While composite fillings are cured with LED light, the outermost microscopic layer (~10-50 microns) of the filling’s surface that comes into contact with air (oxygen) cannot fully harden because oxygen inhibits the polymerization reaction; it remains as a sticky, monomer-rich, soft layer. This is called the “Oxygen Inhibition Layer.” If the dentist does not completely scrape away this sticky layer with special finishing burs and polishing discs at the end of the filling process, that soft area will absorb cigarette, tea, and coffee pigments like a sponge in the following days, and the surface of the filling will quickly turn a dark brown color, accelerating plaque accumulation. A flawless polish is completed by completely removing this inhibition layer.
