Final answer:
A liner is an insulation layer consisting of dental cement with an added sedative effect that protects the dental pulp.
Step-by-step explanation:
An insulation layer, consisting of dental cement with an added sedative effect, used to protect the dental pulp is known as a liner. This layer serves to protect the pulp after a tooth has been prepared for a filling when the removal of tooth structure has approached close to the pulp. A liner provides a barrier to protect the pulp from thermal shock, chemical irritation, and provides a therapeutic effect to the pulp in instances where the pulp might be slightly exposed or nearly exposed.