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General product and regulatory information for laboratory, clinic and supply staff. It is not medical or dental advice and does not describe clinical technique.
Short answer
A calcium hydroxide liner is a dental device material that the US FDA defines as one applied to the interior of a prepared cavity, before restorative material such as amalgam is placed, to protect the pulp of the tooth. In the US it is a Class II device under 21 CFR 872.3250 (FDA product code EJK). The name covers more than one type of product, and published testing shows that their pH and calcium release can differ widely.
Definition and scope
The wording comes from the federal regulation itself. Under 21 CFR 872.3250, “a calcium hydroxide cavity liner is a device material intended to be applied to the interior of a prepared cavity before insertion of restorative material, such as amalgam, to protect the pulp of a tooth.” The same section classifies it as Class II.
FDA’s product classification database lists the same item as “Liner, Cavity, Calcium Hydroxide”, product code EJK, medical specialty Dental, device class 2, regulation number 872.3250, and not exempt from GMP requirements.
| Attribute | Value in the FDA record |
|---|---|
| Regulation | 21 CFR 872.3250, “Calcium hydroxide cavity liner” |
| Device name | Liner, Cavity, Calcium Hydroxide |
| Product code | EJK |
| Device class | 2 (Class II) |
| Medical specialty | Dental |
| GMP exempt | No |
How it works in practice
The chemistry is described in a laboratory study published in the Revista de Odontologia da UNESP. Calcium hydroxide dissociates into calcium and hydroxyl ions. The authors report that the hydroxyl ions give a high pH (about 12) that inhibits enzymatic activity of microorganisms, and that calcium ions are important for mineralization.
The same paper notes why liners are used at all: to prevent diffusion of residual or leached components through the dentinal tubules. It also lists the drawbacks it attributes to conventional calcium hydroxide liners: high solubility, no chemical or mechanical adhesion to dentin or to restorative materials, and difficult handling. Resin-based, light-cured liners containing calcium hydroxide were developed to address these.
Conventional versus light-cured resin-based liners
That study compared one conventional liner (Hydro C) with two light-cured resin-based liners (Ultra-Blend plus and Biocal). It used 10 specimens per material, each stored in 10 mL of distilled water at 37 °C and measured at 24 hours, 7 days and 14 days. The values below are the means reported for the cured specimens.
| Material (type) | pH 24 h | pH 7 d | pH 14 d | Calcium release 24 h | 7 d | 14 d |
|---|---|---|---|---|---|---|
| Hydro C (conventional, chemically activated) | 10.59 | 10.76 | 10.68 | 16.99 | 24.86 | 30.63 |
| Ultra-Blend plus (light-cured resin) | 7.35 | 7.20 | 7.50 | 4.85 | 25.72 | 4.84 |
| Biocal (light-cured resin) | 5.57 | 5.25 | 5.54 | 0.13 | 0.15 | 0.07 |
Calcium values are shown as reported in the paper, which does not state units in its table. In this test the conventional liner held a pH above 10 throughout, while the two resin-based products stayed lower, and calcium release differed widely between the two resin-based products. The paper also reports that the uncured Ultra-Blend plus specimens released more calcium than the cured ones, so the result depends on the product and on whether it has set. This is one in-vitro study of three products, not a ranking of products or a statement about clinical outcome.
Where it matters for labs, clinics and supply decisions
- Classification. A product sold as a calcium hydroxide cavity liner falls under 21 CFR 872.3250, Class II, product code EJK. Staff classifying an item for records or compliance files can check the regulation number and product code against the product’s documentation. Our guide to FDA medical device classification explains what Class II means, and the 510(k) premarket notification guide covers the clearance route.
- Type. Documentation should show whether the product is a conventional (chemically activated) liner or a light-cured resin-based one, because the study above found those groups behave differently in water.
- Not covered by this entry. The regulation’s identification is about a lining material for the pulp side of a cavity. Cavity varnish is a separate item; see cavity varnish: definition, FDA class and IFU checklist. Radiopacifying agents used in endodontic materials are covered in bismuth trioxide in dental materials.
Common misunderstandings
- “All calcium hydroxide liners behave the same.” The study above shows pH and calcium release varied between a conventional and two light-cured liners.
- “A liner is a varnish.” They are treated as separate items on this site; the identification in 21 CFR 872.3250 describes a lining material for a prepared cavity, and cavity varnish has its own page.
- “Class II devices are exempt from manufacturing controls.” The FDA product record for EJK lists the item as not exempt from GMP requirements.
FAQ
What FDA class is a calcium hydroxide liner?
Class II, under 21 CFR 872.3250, with product code EJK in FDA’s classification database.
What does 21 CFR 872.3250 say a calcium hydroxide cavity liner is?
A device material intended to be applied to the interior of a prepared cavity before insertion of restorative material, such as amalgam, to protect the pulp of a tooth.
Why does a calcium hydroxide liner raise pH?
According to the UNESP study, calcium hydroxide dissociates into calcium and hydroxyl ions, and the hydroxyl ions provide a high pH of about 12 in the dissociated material. Measured pH in water varied by product, from about 5 to about 11 in the tested liners.
Sources
- US Code of Federal Regulations, 21 CFR 872.3250, “Calcium hydroxide cavity liner” (eCFR), checked 2026-10-31.
- US FDA, product classification database and openFDA device classification record, product code EJK (FDA classification entry), checked 2026-10-31.
- Pereira KF, Cruvinel RFS, Dantas AAR, Kuga MC. “Evaluation of calcium release and pH value of light-cured cavity liners for pulp-capping materials.” Revista de Odontologia da UNESP (SciELO), checked 2026-10-31.
