Calcium hydroxide liner is a dental material applied as a thin protective layer between the floor of a prepared tooth cavity and a permanent restoration, serving to shield the dental pulp from chemical and thermal irritants while encouraging the formation of reparative dentin. It is one of the most widely used liner and base materials in restorative dentistry.

How It Works

Calcium hydroxide has a highly alkaline pH — typically around 12 — that creates an environment hostile to residual bacteria remaining after caries removal. This antimicrobial action reduces the risk of ongoing pulpal inflammation. Equally important is its bio-inductive property: calcium ions released from the material stimulate odontoblasts at the pulp-dentin junction to deposit a bridge of tertiary, or reparative, dentin. This natural defensive response helps isolate the pulp from further insult and is a key reason calcium hydroxide remains clinically relevant despite the availability of newer materials.

Clinical Applications

Calcium hydroxide liner is most valuable in deep or moderately deep preparations where remaining dentin is thin and pulp protection is a priority. Common clinical uses include:

• Indirect pulp capping: Placed over a thin dentin remnant to prevent direct pulp exposure and facilitate healing.
• Direct pulp capping: Applied to a small, cleanly exposed pulp surface to stimulate dentin bridge formation.
• Lining beneath composite or amalgam restorations in deep preparations to neutralize material acidity.
• Intracanal medicament between visits during endodontic treatment for its antibacterial and tissue-dissolving properties.
• Thermal barrier in preparations where the preparation depth approaches the pulp chamber.

Limitations to Consider

Calcium hydroxide liner has relatively low compressive strength and is susceptible to gradual dissolution under oral fluids, which can create voids beneath a restoration over time and compromise the marginal seal. For this reason, it is often covered with a more durable base — such as glass ionomer cement — before the final restoration is placed. Calcium silicate-based materials have emerged as alternatives in pulp-capping applications, though calcium hydroxide remains evidence-supported and in widespread clinical use.

Appropriate case selection — considering remaining dentin thickness, pulp vitality, and the planned restorative material — is essential to achieving predictable long-term outcomes when incorporating calcium hydroxide liner into a treatment plan.