The Journal of Indian Prosthodontic Society

: 2005  |  Volume : 5  |  Issue : 2  |  Page : 94--98

Amalgam-Composite hybrid restorations with amalgam bond: An in vitro marginal leakage study with CA45 radioisotope autoradiography

B Rajkumar, SV Bhagwat 
 Department of Conservative Densitry, Bapuji Dental College & Hospital, Davangere, Karnataka, India

Correspondence Address:
S V Bhagwat
Department of Conservative Dentistry, KLESSQs Institute of Dental Science Belgaum, Karnataka


An in vitro study to evaluate Amalgam-Composite hybrid restoration was conducted and the marginal microleakage of three groups at Amalgam-Tooth interface, Composite-Tooth interface, and Amalgam-Composite interfaces were assessed in a Class V cavities using Ca45 isotope autoradiograhy. Comparing the different groups, the Amalgam bond was found to be superiorthan the Prisma Universal bond, copalite, or just acid etching of Amalgam surface in preventing the marginal microleakage at Amalgam-Composite interface.

How to cite this article:
Rajkumar B, Bhagwat S V. Amalgam-Composite hybrid restorations with amalgam bond: An in vitro marginal leakage study with CA45 radioisotope autoradiography.J Indian Prosthodont Soc 2005;5:94-98

How to cite this URL:
Rajkumar B, Bhagwat S V. Amalgam-Composite hybrid restorations with amalgam bond: An in vitro marginal leakage study with CA45 radioisotope autoradiography. J Indian Prosthodont Soc [serial online] 2005 [cited 2022 Aug 12 ];5:94-98
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Full Text

Dental amalgam and composite resins are accepted universally in day-to-day restorative procedures. Traditionally, dental amalgam is a popular restorative material for the posterior teeth, while composite resins primarily are used in the anterior teeth, providing esthetically favorable restorations. Because of the growing popularity and the ease of availability of composite resins and dental amalgam their eventual use together has become inevitable.

When these two dissimilar materials are combined, both the favorable tooth-colored appearance of composite resin, and the strength and durability of the amalgam is sustained. Because the amalgam portion bears the brunt of the occlusal forces and the composite providing a desirable appearance, this hybrid restoration can serve as a definitive restoration.

Although the idea of camouflaging amalgam restoration beneath a veneer of composite had its inception in 1971, the recent advances in the area of dentin adhesive resins have generated a fresh interest in this field of research.

Several articles have been published about the application of composite resins to mask the unaesthetic appearance of amalgam. Some adhesive resins have been promoted to chemically adhere composite to amalgam. [1],[2],[3] (Train et al. 1989). Amalgam bond is a 4-methacryloxy ethyl trimellitic anhydride, methyl methacrylate/tri- n -butyl borane (4-META/MMA-TBB, Parkell Products, Farmingdale, NY 11735), which is bounded to enamel-etch patterns established by acid pretreatment, to dentin by the formation of a hybrid layer of resin-encapsulated collagen/hydroxyapatite, and to the 'wet' amalgam by penetrating between amalgam crystal phases where it polymerizes and is locked in by amalgam setting.

Amalgam bond has been used for the first time to bond composite to amalgam. The purpose of our study is to assess the usefulness of amalgam bond by evaluating marginal microleakage[11] at,

1. Amalgam-Tooth interface (comparing with and without copalite at the interface).

2. Amalgam-Composite interface (comparing with and without Prisma Universal Bond at the interface).

3. Composite-Tooth interface (comparing with and without Prisma Universal Bond at the interface).

 Methods and materials

Sixty noncarious freshly extracted human permanent mandibular molars were selected and stored in saline. The hybrid restoration of amalgam and the composite to study the microleakage of various phases was prepared by the method described by Kossa.[4] The resulting cavity was completely surrounded by enamel with external dimensions of 5.0 mm 3.0 mm and pulpal depth of 2 mm. The specimens were randomly divided into three groups as shown in [Table 1] and [Figure 1]A-C.

Group A

l Amalgam (GS-80 SDI Australia)-Tooth interface with cavity varnish copalite (Harry J. Bosworth Co., Chicago, IL, USA.) as the liner.

l Amalgam-Composite (Ful-Fil, Caulk Dentspl interface with acid etching of amalgam surfaces.

l Composite-Tooth interface, with acid etching of enamel without any bonding agent.

Group B

l Amalgam-Tooth interface without any liner.

l Amalgam-Composite interface with Prisma Universal Bond (LD Caulk Co. Milford, DE, USA) at the interface.

l Composite-Tooth interface with Prisma Universal Bond at the interface.

Group C

l Amalgam-Tooth interface with Amalgam Bond (Parkell Product, Inc., Farmingdale NY, USA) as liner.

l Amalgam-Composite interface with amalgam bond at the interface.

l Composite-Tooth interface with amalgam bond as dentin bonding agents.

The restored teeth were stored in saline for 7 days followed by thermo cycling between two water baths for 1-minute intervals for a total of 10 cycles. The water baths were maintained at 4 and 60C. Upon completion of the cycling, the samples were evaluated through the use of Ca45sub isotope technique as described by Phillips et al. (1961).

Samples were first sealed to the margins with two layers of clear nail polish. The isotope solution was adjusted to contain 0.1 mci/ml of radioactivity in the form of calcium chloride with ph adjusted to seven in 100 ml of normal saline. The specimen was immersed in the isotope solution for 2 h. The teeth were washed under running water and gently scrubbed with detergent and wiped with an absorbent paper to reduce the activity of isotope on the surface of the specimen, using a diamond disc. In a straight hand piece, the teeth were sectioned longitudinally through the midline of the restored cavity preparation.

The sectioned teeth were placed on the standard intra-oral Kodak Ekta speed dental X-ray film for 17 h, after which the films were developed in an automatic developer for autoradiography.

Microleakage was expressed by the degree of Ca45sub isotope penetration, as shown in [Table 2] and [Figure 2].

Statistical comparison of leakage was made between the groups at various interfaces using student ' t ' (Unpaired) test.

 Results and observations

In this study, three groups of Amalgam-Composite hybrid restorations were compared. The depth of penetration of the radio-isotope Ca45sub, as evaluated from the auto-radiographs, in various groups, between Amalgam-Tooth, Amalgam-Composite, and Composite-Tooth interfaces is shown in [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8] and [Figure 3] and [Figure 4] show comparison of leakage at various interfaces between the groups. From [Table 6], which compares the mean microleakage values of groups A-C at Amalgam-Tooth interface, it is observed that mean leakage value is lowest in group C, and very significantly less than groups A and B ( P P P P <0.001). However, no significant difference in mean values of microleakage is observed between groups B and C.


The success of a restoration depends on the nature and amount of adhesion, or adaptation of the restoration to the cavity walls. In our present study, the results indicate that the presence of copalite between the amalgam restoration and the tooth surface (group A) reduced the marginal leakage when compared with amalgam restorations without any cavity varnish before the condensation of amalgam (group B, [Table 6]). On comparing the mean marginal microleakage of Amalgam-Tooth interface with amalgam bond as liner (group C), with copalite (group A) and without any liner (group B), we observed that the leakage was significantly less with amalgam bond, which is in conformation with a study by Ben-Amar et al.[5] The amalgam bond binds to both tooth and amalgam, this difference in the properties of the two intermediary sealers could account for the difference in marginal microleakage values. Because our study has shown that amalgam bond is superior to copalite varnish in preventing the early marginal microleakage, it establishes that amalgam bond is more useful for high copper amalgam alloys to prevent early microleakage than copalite varnish. However, it remains to be seen whether the corrosion products have a deterrent effect on amalgam bond or not, and long-term studies are necessary to prove the efficacy of amalgam bond.

Both amalgam bond and prisma universal bond proved to be very effective in preventing the marginal leakage of Composite-Tooth interface (groups C and B) when compared to group A, where no adhesive liner had seen to be employed between the composite resin and the tooth surface.

However, the mean microleakage value with amalgam bond was lower than that with prisma universal bond, as shown in [Table 8]. This minor difference in the mean microleakage values of amalgam bond and prisma universal bond is probably because of their nature of bonding. The principle followed with Prisma Universal Bond is to leave the smear layer in place and saturate it with monomer. It has been shown through scanning electron microscopy by Kubo et al.[6] that there is no thorough penetration of the adhesive system-resin into the dentin. Amgalgam bond adhesive system employs 10-3 treatment (10% citric acid, 3% ferric chloride) resulting in the opening of microporosities smaller than dentinal tubules, into which the hydrophilic resins penetrates and creates the resin-dentin 'hybrid' layer.

On evaluating the mean microleakage at the Amalgam-Composite interface, we observed that group C with amalgam bond at the interface showed the least microleakage value (zero) and was statistically significant when compared to groups A (without adhesive liner) and B (with Prisma Universal Bond at the interface). However, there was no statistically significant difference between groups A and B [Table 7]. The reason that could account for the high microleakage associated with Prisma Universal Bond could be the fact that we have acid-etched the roughened amalgam surface before the placement of composite. Hadavi et al.[9] has suggested that better adhesion occurs, if the amalgam is not acid etched. Because our study began long before this finding had been reported, we did not follow this technique. Moreover, metal resin adhesion capability of the Prisma Universal Bond is not known at present.

We can only speculate about that nature of adhesion, which is responsible for the least amount of microleakage with amalgam bond at amalgam teeth Composite interface. 4-META has an affinity for metallic ions and their oxides and this probably accounts for the adhesion of amalgam bond to previously set amalgam which have surfaces that readily oxidize to form a variety of metallic oxides. Composite resin placed over amalgam coated with amalgam bond probably polymerizes and co-polymerizes with the resinous monomers of the bonding agent.

Although comprehensive, our study is by no means conclusive. Several factors such as bond strength and water resorption, of the adhesive resin amalgam bond remain to be evaluated. However, this is the first study to assess the usefulness of amalgam bond as an adhesive liner for Amalgam-Composite hybrid restorations.


This study evaluated the marginal microleakage of Amalgam-Composite hybrid restorations at Amalgam-Tooth, Amalgam-Composite, and Composite-Tooth interfaces. The conclusions of the present study are as follows:

1. Cavity varnish (copalite) is good at preventing marginal leakage of amalgam restorations at Amalgam-Tooth interface, when compared to the lack of a cavity liner.

2. Amalgam bond is better than copalite in reducing the marginal leakage at Amalgam-Tooth interface.

3. Prisma Universal bond is a good adhesive resin linear to reduce marginal microleakage at the Composite-Tooth interface in comparison to plain acid etching of enamel.

4. Amalgam bond and Prisma Universal bond do not have significantly different capacity in the reduction of marginal leakage as adhesive liners at Composite-Tooth interface.

5. Amalgam bond is a better adhesive liner than plain acid etching of amalgam, or employment of Prisma Universal bond for Amalgam-Composite hybrid restorations.

Although our results indicate that amalgam bond is a promising material for placing in juxta position to amalgam for Amalgam-Composite hybrid restorations, further investigations are necessary to evaluate the physical properties of such a combination.


We thank Administration of Bapuji Dental College, Davangere for having provided the necessary facility for this research.


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