Original Article
Effect of Two Forms of Sodium Ascorbate on Microleakage of Composite Restorations Immediately after Bleaching
S. Kimyai 1~, S. Rahimi 2, M. Lotfi 2, H. Valizadeh 3, N. Mohammadi 4, E. Jafari Zareh 5
1Associate Professor, Department of Operative Dentistry, Faculty of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran
2Associate Professor, Department of Endodontics, Faculty of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran
3Associate Professor, Department of Pharmaceutics, Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz, Iran
4Assistant Professor, Department of Operative Dentistry, Faculty of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran
5Dentist, Private Practice
~ Corresponding author:
S. Kimyai, Department of Opera- tive Dentistry, Faculty of Den- tistry, Tabriz University of Medical Sciences, Tabriz, Iran.
[email protected] Received: 7 May 2008 Accepted: 22 October 2008
Abstract:
Objective: The present in vitro study was undertaken to compare the effects of hydrogel and solution forms of sodium ascorbate on microleakage of composite restorations subse- quent to a non-vital bleaching procedure with 10% carbamide peroxide.
Materials and Methods: Forty-eight sound extracted human maxillary incisors were ob- tained. Following root canal therapy, the teeth were randomly divided into an unbleached control group (group 1) and three experimental groups in which bleaching was performed (12 teeth in each group). Non-vital bleaching with 10% carbamide peroxide was carried out for periods of 8 hours a day for one week. In group 2, the specimens were restored immediately after bleaching. Group 3 specimens were treated with sodium ascorbate solu- tion, whereas in group 4 specimens, sodium ascorbate hydrogel was used before place- ment of composite restorations. Following thermocycling, the specimens were subjected to dye leakage (methylene blue) test. Statistical analysis was carried out using Kruskal- Wallis and Dunn multiple comparison tests at a significance level of P<0.05.
Results: Significant differences existed in microleakage scores among the four groups (P<0.0005). Pairwise comparison of groups with Dunn test revealed that higher micro- leakage scores in group 2 compared to each of the other three groups was statistically sig- nificant (P<0.001) while the differences between other groups were not statistically sig- nificant (P>0.05).
Conclusion: Ten percent carbamide peroxide significantly increases microleakage of composite restorations when bonding is performed immediately following non-vital bleaching. Compromised sealing ability of composite restorations is reversed with applica- tion of both forms (hydrogel and solution) of sodium ascorbate, as an anti-oxidant.
Key Words: Tooth Bleaching; Composite Resins; Dental Leakage; Hydrogel; Ascorbic Acid; Marginal Adaptation (Dentistry)
Journal of Dentistry, Tehran University of Medical Sciences, Tehran, Iran (2009; Vol. 6, No.2)
INTRODUCTION
Ten percent of teeth undergoing root canal therapy show tooth discoloration, which re- sults in aesthetic problems [1]. Non-vital bleaching is used successfully for whitening of root-filled teeth [2]. One of the non-vital
bleaching methods is walking technique using 10% carbamide peroxide [3]. However, previ- ous studies have shown that bleaching agents adversely affect the bond strength and sealing ability of composite restorations when bonding procedure is performed immediately after
bleaching [4]. This detrimental effect might be attributed to the possible presence of residual peroxide in enamel and dentin, which inter- feres with resin attachment and inhibits resin polymerization [5]. It has been reported that it takes 1 to 4 weeks for tooth structure to return to conditions leading to normal bond strength and sealing ability, which may necessitate postponement of the treatment [4,6].
Recently, it has been demonstrated that com- promised sealing ability of composite restora- tions can be reversed through application of 10% sodium ascorbate solution as an anti- oxidant before restoration. Furthermore, in a study it was reported that this technique im- proved the reduced sealing ability of resin composite restorations more than the method in which there was a one-week delay in re- storative procedure subsequent to bleaching [4]. In previous investigations, sodium ascor- bate has been used in its solution from [4,7,8].
However, the gel form of sodium ascorbate is easy to apply (because of its higher viscosity and better control) and its application is less expensive for patients compared to the appli- cation of sodium ascorbate solution by the dental practitioner due to the shorter chair time needed [9].
In addition, the solution should be used several times prior to bonding [10]. Patients them- selves can place the gel form of sodium ascor- bate in the bleaching tray before bonding, which can decrease chair time [8,9].
The present study compared the effect of the solution and hydrogel forms of sodium ascor- bate on microleakage of composite restora- tions immediately following non-vital bleach- ing.
MATERIALS AND METHODS
Forty-eight sound extracted human upper max- illary central incisors were selected for the purpose of this in vitro study. The teeth had been extracted for periodontal reasons were caries-free, and had no previous restorations or pre-existing fractures or cracks, when sur- veyed under a stereomicroscope (Olympus SZX9; Olympus, Tokyo, Japan). Subsequent to extraction, the teeth were cleaned of any residues and stored in 0.5% chloramine tri- hydrate at 4˚C for infection control.
Endodontic access cavities were prepared 3 mm in a diameter using a round diamond bur [1.4 mm diameter] (SS White Burs, Inc.
Lakewood, NJ, USA) in a high-speed hand- piece under cooling with air/water. During tooth preparation, each tooth was wrapped in a piece of water-moistened gauze. Used burs were replaced with new burs after every five preparations. Each canal was prepared up to 1 mm short of the radiographic apex. Using K- files (MANI, Inc, Tochigi, Japan), we instru- mented root canal of each tooth with passive step-back technique to file #35 at the apical constriction. Prepared canals then were obtu- rated with gutta-percha and AH 26 root canal sealer (Dentsply, DETREY, GmbH, Konstanz, Germany) and with lateral condensation tech- nique. Following removal of the gutta-percha to a level 2 mm apical to the buccal cemento- enamel junction, light-cured glass ionomer base (Fuji II LC, GC, Tokyo, Japan) with 2 mm thickness was placed. The specimens were randomly divided into four groups of 12 teeth each (n=12). Each group was treated as shown in Table 1. Table 2 shows the details of mate- rials used in the present study.
Table 1. Detailed description of different treatments in the study groups.
Groups Bleaching Treatment Antioxidant
1 None None
2 10% carbamide peroxide gel None
3 10% carbamide peroxide gel 10% sodium ascorbate solution 4 10% carbamide peroxide gel 10% sodium ascorbate hydrogel
Bleaching
In groups 2-4, 10% carbamide peroxide bleaching gel (Opalescence, Ultradent Prod- ucts. Inc, USA) was placed into the pulp chamber and the access cavity so that it would extend onto the lingual surface for eight hours per day. The specimens were partially im- mersed in artificial saliva at 37˚C in a glass laboratory beaker so that bleaching gel did not contact saliva. After the daily bleaching proc- ess, the specimens were thoroughly rinsed with water and air-dried. For the rest of the day the teeth were stored in artificial saliva at 37˚C. The artificial saliva consisted of 1 g so- dium carboxymethylcellulose, 4.3 g gxylitol, 0.1 g potassium chloride, 5 mg calcium chlo- ride, 40 mg potassium phosphate, 1 mg potas- sium thiocyanate and 100 g distilled deionized water [4]. The artificial saliva was changed twice daily. After removing the teeth from the artificial saliva, specimens were rinsed with water for 30 seconds. The bleaching procedure was continued for one week. In group 1 (con- trol), the specimens were not bleached.
Preparation of the Solution and Hydrogel Carbomer (Carbopol 934) was supplied by Noveon (Brussels, Belgium). Sodium ascor- bate (L (+) Ascorbic acid sodium salt) was ob- tained from Fluka (Buchs, Switzerland). All other chemicals were of analytical grade. To prepare solution containing sodium ascorbate
(10%), sodium ascorbate was dissolved in pu- rified water under mixing at room temperature (pH=7.5). The carbopol gel (2.5% wt/wt) con- taining sodium ascorbate (10%) was prepared by dispersing the carbopol resin in purified water containing sodium ascorbate under gen- tle mixing. The mixture was stirred until thick- ening occurred and then neutralized by drop- wise addition of thriethanolamine until a transparent gel appeared. The quantity of thriethanolamine was adjusted to achieve a gel pH of 7.
Application of Antioxidant
Subsequent to completion of bleaching proce- dure, the samples in group 3 were immersed in 10% sodium ascorbate solution for three hours. Ten percent sodium ascorbate hydrogel was placed inside the pulp chamber and the access cavity for three hours at 100% relative humidity in group 4. Then the samples were rinsed with distilled water for 30 seconds and gently air-dried.
Composite Restoration
Access cavities and pulp chambers were etched with 35% phosphoric acid (Scotchbond TM Etchant, 3M Dental Products, St. Paul, MN, USA) for 15 seconds. After rinsing and removing the excess water, bonding agent (Adper Single Bond, 3M Dental Products) was applied according to manufacturer's instruc-
Table 2. The materials used in the present study.
Materials Manufacturer Compositions Batch No.
Opalescence Ultradent Products Inc,
USA 10 % carbamide peroxide bleaching gel B2CQ8 ScotchbondTM Etchant 3M Dental Products, St.
Paul, MN, USA 35% phosphoric acid 7JN
Adper Single Bond 3M Dental Products, St.
Paul, MN, USA
Light-cured adhesive system containing 2- HEMA, Bis-GMA, Amine di-methacrylate, Polyalkanoic acid, Itanoic acid , Ethanol, Water
6KR
Z100 3M Dental Products, St.
Paul, MN, USA
Light-cured composite resin, radiopaque , con- taining zirconia/ silica filler (60% wt – particle
size range 0.01- 3.5 µm), Bis-GMA, TEGDMA 5YA
No=Number
tions and cured for 10 seconds using an As- tralis 7 light-curing unit (Ivoclar Vivadent, Amherst, NY, USA) adjusted to 400 mW/cm2. Resin composite [A3] (Filtek Z100, 3M Dental Products) was placed and polymerized using incremental technique (in three layers). Each layer was light-cured for 40 seconds. After fin- ishing with finishing diamond burs (Diamant Gmbh, D & Z, Goerzallee, Berlin, Germany) and finishing disks (Sof-LexTM, 3M ESPE, Dental Products), the specimens were stored in distilled water at 37 ˚C for one week, and thermocycled at 5˚C (SD=5) / 55˚C (SD=5) (500 times) with a dwell time of 30 seconds and 10 seconds for specimen transfer.
Microleakage Assessment
The apices of the teeth were sealed with utility wax, and all tooth surfaces were covered with two coats of nail polish with the exception of 1 mm around the tooth-restoration interface. The teeth were immersed in 0.5% methylene blue for 8 hours. Then the specimens were re- moved, rinsed with tap water, and sectioned with a diamond disk (D & Z Diamant GmbH, Berlin, Germany) along the bucco-lingual di- rection corresponding to the center of the res- toration. All samples were prepared by one operator. Two examiners evaluated both hemi- sections of each tooth at magnification ×20 under a stereomicroscope for dye penetration.
The examiners were blind to which group the
teeth belonged. Microleakage was scored on a 0 to 3 scale [4]:
0: No dye penetration
1: Dye penetration up to half of the cavity depth
2: Dye penetration greater than scale I without involvement of gutta-percha
3: Dye penetration with involvement of gutta- percha
Any discrepancies between the two main ex- aminers were reevaluated, and when necessary a third examiner decided on the score.
Statistical analysis was carried out using the Kruskal-Wallis, and two-by-two comparisons were made by the Dunn test at a significance level of P<0.05.
RESULTS
Microleakage scores obtained from four groups have been shown in Table 3. Kruskal- Wallis analysis indicated significant differ- ences in microleakage scores among the four groups (χ2=25.07, df=3, P<0.0005). Pairwise comparison of groups with Dunn test revealed that higher microleakage scores in group 2 compared to each of the other three groups were statistically significant (P<0.001), while the differences between other groups were not statistically significant (P>0.05).
DISCUSSION
Increased microleakage impairs the long-term
Table 3. Microleakage scores of 48 extracted human incisors allocated to study groups and restored with composite resin.
Microleakage Scores Groups
0 1 2 3 Group 1 No Bleaching
No anti-oxidant application 9 3 0 0
Group 2 Bleaching
No anti-oxidant application 0 3 9 0
Group 3 Bleaching
Application of anti-oxidant solution 5 6 1 0
Group 4 Bleaching
Application of anti-oxidant hydrogel 7 5 0 0
Microleakage Scores (0: No dye penetration; 1: Dye penetration up to half of the cavity depth; 2: Dye penetration greater than scale I without involvement of gutta-percha; 3: Dye penetration with involvement of gutta-percha)
success of both the bleaching procedure and the endodontic treatment [4]. According to the results of the present study bleaching with 10% carbamide peroxide (group 2) resulted in a significant increase in microleakage com- pared to the unbleached group (group 1) when the bonding procedure was performed imme- diately following bleaching. The results of our study coincide with previous investigations [5,11,12]. These findings might be attributed to the poor bonding between composite resto- ration and the tooth structure, since in numer- ous studies decreased bond strength of com- posite resin to the enamel and dentin have been shown when the bonding procedure has been performed immediately after bleaching with carbamide peroxide [13,14]. Furthermore, increased microleakage might be due to enamel structure changes, loss of calcium, mi- crohardness decrease, loss of prismatic forma- tion and alterations in the organic substrate, which might result in a decrease in enamel bond strength and marginal sealing [15-19]. In addition, it has been claimed that the residual oxygen from the bleaching agent interferes with resin infiltration into the tooth structure and inhibits resin polymerization [20,21]. In- adequate penetration and polymerization of resin base materials can lead to poor adhesion between resinous materials and tooth structure [8]. Moreover, in a study carried out by Titley et al [22] there were less resin tags and less penetration depth of those resin tags in bleached enamel compared to unbleached enamel under SEM evaluation. Based on the reports of Dishman et al [23] the bonding effi- cacy of resin composite to bleached enamel can be compromised with the fewer number of resin tags.
The results of the current study revealed that microleakage of composite restorations de- creased significantly following anti-oxidant application (hydrogel and solution of sodium ascorbate) in comparison with group 2 (with- out anti-oxidant treatment). This decreased
microleakage was comparable to that in the control group. These results concur with those of Türkün et al [4], who reported that reduced sealing ability of composite restorations is re- versed by the use of 10% sodium ascorbate solution. In addition, some studies have dem- onstrated that reduced enamel and dentin bond strength significantly improves by sodium ascorbate application [24,25]. Decreased mi- croleakage and improved adhesion between resin composite and tooth structure might be attributed to anti-oxidizing ability of sodium ascorbate. Ascorbic acid and its sodium salt are potent anti-oxidants capable of quenching reactive free radicals in biological systems [26]. Zhao et al [27] reported that following tooth bleaching with carbamide peroxide hy- droxyl radicals in the apatite lattice were sub- stituted by peroxide ions of carbamide perox- ide and produce peroxide-apatite. When the peroxide ions decompose, substituted hydroxyl radicals enter the apatite lattice, resulting in the elimination of the structural changes caused by the incorporation of peroxide ions [28]. Furthermore, it has been reported that sodium ascorbate allows free-radical polym- erization of resin base materials to proceed without premature termination by restoring the altered redox potential of the oxidized bonding substrate, thus reversing the compromised bonding [7].
According to the results of this study, there were no significant differences in microleak- age scores between two forms of sodium ascorbate (hydrogel and solution). These find- ings are consistent with those of previous stud- ies [9, 10], which have shown that both forms of sodium ascorbate act similarly in increasing bond strength following bleaching. Therefore, it is suggested that sodium ascorbate hydrogel might be as effective as solution form of so- dium ascorbate in decreasing microleakage of composite restorations following non-vital bleaching.
None of the specimens showed the highest mi-
croleakage scores (score 3) in our study. This might be attributed to the placement of glass ionomer base. In previous investigations, the preventive effects of glass ionomer base over the gutta-percha on coronal microleakage have been proved [4,29].
Future studies should evaluate microleakage using three-dimensional methods and scanning electron microscope (SEM) to provide addi- tional information. Moreover, further research are required to determine the minimal time necessary for sodium ascorbate hydrogel to neutralize the oxidative effects of bleaching material.
CONCLUSION
Within the limitations of this study, it was con- cluded that: Bleaching with 10% carbamide peroxide significantly increased the micro- leakage of composite restorations when the bonding procedure was performed immedi- ately after bleaching.
Application of both forms of 10% sodium ascorbate after bleaching reversed the sealing ability of composite restorations to the level of unbleached group. No significant differences existed in microleakage scores between both forms (hydrogel and solution) of sodium ascorbate.
ACKNOWLEDGMENTS
The authors would like to thank the vice chan- cellors for research of Tabriz University of Medical Sciences for their financial support.
REFERENCES
1- Demarco FF, Freitas JM, Silva MP, Justino LM.
Microleakage in endodontically treated teeth: in- fluence of calcium hydroxide dressing following bleaching. Int Endod J 2001 Oct;34(7):495-500.
2- Heymann HO. Additional conservative esthetic procedures. In: Roberson TM, Heymann HO, Swift EJ, editors. Sturdevant's Art and Science of Opera- tive Dentistry. 5th ed. St. Louis: Mosby: Mosby;
2006. pp. 625-85.
3- Haywood VB, Berry TG. Natural tooth bleach- ing. In: Summitt JB, Robbins JW, Hilton TJ, Schwartz RS, editors. Fundamentals of Operative Dentistry. A Contemporary Approach. 3rd ed. Chi- cago: Quintessence; 2006. pp. 437-62.
4- Türkün M, Türkün LS. Effect of nonvital bleach- ing with 10% carbamide peroxide on sealing abil- ity of resin composite restorations. Int Endod J 2004 Jan;37(1):52-60.
5- Swift EJ Jr, Perdigão J. Effects of bleaching on teeth and restorations. Compend Contin Educ Dent 1998 Aug;19(8):815-20.
6- Spyrides GM, Perdigão J, Pagani C, Araújo MA, Spyrides SM. Effect of whitening agents on dentin bonding. J Esthet Dent 2000;12(5):264-70.
7- Lai SC, Mak YF, Cheung GS, Osorio R, Tole- dano M, Carvalho RM, et al. Reversal of compro- mised bonding to oxidized etched dentin. J Dent Res 2001 Oct;80(10):1919-24.
8- Lai SC, Tay FR, Cheung GS, Mak YF, Carvalho RM, Wei SH, et al. Reversal of compromised bonding in bleached enamel. J Dent Res 2002 Jul;
81(7):477-81.
9- Kimyai S, Valizadeh H. The effect of hydrogel and solution of sodium ascorbate on bond strength in bleached enamel. Oper Dent 2006 Jul-Aug;
31(4):496-9.
10- Kimyai S, Valizadeh H. Comparison of the ef- fect of hydrogel and a solution of sodium ascorbate on dentin-composite bond strength after bleaching.
J Contemp Dent Pract 2008 Feb 1;9(2):105-12.
11- Sung EC, Chan SM, Mito R, Caputo AA. Effect of carbamide peroxide bleaching on the shear bond strength of composite to dental bonding agent en- hanced enamel. J Prosthet Dent 1999 Nov;82(5):
595-9.
12- Cavalli V, Reis AF, Giannini M, Ambrosano GM. The effect of elapsed time following bleach- ing on enamel bond strength of resin composite.
Oper Dent 2001 Nov-Dec;26(6):597-602.
13- Cvitko E, Denehy GE, Swift EJ Jr, Pires JA.
Bond strength of composite resin to enamel bleached with carbamide peroxide. J Esthet Dent 1991 May-Jun;3(3):100-2.
14- Stokes AN, Hood JA, Dhariwal D, Patel K. Ef-
fect of peroxide bleaches on resin-enamel bonds.
Quintessence Int 1992 Nov;23(11):769-71.
15- McCracken MS, Haywood VB. Demineraliza- tion effects of 10 percent carbamide peroxide. J Dent 1996 Nov;24(6):395-8.
16- Hegedüs C, Bistey T, Flóra-Nagy E, Keszthelyi G, Jenei A. An atomic force microscopy study on the effect of bleaching agents on enamel surface. J Dent 1999 Sep;27(7):509-15.
17- Ben-Amar A, Liberman R, Gorfil C, Bernstein Y. Effect of mouthguard bleaching on enamel sur- face. Am J Dent 1995 Feb;8(1):29-32.
18- Josey AL, Meyers IA, Romaniuk K, Symons AL. The effect of a vital bleaching technique on enamel surface morphology and the bonding of composite resin to enamel. J Oral Rehabil 1996 Apr;23(4):244-50.
19- Cavalli V, Arrais CA, Giannini M, Ambrosano GM. High-concentrated carbamide peroxide bleaching agents effects on enamel surface. J Oral Rehabil 2004 Feb;31(2):155-9.
20- Rueggeberg FA, Margeson DH. The effect of oxygen inhibition on an unfilled/filled composite system. J Dent Res 1990 Oct;69(10):1652-8.
21- Kalili T, Caputo AA, Mito R, Sperbeck G, Matyas J. In vitro toothbrush abrasion and bond strength of bleached enamel. Pract Periodontics Aesthet Dent 1991 Aug;3(5):22-4.
22- Titley KC, Torneck CD, Smith DC, Chernecky R, Adibfar A. Scanning electron microscopy ob- servations on the penetration and structure of resin
tags in bleached and unbleached bovine enamel. J Endod 1991 Feb;17(2):72-5.
23- Dishman MV, Covey DA, Baughan LW. The effects of peroxide bleaching on composite to enamel bond strength. Dent Mater 1994 Jan;10(1):33-6.
24- Türkün M, Kaya AD. Effect of 10% sodium ascorbate on the shear bond strength of composite resin to bleached bovine enamel. J Oral Rehabil 2004 Dec;31(12):1184-91.
25- Bulut H, Turkun M, Kaya AD. Effect of an an- tioxidizing agent on the shear bond strength of brackets bonded to bleached human enamel. Am J Orthod Dentofacial Orthop 2006 Feb;129(2):266- 72.
26- Buettner GR. The pecking order of free radicals and antioxidants: lipid peroxidation, alpha- tocopherol, and ascorbate. Arch Biochem Biophys 1993 Feb 1;300(2):535-43.
27- Zhao H, Li X, Wang J, Qu S, Weng J, Zhang X.
Characterization of peroxide ions in hydroxyapa- tite lattice. J Biomed Mater Res 2000 Oct;52(1):
157-63.
28- Bulut H, Kaya AD, Turkun M. Tensile bond strength of brackets after antioxidant treatment on bleached teeth. Eur J Orthod 2005 Oct;27(5):466- 71.
29- Saunders WP, Saunders EM. Coronal leakage as a cause of failure in root-canal therapy: a re- view. Endod Dent Traumatol 1994 Jun;10(3):105- 8.