Marginal hybrid layer in Class V restorations

The aim of this study was to evaluate the morphology of the hybrid layer (identified as marginal hybrid layer) along the cervical margins of Class V restorations using several bonding systems. Class V restorations were prepared in vitro at the CEJ in extracted third molars. Three different bonding systems were selected: Scotchbond 1 (Single Bond), Scotchbond MP, and Clearfil Liner Bond 2V. After finishing each restoration with disks, each margin was polished for one minute with polishing paste. The margins of half of the restorations were then treated with 10% phosphoric acid for five seconds, washed in deionized water, and then stored in water for 24 hours before SEM analysis. The margins of the other half of the restorations were treated with 10% phosphoric acid for five seconds, then with 1.5% NaOCl gel for two minutes to remove noninfiltrated collagen, then washed and stored in water for 24 hours. Each sample was gold coated and observed under SEM. A one-way ANOVA was performed to determine if there were any statistically significant differences in hybrid layer thicknesses. The thickness of the marginal hybrid layer measured under SEM was 1.5-2.5 microns thick in Scotchbond MP and Scotchbond 1 but varied from 0.0 to 12.0 microns in Clearfil Liner Bond 2V when observed after NaOCl postpolishing procedures. Far more porosities were seen in the marginal hybrid layer of Clearfil Liner Bond 2V. Enamel margins were free from a hybrid layer in both groups. This study demonstrated that collagen fibrils are not completely infiltrated by adhesive resin at the CEJ level along the cavorsurface margin of the restorations. The presence of noninfiltrated collagen along the external margins may reduce the sealing capability of bonding systems, leaving many open spaces and gaps, which may jeopardize the durability of the bond over time.