| Abstract|| |
Background and objectives:
The purpose of this study was to evaluate the effect of pre and post operative bleaching with 10% carbamide peroxide on marginal leakage of amalgam and resin composite restorations.
Three groups were made using 30 extracted, caries free and restoration free molars (n = 10). In the preoperative group, bleaching was performed with 10 % > carbamide peroxide, followed by the placement of resin composite and amalgam restorations on class V cavity preparations. In the post operative group, bleaching was performed after the resin composite and amalgam restorations were fabricated. The third group served as a control in which no bleaching was performed. Dye penetration was used for evaluation of marginal leakage.
In post operatively bleached teeth, statistical analysis revealed significant difference between the control and experimental groups for resin composite restorations, but in amalgam restorations there were no significant difference. In preoperatively bleached teeth marginal leakage scores of the resin composite restorations in the experimental group were significantly higher than the control group, but no significant difference was observed between amalgam and resin composite restorations. No significant difference were found between experimental and control groups of amalgam restorations.
Interpretation and Conclusion:
Bleaching with carbamide peroxide may after the marginal leakage of resin composite restoration, but amalgam restorations are not affected adversely in vitro.
Keywords: Amalgam; Carbamide peroxide; Composite resins; Marginal leakage; Tooth bleaching.
|How to cite this article:|
Jacob AS, Dhanya Kumar N M. Effect of pre and post operative bleaching on microleakage of amalgam and composite restoration using 10% carbamide peroxide - an invitro study. J Conserv Dent 2007;10:33-7
|How to cite this URL:|
Jacob AS, Dhanya Kumar N M. Effect of pre and post operative bleaching on microleakage of amalgam and composite restoration using 10% carbamide peroxide - an invitro study. J Conserv Dent [serial online] 2007 [cited 2020 Feb 25];10:33-7. Available from: http://www.jcd.org.in/text.asp?2007/10/1/33/42278
| Introduction|| |
Bleaching is defined as the process of lightening the colour of a tooth through the application of a chemical agent to oxidize the organic pigmentation on the tooth. There are various techniques and materials used for vital tooth bleaching, of which 10% carbamide peroxide gel has gained the most recent popularity. The techniques were "in-office" or "at-home" bleaching. Carbamide peroxide is used as a vehicle for transporting hydrogen peroxide.  "At-home" bleaching using a custom fabricated night guard appliance and 10% carbamide peroxide gel has received the most recent attention; which was initially described by Haywood and Heymann in 1989. 
The composition of most bleaching products containing carbamide peroxide includes glycerin or propylene glycol, sodium stannate, phosphoric or citric acid and flavor additives. Carbopol, a water soluble poly acrylic acid polymer is also added as a thickening agent that also prolongs the release of active peroxide and improves shelf life. 
The chemistry of bleaching with carbamide peroxide is; 10% carbamide peroxide breaks down to give 3.6% of hydrogen peroxide and 7% of urea, the hydrogen peroxide ionizes as per hydroxyl ion and nascent oxygen, which are highly unstable thus forming stable oxygen and water. The urea degrades into carbon dioxide and ammonia. 
Many questions remain unanswered regarding the effects of the bleaching agent on tooth structure and subsequent restorations. Amalgam is one of the most widely used restoration material for posterior teeth and many patients who undergo mouth guard bleaching procedures may have amalgam restored teeth- Some studies have shown an increase in mercury release from amalgam restorations after exposure to 10% carbamide peroxide. , Other studies about home bleaching agents revealed no side effects with Amalgam, Gold or ceramic Restorations, but studies with composites revealed micro cracks on the surfaces and reduction in surface hardness, wear resistance and its bond strength to bleached enamel. Dishman et al 1994 observed that peroxide bleaching of enamel will result in a reduction in the enamel bond strength that is time dependent. 
It is known that especially resin composite and the enamel organic matrix are affected from these bleaching procedures. The probable cause for bond strength reduction could be due to the interaction between resin and residual peroxide in the enamel. .Another probable cause for microleakage could be that the interaction between the bleaching agent on the resin composite and enamel organic matrix alter their coefficients of thermal expansion. 
The purpose of this study is to investigate the effect of pre and post operative application of 10% carbamide peroxide on marginal leakage of amalgam and composite restorations.
| Methodology|| |
Thirty caries free human molars were cleaned of debris and calculus and were stored in normal saline. They were divided into 3 group with 10 teeth in each.
Group 1: 10 teeth were taken and Class V cavities were prepared on each tooth facially and lingually using a new inverted cone diamond bur. The cavities were measuring approximately about 4.0 X 2.0 X 2.0 mm, were placed 1.0 mm occlusaly to the CEJ. The facial cavity preparations were restored with amalgam dispensed from the amalgamator and condensed using hand instruments and burnished using hand instruments.
The lingual cavity preparations were etched with 37% phosphoric acid and washed thoroughly with water. Single Bond (3M) Bonding agent was applied and cured according to manufactures instructions. Filtek Z250 was the composite used to restore the lingual preparations and they were placed incrementally and cured. These restorations were finally finished and polished using softlex discs (3M) serially.
All these 10 teeth were thermocycled 150 times in distilled water, maintained at 4°c and 55° c (±4°c) with an immersion time of 30 seconds. These teeth were then exposed to a 10% carbamide peroxide gel for 8 hour periods per day for 14 days and the bleaching material was renewed daily. The teeth were stored in normal saline when not under the bleaching process.
Group II : Another 10 teeth were bleached using the same material containing 10% carbamide peroxide and for the same no of days and duration. And these teeth were stored in normal saline for another 14 days, and their cavities were prepared and restored the same way as in group I and they were thermo cycled in the same manner.
Group III : The rest of the 10 teeth served as a control group where in no bleaching procedure was done, cavity preparations were done labially and lingually is in the other groups and were restored in the similar fashion. These teeth were thermocycled in a similar manner.
All the 30 teeth were sealed using sticky wax except for a 1.0 mm diameter ring surrounding the restoration. The teeth were subjected to a dye solution of 1% methylene blue in small closed bottles for 24 hours at 37° C.
The teeth were then cleaned from the wax and encased in a clear casting resin. The resin block's and teeth were sectioned bucco-lingually with a diamond disc, creating two test specimens with exposure of the tooth restoration interface from the cavosurface margin to the pulpal wall.
The specimens are polished an examined by light microscopy for the dye penetration along the toothrestoration interface.
Marginal leakage was scored as follows:
0 = No dye penetration
1 = Dye penetration into the enamel (occlusally or gingivally)
2 = Dye penetration into the dentin (occlusally or gingivally).
The results were evaluated statistically by Chisquare test.
| Results|| |
The present in vitro study was conducted to compare the effect of pre and post operative bleaching on
marginal leakage of amalgam and composite restorations.
Descriptive data are presented as numbers and percentages with corresponding microleakage scores for each group. The chi-square test was used to determine the significant difference in microleakage between the groups.
A p value of 0.5 or less was considered statistical significant.
The 30 extracted teeth were randomly divided into three groups of 10 teeth each. And class V cavities were prepared bucally and lingually.
- Before bleaching procedures were done in Group II
- After bleaching procedures were done in Group I
- No bleaching procedures were done - control group
Marginal leakage scores were as follows: 0 =no dye penetrations; 1 = dye penetration into the enamel (occlusally or gingivally) and 2 = dye penetration into the dentin (occlusally or gingivally).
Marginal leakage scores of 1 and 2 were observed in five and four amalgam restorations on postoperatively bleached teeth, respectively. One amalgam restoration showed no marginal leakage. Only one of the 10 resin composite restorations on postoperatively bleached teeth showed no marginal leakage. Marginal leakage scores of 1 and 2 were observed in four and five of these restorations, respectively. In two of 10 amalgam restorations in preoperatively bleached teeth, no marginal leakage could be observed. Scores of 1 and 2 were observed in two and six of these restorations, respectively. All of the resins composite restorations in this group showed score 2 marginal leakage.
In the control group, six and four amalgam restorations were scored 1 and 2, respectively. Six of the resin composite restorations showed no marginal leakage, and four were scored 1.
In postoperatively bleached teeth, statistical analysis revealed significant differences between the control and experimental groups for resin composite restoration (x 2 = 8.571), but in amalgam restorations there were no significant differences. Comparison between the postoperatively bleached experimental groups revealed no significant differences.
In preoperatively bleached teeth, marginal leakage scores of the resin composite restorations in the experimental group were significantly higher than the control group, but no difference was observed between amalgam and resin composite restorations. No significant differences were found between experimental and control groups of amalgam restorations (x 2 =4.400).
Formulae Used for Analysis
| Discussion|| |
Cosmetic dentistry has focused on tooth whitening in the past few years. Three major bleaching methods for vital teeth are described as heat and light technique, micro abrasion technique and gel technique. The gel technique also involves a combination of "home and office bleach techniques". Hydrogen peroxide and Carbamide peroxide are most commonly used as bleaching agents in the gel technique. 
The result of the present study showed that there was a highly significant increase in microleakage in composite resin restorations in Group II i.e. the Pre operative bleaching group, in which the restorations were done after the teeth underwent bleaching procedures with 10% carbamide peroxide for 14 days, suggesting that bleaching with 10% carbamide peroxide may alter the marginal adaptation of resin composites.
The most probable reasons for the increase in microleakage given by Ulukapi H, Benderli Y and Ulukapi I (2003)  were attributed to the residual substances formed when carbamide peroxide breaks down, namely urea and hydrogen peroxide which possibly inhibit the polymerization of the resin bonding agent. The reasons given by Barkhordar, Daniel Kempler, Octavia Plesh (1997 )  were that, hydrogen peroxide alters the tubular permeability and interprismatic area, facilitating the persistence of peroxide which inhibits polymerization and leading to high rate of microleakage.
Shinohara SS, Rodrigues JA and Pimenta LAF (2001)  say the reason for the increase in microleakage could also be attributed to the difference in the composition of enamel and dentin. Dentin contains less mineral and more organic matrix and can be easily affected by hydrogen peroxide, based materials. These materials are strong oxidizing agents that may cause denaturing of proteins in the organic components producing changes that could reduce the performance of resin bond restorations. Another consideration is the presence of dentin tubules that may enhance the rate of penetration of the bleaching agents and residual oxygen diffusion. The consequences may be a higher concentration of residual oxygen in the more porous dentin margins than on enamel margins, there by increasing micro leakage.
Various Methods to improve shear bond strength of resin composite to enamel and decrease incidence of microleakage were:
- By delaying bonding up to 2 weeks after bleaching ,
- By grinding away superficial bleached enamel surface there by removing the residual peroxidase. 
- Pre-treatment of the bleached enamel with alcohol can be used to decreases the residual water and oxygen and increases the bond strength of composite resin to enamel. 
- By using acetone based dentin adhesive system the adverse effect of bleaching on bond strength can be reversed.
In the present study amalgam restorations did not show any significant increase in microleakage in both pre - operative and post-operative groups when compared to control group. This was in accordance with previous study conducted by Ulukapi et al (2003).
However, due to lack of any long-term clinical observations to substantiate these reports, periodic observation of patients is suggested when any type of bleaching is administered and further studies with larger number of samples are recommended.
| Conclusion|| |
Bleaching with 10% carbamide peroxide may alter the marginal leakage of resin composite. But amalgam restorations are not affected adversely in vitro. In vivo, the majority of the scientific evidences support the fact that bleaching is clinically safe to the patient and the restorations.[Table 1],[Table 2].
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Asha Sarah Jacob
Department of Conservative and Endodontics, College of Dental Sciences, Davangere- Karnataka
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2]