Etching tooth structure? With phosphoric acid?

 ... yes, like car bodywork...

I etch the surface of the cavity with phosphoric acid, dissolving some of the mineral in the surface, rinse away the acid and when I dry the surface it's porous. A drop of bonding agent and the filling sticks to the surface, excluding bacteria and making a longer lasting job of the filling. Simples.

Surely You're Joking, Mr. ^H^H^H^H Green! Err, no actually, the idea was invented by Dr. Michael F. Buonocore in 1955!