Abstract: A cup for use with the handpiece of an apparatus for applying gas to a portion of a tooth comprising a liner (18) configured and arranged to engage a gas dispensing handpiece, a body (16) defining a gas exposure chamber (28), the body having a higher resiliency to deformation than the liner. The body may be so deformable that it forms against the surface of a tooth to effect a seal and to expose a portion of the tooth to gas circulated in the chamber. The body may overmold the liner and may be formed of thermal-plastic rubber, and the liner may be formed of a plastic material. The gas exposure chamber may be cylindrical.