A pellicle, or tertiary enamel cuticle, is an acquired exogenous thin oral biofilm composed of proteins from saliva that is deposited on the tooth surface immediately after tooth brushing. The pellicle is colorless and has a thickness of about 0.5 to 1 µm. It is semi-permeable.
The pellicle has various protective functions (e.g. protection against abrasion by food or the other teeth during chewing; protection against acid attack), but it also allows various bacteria to attach and thus provides the "base" for plaque.
Due to their intrinsic charge, the pellicles form an electrostatic bond with the calcium and phosphate groups of apatite, which causes the pellicles to adhere strongly to the enamel surface. They cannot be removed by brushing the teeth, for example.