This study evaluated the effectiveness of three resin bonding systems, one glass -ionomer cement and one resin cement in reducing microleakage in Class V amalgam restorations. Seventy-two maxillary premolars that were extracted for orthodontic purposes were utilized. The teeth were divided into six groups of 12 each. Three groups were assigned for use with the adhesive resins which were applied onto the prepared cavity walls of these respective groups; the fourth groups was assigned for use with glass-ionomer cement and for the fifth group, resin cement was applied onto the axial wall of the cavity prior to amalgam condensation. In the sixth, control group, the cavity walls were painted with Copalite varnish and air-dried prior to placement of the amalgam restoration. The dye penetration method was employed and the restored teeth were sectioned and examined under reflected-light stereomicroscope. The degree of microleakage was scored using standard scoring criteria. Kruskal-Wallis test with non-parametric post hoc test indicated that microleakage was less in restorations treated with adhesive systems than in those with Copalite varnish (P<0.05). Wilcoxon Ranks test for non-parametric samples indicated that microleakage was more extensive at the gingival margins in all of the restorations than at the occlusal margins (P<0.05). At both margins, the extent of microleakage varied among the investigated materials. The two resin bonding systems (Single Bond and Prime & Bond 2.1) demonstrated superiority in reducing microleakage compared to the controls, the glass-ionomer (Vitrebond) and the resin cement (Time Line). Adhesive resin treatment significantly reduced microleakage indicating improved bonding of Class V amalgam restorations. None of the studied systems bonded adequately at the gingival aspect of the cavity as they did occlusally. At the occlusal margin, Single Bond and Prime & Bond 2.1 compared favorably to the glass- ionomer (Vitrebond) and the resin cement (Time Line). 
 

Amalgam has served effectively as a dental restorative material since its introduction to Europe in the 19th century. It is one of the least technique-sensitive direct restorative materials and it tolerates a great deal of misuse without obvious failure. However, apart from aesthetics and the public concern about possible amalgam toxicity, amalgam has its own distinct set of disadvantages, in particular, microleakage and lack of adhesion to tooth structure. The detrimental effects of microleakage include post-operative sensitivity, staining and discolouration.1 It is also believed that microleakage may lead to secondary caries and pulp irritation.1 However, this is not supported in other studies which reported that "microleakage" does not per se lead to secondary caries.2

Various approaches have been introduced to reduce microleakage in amalgam restorations. Cavity liners, bases and glass-ionomer cements which bond to dentine, have been reported to produce less microleakage under both composite and amalgam restorations.3

Recently, adhesive resins have also been used as cavity liners in an attempt to reduce leakage and to provide retention of amalgam restorations. The usage of adhesives is aimed at forming an effective bond between amalgam and tooth structure. This bond is not merely mechanical, but it includes a molecular interaction.4,5 Resins based on bisphenol A-glycidyl methacrylate (Bis-GMA) monomer or the 4-methacryloxyethyl trimellitate anhydride (4-META) monomer have been used as adhesives for amalgam restorations.6 A review of the literature3-5,7,8 indicated that marketed adhesive systems and glass-ionomer cements based on light-initiated polymerization are effective in improving the marginal seal of amalgam restorations compared to the conventional method of treating cavity walls with varnish prior to placement of amalgam. However, disagreement on the ideal adhesive systems8,9 for the purpose calls for further investigation. The aims of this study were to evaluate and compare the degree of microleakage of Class V amalgam restorations with dental adhesives, glass -ionomer cements and copalite varnish as liners, and study the pattern of microleakage at the occlusal and gingival margins of Class V restorations

Seventy-two sound human maxillary premolars that were extracted for orthodontic reasons were collected for this study. The teeth were divided into six groups of twelve each comprising five test groups and a control group.The test materials comprised three dentine adhesive systems (Table 1), a resin modified glass-ionomer lining cement and a resin cement (Table 2). Copalite varnish* was used as the control material.All the prepared cavities were filled using admixed amalgam.** The degree of microleakage was later evaluated using 2% methylene blue.***

A Class V cavity was prepared on the buccal surface of each tooth (Fig. 1A). The cavity was approximately 3 mm mesiodistally, 2 mm occlusogingivally and 2 mm in depth. In order to compare the extent of microleakage at the occlusal margin with that of the gingival margin, the cavity was prepared in such a way that its coronal part was in enamel-dentine while gingivally, it was in dentin-cementum. Prior to placement of amalgam restorations, the surfaces of the prepared cavity walls were acid-etched or treated with surface conditioner and the investigated dentine-amalgam bonding systems placed according to the individual manufacturer's instructions.The cavities were filled with amalgam and the margins were burnished before carving. The amalgam was then carved and the margins reburnished. All specimens were stored in distilled water at 37° C for 24 hours.

The specimens were dried and the root apices were sealed with the light-cured glass-ionomer cement, Vitrebond. All surfaces of the specimens were then painted with two coats of nail polish except the restoration and approximately 1mm beyond its margins. The specimens were subjected to 1500 thermal cycles by successively immersing them in 5°C and 50°C water baths10 with 30 seconds dwell time at each temperature. Specimens were immersed in 2% methylene blue at room temperature for 4 hours. On removal from the dye, they were gently washed in tap water. Each specimen was sectioned longitudinally in a bucco-lingual direction using a diamond wheel‡ in order for the sectioning plane to pass through the amalgam restoration. The sectioned specimen was examined under light stereomicroscope‡‡ at 4x magnification. The extent of dye penetration was measured three times by the same examiner and the degree of microleakage rated according to a scoring system previously described5,7 and as shown in Table 3 and Figure 1B.

Data Analysis

The frequency of scores was calculated as a percentage to reflect the number of specimens which leaked to a given degree in each group. The reliability of measurements made at different times was evaluated using Kappa statistics. Differences among the independent groups' medians were evaluated using Kruskal-Wallis test with non-parametric post hoc test, and those between the scores attained at the occlusal and gingival margins of the same dependent sample were evaluated using the non-parametric Wilcoxon Signed Ranks test, an appropriate test for dependent samples. All tests were performed at 0.05 level of significance.
 

Fig. 2. Percentage frequency of microleakage occurring at the occlusal margin and the gingival margin of amalgam restorations. The different alphabets denote significant differences(P<0.05).

The results revealed that all the investigated systems leaked at the gingival margin of the restorations and the difference among their performance indicated by their microleakage scores was insignificant.

Within the limitations of this study, the following conclusions can be drawn.

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