A cavity liner is used like a cavity varnish to provide a barrier against the passage of irritants from cements or other restorative materials and to reduce the sensitivity of freshly cut dentin. They are usually suspensions of calcium hydroxide in a volatile solvent. Upon the evaporation of the volatile solvent, the liner forms a thin film on the prepared tooth surface. Cavity varnish is a solution of one or more resins which when applied onto the cavity walls, evaporates leaving a thin resin film, that serves as a barrier between the restoration and the dentinal tubules.