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1. FORMAT
A) Introduction
B) Effect of bleaching agents on properties of restorative materials
C) Reasons for the impact of bleaching agents on properties of restorative materials and clinical
consequences.
D) Effect of bleaching agents on bond strength of restorative materials to enamel and dentin.
E) Reasons for the impact of bleaching agents on bond strength of restorative materials and
clinical consequences.
F) Effect of bleaching agents on marginal quality of restorations.
G) Clinical consequences of the impact of bleaching agents on restorations.
H) Conclusion
I) References.
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2. INTRODUCTION
An Evolving History :
Bleaching is not new ! The earliest efforts to lighten teeth through bleaching took place more
than a century ago, with bleaching agents painted directly on the tooth surface or packed inside a
nonvital tooth.
The earliest agent reportedly used was oxalic acid, described by chapel in 1877. Following
experiments with various forms of Chlorine, Harlan described in 1884 what is believed to be the first
use of hydrogen peroxide, which he called hydrogen dioxide.
Bleaching nonivital or pulpless teeth changed less rapidly. The first reported instance of
bleaching nonvital teeth was in 1895, when a dentist named Garreson applied chloride to the tooth
surface. The results were not inspiring, and there were few followers.
In 1958, Pearson realized the dentist could take advantage of the nonvital tooth’s lack of a pulp.
He packed same hydrogen peroxide agent being used for bleaching of vital teeth, superoxol, in the pulp
chamber for 3 days. By the late 1960s the standard method was established by Nutting and Poe, who
sealed a mixture of 30 5 hydrogen peroxide and sodium perborate in the pulp chamber for up to a week.
Chemistry of Bleaching :
Bleaching is a chemical process for whitening materials which is widely used in industry.
The three most prominent commercial bleaching processes are peroxide, chlorine, and chloride,
in that order. The strength is designated most frequently by volume rather than by percentage of
peroxide. Thus, although they are interrelated proportionately, 27.5 % hydrogen peroxide is termed 100
volume, 35 % is 130 volume, and 50 % is 200 volume, volume indicating the volume of oxygen released
by one volume of the designated H2O2.
Bleaching processes are complex, the vast majority work by oxidation.
The oxidation – reduction reaction which takes place in the bleaching process is known as a
redox reaction.
In a redox reaction of the oxidizing agent (e.g., hydrogen peroxide) has free radicals with
unpaired electrons, which it gives up, becoming reduced ; the reducing agent (the substance being
bleached) accepts the electrons and becomes oxidized).
In dental bleaching (Fig 2-3), hydrogen peroxide diffuses through the organic matrix of the
enamel and dentin. Because the radicals have unpaired electrons, they are extremely electroplcific and
unstable and will attack most other organic molecules to achieve stability, generating other radicals.
These radicals can react with most unsaturated bonds, resulting in disruption of electron conjugation and
a change in the absorption energy of the organic molecules in tooth enamel. Simpler molecules that
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3. reflect less light are formed, creating a successful whitening action. This process occurs when the
oxidizing agent (hydrogen peroxide) reacts with organic material in the spaces between the inorganic
salts in tooth enamel.
Effect of bleaching agents on properties of restorative materials :
Composite resins :
• 10-16 % carbamide peroxide bleaching gels (i.e., 3.6 – 5.76 % H2O2) may lead to a slight, but
significant increased in surface roughness and amount of porosities of microfilled and hybrid
composite resins.
• Cracking was also seen in microfilled composites.
• Changes in the surface reflectance in microfilled and hybrid composites after application of
highly concentrated tooth whiteness with 30 – 35 % H2O2,
• Salivary proteins absorbed on to the surface of composite materials decreased after bleaching
with peroxide containing agents, which is suggested to have an influence on bacterial adhesion
of cariogenic bacteria such as streptococcus sobrinus and streptococcus mutans, but not of
Actinomyces viscosus.
• It has been claimed that under clinical conditions in the mouth, ∆E color difference have been
reported to be relevant and perceptible only when higher than 3.3 or 3.6. App of 10 5 H2O2 or
heated 30 % H2O2 resulted in composite color changes which were presumably clinically
detectable with ∆E ranging between 2 and 11 for the different materials and shades tested.
• In contrast, use of 10 % carbamide peroxide gel led to color changes of composite resins less
than ∆E 2. However, even 10 % carbamide bleaching agents were able to remove extrinsic stains
from composite restorative materials.
• Feldspathic porcelain :
Turker and Biskin (2003) evaluated the effects of bleaching agents on feldspathic porcelain. 10-
16 % carbamide peroxide gels (applied for 8 hour per day for 30 days) were able to significantly
decrease surface hardness of the porcelain material tested.
6 % H2O2 gel on feldspathic porcelain does not have any effect on surface texture.
Polyacid – modified resin – based composites  (Compomer) :
• Highly concentrated bleaching regimes induced
o Surface degradation,
o Softening
o An inc in fluoride release and
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4. o Changes in the coefficient of thermal expansion, when those bleaching agents were
continuously applied for 1-5 days.
o In some products even cracks were observed.
Effects of GIC :
• In glass ionomer cement, silicone dioxide is in high concentrations in the undeserved core
material surrounded by the Al2+
and Ca2+
gel, with a matrix formed by Coo – anions relative to
the Al2+
or Ca2+
cations.
• The result is a set cement consisting of an agglomeration of unreacted powder particles
surrounded by a silica gel held together in an amorphous matrix of hydrated calcium and
aluminum polysalts.
• After application of 10 % carbamide peroxide, more core is exposed because of the erosion of
the matrix represented by an increased of exposed silica particles.
• Jefferson in (1992) examined alterations of atomic weight percentages in GIC after contact with
10 5 carbamide peroxide with pH 4.5 and reported that the dissolution of G1 and silicate cements
included three steps :
a) Surface wash – off
b) Diffusion in the solid state
c) Surface corrosion with the cores of the silica more exposed and a decreased of surface
aluminum content.
• Additionally, it was recently proved that a low concentrated 6 % H2O2 gel did not cause
significant dissolution or increased wear rate of GIC by Mair L. in 2004.
• By using highly concentrated bleaching regimes, no surface microhardness changes were
observed in polyacid modified resin-based composites or resin – modified GIC, by YAP AU in
2002.
Effect on temporary restorations :
Hydrogen peroxide and carbamide peroxide both cause microscopic changes in the surfaces of
some temporary restorative materials.
• Macroscopically, IRM (reinforced ZO-E composition) restorations exposed to H2 peroxide may
appear cracked and swollen.
• Methacrylate temporary resins discolor (become organgish) when exposed to CP.
• Jefferson et al in 1992 described a decrease in aluminum and an increase in porosity in zinc
oxide cement after immersion in acidic 10 % carbamide peroxide solutions.
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5. • The bis- acryl composite region provisional material didn’t change color, same with
polycarbonate crowns.
Practitioners should inform patients that provisional restorations may develop orange
discoloration during the NGVB procedure. For patients who are highly conscious of esthetics
and who need esthetic provisional crown restorations during the bleaching process, bis – acryl
composite resin or polycarbonate crown forms may be the materials of choice.
• Bleaching agents affect the organic substance of the material by rapidly breaking the inter
locking bond between eugenolate and other IRM particles, resulting in relatively high zinc oxide
levels at the surface.
• Disintegration and recrystallization occurs.
Amalgam and other dental alloys :
• Low concentrated hydrogen peroxide gels (6%) donot alter the surface texture of either high
copper amalgam or type III gold alloy.
However, evaluation of corrosion current density of various dental alloys revealed that
the application of 10% carbamide peroxide solution on non-polished amalgam samples and Ni-
Cr may cause corrosion of these materials, but not of noble alloys.
• Bleaching agent caused lower corrosion potential for the polished amalgam compared to non-
polished (According to Canay S, 2002).
• If amalgam is exposed to 10 % carbamide peroxide or 10 % H2O2 preparations, there will be
mercury and silver.
• Active oxidation was held to be responsible for the increased release of amalgam components
and also for greening of the tooth – amalgam interface.
• The Hg release from amalgam also modified by the presence of biofilm on amalgam containing
saliva, bacteria and polysarcharide.
• Carbamide peroxide may have facilitated the degradation of the amalgam surface by removing
the protective surface films, there by exposing the Ag – Hg matrix. The unprotected amalgam
surface was further oxidized, thus leading to chemical dissolution of the mercury phase and
release of available Hg to the surrounding solution.
• Ingestion, in halation, or absorption of Hg by patients may be toxic to body tissues, causing a
variety of systemic adverse effects. from the toxicologic point of view, mercury compounds fall
into several categories.
• Elemental mercury vapor.
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6. • Inorganic mercury salts.
• Organic mercury compounds.
Dental amalgam contains inorganic mercury bound to intermetallic compounds.
• Mercury is released from amalgam either as mercury vapor or mercuric ions. It may then be
absorbed by the oral mucosa and the respiratory and GIT with a risk of toxic systemic effects.
• Hg released from dental amalgams during mouth guard bleaching may increased the total
mercury burden, the clinical must exercise caution and take measures to minimize undesirable
mercury release.
Reasons for the impact of bleaching agents on properties of restorative materials and clinical
consequences :
• Bleaching agents caused erosion on the surface of the composite matrix.
• Bailey and Swift (1992) suggested that the surface changes could have been caused by complex
interactions with in multi-component bleaching products.
• Chemical softening of composite resins is believed to occur in vivo, contributing to wear of resin
in both stress – bearing and non-stress bearing areas.
Softening is caused by chemicals with solubility parameters similar to that of the resin
matrix. The bis – GMA resin polymer can be softened by chemicals with solubility parameters in
the range of 18.2 to 29.7 (MPa). A wide variety of solvents have solubility parameters with in
that range.
• The alterations in color of the restorative materials have been attributed to oxidation of surface
pigments and amine compounds, which have also been indicated as responsible for color
instability of restorative materials over time.
• Increase in porosities are as a result of the deleterious impact of the oxidizing bleaching agent
son the polymer – matrix of resin – based materials.
• Cullen DR (1993) found that there is significant reduction in diametral strength of H2O2 –
bleached microfilled composite resins compared with the results of the posterior or hybrid
composite resins, that if the resinous matrix was the site of oxidation and degradation.
Microfilled composite resins contain a greater concentration of resinous matrix than hybrid
composite resins contain. 30 5 H2O2 is an aggressive oxident, capable of degrading the polymer
matrix of resin rich microfilled composite resins.
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7. • Due to the negative influences of the oxidizing agents on the resin matrix led to water uptake of
the restorative materials with complete or partial debondig of fillers causing reduced surface
integrity and loss of hardness of the materials.
• Polishing of the restorations after bleaching is advisable at least, since the increased surface
roughness is held to be responsible for increased adherence of certain cariogenic microorganisms
to the outer surface of tooth colored restorative materials after contact with different bleaching
agents as assessed by Mor et al (1988).
• In order to reduce patient exposition to amalgam components, polishing of amalgam restorations
prior to starting of a bleaching therapy should be performed to reduce corrosion potential of the
amalgam restorations.
• Additionally, pre-coating of amalgam surfaces with a protective varnish such as copalite (10 5
copal resin in a combination of ether, alcohol and acetone) seems to be advisable to reduce
release of Hg in to the surrounding environment during bleaching with 10 % carbamide
peroxide.
Effect of bleaching agents on bond strength of restorative materials to enamel and dentin :
Bond strength of composite resins to enamel :
• 25 – 35 % H2O2 uniformly showed that both shear bond strength and tensile bond strength of all
composite restorative materials tested were significantly reduced when composite application
(including acid – etching pretreatment) was performed immediately, i.e., with in / day, after
completion of bleaching regime.
• It was shown that resin tags in bleached enamel subsequently acid etched with 37 % phosphoric
were less defined, more fragmented and penetrated to a less depth than in unbleached enamel
controls. (Smith DC 1991).
• Recommendations for application of composite materials onto carbamide peroxide bleached
enamel ranged from 1 day, 3-7 days, to 3 weeks.
• The effect of bonding agent on composite bond strength to enamel bleached with carbamide
peroxide gels seem to depend on the bonding agent used. (acetone)
• Only one study dealt with the adhesion of resin modified GI cements to pre-bleached enamel. It
was shown that the cement used for bracket bonding was not affected by pre-bleaching of
enamel with 10 % carbamide peroxide at 24 hour and 14 days after bleaching according to
Homewood C. (2001).
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8. Bond strength of composite resins and glass ionomer cements to dentin:
There is reduction is dentin bond strength for composite and G.I.C for both bleaching with 30-35 %
H2O2 and 60-21 % CP.
Reasons for the impact of bleaching agents on bond strength of restorative materials and clinical
consequences :
• Bleaching with H2O2 or H2O2 releasing agents may result in significant decrease of enamel
calcium and phosphate content and in morphological alterations in the most superficial enamel
crystallites.
• The enamel and dentin organic matrix was altered by the oxidizing effect of H2O2. These aspects
may lead to an enamel surface, which did not allow for formation of a strong and stable bond
between the composite applied and the superficial etched enamel layer.
• Furthermore, reduction in bond strength in H2O2 treated enamel and dentin could be caused by
residual O2 present in enamel and dentin pores after completion of the bleaching treatment.
• To dissolve remnants of peroxide, cavities can also be cleaned with catalase or 10 % sodium as
corbate. However, approach of these agents might be time – consuming or expensive, so that
further investigations are needed to optimize their use under clinical conditions.
• So it is therefore more feasible to follow the above mentioned recommendations to allow for
contact time of at least 7 days with H2O2 to avoid the reduction of adhesion of composites to
enamel. Proper 3 weeks must.
Effect of bleaching agents on marginal quality of restorations :
Composite resin :
• Pre – restorative nonvial, intra-coronal bleaching in the sense of walking – bleach – technique
using mixtures of 37 % carbamide peroxide or pastes consisting of 30 % H2O2 and sodium
perborate leads to a higher rate of microleakage in composite of both the access cavity and class
–V cavities placed immediately after termination of bleaching.
• In class V restorations, the increase of microleakage after intra-coronal application of 37 %
carbamide peroxide was only detected in dentin margins and not in enamel margins. (Shinohara
et al in 2001).
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9. • Short-term use of intracoronal Ca(OH)2 medicament for 7-days after completion of walking –
bleach therapy was able to reverse the – negative influences of the H2O2 application on
microleakage of access cavities.
• Study done by Vlukapi et al (2003) proved that microleakage rates of labial restorations with
enamel margins only, were significantly increased after 10 % carbamide peroxide bleaching.
• Similar findings were reported by Turkun and Turkum in (2004) that significant reduction in
sealing of access cavities with composite resins up to 1 weeks after application of 10 %
carbamide peroxide into the pulp chamber.
Polyacid – modified resin – based composites, resin – modified GIC, amalgam and temporary
materials :
• Only two studies addressed to the impact of pot operative bleaching (35 % H2O2 or 3-16 % CP)
on restorations with enamel margins fabricated with polyacid – modified resin – based
composites, resin – modified GIC or amalgam. Done by Ownes BM in 1998 and Vlukapi H
(2003).
• In both studies, no deterioration of marginal seal was revealed.
• Marginal leakage of amalgam restorations with enamel margins only were also not negatively
influenced by pre-operative external bleaching with 10 % carbamide peroxide.
• It was indicated that temporary restorative materials, such as ZOE cement and zinc oxide
phosphate cement, did not provide an optimal seal when used for provisional restoration of the
access cavity during internal bleaching with the walking bleach technique using a mix of 30 %
H2O2 with sodium perborate as bleaching agent.
• The most favorable results with respect to cavosurface seal during internal bleaching were
demonstrated for hydraulic filling materials, such as cavil and coltosol.
Penetration of the pulp chamber by bleaching agents in restored teeth :
• It was observed that during external bleaching with 30 % hydrogen peroxide or 10-35 %
carbamide peroxide gel higher levels of H2O2 penetrated into the pulp chamber in teeth with
restorations placed in enamel as compared to sound teeth.
Clinical consequences of the impact of bleaching agents on restorations :
• External root resorption has been related to bleaching of endodontically treated teeth (Heller et al
1992).
• It may be prevented by placing a base in the root canal opening.
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10. Temporary dressing of pulp chamber with Ca(OH)2 has also been indicated to prevent
external root resorption.
• Kehoe (1987) found that bleaching agents reduced the pH in the amelo-cemental junction,
stimulating osteoclastic activity, which could start external root resorption.
Placing Ca(OH)2 paste into the pulp chamber could increase pH, thus, inhibiting the
osteoclastic activity.
The above mentioned studies underline that pre and post operative bleaching procedures
may – very affect marginal seal of restorations.
• Moreover, restorations and margins of restorations could be regarded as a possible pathway
facilitating peroxide penetration into the pulp chamber.
• Peroxide penetration into the pulp chamber is held responsible for Pulpal reactions such as
increase in tooth hypersensitivity, during external bleaching of vital teeth.
Dentists should therefore examine restorations meticulously before starting a bleaching
therapy and renew insufficient fillings prior to bleaching in order to achieve an optimal seal of
the pulp chamber and thus reducing the risk of adverse effects.
Conclusions :
Bleaching procedures can be used with little fear of damage to existing restorations. In addition,
bleaching may improve the outcome of many restorative procedures.
• Like if porcelain veneered teeth become darker over time due to regression of the original
bleaching effect, they may be rebleached by applying CP to the lingual surfaces. This procedure
is effective because peroxide is able to diffuse freely Thro’ the tooth from the unrestored areas of
enamel, as porcelain veneers are translucent and life like.
• In case of ceramic crowns – frequently, when a single anterior crown is required, the adjacent
teeth have a shade that is very difficult to match with ceramic materials. Bleaching can be used
to change the shade of the adjacent teeth to one that is more easily replicated in porcelain. Also, a
single ceramic crown that originally matched the adjacent teeth will appear lighter than adjacent
teeth because those teeth have discolored over the years from aging and dietary habits.
• In many cases, the adjacent natural teeth can be bleached to improve their match with the
crown, eliminating the need to replace the crown to correct the aesthetic mismatch.
• Home bleaching agents should not be used indiscriminately when composite resin restorations
are present.
• The patient should be informed that bleaching may accelerate the natural aging process of
composite resin restorations.
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11. • The patient must also realize that restorations frequently must be replaced to ensure proper
shade matching if bleaching is successful.
• Finally, if posterior composite resin restorations are present, the patient should be instructed to
be careful to confine the bleaching gel to the anterior segment of the tray.
• Bonding of adhesively attached restorations to prebleached dental hard tissue is significantly
reduced. Therefore, it is recommended to delay placement of restorations after termination of
bleaching therapy for at least 1-3 weeks.
• Before deciding whether to veneer or bleach, carefully examine the patient’s enamel, tooth
position, and arch form. First look at the enamel shade and structure. How much translucency is
present and where is it located ? The danger of bleaching translucent enamel is that it may
become more translucent, there by possibly creating the illusion of a darker, rather than lighter,
tooth is darkness from the back of the mouth bleeds Thro’.
• Compromised tooth position or arch arrangement may influence the decision whether to bleach
or bond. Although bleaching may well lighten the teeth, the end result may still not please the
patient, whiter may still be malpositioned and hence unattractive. Therefore, either bonding or
laminating may be a better choice where it is possible to simultaneously create the illusion of
straighter teeth
REFERENCES:
1)Effect of three bleaching agents on the surface properties of three different esthetic restorative
materials.
J Prosthet Dent 2003; 89 : 466-73.
2) Effects of home bleaching products on composite resins.
Quintessence Int 1992 ;23 :489-94.
3) The effect of bleaching agents on the microhybridness of dental aesthetic restorative materials.
J Oral Rehabil 2002 ; 29: 657-61.
4) Peroxide bleaches – effect on tensile- strength of composite resins.
J Prosthet Dent 1993; 69: 247-9.
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12. 5) The effect of current bleaching agents on the color of light polymerized composites in vitro.
J Prosthet Dent 2003; 89: 474-8.
6) Effects of carbamide peroxide on dental luting agents.
J Endod 1992; 18: 128-32.
7) In vitro evaluation of the effect of a current bleaching agent on the electrochemical corrosion of
dental alloys.
J Oral Rehabil 2002; 29:1014-9.
8) In vitro microleakage of composite restorations after non vital bleaching.
Quint Int 2001; 32: 413-7.
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