|Year : 2014 | Volume
| Issue : 3 | Page : 207-211
An in vitro study to evaluate the effect of two ethanol-based and two acetone-based dental bonding agents on the bond strength of composite to enamel treated with 10% carbamide peroxide
Deepa Basavaraj Benni1, Satyajith N Naik2, VV Subbareddy2
1 Department of Pedodontics and Preventive Dentistry, Maratha Mandal's Nathajirao Guruanna Halgekar Institute of Dental Sciences and Research Centre, Belgaum, Karnataka, India
2 Pedodontics and Preventive Dentistry, College of Dental Sciences, Davangere, Karnataka, India
|Date of Web Publication||2-Jul-2014|
Deepa Basavaraj Benni
Department of Pedodontics and Preventive Dentistry, Maratha Mandal's Institute of Dental Sciences and Research Centre, Belgaum - 590 001, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background and Objective: Carbamide peroxide bleaching has been implicated in adversely affecting the bond strength of composite to enamel. The objective of this in vitro study was to evaluate the effect of ethanol-based (Clearfil S 3 bond, Kuraray, Adper Single bond 2, 3M ESPE dental products) and acetone-based (Prime and Bond NT, Dentsply, One Step, Bisco) bonding agents on the shear bond strength of composite to enamel treated with 10% carbamide peroxide bleaching agent. Materials and Methods: A total of 120 extracted human noncarious permanent incisors were randomly divided into two groups (control and experimental). Experimental group specimens were subjected to a bleaching regimen with a 10% carbamide peroxide bleaching system (Opalescence; Ultradent Products Inc, South Jordan, USA). Composite resin cylinders were bonded to the specimens using four bonding agents and shear bond strength was determined with universal testing machine. Results: There was no statistically significant difference in the shear bond strength between control and experimental groups with both ethanol-based (Clearfil S 3 Bond and Adper Single Bond 2) and acetone-based bonding agent (Prime and Bond NT and One Step). Interpretation and Conclusion: The adverse effect of bleaching on bonding composite to enamel can be reduced or eliminated by using either ethanol- or acetone-based bonding agent. Clinical Significances: Immediate bonding following bleaching procedure can be done using ethanol- or acetone-based bonding agent without compromising bond strength.
Keywords: Acetone-based bonding agent, carbamide peroxide bleaching, ethanol-based bonding agent, SBS
|How to cite this article:|
Benni DB, Naik SN, Subbareddy V V. An in vitro study to evaluate the effect of two ethanol-based and two acetone-based dental bonding agents on the bond strength of composite to enamel treated with 10% carbamide peroxide. J Indian Soc Pedod Prev Dent 2014;32:207-11
|How to cite this URL:|
Benni DB, Naik SN, Subbareddy V V. An in vitro study to evaluate the effect of two ethanol-based and two acetone-based dental bonding agents on the bond strength of composite to enamel treated with 10% carbamide peroxide. J Indian Soc Pedod Prev Dent [serial online] 2014 [cited 2019 Dec 10];32:207-11. Available from: http://www.jisppd.com/text.asp?2014/32/3/207/135826
| Introduction|| |
Tooth discoloration is becoming a greater concern as more of emphasis is placed on esthetics. With the growing awareness of esthetic options, there is a greater demand for solutions to such unpleasant problems like food staining, fluorosis, and tetracycline staining. 
Bleaching system has been one of the most conservative and economical method of improving appearance of teeth. Various whitening systems like different concentrations of carbamide peroxide agents (10-22%), hydrogen peroxide agents, and McInnes solution are being currently used to bleach teeth, of that 10% carbamide bleaching system, introduced by Haywood and Heymann in 1989,  has been a procedure that has grown dramatically in popularity because of its efficiency and simplicity to remove the intrinsic stains from the teeth. 
After the use of bleaching material, teeth are usually significantly lighter; preexisting restorations do not change and hence should be replaced to match the color of the teeth achieved with the bleaching treatment for the esthetic enhancement.
Bleaching and bonding have become new reality in dentistry, not only because of the availability of new technologies and materials but also as a result of the increase in knowledge and understanding of mechanism of action of bleaching agents and adhesive systems. 
Although prerestorative carbamide peroxide bleaching is gaining popularity, its effect on the bond strength to composite has been inconclusive. There have been reports regarding the interaction between bleaching agents and the bond strength of composite materials to enamel. 
Several studies have shown a reduction in enamel bond strength when the bonding procedure is carried out immediately and up to 1 week after vital bleaching with hydrogen peroxide and carbamide peroxide-based bleaching agents. ,, This reduction in enamel bond strength has become a concern in cosmetic dentistry with regard to clinical operative procedures that involve resin bonding, such as porcelain veneers, composite veneers, or future composite restorations, where vital bleaching is often considered a first step in improving the appearance of teeth prior to applying a bonded restoration. 
One of the mechanisms proposed in the literature that may account for this reduction in bond strength is the presence of residual oxygen, which inhibits free radical polymerization. , Methods have been indicated to counteract these adverse effects related to the lower bond strength values that follow bleaching. The delaying of bonding procedures until 24 h to 2 weeks after bleaching is the most common recommendation. The removal of superficial enamel has been suggested to restore bond strengths to normal levels.
Data from some experiments have shown that the use of organic solvent-based adhesives may result in less compromised composite bond strength when restorative work is to be completed immediately after bleaching procedure, eliminating the need for any treatment delays or enamel resurfacing. 
Kalili and Yoshida proposed that free radical polymerization inhibition could result from oxygen released by the bleaching agents and also suggested that the application of an alcohol-based bonding agent may be able to minimize the inhibitory effects of the bleaching process by the interaction of alcohol with residual oxygen. 
The fact that studies investigating the effect of organic solvent-based adhesives on bleached enamel are conflicting, merits further research in this area. As a result, this study was designed to evaluate and compare the effect of ethanol-based (Clearfil S 3 bond, Kuraray; Adper Single bond 2, 3M ESPE dental products) and acetone-based (Prime and Bond NT, Dentsply; One Step, Bisco) bonding agents on the bond strength of composite to enamel treated with 10% carbamide peroxide bleaching agent (Opalescence; Ultradent Products Inc, South Jordan, USA).
| Materials and Methods|| |
A total of 120 freshly extracted noncarious human permanent incisor teeth were collected and stored in normal saline until they were used for the study. Roots were sectioned 2 mm below the cementoenamel junction and the crowns were embedded in acrylic resin block (1 inch diameter and 1 inch height) with the labial surface exposed. The samples were then randomly divided into two groups of 60 each: Group I - control and Group II - experimental. Specimens in the experimental group (60 teeth) were subjected to a bleaching regimen with 10% carbamide peroxide bleaching system (Opalescence; Ultradent Products Inc, South Jordan, USA) of one application per day of 6-h duration for 5 consecutive days. 10% carbamide peroxide gel was applied using custom trays fabricated for each tooth specimen.
After bleaching, all the specimens in control group and experimental group were subdivided into eight groups as Groups I A, I B, I C, I D, II A, II B, II C, and II D each containing 15 specimens [Table 1].
Samples in control and experimental group were etched using the 37% etching gel (Prime Dental Products; India) for 15 s, rinsed, and gently air dried. Application of the adhesives was done according to the manufacturer's instructions.
The bonding protocol for each group was as follows
Group I A: Ethanol-based bonding agent (Clearfil S 3 Bond, Kuraray) was applied to the enamel and left for 20 s followed by blowing high pressure air for more than 5 s and light-cured for 10 s.
Group I B: Two to three consecutive coats of ethanol-based bonding agent (Adper Single Bond 2, 3M ESPE dental products) was applied to the enamel and gently air thinned for 5 s to evaporate solvents followed by light curing for 10 s.
Group I C: Ample of acetone-based bonding agent (Prime and Bond NT, Dentsply) was applied to the enamel to wet the tooth surface for 20 s and gently air blown for 5 s followed by light curing for 10 s.
Group I D: Two generous coats of acetone-based bonding agent (One Step, Bisco, Inc, Itasca) were applied to the enamel gently and thoroughly air-dried for 10-15 s followed by light curing for 10 s.
Group II A: Ethanol-based bonding agent (Clearfil S 3 Bond, Kuraray) was applied to the bleached enamel and left for 20 s followed by blowing high pressure air for more than 5 s and light cured for 10 s.
Group II B: Two to three consecutive coats of ethanol-based bonding agent (Adper Single Bond 2, 3M ESPE dental products) was applied to the bleached enamel and gently air thinned for 5 s to evaporate solvents followed by light curing for 10 s.
Group II C: Ample of acetone-based bonding agent (Prime and Bond NT, Dentsply) was applied to the bleached enamel to wet the tooth surface for 20 s and gently air blown for 5 s followed by light curing for 10 s.
Group II D: Two generous coats of acetone-based bonding agent (One Step, Bisco, Inc, Itasca) were applied to the bleached enamel gently and thoroughly air dried for 10-15 s followed by light curing for 10 s.
Once the bonding protocol was completed, composite resin (Filtek Z 350 3M ESPE dental products) cylinders were built incrementally (1 mm) on all the specimens using acrylic resin mold of 3 × 2 mm dimension and cured using a light-emitting diode curing unit (Ellipar 3M ESPE) for a period of 20 s for each increment as per manufacturer's instructions. After the composite build up, molds were removed and all the samples were subjected to shear bond strength analysis.
Shear bond strength analysis
Shear bond strength assessment was done using Instron Universal Testing Machine (Instron Corp, Canton, Mass). Peak failure load was measured in the machine with a crosshead speed of 0.5 mm/min until the cylinders got debonded from the enamel. The values were converted into shear bond strength in megapascals (MPa). Intergroup comparison of the results of shear bond strength test was done by the Student's unpaired t-test. The level of significance for all the tests was chosen as P < 0.05.
| Results|| |
The mean shear bond strength and standard deviation of control and experimental groups are shown in [Table 2]. The results showed that, there was no statistically significant difference in the shear bond strength between control and experimental groups with both ethanol-based (Clearfil S 3 Bond and Adper Single Bond 2) and acetone-based bonding agent (Prime and Bond NT and One Step). The results also revealed that acetone-based bonding agent showed shear bond strength higher than its control group.
|Table 2: Mean shear bond strengths (in megapascals) and standard deviation of control and experimental group|
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| Discussion|| |
The demand for conservative esthetic dentistry has grown dramatically and so has the development of new nonrestorative treatments for discolored teeth. Both older 35% hydrogen peroxide-based systems and newer 10% carbamide peroxide-based systems have been used successfully in lightening teeth. However, older systems have been consistently associated with greater risks than the newer systems. Several recognized hazards to the oral cavity include preneoplastic lesions, tooth hypersensitivity, chronic inflammation, enamel demineralization, and chemical leakage to gingiva. , Carbamide peroxide decomposes intraorally to urea, ammonia, carbonic acid, and hydrogen peroxide at a low concentration.  Carbamide peroxide-based systems have been reported to be less acidic because of the presence of ammonia and carbon peroxide, both of which are byproducts of the urea breakdown cycle. These more stable and alkaline pH conditions are kinder to oral tissues. The 10% carbamide peroxide solutions have a 3-3.5% equivalent concentration of hydrogen peroxide, an effective yet safe level for tooth whitening that is more dilute than the potent 35% hydrogen peroxide concentrations. For these reasons, 10% carbamide peroxide bleaching agent has been suggested as a safer alternative to the harsher hydrogen peroxide-based systems  and has been recommended by American Dental Association (ADA).
The bleaching mechanism occurs through a complex oxidation reaction in which hydrogen peroxide solution with a low molecular weight (34 g/mol) is deposited on the tooth enamel and activated by either heat or light radiation depending on the bleaching system used. The hydrogen peroxide is decomposed into water and nascent oxygen with the latter penetrating rapidly through the enamel porosities and the organic matrix of the enamel and dentin. The oxygen reacts promptly with pigments, possibly causing weak links between the chromatogenic molecules and the organic matrix to rupture. The chromophoric molecules are oxidized by the nascent oxygen ions and are broken down into smaller, less complex, and lighter molecules. 
Clinicians are obviously interested in determining whether any changes in the enamel surface also result in alteration of its adhesive characteristics to restorative bonding materials.  There have been reports regarding the interaction between bleaching agents and bond strength of the composite materials to the enamel. Some authors have reported a severe decrease in the average bond strength of the composite to the bleached enamel as compared with the unbleached one. ,, However, others have indicated means to counteract the adverse bleaching effects so that there were no statistical differences between the bleached and unbleached groups.  On the other hand, some studies reported a significant decrease in the bond strength only when the composite was bonded immediately after completion of bleaching.  Various rationales have been proposed to reconcile these observations.
The lower shear bond strengths immediately after bleaching procedures can be explained by physical and chemical alterations. Although the roughness of the surface and an increase in porosity caused by the loss of mineral content might eliminate the effects of a decrease in adhesiveness, it is suggested that the quality of the composite bond is compromised through a decreased number of resin tags, owing to the polymerization inhibition taking place and the relative amount of calcium on the enamel surface. The inhibition is a result of bleaching agent used, since dentin may act as an oxygen reservoir and the oxygen interferes with the curing of resin tags. The loss of minerals during bleaching procedures has also been suggested as a possible cause for a decrease in adhesiveness. 
Data from some experiments have shown that the use of organic solvent based adhesives may result in less compromised composite bond strength when restorative work is to be completed immediately after bleaching procedure, eliminating the need for any treatment delays or enamel resurfacing.  Jacobsen and Soderholm  suggested that the type of solvent used in adhesive systems appears to have an influence on the bond strength of bleached teeth, with acetone and ethanol being the two most indicated types of solvents. This may be attributed to the ability of these two solvents to carry the hydrophilic monomers of the adhesive system more effectively into dentin tubules, whereas, the water-based solvents with a greater presence of humidity may inhibit polymerization.
Several studies have shown a significant reduction in enamel bond strength when the bonding procedures is carried out immediately, due to which authors have advised bonding to be delayed up to 3 weeks after bleaching.  A period of up to 3 weeks is required before resin enamel bond strengths return to values obtained for unbleached enamel. 
As per the findings of the present study, it was observed that, the difference in shear bond strength between the control and experimental groups was not statistically significant (P > 0.05). Although the bond strength of groups II C and II D appeared to be numerically higher than their respective control group, the difference was not statistically significant.
This observation supports the hypothesis and findings of Barghi and Godwin (1994)  and Sung and others (1999),  that stated adhesives containing organic solvents may reverse the drop in bond strength found immediately after bleaching.
It has been suggested that acetone is the best solvent for carrying resin into the conditioned tooth surface, because of its effective role as a "water chaser" that displaces water from the tooth surface. This role is supported by experimental evidence (Jacobsen and Soderholm, 1995;  Perdigγo et al., 1998;  Gwinnett and Matsui, 1967;  Kanca, 1992).
Lai and others (2002)  reported no difference between the effects of acetone- and ethanol-based adhesive. They also found that, for both adhesives, bond strengths were reduced significantly when bonded to carbamide peroxide bleached enamel.
Results of this study support those of Kalili and Yoshida  showing that pretreatment of bleached enamel with alcohol decreases the residual water and oxygen and increases the bond strength of composite resin to bleached enamel.
Based on the findings of the current study and previous one, it is reasonable to assume that ethanol- and acetone-based bonding agents could be used to reverse the adverse effects of bleaching on the bond strength. If elective dental treatment may be postponed for several days, the choice of bonding agent becomes less critical.
| Conclusion|| |
- The adverse effect of bleaching on bonding to enamel caused by the oxygen inhibition of the bleaching agent can be reduced or eliminated by using either ethanol- or acetone-based bonding agent. However, our study could not draw a conclusion regarding the most effective solvent among the ethanol- and acetone-based bonding agent.
- Acetone-based bonding agent showed shear bond strength higher than its control group, so can be regarded as the best solvent. Further investigation into this area is necessary.
Immediate bonding following bleaching procedure can be done using ethanol- or acetone-based bonding agent without compromising bond strength.
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[Table 1], [Table 2]