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Table of Contents   
ORIGINAL RESEARCH  
Year : 2011  |  Volume : 22  |  Issue : 6  |  Page : 799-803
Repair of amalgam restorations with composite resin and bonded amalgam: A microleakage study


1 College of Dentistry, Federal University of Minas Gerais, Belo Horizonte, Brazil
2 State University of Montes Claros, Montes Claros, MG, Brazil
3 University of Florida P. O. Box 100415, Gainesville, FL 32610, USA

Click here for correspondence address and email

Date of Submission16-Sep-2010
Date of Decision29-Dec-2010
Date of Acceptance31-Jul-2011
Date of Web Publication5-Apr-2012
 

   Abstract 

Background: Total replacement is the most common technique for defective amalgam restorations, and it represents a major part of restorative dental treatment. Repair is an alternative option for amalgam restorations with localized defects.
Aims: This study compared microleakage of amalgam restorations repaired by bonded amalgam or composite resin.
Materials and Methods: Thirty extracted human pre-molars were prepared and restored with class I amalgam. A simulated defect was prepared that included the cavosurface margin on restorations, and the pre-molars were assigned to two treatment groups (n=15): In group 1, premolars were treated by composite resin (34% Tooth Conditioner Gel + Adper Single Bond 2 + Z100) and in group 2, premolars were repaired by bonded amalgam (34% Tooth Conditioner Gel + Prime and Bond 2.1 + Permite C). The teeth were immersed in a 50% silver nitrate solution, thermocycled, sectioned longitudinally and then observed by three examiners using a stereomicroscope. Microleakage was evaluated using a 0-4 scale for dye penetration, and data was analyzed by Kruskal Wallis and Dunn tests.
Results: Neither of the two methods eliminated microleakage completely. Composite resin was significantly the most effective for repair/tooth interface sealing (score 0 = 80.0%; P=0.0317). For the repair/restoration interface, composite resin was also statistically more effective as a sealant (score 0=66%; P=0.0005) when compared to the bonded amalgam technique (score 0=13%; P=0.0005).
Conclusions: The use of adhesive systems significantly affected the ability to seal the repair/ tooth interface. However, at the level of the repair/restoration interface, the bonded amalgam technique may increase microleakage.

Keywords: Dental amalgam, dental leakage, dental resin, dental restoration failure

How to cite this article:
Popoff DV, Gonçalves FS, Magalhães CS, Moreira AN, Ferreira RC, Mjör IA. Repair of amalgam restorations with composite resin and bonded amalgam: A microleakage study. Indian J Dent Res 2011;22:799-803

How to cite this URL:
Popoff DV, Gonçalves FS, Magalhães CS, Moreira AN, Ferreira RC, Mjör IA. Repair of amalgam restorations with composite resin and bonded amalgam: A microleakage study. Indian J Dent Res [serial online] 2011 [cited 2014 Dec 19];22:799-803. Available from: http://www.ijdr.in/text.asp?2011/22/6/799/94672
Dental amalgam has been used by dentists for more than a century. However, amalgam fillings have a number of drawbacks, such as, constant corrosion; they do not fulfill cosmetic-esthetic demand; and, they lack adhesion to tooth structures. Despite advancements in resin-based composite technology, amalgam restoration remains a restorative treatment option in many dental practices. [1],[2],[3],[4] Such popularity can be attributed to its good clinical performance, relatively low cost and long-term cost-effectiveness. [2] Secondary caries and fractures are common failures related to amalgam restorations and represent the main reasons for the replacement of defective amalgam restorations. Other reasons for replacement include inadequate marginal integrity and inadequate interproximal contact. [1],[3],[5],[6]

Total restoration replacement is the most common treatment for defective amalgam restoration and represents a major part of restorative dental treatment. [1],[5],[6] However, this approach contradicts the current trend toward minimal interventional procedures to decrease the risk of pulpal injuries and save tooth structures. [4] An aim for current restorative dentistry is to maintain restorations, i.e., to work with materials and techniques that allow the repair of localized defects. [7]

Repair is an alternative option for the treatment of amalgam restoration with localized defects. It involves the removal of part of the restoration and any defective tissue adjacent and subjacent to the defective area and the restoration of the prepared site. [8] This procedure allows for the preservation of sound tooth structure. [9] The marginal sealing of amalgam restorations remains important in clinical practice. [1],[10],[11] The use of amalgam bonding agents has become popular in the restoration of posterior teeth and demonstrates many potential advantages, including tooth reinforcement, decreased postoperative sensitivity, better marginal adaptation, decreased microleakage, reduction of secondary caries and a more conservative preparation. [12],[13],[14],[15],[16]

Many resin adhesives have been employed, and successful reports indicate their effectiveness as amalgam bonding agents. Based on the way materials are applied, bond strength values and sealing data vary considerably, [14] and are possibly influenced by cavity size, indicating that bond strength is inversely proportional to the bonding area. [3],[15] Meanwhile, in a recent systematic review, authors concluded that there is no evidence to support or refute a difference in survival between bonded and non-bonded amalgam restorations. [16]

Resin-based tooth colored materials have become increasingly popular as overall restorative materials, including posterior restoration applications. Resin composites have also been shown to successfully repair amalgam restorations. The clinical conditions for placement of composite resin adjacent to existing dental amalgam have been described in several publications. Various repair techniques have been suggested in the literature, many of which are based on either mechanical and/or adhesive techniques. [4],[6],[17],[18] Although several studies have shown that adhesive systems form ionic bonds with amalgam, the data published on amalgam repair show contradictory results. [4],[17],[18] In view of the lack of evidence on the additional benefits of adhesively bonded amalgam compared to non-bonded amalgam or composite resins for the repair of amalgam restorations, it is important to investigate whether it is desirable to use these techniques for this application.

Despite the limitations of in vitro studies in predicting clinical conditions, this study may help in the establishment of scientific evidence to justify the inclusion of bonded amalgam and composite resins as feasible for the repair of amalgam restorations. Thus, the objectives of this study were to evaluate the marginal microleakage of defective amalgam restorations repaired with composite resin and bonded amalgam. The null hypothesis tested was that microleakage at amalgam repair margins is not affected by the use of bonding agents.


   Materials and Methods Top


This study was submitted to and approved by the ethics committee at the College of Dentistry, Federal University of Minas Gerais in Brasil; process number 105/19-07-2004.

Teeth selection

Thirty non-carious human premolars freshly extracted for orthodontic purposes were utilized in this study. The roots were cleaned by scraping to remove debris and disinfected in 0.5% thymol solution before use.

Specimen preparation

Class I cavities were prepared on the occlusal surface of the extracted teeth to be 2 mm wide, 4 mm deep and 3 mm long using a high speed handpiece with air-water coolant and a carbide plain fissure bur # 245 (KG Sorensen Ind and Com Ltda, Barueri, SP Brazil). The burs were replaced after five cavity preparations. Preparation dimensions were measured with a periodontal probe to maintain uniformity. One operator prepared all the cavities to ensure a consistent size and depth to minimize preparation variability.

Restorative procedure

The teeth were restored by an admixed, high copper amalgam alloy (Permite C, SDI, Bayswater, Victoria, Australia) that was hand condensed into the preparations to cover all walls and cavosurface margins, and then carved to the tooth contour with a sharp carve. Seventy-two hours later, the restorations were polished and stored in saline solution at 37°C.

Repair procedure

New Class I cavity preparations (1 mm wide, 2 mm deep and 3 mm long) were prepared along the cavosurface margin of the amalgam restorations in order to simulate a defect. A high-speed handpiece with air-water coolant and carbide plain fissure burs # 245 (KG Sorensen Ind and Com Ltda, Barueri, SP Brazil) was used. The burs were replaced after five such 'defects' had been prepared. Preparation dimensions were measured with a periodontal probe to maintain uniformity. One operator prepared all teeth to ensure a consistent calibrated size and depth to minimize preparation variability.

The teeth were randomly divided into two experimental groups (n=15): G1 - Composite resin repairs (Caulk 34% Tooth Conditioner Gel - Dentsply, Milford, Delaware, USA + Adper Single Bond 2-3M, St Paul, MN, USA + Z100-3M, St Paul, MN, USA) and G2 - Bonded amalgam repairs (Caulk 34% Tooth Conditioner Gel - Dentsply, Milford, Delaware, USA + Prime and Bond 2.1 - Dentsply, Milford, Delaware, USA + Permite C, Victoria, Australia).

Thermal cycling and microleakage testing

The specimens were subjected to thermal cycling for 500 cycles between 5°C and 55°C with a 60 second dwell time. The teeth apices were filled with glass-ionomer (Ketac Bond - 3M ESPE, St Paul, MN, USA) and then coated with two layers of nail varnish (Niasi, Taboão da Serra, SP, Brazil), leaving the repair margins uncoated. They were then immersed in a 50% silver nitrate solution for 24 hours at 37°C in the absence of light. Next, they were washed in running water and immersed into another vial with photo-developing solution (Decktol, Kodak, São José dos Campos, SP, Brazil) for six hours under continuous illumination to reduce the formation of precipitated silver ions. Each specimen was longitudinally sectioned by a cutting machine (Labcut 1010 - Extec Technologies Inc.,USA) in a buccolingual direction through the restoration center. Sections were examined with a stereomicroscope (Zeiss - Oberkochen, Germany) at ×50 magnification by three trained examiners. The agreement between examiners was evaluated by Cohen's Kappa test (K=0.78 to 1.00), with the result being considered the median of the scores assigned by each examiner.

Each section was graded for microleakage at both the repair/tooth and repair/restoration interfaces as follows [Figure 1]:
Figure 1: Scores of 0 to 4 in a dye penetration test serve as indicators of marginal microleakage for the repair/tooth and repair/restoration interfaces

Click here to view


  • Score 0 - No dye infiltration
  • Score 1 - Dye penetration up to the first third of the repair axial wall
  • Score 2 - Dye penetration up to the second third of the repair axial wall
  • Score 3 - Dye penetration onto the entire repair axial wall
  • Score 4 - Dye penetration onto the pulpal wall of the repair.
Statistical analysis

The percentage of microleakage scores was compared for both treatment groups at the repair/tooth and repair/restoration margins using Kruskal-Wallis and Dunn tests. Results were considered significant for a confidence level of 5%.


   Results Top


The non-parametric Kruskal-Wallis test detected significant differences between the tested materials for both repair/tooth (P value = 0.000) and repair/restoration (P value = 0.000) interfaces. The Dunn test showed that dye penetration was significantly deeper when bonded amalgam was used for sealing of repair/tooth (Z=1.31; P=0.0317) [Figure 2] and repair/restoration interfaces (Z=2.93; P=0.0005) [Figure 3]. For repair/tooth interfaces, 40% of restorations repaired by bonded amalgam had dye penetration registered up to the first third of the repair axial wall, and only 53.5% lacked dye infiltration [Figure 2]. When the repair/restoration interfaces were analyzed, 53.3% of restorations repaired by bonded amalgam had dye penetration registered onto the pulpal wall of the repair, and only 13.3% lacked dye infiltration [Figure 3].
Figure 2: The frequencies of dye penetration scores are indicators of marginal microleakage for repair/tooth interfaces

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Figure 3: The frequencies of dye penetration scores are indicators of marginal microleakage for repair/restoration interfaces

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Eighty percent of restorations repaired by composite resin registered no dye infiltration when the repair/tooth interfaces were analyzed, and no dye penetration was observed onto the entire repair's axial wall (score 3) or pulpal wall (score 4) [Figure 2].


   Discussion Top


The present study tested the effects of two restorative materials on the marginal microleakage of amalgam repairs using a 50% silver nitrate solution as a tracer. Silver ions, being extremely small (0.059 nm), have the ability to greatly penetrate tooth-restoration interfaces when compared to bacteria, which measure about 0.5 to 1.0 micrometers. [19] The repair of amalgam restorations has been considered to be a viable, cost-effective alternative treatment to complete replacement. It allows for the removal of localized defects with maximal preservation of tooth structure. Other advantages of repairs include minimal stress on the pulp, the simplicity of the technique and the saving of time and material. [1],[7],[8],[9],[17] A successful technique for the repair of existing amalgam restorations would be advantageous for clinicians interested in conservative dental treatments. [6] Total replacement is the most common treatment for amalgam restorations clinically diagnosed as defective. Occasionally, the criteria for replacing a restoration are subjective. Small deviations from ideal concepts determine the need for replacement, especially in cases where the restorations are clinically acceptable except for localized defects. [5],[6] Localized active caries may also be considered for repair rather than complete restoration. The selection process of cases should include strict clinical and radiographic examinations to ascertain the extent of the caries. This technique is rarely suggested for fractures of the restoration body, exposure of the base material, several failures in the same restoration, areas of high stress concentration, or recurrent caries with evidence of extension, especially in patients at a high risk for caries. [5],[7],[8]

A standard for determining which restorative procedure would be more appropriate for the repair of amalgam restorations has yet to be established. Within the limitations of in vitro tests and the results from in vivo studies, the available data lead to the conclusion that the repairs, when well designed, effectively increase the longevity of amalgam restorations, as indicated by previous studies. [5],[8],[20] The present results found marginal sealing at the repair/tooth interface in up to 80% of the teeth tested when composite resin was used as the repair material. Marginal microleakage is a major concern in restorative dentistry as it is related to pulpal changes, sensitivity and the development of secondary caries. [21] Microleakage tests are useful methods to evaluate the sealing performance of adhesive systems. Among the different methods employed, dye penetration measurement performed on sections of restored teeth is the most commonly used technique due to its low cost and simplicity. [6],[22] Furthermore, measurements of marginal-sealing effectiveness and bond-strength testing are the two of the most commonly employed methods for determining bonding capacity in laboratory testing. [23]

Thermal cycling aims to simulate the thermal fluctuations of the oral cavity and imitate what could occur with the restorations under clinical conditions. In this study, the specimens were submitted to thermal cycling for 500 cycles between ± 5°C and ± 55°C with a dwell time of 60 seconds that was long enough to establish thermal equilibrium between the specimen and fluid, and create tensions capable of leading to microleakage by breaking the union between them. [7] Furthermore, in a previous study about the influence of thermal stress on the marginal integrity of restorative materials with different degrees of adhesiveness, all thermal cycling regimens, including those of 500 and 1000 cycles, increased leakage in all amalgam restorations. Their effects on resin-based composite and glass ionomer restorations were only significant when a 60- seconds dwell time was used, [24] thus justifying the regimen and dwell time used in our study.

Several investigations have reported significant reductions in marginal leakage for adhesive systems that were placed under amalgam restorations when compared to those with varnish or no liner. The use of adhesive systems with amalgam restorations has been common, and studies have shown that this technique increases the initial sealing, reinforces the tooth, decreases postoperative sensitivity, improves marginal adaptation, decreases microleakage, reduces the possibility of the development of secondary caries, and allows for conservative cavity preparations. [2],[8],[13],[17] However, there is a discrepancy between authors about the relevance of these findings. In some studies, no differences in marginal integrity were found between teeth treated with adhesive systems and those not treated. [3],[16],[25]

Despite the advantages of adhesive technologies, clinical and laboratory studies have found no differences in the marginal integrity and postoperative sensitivity of teeth treated with the use of adhesives. [3],[25],[26] These results are consistent with our findings, which demonstrated poor sealing when bonded amalgam was used for both repair/tooth and repair/restoration interfaces.

Scanning electron microscopy (SEM) studies have shown micromechanical interlocking between amalgam and adhesive, but they have also demonstrated that most of the adhesion comes from the adhesive/tooth interface. [27] The present findings confirm the results from these studies that indicate a reduction of marginal microleakage associated with amalgam restorations repaired with adhesive only for repair/tooth interfaces and not for repair/restoration interfaces.

Composite resins have been described in the literature for the repair of amalgam restorations. One of the advantages of resin dental materials is their excellent aesthetics. Since their commercial introduction in the 1960s, resin composites have undergone significant development. Furthermore, new monomers have been developed to obtain materials with a suitable degree of conversion, shrinkage and marginal leakage. [28],[29] Various repair techniques have been suggested, many of which are based on either mechanical and/or chemical techniques. Mechanical techniques include roughening the amalgam, preparing undercuts or creating grooves. Chemical techniques include the use of multipurpose adhesive agents. [4],[6],[17],[18] Although several studies have shown that primers and adhesives form ionic bonds with metal oxides or with the active metal compounds of the amalgam, the existence of a true chemical bond between composite resin and amalgam is controversial, and the data collected in studies on amalgam repairs have contradictory results. [4],[17],[18] The present study demonstrated marginal sealing in up to 80% of teeth for the repair/tooth interface when a composite resin was used as the repair material. For the repair/restoration interface, almost marginal sealing was achieved in almost 70% of teeth; these results are in agreement with previous findings that composite resin may be an effective way to repair or mask the appearance of amalgams placed in visible areas of the mouth. [6],[17]

It is clear that the need to identify the most suitable material for performing amalgam repair highlights the need for clinical studies. Although the present data indicate composite resin as the material of choice for preventing marginal microleakage at the repair/tooth interface, its performance was not equally good for the repair/restoration interface in this in vitro study. Furthermore, the bonded amalgam technique could not provide more than a 53% sealing rate for the repair/tooth interface. Knowing the limits of each material is essential for dentists, and the need for more clinical research about the repair technique is justified by the lack of restorative materials that can provide optimal marginal adaptations.


   Conclusions Top


Within the limitations of this study, our results show that

  • None of the restorative techniques evaluated were able to completely eliminate marginal microleakage.
  • For the repair/tooth interface, repair with composite resin demonstrated a greater sealing ability than repair with bonded amalgam.
  • For the repair/restoration interface, bonded amalgam showed a higher level of microleakage than repair with composite resin.


 
   References Top

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Correspondence Address:
Daniela Araújo Veloso Popoff
College of Dentistry, Federal University of Minas Gerais, Belo Horizonte
Brazil
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DOI: 10.4103/0970-9290.94672

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