Liners, bases and protecting the pulp
- Dental material
A deep cavity may get a thin layer over the dentine nearest the pulp. The best protection is keeping dentine and a good seal, not a thick base.
What it is
Liners are thin layers placed on the deepest dentine; bases are thicker layers that replace lost dentine under a restoration. Their roles are to seal the dentine tubules, to calm or protect the pulp, and, for some materials, to stimulate a new layer of hard tissue. The single most protective factor is the thickness of sound dentine left over the pulp and a restoration that seals out bacteria.
Composition and properties
- Calcium hydroxide: strongly alkaline and antibacterial, it stimulates reparative dentine, but it dissolves over time and does not seal.
- Calcium silicate cements (mineral trioxide aggregate and newer ones): seal well and form a more reliable hard tissue bridge; preferred for pulp capping.
- Glass ionomer or resin-modified glass ionomer: seals and bonds, used as a liner or base under composite.
- Zinc oxide–eugenol: soothing and sealing as a temporary filling, but eugenol stops resin from setting, so not under composite.
- The pulp reacts to deep caries by forming tertiary dentine beneath the lesion.
Uses, limits and safety
- Indirect pulp capping: a liner over thin dentine without exposure. Direct pulp capping: material placed on a small exposure of healthy pulp.
- A thick base is no substitute for a sealed restoration: bacteria leaking at the margin harm the pulp more than the filling material.
- Lingering pain after a deep filling suggests irreversible pulpitis, not just irritation from the material.
Next step / Initial management
- Deep lesion with no pain or only short pain to cold: selective removal, a liner where needed and a sealed restoration, then review vitality.
- Spontaneous or lingering pain after a deep filling: refer to the dentist for pulp assessment.
- Do not place eugenol-containing materials under composite restorations.
Test yourself
Think of the answer, then tap the question to see it.
What is the difference between a liner and a base?
A liner is a thin layer on the deepest dentine; a base is a thicker layer that replaces lost dentine under the restoration.
Why is zinc oxide–eugenol not placed under a composite?
Eugenol inhibits the polymerisation of the resin, weakening the restoration and its bond.
Which material is preferred for direct pulp capping and why?
A calcium silicate cement, because it seals well and induces a more reliable dentine bridge than calcium hydroxide.
Connections
Educational content; it does not replace assessment by a dentist or doctor and is not a clinical instruction. For facial or neck swelling with difficulty swallowing or breathing, a knocked-out tooth or bleeding that will not stop, go to an emergency department at once.
Sources: Dental Materials: Biodentine, a Calcium Silicate Bioactive (StatPearls Publishing (NCBI Bookshelf), 2024); Current and future options for dental pulp therapy (Japanese Dental Science Review (PMC open access), 2019); Biological Characteristics and Odontogenic Differentiation Effects of Calcium Silicate-Based Pulp Capping Materials (Materials (Basel) (PMC open access), 2021); Anatomy, Head and Neck, Dental Pulp (StatPearls Publishing (NCBI Bookshelf), 2025).
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Representative model, for educational purposes only.