The Saudi Journal for Dental Research (2014) 5, 81–92

King Saud University

The Saudi Journal for Dental Research

www.ksu.edu.sawww.sciencedirect.com

ORIGINAL ARTICLE

Effects of pre- and post-simulated home bleaching

with 10% carbamide peroxide on the shear bond

strengths of different adhesives to enamel

* Corresponding author. Address: Restorative Dental Sciences

Dept., College of Dentistry, King Saud University, P.O. Box 60169,

Riyadh 11545, Saudi Arabia. Mobile: +966 503486898.

E-mail address: malqathani@ksu.edu.sa (M.Q. Alqahtani).1 Demonstrator and Postgraduate Student.2 Associate Professor.

Peer review under responsibility of King Saud University.

Production and hosting by Elsevier

2352-0035 ª 2014 Production and hosting by Elsevier B.V. on behalf of King Saud University.

http://dx.doi.org/10.1016/j.sjdr.2014.01.002

Aminah M. Elmourad1, Mohammed Q. Alqahtani

2,*

Restorative Dental Sciences Dept., College of Dentistry, King Saud University, Saudi Arabia

Received 7 December 2013; revised 10 January 2014; accepted 10 January 2014Available online 22 February 2014

KEYWORDS

Pre-bleaching, Post-bleach-

ing;

Bond strength;

Etch-rinse adhesive;

Self-etch adhesive

Abstract Aim: This in vitro study was undertaken to investigate the effects of pre- and post-sim-

ulated bleaching procedures with 10% carbamide peroxide on the shear bond strengths of different

adhesives to enamel and to determine the failure modes of tested specimens.

Materials and methods: The specimens were randomly divided into three groups (n= 30) accord-

ing to the sequence of bleaching and bonding procedures (control non-bleach, pre- and post-bleach

groups). Each group was then subdivided into three subgroups (n= 10) according to the three

types of adhesives: OptiBond Solo Plus (Kerr) and Single Bond Universal (3M-ESPE) used as

etch-and-rinse and self-etch techniques. Resin composite cylinders were then placed with Filtek Z

250 (3M ESPE). The specimens were stored in distilled water at 37 �C for 24 hours prior to being

thermocycled for 1000 cycles (at 5 and 55 �C). The samples in the pre- and post-bleach groups were

also immersed daily in artificial saliva at 37 �C, and for two weeks after completion of the bleaching

process. Shear bond strengths were measured with a cross-head speeds of 0.5 mm/min. Failure

modes of debonded specimens were determined by stereomicroscopy (30·). The interface margins

of resin composite to the different enamel conditions were observed by scanning electron micros-

copy (1000·) before shear bond strength testing.

82 A.M. Elmourad, M.Q. Alqahtani

Results: There were no significant effects of different enamel conditions (control non-bleach, pre-

bleach and post-bleach) on the shear bond strengths of OptiBond Solo Plus Adhesive Agent or etch-

and-rinse Single Bond Universal Adhesive Agent. Pre- and post-simulated home bleaching of

enamel with 10% carbamide peroxide had an adverse effect on the shear bond strengths of self-etch

Single Bond Universal Adhesive Agent.

Conclusion: In enamel, an etch-and-rinse approach with phosphoric acid remains the procedure of

choice, since it guarantees the most durable bond to enamel. Therefore, selective phosphoric-acid-

etching of enamel is highly recommended, followed by self-etching.

ª 2014 Production and hosting by Elsevier B.V. on behalf of King Saud University.

1. Introduction

Stained teeth are frequently seen in the dental office and are

one of the major challenges faced by dentists. In fact, toothdiscoloration creates a wide range of esthetic problems, andpeople often expend much time and money to improve the

appearance of their discolored teeth.37 Therefore, in recentyears, the demand for esthetic dental procedures and toothbleaching has increased dramatically.

In general, tooth staining can be classified into intrinsic

stains, extrinsic stains, or a combination of both. Moreover,

tooth discoloration might be limited to a single tooth or to sev-

eral teeth in a single arch, or may be more generalized. In somecases, scaling and polishing of the teeth will improve the situ-ation; however, more extensive treatment; such as vital and

non-vital bleaching, microabrasion, resin composites, porce-lain veneers, or all-ceramic crowns; is usually needed toachieve a more satisfying result. In some instances, these treat-

ment measures are combined.36

Dental bleaching is considered to be the most conser vativetreatment for discolored teeth. It can be defined as the processof removing stains or pigments from teeth by the application

of chemicals, such as hydrogen peroxide or urea peroxide.36

Tooth-bleaching materials usually contain a strong oxidizingagent, and their ability to whiten teeth is mainly due to oxida-

tion reactions.4 Hydrogen peroxide or one of its precursors

(carbamide peroxide or sodium perborate) is a popular oxidiz-

ing agent used to whiten teeth.4 Tooth bleaching occurs due to

the decomposition of peroxide into free oxygen radicals, whichcan break down the large pigmented molecules that accumu-

late in teeth into smaller, less-pigmented molecules.22

The population’s increasing demand for tooth bleachinghas driven many manufacturers and researchers to developbleaching products to be used either in the dental office or at

home. It has been estimated that bleaching has been performedfor more than one million patients in dental offices.45 In addi-tion, the fact that more than 35 million tooth-whitening kits

have been sold worldwide from May 2001 to March 200535

indicates that large numbers of people have utilized self-ap-

plied at-home bleaching products.

Although tooth bleaching is considered to be a conser va-

tive and economical method of treating discolored teeth, this

procedure is known to have an effect on the natural tooth

structure,1,2,5,6,16,26 adhesive bonding,40 and restorative materi-als.7,9,13 The interaction of tooth bleaching with any previousor subsequent dental treatments should be considered.

The effects of bleaching agents on the bonding interface ofresin restorations to tooth substrates with different adhesivesare controversial. Most available research in the current

literature documents enamel bleaching performed prior toadhesive and restorative procedures; however, analysis of theinfluence of bleaching agents on enamel, dentin, adhesives,

and pre-existing resin restorations that are not indicated forreplacement; has been of notable importance in obtaining use-ful information about tooth-restoration bond degradation and

the possible need to replace these pre-existing resinrestorations.

The objectives of this study were to investigate the effects of

pre- and post-simulated bleaching procedures with 10% car-bamide peroxide on the shear bond strengths (SBSs) of differ-ent adhesives to enamel, and to determine the failure modes of

tested specimens.The hypotheses tested were that:

(1) pre-simulated home bleaching will reduce the adhesive

bond strength of resin-based composite material toenamel; and

(2) post-simulated home bleaching will not have an effect

on the adhesive bond strength of resin-based compositematerial to enamel.

2. Materials and methods

A pilot study was conducted at the beginning of our experi-

ment to investigate the reliability of the test that was used.

2.1. Tooth selection

Ninety sound human molars were selected for use in this study.All teeth were cleaned with an ultrasonic scaler and polishedwith non-fluoridated pumice in a rubber cup mounted in aslow-speed handpiece (Kavo EWL, No. 6412500, Germany).

After being cleaned and polished, the teeth were stored in dis-tilled water with 0.05% thymol solution in a dark container atroom temperature until being mounted. The teeth selected for

study were free of caries, cracks, abrasion facets, fluorosis,and damage due to extraction. Each tooth was examined undera stereomicroscope (Stereoscopic ZoomMicroscope SMZ1000,

Nikon) to eliminate teeth with cracks or hypoplastic defects.

2.2. Preparation of specimens

Crowns of teeth were separated from the roots 2 mm apical tothe cemento-enamel junction by water-coolant spray and aslow-speed diamond saw (Isomet 2000, Buehler, IL, USA).Self-cure acrylic resin was loaded in polyvinyl chloride (PVC)

cylindrical molds (diameter, 34 mm; height, 20 mm), which

Effects of pre- and post-simulated home bleaching 83

were used for mounting the teeth. Each tooth was embedded inthe acrylic resin in such a way that its buccal surface was facingupward for bonding procedures. To avoid the effects of ther-

mal generation by acrylic resin on the teeth, the specimenswere kept in cold water until the completion of the polymeri-zation process.

After each specimen was mounted, the buccal surface wasground and polished with wet silicon carbide papers (240-,400- and 600-grit) (Buehler) mounted in an Automata Ma-

chine (Jean-Wirtz GmbH, Dusseldorf, Germany) to create auniform, flat enamel surface before bonding procedures. Afterbeing ground and polished, all specimens were examined bystereomicroscopy (Stereoscopic Zoom Microscope SMZ

1000, Nikon) to verify that the exposed tooth structure was en-amel only.

2.3. Experimental materials

Table 1 lists the materials used in the current study: one resincomposite material (Filtek Z 250), one at-home bleaching

material (Nite white – 10% carbamide peroxide), one acidetchant (Ultra-etch), and two adhesive bonding systems (Opti-Bond Solo plus and Single Bond Universal).

2.4. Experimental groups

The specimens were randomly divided into three main groups(n= 30) according to the sequence of bleaching and bonding

procedures as:

Group 1: Control – no bleaching,

Group 2: Pre-simulated home bleaching,Group 3: Post-simulated home bleaching.

Each main group was subdivided into three subgroups(n= 10) according to the three types of adhesives:

a. Etch-and-rinse adhesive (OptiBond Solo Plus, Kerr,Orange, CA, USA),

b. etch-and-rinse adhesive (Single Bond Universal, 3MESPE, Seefeld, GERMANY),

c. Self-etch adhesive (Single Bond Universal, 3M ESPE,Seefeld, Germany).

Main groups’ description:

1. First group (control – no bleaching)

Bonding procedures and resin composite application werecarried out, followed by the thermocycling procedure andthen a shear bond test.

2. Second group (pre-simulated home bleaching)Home bleaching of enamel was performed for 14 consecu-tive days according to the manufacturer’s instructions,and then samples were stored for two weeks in artificial sal-

iva at 37 �C, followed by bonding procedures and resincomposite application, thermocycling procedure, and thena shear bond test.

3. Third group (post-simulated home bleaching)Bonding procedures and resin composite application werecarried out, followed by thermocycling procedures, home

bleaching for 14 consecutive days according to the

manufacturer’s instructions, then storage for two weeks in

artificial saliva at 37 �C and a shear bond test.

2.5. Bonding procedures

All bonding procedures were performed according to the man-ufacturers’ instructions (Table 1). A light-curing procedure wascarried out with a high-power light-emitting diode (LED) cur-

ing light (Elipar� S10, single-peakBlue, 3M ESPE, MN, USA)within the range of 900–1000 mW/cm2 and verified with a cur-ing radiometer (Optilux Model 100, SDS Kerr, CT, USA).

2.6. Resin composite application

After the bonding procedure, each specimen was placed in the

compression bonding apparatus for application of the resincomposite (Filtek Z 250 – shade A2, 3M ESPE Dental Prod-ucts, MN, USA) in the vinyl tube (2 mm high and 4 mm in

diameter) (Fig. 1). The resin composite was then condensedagainst a cured adhesive bonding agent to form a resin post,followed by light-curing for 40 s.

2.7. Bleaching procedure

Bleaching was done with 10% carbamide peroxide (NiteWhite, Discus Dental Inc., CA, USA) for 14 consecutive days

according to the manufacturer’s instructions, simulating thehome bleaching procedure (Figs. 2 and 3). The bleaching pro-cedure was performed on the top surfaces of the specimens in

the second and third groups. At the end of every bleachingapplication, the treated specimens were washed under flowingdistilled water and brushed with a soft toothbrush. Specimens

were placed in an ultrasonic cleaner for 5 min. Then, they wereplaced in fresh artificial saliva in a universal oven (Memmertuniversal oven, 80343, Memmert GmbH, Germany) at 37 �Cuntil the next day’s bleaching application. The artificial saliva

was replaced daily.

2.8. Thermocycling

After the bonding procedure, the samples were stored in dis-tilled water at 37 �C for 24 h, then subjected to 1000 cyclesin a thermocycling apparatus (Thermocycler 1100/1200, SD

Mechatronik, Germany) between baths of 5 and 55 �C witha dwell time of 30 s.11 After being thermocycled, samples werestored in artificial saliva at 37 �C until the one week storagetime was completed.

2.9. Artificial saliva storage

The samples in all groups were stored in 250 mL of artificial

saliva at 37 �C for 1 week after being thermocycled. In addi-tion, samples in Groups 2 and 3 were also immersed daily in250 mL of artificial saliva at 37 �C, for two weeks after the

end of the bleaching process. The solution of artificial salivaused in this study was composed of sodium chloride (NaCl,0.4 g), potassium chloride (KCl, 0.4 g), calcium chloride

(CaCl2.H2O, 0.795 g), sodium-di-hydrogen phosphate (NaH2-

PO4ÆH2O, 0.69 g), sodium sulfide (Na2S9ÆH2O, 0.005 g), and

Table 1 Materials used in the study, with their compositions, manufacturers, and application procedures.

Material Manufacturer Material composition Application procedure

Filtek

Z 250

Micro-hybrid

resin composite

3M ESPE Dental

Products, St. Paul,

MN, USA

Bis-GMA, Bis-EMA, UDMA, Zirconia/silica (78% w/

w), barium glass, Ytterbium trifluoride, mixed-oxide

prepolymer

� Place Filtek Z 250 –shade A2

� Light-cure each increment for 40 s

Nite white

ACP

Discus Dental Inc.,

Los Angeles, CA,

USA

10% carbamide peroxide, hydrogen peroxide,

propylene glycol, glycerine, water, dicetyl phosphate,

cetearylalcohol, ceteth-10 phosphate, silica,

hydroxprolylcellulose, potassium nitrate, flavor,

sodium phosphate, calcium nitrate, calcium carbonate,

potassium hydroxide

Bleaching gel for at-home bleaching simulation, 8 h/

day for 14 consecutive days

Ultra-etch acid

etchant

Ultradent Products

Inc., South Jordan,

UT, USA

35% phosphoric acid Enamel will be etched with the acid etchant for 20 s,

rinsed and air-dried to create frosty enamel appearance

Optibond

Solo Plus

Used as etch-rinse

technique

Kerr, Orange, CA,

USA

Bis-GMA, HEMA, GPDM, ethanol, barium,

aluminum borosilicate glass, fumed silica, sodium

hexafluoro-silicate, photoinitiator

Enamel will be etched with the acid etchant for 20 s,

rinsed and air-dried to create frosty enamel

appearance, followed by adhesive application, air-

thinning for 3 seconds and light curing for 20 s

Single Bond

Universal

Used as etch-

andrinse and self-

etch techniques

3M ESPE,

Seefeld,Germany

MDP phosphate monomer, dimethacrylate resins,

HEMA, vitrebond copolymer, filler, ethanol, water,

initiators, silane

If used as etch-and-rinse technique, enamel will be

etched with the acid etchant for 20 s, rinsed and air-

dried to create frosty enamel appearance, followed by

adhesive application, air-thinning for 5 seconds, and

light-curing for 10 s

If used as self-etch technique, the adhesive will be

applied directly without the enamel-etching technique

84

A.M

.Elm

ourad,M.Q

.Alqahtani

Fig. 1 The compression bonding apparatus.

Fig. 2 One specimen to show the application of bleaching gel to

enamel structure before the bonding process in Group 2.

Fig. 3 One specimen to show the application of bleaching gel

after the bonding process in Group 3.

Effects of pre- and post-simulated home bleaching 85

distilled water 1000 mL (pH = 7).3 The artificial saliva waschanged daily during the storage period. Each time the sam-ples were removed from the artificial saliva, the enamel surface

was rinsed with an air/water syringe for 30 s.

2.10. Shear bond strength (SBS) testing

The samples were subjected to SBS testing in a universal test-

ing machine (Instron 8500, England) with a load cell of 10 kN.The sample was mounted in a customized metal jig while a

knife-edged rod with a width of 0.5 mm was applied at theadhesive-enamel interface at a cross-head speed of 0.5 mm/min. The SBS was expressed in megaPascals (MPa), obtained

by dividing the load at failure by the bonded cross-sectionalarea.

2.11. Failure analysis

After shear testing, all fractured samples were analyzed by ste-reomicroscopy (Stereoscopic Zoom Microscope SMZ 1000,Nikon) at 30· magnification for failure analysis. Failure modes

were classified as: ‘‘Adhesive failure’’, between the bondingagent and enamel (AE) or between the bonding agent and resincomposite (AR); ‘‘Cohesive failure’’ within the resin composite

material (CR) or the enamel structure (CE); or ‘‘Mixed failure’’.

2.12. Testing by scanning electron microscopy (SEM)

The interface bonding margins of resin composite cylindricalposts with different adhesive agents (OptiBond Solo Plus,etch-and-rinse Single Bond Universal and self-etch Single BondUniversal) to different enamel conditions (control-non-bleach,

pre- and post-bleach) were observed by SEM before SBStesting (JSM, 6360LV, JEOL, Japan) at 1000· magnification.

2.13. Statistical analysis

Data were analyzed with SPSS Pc+ 21.0 version statisticalsoftware (IBM). Descriptive statistics (mean, standard devia-

tion, and percentages) were used to describe the quantitativeand categorical outcome variables. A one-way analysis of var-iance and Tukey’s multiple comparison tests were used to com-

pare the mean values of SBS across the categorical studyvariable. A p-value of 60.05 was considered statisticallysignificant.

3. Results

The results for mean SBSs and the failure modes of OptiBondSolo Plus, etch-and-rinse Single Bond Universal, and self-etch

Single Bond Universal bonding agents and resin composites to

86 A.M. Elmourad, M.Q. Alqahtani

human enamel under the different conditions (control withoutbleaching, pre- and post-simulated home bleaching) are pre-sented in Table 2 and Fig. 4. Different statistical analysis tests

are summarized in Table 2.

3.1. OptiBond Solo Plus Adhesive Agent

Enamel conditions had no significant effect on bond strength(p = 0.991) when the OptiBond Solo Plus Adhesive Agentwas used. The conditions are listed from the highest mean

SBS to the lowest: control non-bleached enamel(24.687 ± 7.286 MPa), post-simulated home-bleached enamel(24.153 ± 12.885 MPa), and pre-simulated home-bleached en-

amel (24.112 ± 11.836 MPa) (Table 2 and Fig. 4). Mean SBSvalues of this adhesive agent to the enamel were minimally re-duced in the different bleaching groups (pre-bleach and post-bleach) compared with that of the control group (non-bleach),

but with no significant difference (p= 0.992 and p= 0.993,respectively), and there was no significant difference betweenthe two bleaching groups (p = 1.000).

3.2. Etch-and-rinse Single Bond Universal Adhesive Agent

Enamel conditions had no significant effect on bond strength

(p = 0.794) when the etch-and-rinse Single Bond UniversalAdhesive Agent was used. The conditions are listed from thehighest mean SBS to the lowest: control non-bleached enamel(54.124 ± 13.001 MPa), pre-simulated home-bleached enamel

(54.028 ± 7.553 MPa), and post-simulated home-bleached en-amel (50.310 ± 19.559 MPa) (Table 2 and Fig. 4). Mean SBSvalues of this adhesive agent to the enamel were minimally re-

duced in the different bleaching groups (pre-bleach and post-bleach) compared with that of the control group (non-bleach),but with no significant difference (p= 1.000 and p= 0.882,

respectively). The post-bleaching of enamel had more effecton the SBS of this adhesive agent compared with the pre-bleaching procedure but with no significant difference between

groups (p = 0.830).

3.3. Self-etch Single Bond Universal Adhesive Agent

Enamel conditions had a significant effect on bond strength

(p < 0.0001) when the self-etch Single Bond Universal Adhe-sive Agent was used. The conditions are listed from the highest

Table 2 Shear bond strength means and SDs of different adhesive

summary.

Adhesive Agents Mean shear bond strength ± SD

Group Value (MPa)

OptiBond Solo Plus Control 24.687 ± 7.286

Pre-bleaching 24.112 ± 11.83

Post-bleaching 24.153 ± 12.88

Etch-and-rinse Single Bond Universal Control 54.124 ± 13.00

Pre-bleaching 54.028 ± 7.553

Post-bleaching 50.310 ± 19.55

Self-etch Single Bond Universal Control 51.267 ± 17.96

Pre-bleaching** 24.880 ± 10.41

Post-bleaching** 23.016 ± 13.94

N= 10 for each group. Groups with ** for each adhesive agent had no

mean SBS to the lowest: control non-bleached enamel(51.267±17.966 MPa), pre-simulated home-bleached enamel(24.880±10.417 MPa), and post-simulated home-bleached

enamel (23.016±13.948 MPa) (Table 2 and Fig. 4). MeanSBS values of this adhesive agent to the enamel were signifi-cantly reduced in the different bleaching groups (pre-bleach

and post-bleach) compared with that of the control group(non-bleach) (p = 0.001 and p < 0.0001, respectively). Thepost-bleaching of enamel had more effect on the SBS of this

adhesive agent compared with the pre-bleaching procedurebut with no significant difference between groups (p = 0.955).

3.4. Modes of failure

The failure modes for each group are listed in Table 3. The‘Percentage of adhesive failure’ category in specimens of theself-etch Single Bond Universal adhesive increased to 50% of

the specimens in the pre-bleaching group and to 80% of thespecimens in the post-bleaching group compared with non-adhesive failure of the control group (non-bleach).

3.5. Scanning electron microscopy

The SEM analysis of OptiBond Solo Plus Adhesive is shown in

Fig. 5a–c and demonstrates a good adaptation of the resincomposite to the enamel structure and a clear, uniform, andcontinuous interface-bonded margin in the three groups (con-trol non-bleach, pre-bleach, post-bleach).

The SEM analysis of etch-and-rinse Single Bond UniversalAdhesive Agent is shown in Fig. 6a–c and demonstrates a goodadaptation of the resin composite to the enamel structure and

a clear, uniform, and continuous interface bonded margin inthe three groups (control non-bleach, pre-bleach, post-bleach).The SEM findings of the two etch-rinse previous adhesives,

confirmed that the enamel conditions had no significant effecton bond strength.

The SEM analysis of Self-etch Single Bond Universal

Adhesive Agent is shown in Fig 7a, b and demonstrates a fairadaptation of the resin composite to the enamel structure inthe two groups (control non-bleach, and pre-bleach). How-ever, the interface bonded margin of resin composite with this

adhesive to post-bleaching enamel condition reveals gaps andnon-uniformity margins (Fig. 7c). The SEM findings of thisadhesive, confirmed that the enamel conditions had a signifi-

cant effect on bond strength.

agents in different enamel conditions and the statistical analysis

One-way ANOVA Test Tukey HSD Test

Group Group p-Value

0.991 Control Pre-bleaching 0.992

6 Control Post-bleaching 0.993

5 Pre-bleaching Post-bleaching 1.000

1 0.794 Control Pre-bleaching 1.000

Control Post-bleaching 0.882

9 Pre-bleaching Post-bleaching 0.830

6 <0.0001 Control Pre-bleaching 0.001

7 Control Post-bleaching <0.0001

8 Pre-bleaching Post-bleaching 0.955

significant difference at p 6 0.05.

Fig. 4 Shear bond strength means and SDs of different adhesive agents in different enamel conditions.

Table 3 Specimen numbers for the different failure modes.

Materials Groups Failure modes

Adhesive Cohesive Mixed

AE AR CE CR

OptiBond Solo Plus + Z250 composite Control 0 3 (30%) 1 (10%) 0 6 (60%)

Pre-bleaching 1 (10%) 2 (20%) 0 2 (20%) 5 (50%)

Post-bleaching 2 (20%) 1 (10%) 0 2 (20%) 5 (50%)

Etch-and-rinse

Single Bond Universal + Z250 composite

Control 0 0 4 (40%) 3 (30%) 3 (30%)

Pre-bleaching 0 0 3 (30%) 0 (10%) 7 (70%)

Post-bleaching 0 1 (10%) 3 (30%) 1 (10%) 5 (50%)

Self-etch

Single Bond Universal + Z250 composite

Control 0 0 4 (40%) 4 (40%) 2 (20%)

Pre-bleaching 3 (30%) 2 (20%) 1 (10%) 2 (20%) 2 (20%)

Post-bleaching 4 (40%) 4 (40%) 0 (10%) 0 2 (20%)

AE is adhesive failure between adhesive agent and enamel.

AR is adhesive failure between adhesive agent and resin composite.

CE is cohesive failure within tooth.

CR is cohesive failure within resin composite.

Effects of pre- and post-simulated home bleaching 87

4. Discussion

Nightguard vital bleaching has gained popularity as a conser-

vative technique to whiten natural teeth; therefore, manufac-turers have rapidly introduced many home-bleachingproducts into the market. Many of the newer systems contain

carbamide peroxide in various concentrations,32 with carbo-pol, which is considered to be a thickening agent capable ofimproving the retention of bleaching gel in the tray and allow-ing for a sustained release of the whitening agent.21 Nite White

ACP, which contains 10% carbamide peroxide, was selectedfor use in our study because it is the most frequently used con-centration for at-home bleaching, as described by Haywood

and Heymann,20 and has been approved by the American Den-tal Association.23

Any bleaching treatment, including in-office bleaching with

hydrogen peroxide at a concentration of 35% or at-homebleaching with 10% carbamide peroxide, is known to reducethe immediate post-bleaching bond strength of composite resinmaterial to enamel.14,17,38,40,41 The lower SBSs resulting imme-

diately after these bleaching procedures can be attributed to

the physical and chemical alterations in enamel. It has beensuggested that the quality of the composite bond is compro-

mised through a decreased number of resin tags, due to thepresence of residual peroxide on the tooth surface, which inter-feres with the resin bonding and prevents its complete poly-

merization, or due to the alteration of protein and mineralcontent in the superficial layers of enamel after the vitalbleaching process.14,33 According to the literature, the best

method for recovery of the decreased bond strength afterbleaching is to delay bonding resin restorations for one to

two weeks, which is a common procedure,10,42,43 even when

10% carbamide peroxide agents have been used. In our study,

composite resin bonding procedures were delayed for two

weeks after the end of the bleaching procedure. In addition,

samples were kept immersed in artificial saliva to simulatethe oral cavity conditions during the delay period. This artifi-cial saliva contained calcium and phosphate ions, which might

have contributed to the mineral gain.8

In general, many dental practitioners or patients require theplacement or replacement of existing esthetic restorations afterbleaching treatment; thus, the reduction of enamel bond

(a)

(b)

(c)

Resin Composite

Resin Composite

Resin Composite

Enamel

Enamel

Enamel

Fig. 5 Scanning electron microscope images (·1000) showing

interface bonding area of resin composite with OptiBond Solo

Plus bonding agent to enamel under different conditions. a:

control without bleaching, b: pre-bleaching, c: post-bleaching.

(a)

(b)

(c)

Enamel

Enamel

Enamel

Resin Composite

Resin Composite

Resin Composite

Fig. 6 Scanning electron microscope images (·1000) showing

interface bonding area of resin composite with etch-and-rinse

Single Bond Universal to enamel under different conditions. a:

control without bleaching, b: pre-bleaching, c: post-bleaching.

88 A.M. Elmourad, M.Q. Alqahtani

strengths after bleaching is clinically significant.30 In addition,an analysis of the influence of these bleaching agents on enam-el, dentin, adhesive, and resin composite in pre-existing resto-

rations that are not indicated for replacement, has been ofnotable importance in obtaining useful information abouttooth-restoration bond degradation and the possible need to

replace these pre-existing resin restorations.Based on our results, the first null hypothesis was rejected

for both OptiBond Solo Plus and etch-and-rinse Single Bond

Universal Adhesive Agents, where pre-simulated home bleach-ing with 10% carbamide peroxide did not reduce the adhesivebond strength of resin-based composite material to enamel;however, this null hypothesis was accepted for self-etch Single

Bond Universal Adhesive Agent, where pre-simulated homebleaching with the same material reduced the adhesive bondstrength of resin-based composite material to enamel. Regard-

ing the second null hypothesis, it was accepted for both Opti-Bond Solo Plus and etch-and-rinse Single Bond UniversalAdhesive Agent, where post-simulated home bleaching with

10% carbamide peroxide had no effect on the adhesive bondstrength of resin-based composite materials to enamel; how-ever, this null hypothesis was rejected for self-etch Single Bond

Universal Adhesive Agent, where post-simulated home bleach-ing with the same material had a deleterious effect on the adhe-sive bond strength of resin-based composite material toenamel.

Resin Composite

Resin Composite

Resin Composite

Enamel

Enamel

Enamel

(a)

(b)

(c)

Fig. 7 Scanning electron microscope images (·1000) showing

interface bonding area of resin composite with self-etch Single

Bond Universal to enamel under different conditions. a: control

without bleaching. b: pre-bleaching, c: post-bleaching.

Effects of pre- and post-simulated home bleaching 89

The findings of this study showed no statistically significant

difference between the SBS values of OptiBond Solo Plus eth-anol-based adhesive in pre-bleach and control (non-bleach)groups, and these findings were consistent with the results ofSung et al.38 and Kalili et al.,27 who reported that utilizing

an ethanol-based adhesive agent improved the bond strengthof bleached teeth. Moreover, Kalili et al.27 proposed that suchinhibition could result from bleaching agents that might cause

oxygen to penetrate and concentrate on the surface of enamel,thus inhibiting the cure of some resin tags. They also proposedthat the application of an alcohol-based bonding agent such as

OptiBond adhesive was able to minimize the inhibitory effectsof the bleaching process by residual oxygen through the inter-action of alcohol with this residual oxygen. Sung et al.38 re-

ported that the use of alcohol-based bonding agents might

result in a less compromised composite bond strength whenrestorative work was to be completed immediately afterbleaching, and if elective dental treatment could be postponed

for several days, the choice of the bonding agent would be-come less critical.

In addition, the mean SBS value of OptiBond Solo Plus

Adhesive to the enamel was minimally reduced in the post-bleach group when compared with that of the control group(non-bleach), but with no significant difference, and there

was no significant difference between the two bleaching groups(pre- and post-bleach). Therefore, bleaching treatment had noharmful effect on the SBS of composite resin restorationsbonded with this etch-and-rinse adhesive agent, and this was

in agreement with the results of a study by Dudek et al.,15

who found that increased risk of adhesive bond degradationby bleaching should be considered when simplified self-etching

adhesives are used in comparison with the etch-and-rinse adhe-sive Gluma Comfort Bond. OptiBond Solo Plus Adhesive isthe gold standard fifth-generation bonding agent, known for

its durable and strong associated bond strength; it requires aseparate etch-and-rinse phase, followed by the application ofa combined primer-adhesive resin solution, as previously de-

scribed. This acid-etching process of enamel had modified itto achieve a good micromechanical bond; therefore, this adhe-sive offers constant and durable bond strength, even after theapplication of peroxide bleaching material and the resistance

to degradation by the oxygen radicals.The predominant failure mode in OptiBond Solo Plus

Adhesive was a mixed-failure type (adhesive and cohesive) in

all of the groups; control (non-bleach) and bleaching groups(pre- and post-bleach) (Table 3), and this might be correlatedto the constant and durable bond strength of this type of

adhesive.Single Bond Universal Adhesive Agent is a universal bond-

ing material that is designed to work well with either an etch-

and-rinse, self-etch, or selective-etch technique. It contains theacidulated monomer MDP, which is intended to create greaterproduct stability, significant adhesion to metal and zirconiumoxide, and excellent adhesion to enamel, as was confirmed in

our study. As previously mentioned, Single Bond Universaladhesive is an ethanol-/water-based solvent system. The inclu-sion of solvent has led to an increase in bond strength,24 More-

over, the presence of water is essential for both etch-and-rinseand self-etch adhesives. In etch-and-rinse adhesives, water hasa plasticizing effect on collagen fibrils and decreases the stiff-

ness of collapsed fibrils,29 which is important for the expansionof the dried dentin collagen.31 In self-etch adhesives, it offersan ionization medium to facilitate self-etching activity.39 Ide-ally, all solvents and water should be completely eliminated

from the adhesive before light-curing, since they may havean adverse effect on the polymerization of adhesive resinmonomers.25 In our study, we achieved this by allowing an

adequate evaporation time between application and curing ofthe adhesive resin.

The high bond strength associated with etch-rinse Single

Bond Universal Adhesive Agents in the control (non-bleach)and pre-bleach groups could be attributed to the reliable chem-istry of this adhesive in addition to the use of phosphoric acid

etching step to modify the enamel in order to achieve an excel-lent micromechanical bond.44

In the pre-bleach group, the acid-etching step had removedthe remaining oxygen inhibition layer along with the available

90 A.M. Elmourad, M.Q. Alqahtani

minerals in the enamel to achieve a good micromechanicalbond; therefore, this step restored the compromised bondstrength after dental bleaching and resulted in high bond

strength value. In addition, the post-bleach group of this adhe-sive had achieved a high bond strength, but it was lower thanthat of the pre-bleach group, with no significant difference be-

tween them. This might be due to some residual peroxide onthe enamel structure and around the bonded margin of resincomposite, but this peroxide could not cause deterioration of

the bond interface in this case because of the pre-existingstrong bond due to the acid-etching step.

The predominant failure mode in etch-and-rinse SingleBond Universal Adhesive Agents was either mixed failure or

‘cohesive in enamel’ failure in the control (non-bleach) andbleaching groups (pre- and post-bleach). The ‘cohesive in en-amel’ failure type indicated the high bond strength values of

this material (Table 3).However, we found that the enamel conditions had a signif-

icant effect on bond strength when the self-etch Single Bond

Universal Adhesive Agent was used. The mean SBS valuesof this adhesive agent to the enamel were significantly reducedin the different bleaching groups (pre- and post-bleach) com-

pared with that of the control group (non-bleach). Moreover,we found that post-bleaching of enamel had more effect on theSBS of this adhesive agent when compared with the pre-bleaching procedure but with no significant difference between

groups.The performance of the self-etch Single Bond Universal

Adhesive Agent in the control group was generally excellent;

its SBS was lower than that of the control group of etch-and-rinse Single Bond Universal Adhesive but was not statisti-cally significant. These results were in contrast to those of

other studies.18,28 Goracci et al.18 showed that self-etchingadhesives (Adper Prompt-L-Pop, Xeno CF II, AdheSE) per-formed significantly worse than the total-etch system two-step

system (Excite) when bonded to enamel. Lopes et al.28 re-ported that an etch-and-rinse approach still results in the high-est bonding strength values when bonding to enamel,compared with the self-etch approach.

Therefore, this contrast to the other self-etch adhesivesmight to the presence of a unique chemistry ‘‘VMS’’ technol-ogy: Vitrebond Copolymer which provides more consistent

bond performance to dentin under varying moisture levels;MDP phosphate monomer, which offers self-etching proper-ties, higher enamel bond strength, higher bond strength to zir-

conia, alumina, metals and higher hydrophilic stability, so norefrigeration is needed; Silane which allows the adhesive tochemically bond to glass ceramic surfaces without using a sep-arate ceramic primer.

The actual bonding performance attained by self-etch adhe-sives is variable, depending not only on the actual class of self-etch adhesives, but also on the actual composition and, more

specifically, on the actual functional monomer included inthe adhesive formulation. In general, the fundamental mecha-nism of bonding to enamel and dentin depends on an exchange

process, in which minerals are eliminated from the dental hardtissues and are replaced by resin monomers that, upon poly-merization, become micromechanically interlocked in the cre-

ated porosities.44 Unlike etch-and-rinse adhesives, self-etchadhesives do not require a separate etching step to removethe minerals from the dental hard tissues, since they includeacidic monomers that simultaneously ‘condition’ and ‘prime’

the dental substrate; therefore, a reduced bond strength is usu-ally recorded in one-step adhesives in comparison with that inmulti-step adhesives.34

In fact, micromechanical interlocking is still the best strat-egy for bonding to enamel. The low bond strength valuesfound in the pre- and post-bleach groups of self-etch Single

Bond Universal Adhesive Agent can be attributed to the ab-sence of the etching step with self-etch adhesives and the poormicromechanical bond associated with them.

In the pre-bleach group, the oxygen inhibition layer result-ing from the bleaching process was not eliminated by the acidetchant, as was the case with pre-bleach groups of OptiBondSolo Plus Adhesive and etch-and-rinse Single Bond Universal

Adhesive. Our results in the pre-bleach group were consistentwith those of Gurgan et al.,19 who suggested that, followingthe bleaching treatment, the use of an etch-and-rinse adhesive

system (Excite) provided higher bond strength values than aself-etching adhesive (AdheSe).

In the post-bleach group treated with self-etch Single Bond

Universal Adhesive Agent, the interface bonded margin of re-sin composite with this adhesive was challenged by the perox-ide radicals of the bleaching material, and since there was no

previously achieved reliable micromechanical bond in thiscase, this bond interface was subjected to gradual penetrationby the bleaching gel reactive radicals, resulting in degradationand deterioration of this adhesive joint (Fig. 7c).

Our findings in the post-bleach group were in agreementwith other studies.12,15 Cavalli et al.12 indicated that bleachingwith 10% carbamide peroxide had significantly reduced the

bond strength of self-etch Clearfil SE Bond to enamel in com-parison with the etch-and-rinse adhesive Single Bond. More-over, Dudek et al.15 demonstrated that bleaching gel

containing 20% carbamide peroxide significantly decreasedthe bond strength on both enamel and dentin for the simplifiedsingle-step self-etch adhesives Adper Prompt and iBond, com-

pared with the etch-and-rinse adhesive Gluma Comfort Bond,and markedly affected the fracture pattern of Adper Promptspecimens at the periphery of their bonded area.

The predominant failure modes in the non-bleach control

group of self-etch Single Bond Universal Adhesive Agent wereeither cohesive failure in the enamel or resin or mixed failure,and this might be correlated to high bond strength values.

However, in the specimens of the pre-bleach group of thisadhesive, the percentage of adhesive failure increased to 50%of the specimens. Meanwhile, in the specimens of the post-

bleach group of this adhesive, the percentage of adhesive fail-ure category increased to 80% of the specimens.

5. Conclusions

Within the limitations of this study, the following conclusionscan be drawn:

1. There were no significant effects of enamel conditions (con-trol non-bleach, pre- and post-bleach) on the SBSs whenOptiBond Solo Plus Adhesive Agent or etch-and-rinse

Single Bond Universal Adhesive Agent was used.2. Pre- and post-simulated home bleaching of enamel

with 10% carbamide peroxide had an adverse effect on

the SBSs of the self-etch Single Bond Universal AdhesiveAgent.

Effects of pre- and post-simulated home bleaching 91

3. For enamel, an etch-and-rinse approach with phosphoric

acid remains the procedure of choice, since it guaranteesthe most durable bond to enamel. Therefore, selective phos-phoric-acid etching of the enamel is highly recommended,

followed by the application of the self-etch procedure.

Conflict of interest

None.

Acknowledgments

The author would like to thank the College of Dentistry Re-search Center and Deanship of Scientific Research at KingSaud University, Saudi Arabia for their support in this re-

search (Research project # NF 2357).

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