An overview of tooth-bleachingtechniques: chemistry, safety andefficacy

MU N T H E R A.M. SU L I E M A N

Tooth discolouration results from varied and com-

plex causes that are usually classified as being either

intrinsic or extrinsic in nature. Extrinsic discoloration

arises when external chromogens are deposited on

the tooth surface or within the pellicle layer. Intrinsic

discoloration occurs when the chromogens are

deposited within the bulk of the tooth (usually in the

dentine) and are often of systemic or pulpal origin (1,

150). A third category of �stain internalization� has

been described to include those circumstances where

extrinsic stain enters the tooth through defects in the

tooth structure (1).

Tooth discoloration creates a wide range of cos-

metic problems, and, as the dental profession and

the public strive for a more esthetically pleasing

appearance, considerable amounts of time and

money are being invested in attempts to improve the

appearance of discolored teeth. A study assessing the

impact of teeth on personal esthetic satisfaction

found that dental variables (including tooth color)

were more important than orthodontic variables,

suggesting that the appearance of the teeth was a

greater contributing factor to an esthetic smile than

their position within the arch (101). In another study,

of 254 patients, it was found that the appearance of

the dentition was more important to women than to

men and that the esthetics of the dentition was more

important to younger patients (147).

The methods available to manage discolored teeth

range from the removal of surface stain, bleaching or

tooth-whitening techniques and surgical techniques

to camouflage of the underlying discoloration, using

veneers and crowns.

The use of a variety of bleaching techniques has

attracted most interest from the dental profession

because these techniques are noninvasive and rela-

tively simple to carry out. Contemporary bleaching

systems are based primarily on hydrogen peroxide or

one of its precursors, notably carbamide peroxide,

and are often used in combination with an activating

agent such as heat or light. Bleaching agents can be

applied externally to the teeth (vital bleaching), or

internally within the pulp chamber (nonvital

bleaching) (41, 54). Both techniques aim to bleach

the chromogens within the dentine, thereby changing

the body color of the tooth.

Tooth discoloration

Natural color of teeth

Teeth are made up of many colors, with a natural

gradation from the darker gingival third to the lighter

incisal third of the tooth. This variation is affected by

the thickness and translucency of enamel and den-

tine, as well as by the reflectance of different colors.

Typically, canine teeth are naturally darker than

central and lateral incisors and teeth become darker

with age, whereas lighter teeth are common in

younger people, especially in the primary dentition.

The color of teeth is primarily determined by the

dentine but is influenced by the color, translucency

and varying degrees of calcification of enamel as well

as its thickness, which is notably greatest at the

occlusal or incisal edge. The normal color of teeth is

determined by the blue, green and pink tints of

enamel and is reinforced by the yellow through to

brown shades of the dentine beneath.

Classification of tooth discoloration

The appearance of teeth depends on their absorptive

or reflective properties of light and is influenced by

148

Periodontology 2000, Vol. 48, 2008, 148–169

Printed in Singapore. All rights reserved

� 2008 The Author.

Journal compilation � 2008 Blackwell Munksgaard

PERIODONTOLOGY 2000

all the structures that make up the tooth, including

the enamel, dentine and pulp. Any changes to these

structures during formation or throughout develop-

ment and post-eruption (3 months in utero to 20

years) can cause a change in the light-transmission

properties and hence discoloration.

Table 1 shows the types of tooth discoloration and

the typical tooth colors they produce.

Intrinsic discoloration

Intrinsic discoloration occurs following a change to

the structural composition or thickness of the den-

tinal hard tissues during tooth development.

This classification can be further subdivided into

the following categories:

• metabolic causes.

• inherited causes.

• iatrogenic causes.

• traumatic causes.

• idiopathic causes.

• ageing causes.

Metabolic causes of discoloration

A number of metabolic disorders, such as alkap-

tonuria, congenital erthropoietic porphyria and

congenital hyperbilirubinemia, cause tooth discol-

oration. Alkaptonuria is an inborn error of metabo-

lism that results in a brown discoloration of the

permanent dentition (79), whereas congenital

erythropoietic porphyria, a rare, recessive, autoso-

mal metabolic disorder, gives a red ⁄ purple–brown

discoloration of teeth (37). Congenital hyperbiliru-

binemia is characterized by yellow–green discolor-

ation caused by the deposition of bile pigments in

calcifying dental hard tissues, particularly at the

neonatal line, as a result of massive hemolysis in

rhesus incompatibility.

Inherited causes of discoloration

Amelogenesis imperfecta is a hereditary condition

in which the mineralization or matrix of enamel

formation is disturbed. There are currently 14 dif-

ferent subtypes based on clinical appearance, with

the majority inherited as an autosomal-dominant or

X-linked trait with varying degrees of expressivity

(139, 158, 160). The appearance can be badly

affected with hypoplastic thin enamel that is yellow

to yellow–brown in color or the enamel can be quite

mildly hypomineralized (�snow-capped�), depending

on the type of amelogenesis imperfecta present.

The color of the teeth is presumed to reflect the

degree of hypomineralization of the enamel: the

darker the color the more severe the degree of

hypomineralization (18).

Dentine defects can either be inherited or caused

by environmental factors (120). Genetically deter-

mined defects may occur in isolation or may be

associated with a systemic disorder.

Dentinogenesis imperfecta is an inherited disorder

of dentine, which may or may not be associated

with osteogenesis imperfecta (18). Dentinogenesis

imperfecta type I is associated with osteogenesis

imperfecta (mixed connective tissue disorder of type

I collagen) and is characterized by opalescent pri-

mary teeth, especially when the condition is the

result of a dominant inheritance pattern. Dentino-

genesis imperfecta type II or hereditary opalescent

dentine may be more severe in the primary than in

the secondary dentition, the pulp chambers often

become obliterated and the dentine undergoes rapid

wear once the enamel has chipped away. Clinically,

the appearance is an amber, grey to purple–blue

discoloration or opalescence, thought to be a result

Table 1. Colours produced by various causes of toothdiscolouration

Types of discolouration Colour produced

Extrinsic (direct stains)

Tea, coffee and other foods

Cigarettes ⁄ cigars

Plaque ⁄ poor oral hygiene

Brown to black

Yellow ⁄ brown to black

Yellow ⁄ brown

Extrinsic (indirect stains)

Polyvalent metal salts and

cationic antiseptics

(e.g. chlorhexidine)

Black and brown

Intrinsic

Metabolic causes

(e.g. congenital

erythropoietic porphyria)

Inherited causes

(e.g. amelo ⁄dentinogenisis)

Iatrogenic causes

Tetracycline

Fluorosis

Traumatic causes

Enamel hypoplasia

Pulpal haemorrhage

products

Root resorption

Ageing causes

Purple ⁄ brown

Brown or black

Banding appearance

Classically yellow, brown,

blue, black or grey

White, yellow, grey or black

Brown

Grey black

Pink spot

Yellow

Internalized

Caries

Restorations

Orange to brown

Brown, grey, black

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An overview of tooth-bleaching techniques

of the absorption of chromogens into the porous

dentine after exposure of the dentine. This condition

is clearly demonstrated by opalescence on trans-

illumination.

Unlike dentinogenesis imperfecta type II, denti-

nogenesis imperfecta type I shows enamel that is

much less prone to fracture and the dentine seldom

obliterates pulp chambers; hence, radiographic

examination can differentiate between the two types.

A third type of dentinogenesis imperfecta has been

described (157) that is similar in appearance to

dentinogenesis imperfecta types I and II but with the

radiographic appearance of �shell teeth� with multiple

pulpal exposures in the primary dentition.

There is some controversy as to whether dentinal

dysplasias are a separate entity from dentinogenesis

imperfecta (18). The primary and secondary denti-

tions in type I dentinal dysplasia are of normal

shape and form but have an amber translucency.

The pulp chambers in the primary dentition are

frequently obliterated while only crescentic pulpal

remnants are found parallel to the cemento–enamel

junction of the secondary dentition. Type II dentinal

dysplasias are thought to involve thistle-shaped pulp

chambers and pulp stones with a brown tooth dis-

coloration (126).

Iatrogenic causes of discoloration

Tetracycline staining results from systemic adminis-

tration of the drug and its subsequent chelation to

form complexes with calcium ions on the surface of

hydroxylapatite crystals primarily within dentine, al-

though enamel is also affected (140). Tetracycline

should be avoided in expectant and breast-feeding

mothers, and in children up to the age of 12 years, to

avoid discoloration of the developing teeth. The dis-

coloration produced depends on the type of tetracy-

cline used, the dosage and the period of time for

which it is taken, as well as the age of the patient at

the time of administration. Generally, the affected

teeth tend to be yellow or brown–grey in color and

the appearance is worse on eruption and diminishes

with time. This is because once erupted the teeth are

susceptible to color changes by photo-oxidation

(exposure to light), causing lightening of the intrinsic

stain. Various analogues of tetracycline produce dif-

ferent color changes, for example, chlorotetracycline

produces a slate-grey color, and a creamy discolor-

ation is produced by oxytetracycline (10, 94).

Tetracycline staining has also been classified

according to the extent, degree and location of the

tetracycline involvement (64).

• degree I: there is minimal expression of tetracy-

cline stain, which is uniformly confined to the

incisal three-quarters of the crown and is light

yellow in color.

• degree II: there is more variability in staining,

ranging from a highly uniform deep yellow to a

grey-banded discoloration in which a distinctive

difference in discoloration is noted between the

cervical region and the incisal four-fifths of the

crown.

• degree III: there is very dark blue or grey uniform

discoloration.

Post-eruptive staining with minocycline used for the

treatment of acne in adolescents and adults has been

described as a result of chelation with iron to form

insoluble complexes (14) or by the formation of

complexes of the drug with secondary dentine (117).

Fluorosis may be the result of the natural occurrence

of fluoride in water supplies or from fluoride in

mouthrinses, tablets or toothpastes. This type of

staining is most often confined to the enamel, varying

from areas of flecking to diffuse opaque mottling

superimposed onto a chalky white or dark brown–

black background. The dark discoloration is thought to

be post-eruptive by a process of internalization of

extrinsic stain into the porous enamel (151). The

severity of the discoloration is related to the age and

dose administered and can affect both the primary and

secondary dentitions in endemic cases of fluorosis.

Traumatic causes of discoloration

One of the most common causes of tooth discolor-

ation seen in everyday general practice is that caused

by pulpal hemorrhagic products following trauma.

The major cause of the discoloration is thought to be

the accumulation of the hemoglobin molecule or

hematin molecules in the traumatized tooth, and

their penetration into the dentine determines the

severity of the discoloration.

Root resorption following trauma often presents as

a pink spot lesion at the cemento–enamel junction in

an otherwise symptomless tooth. The resorption al-

ways begins at the root surface but may be internal

(of pulpal origin) or external (of periodontal origin).

Enamel hypoplasia in permanent teeth may be the

result of disturbance of the developing tooth germ

following trauma or infection of the deciduous tooth,

giving rise to a localized enamel defect. Pitting or

grooving may predispose to later internalization of

external chromogens. Generalized hypoplasia may

result from any disturbance of the developing tooth

germ by many different fetal or maternal conditions,

150

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such as rubella infection or even drug intake during

pregnancy. The defect is usually directly related to

the degree of the systemic upset and can be chro-

nologically traced back to the time of the upset.

Dentine hypercalcification may result following

trauma temporarily disturbing the blood supply of a

tooth and affecting the odontoblasts, giving rise to

excessive irregular dentine deposition in the pulp

chamber and canal walls. The tooth gradually

decreases in translucency and becomes yellow or

yellow–brown in color but is still vital (113).

Idiopathic causes of discoloration

Molar incisor hypomineralization is a condition of

unknown etiology that is characterized by severely

hypomineralized enamel affecting the incisors and

permanent first molars (154). The appearance of the

hypomineralized enamel is asymmetrical, affecting

one molar severely while leaving the contralateral

molar relatively unaffected or only with minor sub-

surface defects (152). The incisors also show asym-

metry but not usually with loss of enamel substance.

The enamel defects can vary from white to yellow or

brownish areas, but they always show a sharp de-

marcation between sound and affected enamel (153).

The enamel is porous and brittle, breaking down

shortly after eruption under masticatory forces, and

often resembles enamel hypoplasia but is distin-

guished by having irregular borders with normal en-

amel as opposed to smooth borders with hypoplastic

lesions (153).

The suggestions of possible etiologies for molar

incisor hypomineralization include environmental

changes during a limited time period, infections

during early childhood, dioxin in breast milk and

genetic factors.

Ageing causes of discoloration

The natural darkening and yellowing of teeth with age,

and the change in their light-transmission properties,

is the result of a combination of factors involving both

enamel and dentine. The enamel undergoes both

thinning and textural changes (96), while the deposi-

tion of secondary and tertiary dentine and pulp stones

all contribute to the darkening process of ageing.

Extrinsic discoloration

External staining may be divided into two main cat-

egories: direct staining by compounds incorporated

into the pellicle layer and producing a stain as a result

of the basic color of the chromogens; and indirect

staining where there is chemical interaction at the

tooth surface with another compound that produces

the stain.

Direct staining

Direct-staining chromogens derived from dietary

sources such as tea and coffee are taken up into the

pellicle and their natural color imparts the stain onto

the tooth surface. Smoking or chewing tobacco,

medicines, spices, vegetables and red wine are also

known to cause direct staining. It is the polyphenolic

compounds found in food that are thought to give

rise to the color of the stain (105). The actual mech-

anism of staining is not fully understood but certainly

involves pellicle constituents. Naked enamel does not

take up chromogens easily and pellicle proteins are

often cited as reacting with chromogens, but how

specific this reaction is has not been clarified and

some degree of nonspecificity is probable; the chro-

mogen is merely incorporated within the pellicle

layer much as a sponge can soak up and hold fluids.

Dentine chromogens may be absorbed into the tissue

itself as dentine is more porous than enamel, both in

respect of intertubular dentine and the tubules

themselves (125).

Traditionally, extrinsic tooth discoloration has

been classified according to its origin and whether it

is metallic or nonmetallic (47).

Nonmetallic extrinsic stains caused by beverages,

tobacco, mouthrinses and other medicines are ad-

sorbed on to the tooth surface by incorporation into

the plaque or the acquired pellicle. Chromogenic

bacteria have also been implicated in extrinsic

staining in children who have poor oral hygiene

(causing green and orange stains) and in those who

have good oral hygiene (causing black–brown stains)

but the mechanism involved has not been estab-

lished (150).

Indirect staining

Indirect dental stains are associated with cationic

antiseptics and metal salts that are either colorless or

a different color from the stain produced as a result of

a chemical interaction with another compound.

Polyvalent metal salts are known to be associated

with extrinsic staining, such as the black discolor-

ation seen in people using iron supplements and in

iron foundry workers exposed occupationally to these

metal salts. Other examples include the green dis-

151

An overview of tooth-bleaching techniques

coloration resulting from use of mouthrinses con-

taining copper salts or the violet–black color resulting

from the use of potassium permanganate-containing

mouthrinses (149).

Cationic antiseptics, such as chlorhexidine, hexe-

tidine, cetylpyridinium chloride and others mouth-

rinses, also cause staining after prolonged use.

Chlorhexidine, for example, produces the brown–

black discoloration seen around the labial and lingual

surfaces of anterior teeth after only about 7–10 days

of use.

The mechanism of staining by metal salts, and

particularly by cationic antiseptics, has attracted

much interest from the dental profession and has

been much debated (1, 150). The majority of the data

drawn from randomized controlled laboratory and

clinical studies support a dietary etiology. Thus,

staining is thought to be a result of the precipitation

of anionic dietary chromogens, such as polyphenols,

onto adsorbed cationic antiseptics or polyvalent

metal salts on the tooth surface (1, 150).

Internalized discoloration

Extrinsic stains are taken up into the enamel or

dentine via a developmental or acquired defect. The

incorporation of extrinsic stain into the porous tooth

structure of developmental defects has already been

discussed under the intrinsic staining section above.

Acquired defects of teeth resulting from function

and parafunction, dentinal caries and restorative

materials can all lead to tooth discoloration, directly

or indirectly.

• tooth wear and gingival recession: the loss of en-

amel and dentine by erosion, abrasion and attrition

can result in the exposure of dentine to extrinsic

chromogens. The exposure of dentine, or the loss

of enamel, gives rise to darker looking teeth as

more of the yellow color of dentine is apparent.

Cracks as a result of trauma to the enamel, or

gingival recession and exposure of dentine, pre-

dispose the teeth to extrinsic stain internalization.

• dentinal caries: the progression of the carious le-

sion is usually associated with changes in color,

ranging from the initial white spot lesion to the

black arrested lesion that picks up stain from an

extrinsic source (145).

• restorative materials: the classic grey–black dis-

coloration seen around old amalgam restorations

is thought to be caused by the migration of tin into

the dentinal tubules (155). Eugenol-containing

medictions cause an orange–yellow stain, and

silver points in root canals give a grey or pink

appearance to a root-treated tooth.

Development of night guard vitalbleaching

A successful home bleaching technique using

hydrogen peroxide was first described by Klusmier in

1968 (52) when it was noticed that teeth became

whiter after treatment of a mouth injury with Gly-

oxide (hydrogen peroxide mouthwash) in an ortho-

dontic retainer. The results were lighter teeth in

addition to healing of the injury. However, this

technique received worldwide acceptance when de-

scribed in 1989 by Haywood & Heyman (53), who

employed 10% carbamide peroxide in a custom-

made tray worn at night: the �night guard vital

bleaching technique� (53).

Development of power bleaching

In-surgery bleaching techniques used since the early

1900s were further modified in 1991 with the intro-

duction of 30% hydrogen peroxide gels activated by

conventional light-curing units rather than a heat

source. This technique is often referred to as �power

bleaching�. Although these power gels could be con-

trolled easily compared with the liquids used previ-

ously, full-mouth isolation was still needed to protect

the gums and the surrounding soft tissues. Power

bleaching was frequently combined with home-use

tray systems to maximize the bleaching effect and

give a kick start to the whitening procedure before the

patient continued with night guard vital bleaching at

home.

A further modification to the power bleaching

system was the use of an argon laser as an activating

light source to replace conventional curing lights

(110). The present-day systems are activated by a

variety of light sources: plasma arc lamps, Xenon-

halogen, light emitting diode (LED) light and diode

lasers. However, light sources are not essential and

there are systems that require chemical activation

only and are merely painted onto the teeth with the

usual use of gingival and mucosal isolation (22).

Current bleaching materials

The home bleaching materials currently available are

a combination of different concentrations and fla-

152

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vours of both carbamide peroxide or hydrogen per-

oxide used in either custom-made trays or �one size

fits all� type trays. In addition to these are the rela-

tively new hydrogen peroxide gels on polyethylene

strips (Whitestrips; Procter & Gamble, Cincinnati,

OH, USA), which are applied like medical plasters

onto the surface of the labial tooth and lap over the

incisal edges of the teeth. Other over-the-counter

bleaching agents include paint-on carbamide perox-

ide preparations of various concentrations used in a

similar way to the bleaching strips. Disposable trays

that are prefilled with 9% hydrogen peroxide with

inbuilt gingival protection have recently been intro-

duced (Ultradent Products Inc., South Jordan, UT,

USA).

Glycerine-based home bleaching solutions have

now been largely replaced because they dehydrate

the tooth, increasing the risk of thermal sensitivity.

Less viscous solutions of both hydrogen peroxide and

carbamide peroxide are now available that are ap-

plied for shorter time periods, but their low viscosity

may lead to leakage onto the gingivae, increasing the

potential gingival irritation (76).

The �deep bleaching technique� has recently be-

come popular among the profession, with its pro-

claimed predictability of shade B1 (Vita, Zahnfabrik,

Germany) results for every patient. This technique

involves night guard vital bleaching for 14 nights

using 16% carbamide peroxide in specially made

trays that is followed, on the 15th day, by a 1-h in-

surgery power bleaching session using 9% hydrogen

peroxide in the same trays. The manufacturers

claim that the home bleaching conditions the teeth

by increasing their permeability so that the in-sur-

gery procedure is a lot more effective. The trays are

made by first taking impressions in metal trays

using a medium-bodied silicone for greater accu-

racy. The reservoirs on the trays are made by adding

a colored stone to the cast models instead of the

resin usually used in this procedure. This, coupled

with the use of a greater force ⁄ pressure in the

vacuum moulding machine, gives rise to a better

seal to the bleaching tray about 1 mm below the

gingival margin. It is this better sealing of the tray,

enabling the bleaching agent to be active all night,

which is believed to be key to the procedure. In

addition, the patient must continue with the home

bleaching for 14 consecutive days and, to reduce the

inevitable sensitivity, the patient is given a desen-

sitizing agent containing benzalkonium chloride and

fluoride. There is no scientific evidence yet available

to support the claims made regarding this tech-

nique.

Bleaching chemistry

Hydrogen peroxide acts as a strong oxidizing agent

through the formation of free radicals, reactive oxy-

gen molecules and hydrogen peroxide anions (32).

These reduce or cleave pigment molecule double

bonds to either break down pigments to small en-

ough molecules that diffuse out of the tooth or to

those that absorb less light and hence appear lighter.

Such pigmented molecules tend to be organic, al-

though inorganic molecules can be affected by these

reactions.

Hydrogen peroxide forms a loose association with

urea to produce urea peroxide (carbamide peroxide),

which is easily broken down in the presence of water

to release free radicals that penetrate through the

enamel pores and into the dentine to produce the

bleaching effect. The urea can theoretically be further

decomposed to carbon dioxide and ammonia, which

elevates the pH to facilitate the bleaching procedure

further (138). This can be explained by the fact that,

in a basic solution, lower activation energy is re-

quired for the formation of free radicals from

hydrogen peroxide, and the reaction rate is higher,

resulting in an improved yield compared with an

acidic environment (27).

The breakdown of hydrogen peroxide into free

radicals is summarized in Fig. 1.

Stains caused by inorganic substances locked into

the crystal lattice of the enamel structure, or held

superficially by salivary protein interactions, require

the oxidation of the sulphide or thiolate bonds via

suitable catalysts, such as Fe(II), before they are

receptive to bleaching agents. Often these catalysts

are either unavailable or in short supply, causing the

degradation of hydrogen peroxide to proceed very

A

H2O2 2HO·

HO· + H2 O2 H2O + HO·2

HO·2 H+ + O·

2

B

2H2O + 2{O} 2H2O + O2

C

H++ HOO-

2 H2O2

H2O2

Fig. 1. Hydrogen peroxide forms free radicals like hydroxyl

and perhydroxyl radicals and superoxide anions (A),

reactive oxygen molecules that are unstable and trans-

formed to oxygen (B), and hydrogen peroxide anions (C).

153

An overview of tooth-bleaching techniques

slowly, and therefore extended treatment times are

usually required for these stains (103).

The perhydroxyl (HO2•) free radical is thought to be

the most reactive species in tooth bleaching, the

formation of which is favoured by high pH, but this is

rarely the situation as the product shelf life is

adversely affected under these conditions. Although

the perhydroxyl free radical is a very reactive species,

it does need metal trace elements in the mouth to

catalyse its action.

With use of both carbamide peroxide and hydrogen

peroxide the teeth should ideally be dry and free of

debris because enzymes and proteins found in saliva

are capable of catalyzing the nonbleaching break-

down of peroxides to water and oxygen.

In addition to their use in nonvital bleaching

techniques, perborates in gel form, very much like

carbamide peroxide, have been used for tray-applied

vital bleaching. However, when dispatched in powder

form, perborates can be incorporated into a paste

after mixing with water, saline or hydrogen peroxide

and placed in the pulp chambers of nonvital teeth.

Sodium perborate is stable when in the form of a dry

powder but in the presence of acid, moist air or water

it decomposes to form metaborate, hydrogen per-

oxide and nascent oxygen (Fig. 2). Hydrogen peroxide

mixed with sodium perborate potentiates its effect

and is believed to produce a better bleaching effect

(103, 114), although no evidence to support this is

available. These compounds have also been shown to

remove chlorhexidine-induced extrinsic stain both

in vitro and in vivo (2). Other products marketed as

peroxide-free bleaching agents employ an oxygen

complex made up of a mixture of sodium perborate,

sodium chlorite and oxygen.

Bleaching safety

A number of authors have investigated the safety of

bleaching procedures (11–13, 22, 28, 60, 61, 66–69, 73,

89, 90, 97, 118, 122, 123, 131, 162) but have tended to

concentrate mainly on the use of carbamide peroxide

used in at home bleaching systems (11, 13, 28, 60, 66–

69, 89, 90, 97, 118, 122, 123, 162). The evidence on

safety published to date on the whole tend to suggest

that bleaching is a relatively safe procedure (28, 60,

61, 67–69, 73, 90, 97, 122, 131, 162) but some workers

have voiced concerns about potential structural

changes that may occur as a result of bleaching (11–

13, 89, 123). Adverse effects reported by frequency for

all home bleaching products show that 27% of pa-

tients suffer an unpleasant taste and a further 27%

complain of a burning palate sensation. Other ad-

verse effects included burning throat or gingival tis-

sues, gingival ulceration and tooth sensitivity (60). All

such ill effects usually resolve on cessation of treat-

ment.

A number of studies have reported an increase in

gingival health following bleaching procedures (109)

and two reasons have been put forward for this. The

first is that the bleaching solution is toxic to the

bacteria within the gingival crevice (8) and the sec-

ond is that patients undergoing bleaching might take

more interest in their teeth and as a result may

improve their oral hygiene during the treatment.

Tooth sensitivity

The sensitivity of teeth in some individuals during

bleaching is a problem that has attracted little re-

search attention, even though two-thirds of patients

generally experience sensitivity during home

bleaching, which usually lasts between 1 and 4 days

(67, 99, 112, 119). However, a number of studies have

assessed the occurrence of the sensitivity relative to

its time of onset and duration of the symptoms. The

incidence of sensitivity ranges from 11 to 93% of

patients using 10% carbamide peroxide (32, 71, 73,

79) and the average first report of sensitivity was after

4.8 days (±4.1 days), usually lasting for 5 days (±3.8

days) (142).

Tooth sensitivity is believed not to relate to ex-

posed root surface or dentine or caries, but instead is

explained by the easy passage of the hydrogen per-

oxide molecules through the enamel and dentine into

the pulp (50). This results in pulpal inflammation

affecting the pulpal sensory nerves that trigger in

response to stimuli, such as cold drinks, until the

inflammation subsides. However, dentine exposure

may be a factor in tooth sensitivity as it is often

misdiagnosed as not being present clinically (9). In

fact, other workers (65) have correlated the incidence

and severity of thermal sensitivity with gingival

recession and the frequency, not actual duration, of

the treatment (76).

Risk factors for the development of tooth sensitivity

and gingival irritation that are associated with night

guard vital bleaching were reported by Leonard et al.

(74). No statistical relationship existed between age,

gender or tooth characteristics, with the dental arch

bleached and the development of side effects. Ini-

tially, a statistically significant association existed

Na2[B2(O2)2 (OH)4 ] + 2H2O 2Na BO3+ 2H2O2

Fig. 2. The formation of hydrogen peroxide from sodium

perborate.

154

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between the side effects and the whitening solution

used. However, when the analysis was controlled for

usage pattern, this relationship disappeared. Patients

who changed the whitening solution more than once

a day reported more statistically significant side

effects than did those who did not change the

whitening solution during their usage time.

Schulte et al. (119) reported on a clinical study

involving the use of 10% carbamide peroxide on 28

people. Four subjects discontinued bleaching because

of thermal sensitivity, whereas the remainder showed

no change in pulpal readings recorded before the start

of the treatment and at any time during the study.

Sterrett et al. (129) found that all the individuals

experienced mild, transient sensitivity during a 3-

week trial. However, the consensus view from other

trials was that two-thirds of patients experienced

mild, transient thermal sensitivity, which disap-

peared on the cessation of bleaching (67, 99, 112,

119). The penetration into the pulp of various com-

mercially available 10% carbamide peroxide bleach-

ing products has been shown to differ significantly

and may therefore account for the varying levels of

sensitivity reported (144).

Although there is a widely held belief that higher

concentrations of bleaching agents produce a greater

prevalence of tooth sensitivity, studies reported

disprove this theory (68, 86).

Cohen & Parkins (24) monitored vital bleaching for

six children with tetracycline-stained teeth involving

heat and hydrogen peroxide application for eight

consecutive 30-min sessions at 1-week intervals. Pre-

treatment and post-treatment vitality tests were

performed on test and control teeth, and no changes

in vitality were found throughout the study.

Cohen (23) also attempted to relate the prevalence

of tooth sensitivity in vital bleaching with possible

histological pulpal changes. The study involved 19

patients in whom 51 premolars were bleached with

35% hydrogen peroxide and heat in 30-min sessions.

All test and control teeth were extracted for ortho-

dontic reasons and subsequently histologically

examined. Of the patients treated, 78% experienced

some form of sensitivity, lasting for 24 h, from

bleaching; in one individual the discomfort lasted for

48 h. Histological findings from the study showed

that all pulps were normal except for moderate

vasodilation and aspiration of odontoblast nuclei into

the dental tubules, which was found to occur with

equal frequency in both test and control teeth. Cohen

(23) concluded that sensitivity and discomfort during

and after bleaching procedures are caused by heat

application increasing the intrapulpal pressure that

leads to the sensation of pain. Histological changes to

the pulp after night guard vital bleaching with 10%

carbamide peroxide have recently been reported to

be minor; they did not affect the overall health of the

pulp tissue and were reversible within 2 weeks post-

treatment (40). In a previous study in which the pulps

were evaluated after overnight bleaching with 10%

carbamide peroxide for either 4 or 14 days, mild

inflammatory changes were demonstrated in four out

of 12 teeth, irrespective of treatment duration (46).

However, in those teeth treated for 14 days, followed

by a rest period of 14 days, no inflammation was

detected.

In a clinical study monitoring post-operative dis-

comfort associated with vital bleaching, Nathonson &

Parra (99) found that 30% of patients had no sensi-

tivity, whereas the majority of the others only expe-

rienced mild symptoms lasting less than 24 h, with

patient age having no effect on the degree of sensi-

tivity experienced. This was contrary to the widely

held view that younger patients with wider pulp

horns would develop more sensitivity.

The efficacy of desensitizing agents used in pa-

tients who experience tooth sensitivity during tooth

whitening has been reported in a study of such pa-

tients who had pre-existing symptoms prior to the

start of the whitening procedure (76). This study

suggested that the use of a 3% potassium nitrate and

0.11% fluoride desensitizing agent for 30 min prior

to whitening may decrease tooth sensitivity when

compared with a placebo gel.

Effects on the pulp

A study of the penetration of hydrogen peroxide re-

ported that the compound enters readily through the

enamel and dentine to reach the pulp chamber of

extracted teeth (16). Bowles & Thompson (15) have

shown that hydrogen peroxide concentrations as low

as 5% can dramatically inhibit pulpal enzyme activity.

These enzymes were quite sensitive to the combina-

tion of hydrogen peroxide and heat, but the quantities

required to produce this inhibitory effect were in the

region of 50 mg. A follow-up study then went on to

show that although dental hard tissues exhibited

substantial permeability to hydrogen peroxide, espe-

cially with the application of heat, the quantities that

diffuse into the pulp chamber were in the order of only

micrograms: too low to produce inhibitory effects on

enzymes and therefore unable to cause permanent

pulpal damage (16). The effects of carbamide peroxide

penetration were also studied and it was found that

for the same effective concentration, there was less

155

An overview of tooth-bleaching techniques

penetration of the pulp from carbamide peroxide than

from free hydrogen peroxide (26).

The effects of light-enhanced bleaching on the

in vitro surface and on intrapulpal temperature rise

have been reported (4, 134, 137). Baik et al. (4) inves-

tigated the effect of the presence, absence and ageing

of heat-enhancing colorant added to the bleaching gel

on the temperature rise of the gel itself, as well as on

the temperature rise within the pulp chamber, when a

tooth was exposed to a variety of lights. The results

showed that the freshness of this bleaching agent

influences the temperature rise of the bleaching gel

and may also increase the intrapulpal temperature.

Use of the lights elevated the bleach temperature,

which resulted in an increased intrapulpal tempera-

ture that may further impact on patient sensitivity and

pulpal health. A variety of different bleaching lights,

including a diode laser, were investigated by Sulieman

et al. (134, 137) who found that these lights did not

increase the intrapulpal temperature above the critical

5.5 �C (161) as long as they were used within the

manufacturers� guidelines.

Root resorption

Cervical resorption is seen occasionally in bleached,

root-filled teeth and has been attributed to a combi-

nation of trauma and bleaching with high-concen-

tration hydrogen peroxide (30%) and heat (39).

Heithersay et al. (57, 58) studied the radiographs and

records of 204 teeth from 158 patients who had re-

ceived tooth-bleaching treatment in a specialist end-

odontic practice in the past 1–19 years. Seventy-eight

per cent of these teeth had prior incidents of trau-

matic injury. All teeth were bleached using a combi-

nation of thermocatalytic or heat-activated 30%

hydrogen peroxide and walking bleach techniques.

Only four of these teeth (2%) had developed invasive

cervical resorption during the review period, which

might have been a result of the original trauma.

Effects on physical properties

Scanning electron microscopy of enamel bleached

with carbamide peroxide showed little or no change in

morphology (55), whereas other work showed areas of

shallow erosions (54) or more substantial changes in

enamel structure (11, 12, 123). Surface hardness and

wear resistance has also been investigated with results

showing a lack of agreement on the overall effect of

bleaching. The results range from no effect on tooth-

wear (70, 73, 156) to a significant decrease in the

hardness and fracture resistance of enamel (13, 89).

Bleaching does not cause any perceptible etching of

the teeth, and morphological changes in the outer 25

lm of the enamel are clinically insignificant (90, 146).

Abrasion, erosion, surface hardness and morphologi-

cal changes of enamel and dentine following power

bleaching using 35% hydrogen peroxide were inves-

tigated (131). There were no significant changes

following the bleaching procedure as the high con-

centration of hydrogen peroxide did not affect the

abrasion, erosion or hardness of both enamel and

dentine. One possible reason for the reported delete-

rious effect on enamel and ⁄ or dentine of bleaches is

not the bleach itself but the pH of the formulation

used. The pH of various commercially available tooth-

whitening agents was analysed in a study by Price et

al. (108) who found the range was from highly acidic

(pH 3.67) to highly basic (pH 11.13), with the over-the-

counter preparations having a significantly different

pH to both the at-home and in-surgery bleaching

materials. The over-the-counter bleaching agents

have been found to have very acidic pH values, which

may cause erosion of the enamel, and the toothpastes

supplied with them can be quite abrasive (62).

There may be a loss of organic components from

bleached enamel and dentine surfaces. The cal-

cium:phosphate ratio of dentine was found to be

significantly reduced by bleaching with 30% hydro-

gen peroxide and 10% carbamide peroxide in a study

by Rotstein et al. (115). In another study, by

McCraken & Haywood (90), teeth exposed to 6 h of

bleaching using carbamide peroxide lost an average

of 1.06 lg ⁄ mm2 of calcium, which was found to be

similar to the amount lost from the enamel after a

2-min exposure to carbonated cola, orange juice or

carbonated diet cola (48). The potential for reminer-

alization in vivo could counteract these effects but to

date this has not been investigated.

Bleaching has no effect on the erosion and

demineralization of enamel (17, 80, 106, 123), but the

methods of assessment have been debated as mi-

crohardness has often been the sole method of

measurement. The argument is that measuring only

the softened portion of the lesion is unable to

quantify the bulk loss of tissue, which would require

assessment methods such as profilometry.

Effects on enamel ⁄ dentinebonding

Bonds to enamel ⁄ dentine may be altered following

bleaching because of the presence of hydrogen

156

Sulieman

peroxide. Resin tags in bleached enamel are less

numerous, less well defined and shorter than those

in unbleached enamel (100). Bonding to dentine

may be altered after bleaching (33) and the smear

layer may be removed (61). Bonding between glass

ionomer and dentine may also be affected by the

possible precipitation of hydrogen peroxide and

collagen that forms on the cut dentine surface after

tooth bleaching (100).

The residual oxygen in the tooth surface also

inhibits the polymerization of the composite resin

and disrupts the surface (62, 93). However, bond

strength improves if the procedure is delayed for 2

weeks post-bleaching.

Effects on restorative materials

The effects of bleaching agents on composite resins

are conflicting, ranging from no effect (7, 67, 83) to

alteration of surface hardness (5, 42), surface rough-

ening ⁄ etching (127) and changes in tensile strength

(31). However, these effects were very small and

considered unlikely to be clinically significant (140).

Prolonged bleaching treatment may cause micro-

structural changes in amalgam surfaces and this may

increase exposure to the patient of toxic by-products

(115). Existing amalgams may change in color from

black to silver, but not all combinations of amalgam

and bleaching agents result in higher mercury levels.

Little effect is reported on gold or porcelain resto-

rations; however, the glass ionomer matrix may show

alteration in its matrix (63). Provisional crowns made

of methyl methacrylate may discolor to become

orange, but other materials are not affected (111).

Toxic effects

Carbamide peroxide administered as a home

bleaching agent breaks down to produce hydrogen

peroxide and urea in the mouth. The toxicology of

hydrogen peroxide has been reviewed by the Euro-

pean Centre for Ecotoxicology and Toxicology of

Chemicals (36), and others (77), who reported that

hydrogen peroxide is found to occur naturally in

many vegetables and is produced in humans during

normal metabolism of aerobic cells. In addition to

this, phagocytic cells, such as neutrophils and mac-

rophages, provide an important source of endoge-

nous hydrogen peroxide and play an essential role in

defence against various pathological microorganisms

(148). However, free radical oxidative reactions with

proteins, lipids and nucleic acids have a number of

potential pathological consequences (38). To prevent

these potential dangers, the body has a number of

defense mechanisms at the tissue and cellular level

that work to repair any damage sustained. Enzymes

such as catalase, peroxidase and superoxide dimu-

tase are commonly found in body fluids, tissues and

organs to metabolize hydrogen peroxide (37, 57).

Salivary peroxidase has been suggested to be the

body�s most important and effective defence against

potential adverse effects (19). The hydrogen peroxide

exposure dose has been estimated to be approxi-

mately 3.5 mg for a treatment of both arches using

10% carbamide peroxide (77), while the oral cavity is

capable of decomposing more than 29 mg of hydro-

gen peroxide per minute (84).

The dermal toxicity of hydrogen peroxide is low,

with concentrations of up to 35% not considered as

being irritant to rabbit skin; however, concentrations

of greater than 50% are corrosive. Various mouth

rinses and oral antiseptics (10 and 15% carbamide

peroxide, and hydrogen peroxide up to a concentra-

tion of 3%) have been used for some time with no

detectable ill effect on humans and have been ap-

proved by the US Food and Drug Administration

since 1979. On the contrary, reports are of beneficial

effects on gingival irritation and plaque accumula-

tion, and an anticariogenic action (124).

Hydrogen peroxide has been found not to be car-

cinogenic, mutagenic or teratogenic (37, 78, 159), and

concerns of toxicity or serious damage to soft tissues

appear to be unfounded (49). Initially, concerns were

raised about the role of hydrogen peroxide in muta-

genesis on the basis of some in vitro tests that were

not reproduced in vivo (67). In fact, the frequency of

genetic mutation induced by 10% carbamide perox-

ide is not significantly different from that of a phys-

iological saline control (159). The only side effect

reported from ingesting large quantities of a car-

bamide peroxide home bleaching product was a

laxative effect from the presence of glycerine found

within the gel (3).

Evidence of efficacy oftooth-whitening techniques

A variety of case reports and small clinical studies

have shown that a 10% carbamide peroxide gel used

in night guard vital bleaching techniques produces

predictable results (66, 69, 74, 75, 85, 88, 104, 109,

116) as do hydrogen peroxide strips (44). Similarly,

�power bleaching� using 35% hydrogen peroxide, with

157

An overview of tooth-bleaching techniques

or without light and ⁄ or heat activation, has also been

shown to be effective (60, 130, 131, 133).

Heyman et al. (59) reported a mean change of 7

units on the Vita shade guide after bleaching with a

10% carbamide peroxide gel over 7 days. However,

there was a wide range of responses, ranging from 3

to 13 units, which highlights the unpredictable nature

of teeth. Papathanasiou et al. (104) reported a mean

change of 8 Vita units when using a 15% in-office

hydrogen peroxide system, whereas Gerlach & Zhou

(44) reported a mean change of 5.5 units when using

a whitening strip, but 25% of their sample had a

shade change in excess of 8 units.

Clinical and laboratory studies have also reported

tooth-whitening changes using the L*a*b* system of

measurement (25). For example, an in vitro study on

dentine by White et al. (156) reported an improve-

ment of DL* of 7 units when a 10.5% carbamide

peroxide gel was used for 30 h. Similarly, Gerlach &

Zhou (44) reported an improvement of DL* of 2 units

with a whitening strip product.

Various workers have compared two or more night

guard vital bleaching agents clinically; very similar

results were obtained, usually in the magnitude of

about 7 shade guide units improvement (82). Ro-

senstiel et al. (112) reported on a single power

bleaching session in a group of 20 young adults,

which produced an average whitening effect of 6.2 L*

units (as measured using a colorimeter) that was still

detectable 6 months post-treatment. In-surgery

bleaching has been compared with night guard vital

bleaching using 10% carbamide peroxide in a 3-

month single blinded clinical study (163). Compari-

sons were made of the color change, color relapse as

well as tooth and gum sensitivity. A 14-day home

treatment was compared with 60 min of in-surgery

bleaching consisting of two clinical bleaching ses-

sions of three 10-min applications. The at-home

bleaching produced significantly lighter teeth, but

significantly higher cervical sensitivity. Colour

relapse for both bleaching techniques stabilized by 6

weeks.

Long-term results of bleaching efficacy were re-

ported by Leonard (72), with at least 43% shade

retention without retreatment at 10 years.

The effect of the lights used for in-surgery bleach-

ing techniques have been the subject of various de-

bates as to their efficacy in improving the bleaching

process (6, 70, 81). Hein et al. (56) reported that the

three lights used in their study (halogen curing light,

Xe-halogen light and metal halide light) did not

lighten teeth more than their bleach gels alone and

concluded that output from any of the lights used

resulted in heat or light that catalysed breakdown of

the gels. They also concluded that proprietary

chemicals added to the gels caused them to perform

differently from the 35% aqueous hydrogen peroxide

liquid controls used in the laboratory tests. Further-

more, these chemicals were also probably responsi-

ble for the reduced time required to bleach with the

Xe-halogen light. Contrary to these results, Luk et al.

(81) reported that color and temperature changes

were significantly affected by an interaction of the

bleach and light variables. The application of lights

significantly improved the whitening efficacy of some

bleaching materials but it caused a significant tem-

perature increase in the outer and inner tooth sur-

faces. Other workers have also reported a study on

the use of lights for in-surgery bleaching and con-

cluded that the use of lights with the peroxide gel

significantly lightened teeth more than peroxide or

light treatment alone (143). The results of this study

must be interpreted with caution as the reported

shade improvement with light-only application was

4.9 shade guide units, which was probably the result

of a great deal of tooth dehydration. In another

in vitro study, it was found that an activating light

source did improve the whitening effect but the

freshness of the hydrogen peroxide was probably

more of a contributing factor (135).

Researchers at Procter & Gamble have reported on

many trials using a whitening strip and various con-

centrations of carbamide peroxide (44). In general,

the magnitude of the whitening response decreased

with age and, on average, for every 10 years of aging,

individuals should expect approximately 0.3 units

less whitening benefit. Baseline color also affected

the response, with the greatest average whitening

seen in individuals with more yellow teeth. For both

strip and tray systems used, increasing the peroxide

concentration was observed to improve the whiten-

ing response (47, 48, 141). When treatment time was

doubled to 28 days using these whitening strips, an

additional 29% whitening effect was achieved com-

pared with the normal treatment duration of 14 days

(34, 50). Pre-brushing teeth prior to the application of

whitening strips was also found to yield a signifi-

cantly more efficacious whitening result (50), al-

though no explanation for this was offered.

After the introduction of a new higher-concentra-

tion whitening strip (14% hydrogen peroxide), which

was thinner and incorporated a smaller volume of

bleaching gel, various comparative trials were re-

ported in a pooled report (43). Efficacy results for

these strips were significantly better than placebo or

pooled positive controls evaluated in clinical trials

158

Sulieman

assessing tooth shade. The reported irritation and

patient tolerability were similar to those reported

with previous lower-concentration strips and other

marketed positive bleaching controls.

Hydrogen peroxide (8.7%), carbamide peroxide

(18%) and sodium percarbonate (19%) paint-on-

bleaching agents have been introduced directly to the

public as over-the-counter preparations. The shade

improvements with these agents were reported to be

about 4 shade guide units from baseline (41) with a

reduction in yellowness (Delta b*) of about )0.95

units (43).

Long-term efficacy has been reported by Leonard

(72), with shade retention without retreatment in at

least 43% of subjects at 10 years post-treatment. The

initial efficacy of the night guard vital bleaching

technique was 98% for nontetracycline-stained teeth,

and, with extended treatment times for tetracycline-

stained teeth, 86% of these teeth were lightened.

Laboratory studies have reported on the efficacy of

different concentrations of carbamide peroxide. Al-

though higher concentrations of 10 and 16%

produced a quicker 2-shade shift than a 5% con-

centration, the eventual result on whitening was the

same for all concentrations (75). Other studies that

compared various concentrations of carbamide per-

oxide and hydrogen peroxide also found that the

eventual result was the same, but the time taken to

reach that end point was quicker with high concen-

trations of bleaching agents (130, 136). In a similar

clinical study on patients with tetracycline-stained

teeth, more rapid bleaching effects were achieved

with a higher concentration of carbamide peroxide

(15 and 20%) but the end results were the same as

those for a lower concentration of carbamide perox-

ide (10%) (87). In a separate study comparing the

clinical effect of 10 and 15% carbamide peroxide

using three different shade-assessment methods, re-

sults at 2 weeks showed a significantly better shade

improvement for the higher-concentration product.

However, by 6 weeks there were no statistical signif-

icant differences between the two concentrations

(86).

To establish the efficacy of both 20% carbamide

peroxide and the equivalent concentration of 7.5%

hydrogen peroxide used in an in vivo study of day-

time use of bleaching agents, it was found that there

were no significant differences between the two

products in terms of tooth lightness, and gingival and

tooth sensitivities (95).

The mechanism of tooth color change during

bleaching is poorly understood. Many workers sug-

gest that tooth color is primarily determined by the

dentine, which can be changed by bleaching tech-

niques (121, ten Bosch and Coops, 1995). Some

studies, using 35% hydrogen peroxide, have reported

color changes in both enamel and dentine (3, 52, 91,

92, 98, 132). Others dispute the idea of color change

in dentine and believe that this occurs in enamel

only, thereby masking the unchanged dentine (21).

However, the successful bleaching of tetracycline-

stained teeth, and those with dentinogenesis imper-

fecta (30, 61), add weight to the argument that the

color change takes place primarily within dentine.

McCaslin et al. [1999] reported on a study using 10%

carbamide peroxide and its effect on dentine color

changes, and found that the color change in dentine

occurred at a uniform rate.

A study by Carrillo et al. (20), of inside ⁄ outside

bleaching of nonvital teeth and the surrounding vital

teeth, reported an average Vita shade change of 15

and 6 for the nonvital and vital teeth respectively.

Friedman (39) also reported very favourable shade

changes for nonvital bleaching, but was cautious over

long-term results (1–5 years) with 50% shade relapse

observed.

Indications and contraindicationsfor bleaching

Nearly every patient can have their teeth bleached,

but not every case is guaranteed to have a successful

outcome or be enough to satisfy the esthetic needs of

the patient. The indications for bleaching are basi-

cally the same for both in-surgery and home

bleaching but the clinician must decide which

method is best suited to the patient�s needs.

Indications

• generalized staining.

• ageing.

• smoking and dietary stains such as those of tea and

coffee.

• fluorosis.

• tetracycline staining.

• traumatic pulpal changes.

• pre-restorative and post-restorative treatments.

Very severe tetracycline staining may not be amena-

ble to bleaching alone and therefore combination

treatments, such as bleaching and veneers, may be

considered. Prior bleaching reduces the amount of

tooth substance removed in preparation for the ve-

neers, which would otherwise have been necessary in

order to mask the stain and allow for porcelain build

159

An overview of tooth-bleaching techniques

up. Fluorosis with multiple spots of varying colors

may require a combination of bleaching and micro-

abrasion using hydrochloric acid and abra-

sives ⁄ polishes (29). Bleaching is also indicated prior

to extensive restorative cosmetic work in the anterior

region of the mouth in order to allow general

improvement of the shade of the teeth, which are

then matched with the new restorative restorations.

Bleaching can also be used post-restoratively when

patients present with incorrectly made restorations

whose shades are lighter than the natural dentition.

As mentioned above, bleaching can be undertaken

in most cases but some contraindications are worthy

of mention. Patients with high expectations may

never be satisfied and should be identified by asking a

simple question as to what they hope to achieve with

the bleaching procedure. Patients who reply �dazzling

white� or words to that effect should be treated

cautiously, while more reasonable replies may be �afreshening look to the teeth� or a �little lighter�. Decay,

peri-apical lesions and sensitivity does not preclude

those patients from bleaching, but these conditions

have to be resolved prior to bleaching.

Contraindications

• patients� high expectations.

• decay and peri-apical lesions.

• pregnancy.

• sensitivity, cracks and exposed dentine.

• existing crowns or large restorations in the smile

zone.

• elderly patients with visible recession and yellow

roots.

Existing crowns or restorations that need to be

changed following bleaching may be considered as a

contraindication for patients who do not want or

cannot afford this extra financial burden. It is not

always necessary to change composites following

bleaching because some types of composites display

a chameleon effect, taking on the shade of the sur-

rounding tooth and blending in well, if not quite

perfectly. The other contraindications mentioned

above can be rectified before embarking on a

bleaching course of treatment. For instance, in the

case of decay, a restoration can be preformed and

resurfaced for the correct bleached shade about 2

weeks post-bleaching once the end shade has stabi-

lized and to allow for the dissipation of the residual

oxygen that may inhibit the composite bond to

enamel ⁄ dentine. Similarly, apical lesions should be

treated and the root canal filling sealed effectively

using a glass ionomer material prior to bleaching.

The sensitive patient can have fluoride-desensitizing

gels applied to teeth in the bleaching trays for a

period of a few weeks prior to bleaching. Elderly pa-

tients with yellow receded roots present a problem in

that the roots do not bleach as readily compared with

the crowns, leaving an obvious mismatch that re-

quires to be corrected by restorative dentistry. If the

patients are aware of this and are willing to undergo

restorative work to address this issue, then it cannot

be considered as a contraindication.

Who best to bleach?

Although it is difficult to predict the result of

bleaching teeth for every individual, there are some

guidelines gained from various studies, reports and

personal experience. For instance, the effect of

bleaching in older patients who have teeth with small

pulps and various accumulated dietary stains, as well

as the aging discoloration caused by secondary den-

tine deposition, is relatively predictable. In the au-

thors� experience, teenagers with yellow teeth or with

basically white teeth except for the yellow canines

tend to respond well to bleaching. Browns stains are

more difficult to bleach but generally respond to

longer bleaching regimens than stains caused by

nicotine (51). White fluorosis spots tend not to bleach

but will become less obvious as a result of the light-

ening of the surrounding tooth area (51).

Severe tetracycline staining may be very difficult to

bleach but mild-to-moderate tetracycline staining

tends to respond to extended bleaching regimes of 3

to 6 months (51). Different brands of tetracycline

present with different colored tooth banding, which

is especially difficult to treat as not all respond well to

bleaching, leaving the possible need to use restora-

tions to cover the nonresponsive band (51). Figure 3

shows an example of fluorosis brown stain removed

using 10% carbamide peroxide.

Bleaching protocol

Diagnosis of the cause of the discoloration should be

made and recorded in the patient�s notes. The op-

tions for treatment can be extrinsic stain removal,

bleaching or both. Other options, such as veneers and

crowns, should also be discussed with the patient and

recorded in the notes.

The teeth that are to be bleached should be iden-

tified and checked for the following:

• vitality.

• caries.

160

Sulieman

• cracks.

• recession, exposed dentine.

• developmental defects such as white spots.

In addition, the presence of composite fillings, ve-

neers, crowns or highly translucent teeth should be

noted. Patients must be warned that these will not

change shade but their margins may merely be

cleaned up by the bleaching agent acting on the

surrounding tooth structure. Hence, they may need

replacement following the bleaching treatment.

Highly translucent teeth do not bleach well and

sometimes appear greyer rather than whiter (45).

Patients need to be aware of all these points and the

information again needs to be recorded in the notes.

Some authors advocate the use of full-mouth peri-

apical radiographs to document the size and vitality

of pulps to predict sensitivity levels or check for peri-

apical pathology (51). In view of the current ioniza-

tion radiation regulations and the unnecessary

exposure of the patient to high levels of radiation,

other forms of vitality testing, such as ethyl chloride

or electric pulp testers, are advised instead. Any teeth

that require root canal therapy should have this car-

ried out prior to the bleaching procedure. Following

the assessment of the teeth, the shade should be

agreed with the patient and recorded in the notes. A

pre-operative photograph with the shade tab in situ

should always be taken under standardized lighting

conditions without using the dental operating light,

which would result in washout of the shade. After all

the relevant explanations, options, limitations and

prognosis have been discussed with the patient, a

consent form should be signed and the patient

referred for a hygiene session about 7–10 days prior

to the bleaching procedure.

Home bleaching

Bleaching material ⁄ regimen

Nearly all the bleaching materials on the market have

been shown to work to a comparable extent (82).

Generally, the higher-concentration, thicker, more

viscous materials produce a lightening effect more

quickly than lower-concentration, less viscous

materials. However, higher concentrations tend to

produce more cases of thermal sensitivity (107).

The choice of material to use depends on a number

of factors, including the type of discoloration present

and how dark the teeth are initially. However, the

most important consideration has to be the patient,

their lifestyle, the time available for bleaching

and whether there are existing problems with tooth

sensitivity.

The bleaching regimen is therefore determined by

the patients� lifestyle, preference and schedule. If the

patient is happy and able to wear trays overnight,

then 10% carbamide peroxide worn for 8 h overnight

is the treatment of choice (Fig. 4). However, if time is

at a premium, this regimen is not recommended as

bleaching will take about 4 weeks in total as the top

and the bottom teeth are bleached separately. In the

authors� experience, some patients are able to wear

both upper and lower trays simultaneously overnight,

Fig. 3. The use of 10% carbamide peroxide to remove a

brown flourotic stain from a maxillary right central

incisor.

Fig. 4. Loaded tray inserted into the patients mouth before

removal of excess bleaching agent.

161

An overview of tooth-bleaching techniques

thereby reducing the bleaching period to 2 weeks, but

many patients cannot cope with this regimen. Higher

concentrations of carbamide peroxide, such as 15 or

20%, can be selectively used to treat darker teeth

within an arch such as canines while still using 10%

carbamide peroxide to bleach the lighter teeth within

the arch at the same time.

Some patients are unable to wear trays overnight

and prefer daily use, which has the advantage of more

frequent replenishment of the bleaching gel for

maximum bleaching effect, but both occlusal pressure

and increased salivary flow may dilute the gel (35).

Home bleaching side effects

Some patients experience problems with gingival or

soft tissue irritation during home bleaching, but the

vast majority of problems are those of tooth sensi-

tivity, which have been reported to affect about two-

thirds of patients (61, 99). Painful gums may be the

result of incorrectly fitting trays impinging on them

or the use of excess material in the trays. The trays

can be easily trimmed back and polished, while the

patient can be instructed to use less material if other

areas of mucosa or soft tissues are irritated. Some

patients who bleach teeth overnight report a metallic

taste sensation immediately following tray removal,

but this usually disappears after about 2 h (42).

Thermal tooth sensitivity is a common side effect

noticed by patients as early as the third day of

bleaching following the removal of trays and may

persist for 3–4 h afterwards. Patients who experience

severe sensitivity should be advised to stop bleaching

and the sensitivity should be treated. Treatment can

take the form of fluoride-containing toothpastes or

neutral sodium fluoride gels in the bleaching trays

worn overnight. Desensitizing potassium nitrate, or

potassium nitrate and fluoride-containing gels, are

also available for use in trays for about 2 h before or

after the bleaching procedure. Potassium nitrate in

toothpastes takes about 3 weeks to reduce sensitivity

measurably, but when put in a tray for 10–30 min,

relief is almost immediate. Lower degrees of sensitivity

can be treated with desensitizing toothpaste rubbed or

brushed onto the cervical necks of the affected teeth.

Fluoride acts primarily as a blocker of dentinal

tubules, which acts to slow down the dentinal fluid

flow that causes sensitivity, while potassium nitrate

acts like an anesthetic by preventing the nerve from

repolarizing after it has depolarized in the pain cycle

(51).

Other forms of treating sensitivity are passive in

terms of not involving specific desensitizing prod-

ucts; they are aimed at reducing the concentration

and amount of bleaching gel used, or the bleaching

time. The trays are trimmed back, if necessary, and

less gel is used in the trays with the excess thoroughly

removed. The patients can be instructed to apply the

bleaching materials only on alternate nights, or even

every third night, to reduce the problems of sensi-

tivity. This can delay the treatment time but ensures

that the patient is comfortable with the bleaching

regime.

Nonvital bleaching techniques

There are a number of nonvital bleaching techniques

available, which include �walking bleach and modi-

fied walking bleach�, nonvital power bleaching, also

known as �thermo ⁄ photo bleaching�, and �inside ⁄outside bleaching�.

Walking bleach technique

First described by Spasser (128), the walking bleach

technique involved sealing into the tooth a mixture of

sodium perborate with water by introducing it into

the pulp chamber. After 1 week the patient would

return and the procedure would be repeated until the

desired whitening had occurred. The technique was

modified using a combination of 30% hydrogen

peroxide and sodium perborate sealed into the pulp

chamber for 1 week �modified or combination walk-

ing bleach technique� (102, 103). Sodium perborate is

stable when in the form of a dry powder, but in the

presence of acid, warm air or water it decomposes to

form metaborate, hydrogen peroxide and nascent

oxygen. Hydrogen peroxide mixed with sodium per-

borate potentiates its effect and produces a better

bleaching effect (114).

Prior to any bleaching procedure the nonvital tooth

must be radiographed to assess the quality of the root

canal obturation and the apical tissues. Any defi-

ciencies must be rectified before bleaching.

The �combination bleach technique� differs from

the above only in that sodium perobrate is mixed

with 30% hydrogen peroxide (or lower concentra-

tions), instead of water, to form a thick paste that is

sealed into the cavity. The procedure is quicker acting

and hence can produce results after 1 week. The

current walking bleach technique involves sealing in

10% carbamide peroxide instead of sodium perbo-

rate without needing to mix the product, simply

syringing the gel into the cavity and reviewing the

patient in 3 days.

162

Sulieman

Internal nonvital power bleaching

This technique is the least favoured because of its use

of high temperatures and the probable increased risk

of internal resorption. Hydrogen peroxide gel at a

concentration of 30–35% is applied into the pulp

chamber and activated either by light or heat. The

temperature is usually between 50 and 60 �C and

maintained for 5 min before the tooth is allowed to

cool down for a further 5 min before the gel is re-

moved by washing with water for a further minute

(114). The tooth is dried and the �walking bleach

technique� is used between visits until the tooth is

reviewed 2 weeks later to assess if further treatment is

necessary.

A variation of this technique uses 35% hydrogen

peroxide gel applied both internally to the pulp

chamber and externally to the labial surface of the

tooth, with light activation internally and externally.

High temperatures are not involved and the same

preparation protection techniques are used on the

tooth. Light activation both internally and externally

can be in the form of a conventional halogen-curing

light, plasma arc lamp or a diode laser. Following this

procedure, the tooth is washed and dried before being

sealed with a temporary restoration. The patient is

reviewed 2 weeks later when the shade would have

stabilized and the tooth is ready for a definitive res-

toration to be placed or is bleached further if required.

Inside ⁄ outside bleaching

This technique is a combination of internal bleaching

of nonvital teeth using the home bleaching tech-

nique. The preparation of the nonvital tooth is exactly

the same as for the �walking bleach technique� in that

a protective barrier is placed over the root canal

system using glass ionomer material and the access

cavity is completely cleaned in readiness for the

bleaching procedure.

The advantage of this technique for bleaching

nonvital teeth is that it utilizes both an internal and

an external approach for the bleaching agent. The use

of a lower concentration of bleach, usually 10% car-

bamide peroxide, is thought to reduce the risk of

external resorption. There is no need for frequent

changes in temporary dressings, as experienced with

the walking bleach when the oxygen build up within

the pulp chamber dislodged the dressing. Addition-

ally, the technique achieves the lightening effects

within a matter of days compared with weeks.

The main disadvantages of this technique are the

need for patient compliance and a little degree of

manual dexterity to place the bleaching agent into

the cavity. Coupled to the ease with which overuse

can lead to overbleaching the tooth, and with the

potential for external resorption still existing, al-

though reduced, this technique is by no means

without its risks.

As with the modified bleaching technique, the in-

side ⁄ outside bleaching technique has been modified

by use of varying concentrations of carbamide per-

oxide, such as 5, 16, 22 or 35%, as used in the waiting

room technique. Figure 5 shows a typical example of

the results achieved using this technique.

Power bleaching

The power bleaching technique is used on those

patients who do not have the necessary time avail-

able for home bleaching, who have a problem with

wearing trays that may cause them to gag or who

even find the taste of the home bleaching gel not to

their liking. Another advantage is that the immediate

results produced in power bleaching can be used to

motivate the patient to continue with home bleach-

ing top-up treatment. It must be emphasized that

although there is an immediate result with power

bleaching, it is by no means necessarily the end point

Fig. 5. Bleaching of a nonvital upper left central incisor

using the inside ⁄ outside technique.

163

An overview of tooth-bleaching techniques

in terms of tooth whiteness and further bleaching

sessions may be necessary. It can be likened to the

home bleaching procedure that produces results

within the first 4 days for most people but over the

next couple of weeks this is further enhanced until it

reaches a terminal end point where the tooth shade

does not improve any further.

The increased surgery time required for in-surgery

bleaching is obviously a disadvantage, as it makes the

procedure more expensive for the patient. Some re-

ports also highlight that power bleaching causes

dehydration of the teeth, thereby giving a falsely

lighter shade immediately post-treatment (6). This

causes further problems, with patients perceiving

that there is color regression or rebound following

rehydration of the teeth. Some manufacturers have

addressed this problem by producing gels that con-

tain 10–20% water, which rehydrates the teeth

throughout the bleaching procedure, while others

have tackled the problem by using lower concentra-

tions of hydrogen peroxide (15%), which is a water-

based solution, thereby increasing the water content

by 20%. However, by far the biggest disadvantage of

the power bleaching procedure is the caustic nature

of the 35–50% hydrogen peroxide used. The need for

a meticulous protocol in handling, applying, removal

and disposal of these materials is essential. The risk

of tissue burns to the lips, cheeks, gingiva, the rest of

the face or eyes makes isolation and protection

techniques mandatory (Fig. 6).

The main safety issue concerning the activating

lights used in power bleaching is heat generation and

its effect on the pulp. Recent research showed that

the increase in the intrapulpal temperature with most

bleaching lamps was below the critical threshold

of a 5.5 �C increase thought to produce irreversible

damage. The only lamp that produced an intrapulpal

temperature increase above this threshold was the

laser-based lamp, and this was also found to be be-

low the critical temperature once the power output

was reduced from 3 to 2 W (137).

There are many different materials available, but

broadly speaking they are either based on 35% car-

bamide peroxide or hydrogen peroxide of the same or

higher concentration. Hydrogen peroxide is more

widely used as the power bleaching agent, but the

range of concentrations in current use varies from

about 17–50% and the bleaching time for which they

are used also varies. Thirty-five per cent carbamide

peroxide yields approximately 10% hydrogen perox-

ide and is used in certain bleaching systems, some-

times known as �waiting room bleach�, because the

patient wears the custom-made trays full of the

material and waits in the waiting room of the surgery.

Thirty-five per cent hydrogen peroxide is available

in a powder–liquid combination mixed together to

produce a gel, or in a ready-made gel to which liquid

is added. There are many different combinations

available depending on the system or activation

method used.

Light activation

Various types of curing lights are used to activate the

bleaching gel or expedite the whitening effect. Ini-

tially, conventional curing lights were used but these

were quickly joined by lasers and plasma arc lamps.

In addition, some systems are activated by a chemi-

cal reaction upon mixing two gels, while others utilize

a dual-activation system.

Halogen curing lights can be used with a number of

different systems and generally activation is via the

light�s bleach mode for 30 s per tooth and the appli-

cation involves three 10-min passes. Plasma arc

lamps are also used in a similar way to halogen cur-

ing lights but, with the aid of a full smile illuminator,

they can act in the same way as Xenonhalogen lights,

irradiating both arches at the same time, which is

generally three 10-min passes. Similarly, metal halide

lamps are used with a two-part 25% hydrogen per-

oxide gel in a dual-arch technique employing three

20-min passes followed by the application of sodium

fluoride gel.

Diode lasers of 830 and 980 nm wavelengths can be

used for tooth bleaching in combination with 35–

50% hydrogen peroxide gel. The gel is produced by

mixing the hydrogen peroxide liquid with a powder

containing mainly fumed silica and a blue dye. The

blue dye absorbs the laser wavelength and heats up

to cause the controlled breakdown of the hydrogen

peroxide to oxidizing perhydroxyl free radicals.Fig. 6. Isolation of teeth and gums typically used in a

power bleaching procedure.

164

Sulieman

Waiting room bleach technique

Thirty-five per cent carbamide peroxide is activated

by holding the syringe under hot running water for a

few minutes prior to use. The gel is transferred into

the custom-made tray and the excess material re-

moved from the patients� mouth before asking the

patient to sit in the waiting room for about 30–60

min. After this time has elapsed the patient returns

and the gel is suctioned and rinsed off the teeth. The

procedure can be repeated two or three times more

in the one session.

Power bleaching may frequently require more than

one visit to produce an optimal result. However, for

many patients a single visit is enough to satisfy their

esthetic needs and no further treatment is required.

Power bleaching should be used in cases where time

is at a premium with patients requiring faster results

and in cases where it is felt that the patient needs a

�kick start� before continuing with home bleaching. It

can also be used on teeth with different stain etiol-

ogies, but must be carried out with meticulous care

and attention as a result of the caustic nature of the

35% hydrogen peroxide used.

The goal of modern dentistry is maximum preser-

vation of tooth substance with excellent esthetics.

Bleaching alone, or in combination with minimally

invasive adhesive dentistry, very often fulfils this goal

without the need to progress to the much more

destructive techniques of veneers, crowns and

bridges.

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