| Abstract|| |
The purpose of the study was to compare the effect of hydrogel and solution of sodium ascorbate on enamel-resin composite shear bond strength after bleaching. 40 buccal enamel surfaces of maxillary molar were taken, divided into 4 groups (n=10). Group I (bleaching with 10% carbamide peroxide), group 2 (bleaching and 10% sodium ascorbate solution), group 3 (bleaching + 10% sodium ascorbate hydrogel) and group 4 (bleaching + 20%) sodium ascorbate hydrogel). All the teeth were restored with composite and subjected to shear bond testing. The results were evaluated. The data was analyzed by ANOVA test and multiple comparisons by Post Hoc tests. It was concluded that there was increase in the bond strength when antioxidants were used after bleaching but there was no significant difference among the different forms of sodium ascorbate.
Keywords: bleaching, carbamide peroxide, antioxidant, sodium ascorbate.
|How to cite this article:|
Paul P, Rosaline H, Balagopal S. The effect of hydrogel and solution of sodium ascorbate on the bond strength of bleached enamel. J Conserv Dent 2007;10:43-7
|How to cite this URL:|
Paul P, Rosaline H, Balagopal S. The effect of hydrogel and solution of sodium ascorbate on the bond strength of bleached enamel. J Conserv Dent [serial online] 2007 [cited 2019 Nov 12];10:43-7. Available from: http://www.jcd.org.in/text.asp?2007/10/2/43/42289
| Introduction|| |
Esthetic dentistry is becoming a great concern as there is a greater demand for solutions to unsightly problems such as food staining, fluorosis and tetracycline staining. Currently, many treatment modalities are available such as laminate veneers, jacket crowns, micro abrasion and bleaching. Tooth-whitening using carbamide peroxide (nightguard bleaching) is currently one of the most commonly used types of esthetic dental treatment  . Although prerestorative carbamide peroxide is gaining popularity, its effect on the bond strength to composite has been inconclusive. Titley et al  in 1992 reported lower bond strength when composite build up was done immediately after the bleaching procedure. It is related to the alterations in enamel surface morphology and presence of residual peroxide which interferes with resin penetration and polymerization. Several studies have reported changes on fracture toughness, hardness and abrasion characteristics of human enamel  Reduced bonding to carbamide peroxide bleached enamel can be reversed with 10% sodium ascorbate before resin bonding , . Hence the aim of our study was to compare the effect of solution and hydrogel forms of sodium ascorbate on the enamel-resin composite shear bond strength after bleaching.
| Materials and Methods|| |
Forty extracted human molars were selected and the teeth were stored in a 1% chloramine solution. The crowns of all the teeth were decoronated from the roots using a water-cooled diamond bur. Specimens were embedded in a self-curing polyester resin in such a way that flat buccal surfaces was placed parallel to the horizontal plane. Then the samples were divided into four groups.
10% carbamide peroxide gel
10% carbamide peroxide gel + 10% sodium ascorbate solution
10% cabamide peroxide gel + 10% sodium ascorbate hydrogel
10% carbamide peroxide gel + 20% sodium ascorbate hydrogel
Preparation of sodium ascorbate solution and hydrogel:
The solution containing 10% sodium ascorbate (Chen Chems, India). The gel was prepared by mixing the carbopol resin (Chen Chems, India) in sodium ascorbate solution to form a thick hydrogel. Then the mixture was neutralized by dropwise addition of triethanolamine (Chen Chems, India).
In group 1, 10% carbamide peroxide gel was placed on the buccal surface of the samples for 8 hours. After completion of the bleaching procedure, specimens were thoroughly rinsed with an air/water spray for 30 s and air-dried.
In Group 2, 10% carbamide peroxide gel was placed on the buccal surface of the samples for 8 hours and then rinsed and dried. Samples were immersed in 10% sodium ascorbate solution for 3 hours to neutralize the oxidizing effect of carbamide peroxide.
In Group 3 and 4, 10% carbamide peroxide gel was placed on the buccal surface of the samples for 8 hours and then rinsed and dried. Samples were immersed in 10% and 20% sodium ascorbate hydrogels for 3 hrs. The samples were again rinsed and immersed in distilled water for 10 minutes.
Samples were etched with 35% phosphoric acid (Dentsply, Germany) for 15 seconds. The acid was rinsed for 15 seconds with water, and dried with a gentle stream of compressed air for 5 seconds. Single bond adhesive (3M-ESPE, USA) was applied according to manufacturer's instructions. Polymeric ring 4mm in diameter and 6mm in length were placed on the tooth and the composite resin (Filtek TM P60, 3M ESPE, USA) was placed in 2 increments and light cured for 40 seconds. After removing the mold the samples were kept in distilled water for 24 hours. Shear bond strength were analyzed in a universal testing machine with a crosshead speed of 1-mm/minute. Data was analyzed by One Way -ANOVA and multiple comparisons by Post-Hoc test.
| Results|| |
The results was analysed by ANOVA (one way analysis of variance) and multiple comparisons by Post Hoc tests.
[Table 1] and [Table 2] shows the mean shear bond strength and standard deviations for the control and experimental groups. Shear bond strength of the groups treated with antioxidant sodium ascorbate hydrogel and solution were significantly higher than group I, which was not treated with any anti oxidant. [Table 1].
There was no significant difference in shear bond strength among 3 groups treated with antioxidant treatments. [Table 2], [Graph 1] & [Graph 2].
| Discussion|| |
The possibility that bleaching might be detrimental to bonding procedures on enamel and thus increasing micro leakage has always been questioned. Previous studies have showed decreased bond strength of composite to enamel bleached with carbamide peroxide , . Cavalli et al  reported that concentration of carbamide peroxide did not affect the bond strength of composite resin to bleached enamel. However Turkun et al  reported that higher concentration of Carbamide Peroxide produced more significant reduction in bond strength than the lower concentration. Thus in our study we had used 10% carbamide peroxide for bleaching. Bleaching with 10% carbamide peroxide adversely affects the immediate sealing ability of resin composite restoration. 10% sodium ascorbate treatment and a 1-week delay in restoration following bleaching improved the reduced sealing ability of resin composite  .1t has been hypothesized that the carbamide peroxide affects the mineral content and organic phase of the superficial layer and the inner structure of enamel  The lower bond strength was attributed to changes in enamel structure due to the presence of residual peroxide on the surface of the enamel. This residual oxide remains on the bleached enamel for up to three weeks, inhibits the resin polymerization and interferes with the resin penetration  . There is a decrease in bond strength of composite upto 25% after bleaching.
Pretreatment of bleached enamel with alcohol and the use of adhesives containing organic solvents resulted in the complete reversal of decreased enamel bond strengths  . Compromised bonding to bleached enamel can be reversed with a 10% sodium ascorbate solution ,
Ascorbic acid and its sodium salts are potent antioxidants capable of quenching reactive free radicals in biological systems  . The results of our study showed higher shear bond strength of composite restoration done after antioxidant application following bleaching than composite restoration done without antioxidant [Table 1] & [Table 2]. It is observed that sodium ascorbate removes the oxidative effect of bleaching agent. There was no statistical difference in the shear bond strength among different forms of sodium ascorbate. The antioxidant restores the altered redox potential and allows free radical polymerization and reverse the compromised bonding , . Since ascorbic acid and its salts are non-toxic and widely used in the food industry as antioxidants, it is unlikely that their intra-oral use will cause any adverse biological effect of clinical hazard. However application of the solution or gel form of sodium ascorbate in this study involves a long period of time, which may not be clinically acceptable. Further studies have to be done to simulate clinical conditions.
| Conclusion|| |
This study revealed that antioxidant applied after bleaching process increases bond strength in enamel. There was no significant difference among different forms and concentration of sodium ascorbate.
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Department of Conservative Dentistry and Endodontics, Sri Ramachandra Dental College, Sri Ramachandra University, Porur, Chennai - 600116
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2]