What penetrates into the layer of collagen that remains after acid etching?

• A. Resin
• B. Adhesives
• C. Hybrid layer
• D. Bonding agents

Answer: (D)

After dentin is acid-etched, a collagen-rich network remains that must be infiltrated by resin to create a durable bond. The bonding system provides primers that are hydrophilic and capable of wetting and penetrating this demineralized collagen. These bonding agents carry resin monomers that diffuse into the collagen matrix and co-polymerize with the adhesive resin, forming the resin-infiltrated layer known as the hybrid layer. So the component that actually penetrates the collagen is the bonding agent (the primer/resin part of the adhesive system). The hybrid layer is the product of that infiltration, not what does the penetrating itself, and while resin or adhesives are involved, the explicit penetrator into collagen is the bonding agent.