19 Zantner et al.20 reported that
a new bleaching lacquer, containing 8% CP for self-
application without the use of a mouth guard, produced
two shade improvements in tooth colour.
A recent systematic review8of home-based chemically-
induced whitening of teeth demonstrated that dentist-
supervised home bleaching systems and OTC products
(paint-on gels and whitening strips) are effective when
compared with placebo or no treatment and the efficacy
varies because of different levels of active ingredients.
However, the majority of the studies are either
sponsored or conducted by the manufacturers and are
of shorter term.8Furthermore, tooth-whitening products
are not regulated in many countries and most of these
products have not undergone clinical evaluation for
safety and effectiveness. Therefore, there is a great
need for independent laboratory and clinical trials which
could provide a good indication of what could be
expected in practice.
In-office bleaching procedures are performed using
higher HP (30 - 38%) concentrations at chair-side under
the close supervision of a dentist. A number of clinical
studies have demonstrated the effectiveness of in-office
bleaching alone21-23 or in combination with further use of
take-home bleaching products.24,25 Auschill et al.,26 in a
randomized clinical trial comparing the efficacy of at-
home, OTC and in-office bleaching techniques, reported
that all treatment methods were able to achieve six
grades of whitening but the time factor involved in the
treatment was significantly different with the in-office
bleaching technique requiring the least time. However,
the most accepted method amongst the patients was the
at-home bleaching technique. In contrast to these
results, another study showed that treatment with an
in-office bleaching (35% HP) product was less effective
compared to a 14-day application of 10% CP in a tray.27
Special lights and heat-generation devices are also
marketed by several companies as a necessary tool for
in-office bleaching to expedite the bleaching efficacy. A
few studies have reported the acceleration or enhancing
effect of different light or laser sources on in-office
bleaching treatments,28-30 while other studies reported
no effect of light-activation on the final outcome of
in-office bleaching with HP.31,32 Hein et al.,33
investigated the contribution of three bleaching lights
(Luma Arch, Optilux 500, and Zoom!) to act as catalysts
for whitening teeth in a split-arch clinical study. He
reported that neither the heat produced by the lights nor
the light outputs per se were responsible for catalytic
activity and the tested lights did not lighten teeth more
than their irrespective bleaching gels alone. Inspite of
contradictory reports in the literature, to date there is no
concrete evidence to show that these devices improve
the final outcome of in-office bleaching treatment.34,35
In-office bleaching products are accepted by the
American Dental Association but due to the
discontinuation of the professional component of the
Seal Program on December 31, 2007, these bleaching
products are not eligible for the ADA Seal.36
Adverse effects: Adverse effects of vital tooth
bleaching procedures on hard and soft tissues of the
oral cavity have been reported in the literature.37 Tooth
sensitivity and gingival or mucosal irritation are the most
common side effects of vital tooth-bleaching. Other
effects include minor orthodontic tooth movement,
temporomandibular dysfunction due to long-term tray
use, and sore throat.38
Tooth sensitivity: Tooth sensitivity occurs in two-third of
the patients treated with home bleaching products. The
majority (55%) may experience mild sensitivity whereas
10% experience moderate and only 4% may experience
severe sensitivity.37 Symptoms are noticed early in the
treatment, usually after 2 - 3 days, and may persist 3 - 4
hours following removal of the tray and disappear shortly
after the treatment ends.39 The aetiology of tooth
sensitivity following bleaching treatment is multifactorial
and is poorly understood.40 Sensitivity is thought to be
caused by the diffusion of by-products produced during
HP and CP breakdown through dentinal tubules.41
Abdul Majeed, Imran Farooq, Sias R. Grobler and RJ Rossouw
2Journal of the College of Physicians and Surgeons Pakistan 2015, Vol. 25 (12): 00

Glycerine, used as a carrier in most bleaching agents, is
hydrophilic and causes dehydration of tooth structure
during bleaching treatment. This can also result in tooth
sensitivity.42 The use of bleaching products with higher
peroxide concentration also increases the risk of tooth
sensitivity.43
Patients with existing sensitivity should be treated
before starting bleaching treatment: Desensitizing
toothpastes and fluoride gels can be used for 2 - 3
weeks prior to the treatment or during treatment.
A neutral sodium fluoride gel in a tray can be worn
overnight or gels containing 3% to 5% potassium nitrate
or fluoride and potassium nitrate in a tray before or after
bleaching for 10 - 30 minutes. Furthermore, the
frequency and / or duration of application can be
reduced and the treatment can also be interrupted, if
necessary.
Gingival or mucosal irritation: Some patients may
experience gingival or mucosal irritation during home
bleaching procedures. Soft tissue irritation may be
caused by an ill-fitting tray impinging on the gingiva
and/or the use of excess material.39 Management
includes simply adjusting and polishing the tray and or
instructing the patient to use less material. During an
in-office bleaching procedure, a higher HP concentration
is usually used. HP is a caustic substance and can
cause burns of the gingival or mucosal tissue.44
Therefore, a rubber dam or light-cured resin, provided by
the manufacturer, should always be used to protect soft
tissues during in-office bleaching procedures.
Effects on tooth structure: Bleaching of vital teeth
involves direct contact with the enamel surface for an
extensive period of time which differs according to
products. This fact increased concerns about the
possible adverse effects of such a strong oxidizing agent
on the enamel or dentine. The available literature is
contradictory. Some scanning electron microscope
studies reported changes in surface morphology of
enamel following bleaching with CP45,46 and/or HP
products47 while others reported no alterations in the
enamel morphology.48,49 Hegedüs et al.,50 in an atomic
force microscopy study, demonstrated that CP and HP
were capable of causing alterations in enamel surface.
In a recent study,51 it was found that all four different
kinds of opalescence teeth whiteners damaged enamel.
The most damage was done by the 10% and 20% CP
products because of the much longer exposure period of
112 hours in comparison to only 7 hours for the
Opalescence Quick PF 45% CP and Treswhite Supreme
10% HP. Certain studies have also reported negative
effects on enamel and dentine microhardness,52-56 while
others reported no change in the microhardness of
enamel57,58 and dentine.59 Lewinstein et al.60 reported
that in-office bleaching products, i.e. 35% HP and
35% CP, reduced hardness of enamel and dentine
significantly more than the home bleaching products, i.e.
10% CP, but the application of 0.05% fluoride solution for
5 minutes completely restored the softened tooth
structure. In an in vitro study, Sulieman et al.61 reported
that 35% HP did not damage enamel or dentine and the
adverse effects reported in the literature may be related
to the pH of the products used. A small reduction in
dentine surface microhardness following exposure to
10% CP in situ was reported by Arcari et al.,62 but they
concluded that this might be clinically insignificant.
Current literature indicates that the experiments vary
greatly in their methodology, the type of bleaching agent
used, the duration of application, load applied and the
position of indents. However, human enamel exhibits
large regional variations in structure related to the
differences in local chemistry (varying levels of
mineralization, organic matter and water) and
microstructure (fractions of inorganic crystals and
organic matrix).63,64 Therefore, enamel microhardness
may vary from area to area. This may be the reason for
controversies found in the literature. There is a great
need to develop a standardized protocol to evaluate the
effects of tooth-bleaching products on microhardness of
enamel and dentine.
Effects on restorative materials: Increasing use of
peroxide bleaching agents has raised concerns about
their effects on different restorative materials. Several
in vitro studies have evaluated the effects of CP (10 - 16%)
and HP (30 - 35%) whitening products on the physical
properties, surface morphology and colour of different
restorative materials.65 Haywood66 reported that a
nightguard vital bleaching technique had no significant
effect on the colour and physical properties of porcelain,
amalgam and gold. An increase in the surface
roughness of porcelain, microfilled composite and
modified glass ionomer following treatment with 10-16%
CP was reported by Turker and Biskin.67 Modified glass
ionomer also showed increased surface porosity and
cracks in certain areas. Controversy exists about the
influence of external pre- and post-operative bleaching
on microleakage of composite restorations. Crim68
reported that pre-restorative bleaching with 10% CP did
not affect the marginal seal of subsequently placed
restorations. Ulukapi et al.69 reported that pre- and post-
operative bleaching with CP increased marginal leakage
of resin composite restorations at enamel and dentine
margins but amalgam restorations showed no
alterations. In contrast, other studies did not report
increased microleakage rate at enamel margins.70
The oxidation of surface pigments and amine compounds
by bleaching agents can alter the colour of restorative
materials. The oxidizing effect on the polymer-matrix
of resin-based materials also increases surface
porosities.64 There is no clear evidence indicating
whether the changes in tooth-coloured restorative
Tooth-bleaching
Journal of the College of Physicians and Surgeons Pakistan 2015, Vol. 25 (12): 00 3

materials are superficial or deep. However, polishing of
resin composite fillings is advisable following bleaching
procedures to decrease the adherence of certain
cariogenic micro-organisms.
Bleaching agents also cause increased release of
mercury from amalgam restorations.71 Coating of
amalgam restorations with a protective varnish such as
Copalite before bleaching procedure has been reported
to reduce release of mercury into the surrounding
environment.72 The corrosion potential of amalgam is
also decreased if restorations are polished prior to the
bleaching therapy.
Effects on bond strength: The effect of various
bleaching procedures on shear or tensile bond strength
of composites to enamel and dentine has been studied
extensively. The majority of the studies reported that the
bond strengths of composite restorative materials to
enamel and dentine73-76 was significantly reduced when
applied immediately after bleaching with HP or CP.
Josey et al.77 reported no negative effects of 10% CP
bleaching on composite-enamel bond strength.
However, controversy exists about the effects of alcohol-
or acetone-based bonding agents on the bond strengths
to enamel and dentine.64
Several factors are responsible for the reduction in
composite bond strengths to enamel and dentine.
Polymerization inhibition of the resin adhesive systems,
due to the presence of oxygen released by the bleaching
process on the enamel surface and within the dentinal
tubules, is the likely mechanism for the reduction in bond
strength.78 Significant loss of enamel calcium and
phosphorus content and morphological alterations of the
majority of the crystals of the surface layer caused by
the peroxide-based bleaching agents also adversely
affects the bond strength.79 Adebayo et al.,80 reported
that the use of conditioners prior to bonding with self
etching adhesive system to bleached enamel may
significantly improve bond strength. However, the
reduction in bond strength is time-dependent and
returns to normal after a few days, when the residual
oxygen is liberated. Recommended waiting time before
performing bonding procedures after tooth bleaching
ranges from 3 to 7 days,81 7 - 14 days78 to 3 weeks.82
Therefore, it is advisable to wait for a while before
performing bonding procedures after bleaching.
CONCLUSION
Different treatment modalities are available to the patient
designing a whiter smile. Tooth sensitivity and gingival or
mucosal irritation are the most common side effects of
vital tooth-bleaching. However, ADA recognised
products tend to include agents to minimize or prevent
these side effects. Dentists should educate themselves
to be able to inform their patients about the benefits and
risks of different whitening methods based on the current
scientific evidence and to suggest the best treatment
option based on a correct diagnosis.
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Abdul Majeed, Imran Farooq, Sias R. Grobler and RJ Rossouw
6Journal of the College of Physicians and Surgeons Pakistan 2015, Vol. 25 (12): 00