Evaluation of the cervical integrity during occlusal loading of Class II restorations

There are many concerns regarding the clinical behavior of packable composite restorations in Class II cavities, particularly when those restorations are subjected to axial mechanical loads. This study evaluated microleakage in vitro in proximal vertical "slot"-type cavities with walls located in enamel and dentin, filled with packable composite, associated or not associated with a flowable composite, a reinforced light-curing glass-ionomer or a compomer, after being submitted to occlusal load cycling. These preparations were subjected to either occlusal load cycling or no occlusal load cycling. Eighty human molars with enamel and dentin margins were treated with standardized cavity preparations (proximal vertical "slot" preparations). After completing the filling process using a packable composite (Filtek P60) with or without a cervical increment of flowable composite (Filtek flow), light-curing glass-ionomer (Vitremer) or compomer (Dyract AP), the molars were separated into two groups: control (without occlusal loading) and test, in which 4,000 one-second cycles of 150 N occlusal loading were applied. All 80 teeth were submitted to a microleakage test, then evaluated utilizing silver nitrate dye penetration. Significant statistical differences (Wilcoxon test, p<0.05) in the amount of leakage in enamel and dentin were found in both the control and test groups. After a paired comparison of the control and test groups, a significant statistical difference was found at the enamel level (Mann-Whitney test, p<0.05). In dentin, the only statistically significant difference found was the relation to the flow material. The Kruskal-Wallis test did not detect any statistically significant difference in the amount of leakage among the four materials studied, with a 5% level of significance for both enamel and dentin. Based on this data, it was concluded that restorations with margins located in dentin had greater microleakage than those restorations with margins located in enamel. When the samples were submitted to occlusal loading, they were negatively influenced, which increased microleakage values in enamel and dentin. There was no statistically significant difference among the four tested materials, when comparing their performance.