Introduction
Before a cavity is filled (obturatio cavi dentis, the third principle of caries treatment), deep dentin needs an intermediate layer between the restoration and the pulp. Liners and insulating bases protect the pulp from chemical, thermal and electrical injury and support the filling; placed wrongly or too thick, they weaken the restoration and cause leakage.
Definitions and thicknesses
- Cavity varnish / sealer: a film only micrometres thick (copal varnish about 2–5 µm) that seals the dentinal tubules and reduces early leakage under amalgam. No insulation, no strength; today an adhesive or a desensitiser usually replaces it.
- Liner: a thin layer, usually up to 0.5 mm, on the dentin nearest the pulp. It is a chemical barrier and, when it contains calcium hydroxide or calcium silicate, a therapeutic (medicated) liner: antibacterial and stimulating tertiary (reparative) dentin.
- Base (insulating base, dentin substitute): a thicker layer, usually 1–2 mm, that replaces lost dentin, insulates the pulp, supports the restoration and gives a flat floor.
Liners protect the pulp biologically; bases insulate and carry load. Both cover only dentin, never the enamel margins.