Is the outer layer of my dental bonding supposed to wear away?

I have dental bonding on the front six teeth. There seems to be more than one layer of bonding: a very smooth layer and an outer layer than seems to be wearing away. The outer layer seems a lot more brittle and prone to trauma and staining. Is it supposed to wear away? I’ve been using interdental brushes on the front (across the teeth not just between them), and I am not sure if this has altered some of this outer layer. Thank you.