Which lining material produces secondary dentine?

Calcium hydroxide is the correct choice because it is known for its therapeutic properties in dental procedures. When used as a lining material under restorations, calcium hydroxide promotes the formation of secondary dentine. This process occurs through its stimulation of the pulp to produce more dentine, acting as a protective agent for the dental pulp in cases of pulp exposure or deep carious lesions. Additionally, calcium hydroxide has favorable bioactivity, encouraging pulp healing and forming a barrier that can protect the pulp from bacteria or toxins.

The other materials listed do not have this specific effect. Glass ionomer is primarily used for its adhesive properties and fluoride release but does not specifically stimulate secondary dentine formation. Composite resin is a restorative material designed for aesthetic purposes and does not promote dentine regeneration. Amalgam is a durable restorative material commonly used in posterior teeth but lacks the therapeutic properties necessary for stimulating secondary dentine production.