Marginal hybrid layer in Class V restorations

The aim of this study was to evaluate the morphology of the hybrid layer (i dentified as marginal hybrid layer) along the cervical margins of Class V r estorations using several bonding systems. Class V restorations were prepar ed in vitro at the CEJ in extracted third molars. Three different bonding s ystems were selected: Scotchbond 1 (Single Bond), Scotchbond MP, and Clearf il Liner Bond 2V. After finishing each restoration with disks, each margin was polished for one minute with polishing paste. The margins of half of th e restorations were then treated with 10% phosphoric acid for five seconds, washed in deionized water, and then stored in water for 24 hours before SE M 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 SERI. A one-w ay ANOVA was performed to determine if there were any statistically signifi cant differences in hybrid layer thicknesses. The thickness of the marginal hybrid layer measured under SEM was 1.5-2.5 mu m thick in Scotchbond MP an d Scotchbond 1 but varied from 0.0 to 12.0 mu m in Clearfil Liner Bond 2V w hen observed after NaOCl postpolishing procedures. Far more porosities were seen in the marginal hybrid layer of Clearfil Liner Bond 2V. Enamel margin s were free from a hybrid layer in both groups. This study demonstrated tha t collagen fibrils are not completely infiltrated by adhesive resin at the CEJ level along the cavorsurface margin of the restorations. The presence o f noninfiltrated collagen along the external margins may reduce the sealing capability of bonding systems, leaving many open spaces and gaps, which ma y jeopardize the durability of the bond over time.