Key Takeaways

• Liners, bases, and pulp caps are defined by the job they do, not by brand or chemistry. One material can sometimes do more than one job.
• Liners are thin protective layers, bases replace missing dentin and add bulk, and pulp caps support the pulp when it's exposed or nearly exposed.
• Remaining dentin thickness and pulp proximity decide which one you need, and sometimes whether you need one at all.
• Modern adhesives have changed the "always line under composite" habit. Deep preps still call for a deliberate choice.

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Somewhere between dental school and your third deep filling of the morning, "liner," "base," and "pulp cap" may have collapsed into one idea: the white stuff that goes in before the composite. You're in good company. Product catalogs describe one material as all three, CE courses use the words interchangeably, and operatory shorthand doesn't help.

The catch is that each term describes a different job, and the job is what protects the pulp. Choose by habit instead of by job, and you can end up overtreating a moderate prep or undertreating one that's a fraction of a millimeter from trouble.

BISCO has spent more than 45 years studying what happens where restorative materials meet tooth structure, and pulp protection is a big part of that work. In this article, you'll learn what liners, bases, and pulp capping materials actually do, where their roles overlap, and a simple depth-based way to decide what goes in the prep and in what order.

What a Dental Liner Actually Does

A dental liner is a thin layer placed on the dentin closest to the pulp. Its job is protective, not structural. It seals the dentinal tubules, puts a barrier between the pulp and everything that comes next, and, depending on the chemistry, releases ions that encourage the pulp to wall itself off with new dentin.¹

Think of it as the pulp's screen protector. It's thin, it covers only what needs covering, and nobody expects it to hold up the phone.

Common liner chemistries include calcium hydroxide, resin-modified glass ionomer (RMGI), and light-cured resin-modified calcium silicates such as TheraCal LC. Each comes with trade-offs. Calcium hydroxide has the longest track record, but it's highly soluble so it can break down under a restoration over time.² RMGI liners bond to dentin and release fluoride. Calcium silicate liners release calcium and create an alkaline environment that supports mineralization.^3-5

What a liner doesn't do is replace missing tooth structure. If you're filling volume, you've moved on to a different job.

What a Dental Base Actually Does

A base is the structural layer. When decay or an old restoration has taken a big bite out of the dentin, a base replaces that lost volume, supports the restoration above it, and evens out the floor of the prep. Bases go in thicker than liners, and in preps for indirect restorations they're often used to block out undercuts. Because they're placed in bulk, many bases are dual-cured, so they set completely even in deeper areas the curing light can't fully reach.

If the liner is the screen protector, the base is the drywall patch. It rebuilds the surface so whatever goes on top has something solid to sit on.

Glass ionomers and RMGIs are the usual base materials today. In posterior composites they often show up in the "sandwich" technique, where the glass ionomer stands in for dentin and the composite takes over toward the enamel.

Because a base is about bulk, in a deep prep it usually goes over a liner, not in place of one.

What Pulp Capping Actually Means

Pulp capping is the therapeutic job. A pulp cap isn't just a barrier; it creates an environment that supports pulp vitality.⁴ Two scenarios fall under this heading, and it's worth keeping them separate.

Indirect pulp capping happens in a deep prep where the pulp isn't exposed but is close. The material goes over the thin layer of remaining dentin to protect the pulp. Calcium-releasing materials like calcium hydroxide, MTA, and TheraCal LC can also stimulate the pulp to lay down tertiary (reparative) dentin, adding another layer of protection.^6,7

Direct pulp capping happens when the pulp is exposed, whether from caries, a mechanical slip, or trauma. Now the material sits directly on living tissue, so the bar is higher. It has to seal the exposure, keep bacteria out, and support a dentin bridge across the opening.

Calcium hydroxide was the default for decades, but calcium silicate materials have largely taken over. A meta-analysis in the Journal of Endodontics found that MTA had a significantly higher success rate than calcium hydroxide for direct pulp capping, with less pulpal inflammation and more predictable dentin bridge formation.⁸ The American Association of Endodontists' 2021 position statement supports vital pulp therapy in properly selected adult teeth. It also calls for complete removal of infected dentin and direct inspection of the exposed pulp, ideally under magnification, before deciding whether the pulp can be saved.⁹

If the inflamed pulp tissue can't be preserved, pulp capping is no longer the right call, and most dentists will move to root canal therapy instead, which is a different procedure with its own material considerations.

Where the Lines Blur: One Material, Multiple Jobs

Here's why the terms get so tangled: the same material can do different jobs depending on where it's placed and how thick it is.

An RMGI can be a thin liner in one prep and a bulk base in the next. A resin-modified calcium silicate like TheraCal LC is indicated as a direct pulp capping agent, an indirect pulp capping agent, a protective liner, and a base.¹⁰ Calling a material "a liner" describes how it was used in that case, not what it is.

The most useful shift you can make is to name the job first and then choose a material indicated for that job. "I need a direct pulp cap" leads to a much shorter list than "I need a liner," because not every liner is indicated for exposed pulp. Before a liner ends up doing a pulp cap's job, check its instructions for use.

Which Material Goes Where: A Depth-Based Decision Guide

The deciding factor is how much dentin is left between the floor of the prep and the pulp. In one human study, odontoblast counts dropped by about 14% under 0.5 to 2.5 mm of remaining dentin, about 34% under less than 0.5 mm, and 99% beneath exposures. The authors concluded that at least 0.5 mm of remaining dentin is needed to avoid evidence of pulp injury.¹¹ Dentin is the best pulp protector there is, and every layer you add makes up for dentin that's gone.

In a shallow to moderate prep with plenty of dentin left, the remaining dentin itself does most of the protecting, and a liner or base usually isn't necessary. A well-placed adhesive seals the dentin, but it isn't a substitute for a liner or base when one is called for. As the prep gets deep and the floor approaches the pulp, a thin liner over the deepest dentin adds protection right where the dentin is thinnest. When decay has removed a lot of structure, a base over that liner restores the volume so the restoration has proper support.

When the remaining dentin over a pulp horn is very thin, whatever goes there is doing an indirect pulp cap's job, so choose a material indicated for it. And if you open into the pulp, you're placing a direct pulp cap: control the bleeding, inspect the tissue, and place a material indicated for direct capping right on the exposure. Then build the liner, base, adhesive, and restoration over it.

In a deep prep with a pinpoint exposure, every layer has a job. Most preps need only some of them.

Whatever combination the case calls for, the order from the pulp outward stays the same: pulp cap if there's an exposure, then liner, then base if you need bulk, then adhesive and restoration.

Do You Still Need a Liner Under Composite?

Lining under every composite used to be standard practice. Modern adhesives have changed that. A properly placed adhesive seals the tubules on its own, and a Cochrane review of eight trials with more than 700 participants found no evidence that liners under Class I and II composites changed how long the restorations lasted. The review found no clear difference in postoperative sensitivity whether or not a liner was used, though the evidence behind that finding was low quality.¹²

That doesn't make liners obsolete. It makes them targeted. When the remaining dentin is thin, when you're close to a pulp horn, or when there's an exposure, a liner or pulp cap is still doing real work. So the question to ask isn't "Do I always line?" It's "Does this prep need one?" (If post-op sensitivity is what keeps you lining, see 3 Tips to Avoid Post-Op Sensitivity.)

Now that you know what goes where, which liner should you use?

Two popular liners can look nearly identical yet differ in chemistry, calcium release, and whether they're indicated for direct pulp capping. See how they compare before your next deep prep.

Compare the Liners →

References

1. Cannon M, et al. Primate pulpal healing after exposure and TheraCal application. J Clin Pediatr Dent. 2014;38(4):333-337.
2. Arandi NZ. Calcium hydroxide liners: a literature review. Clin Cosmet Investig Dent. 2017;9:67-72.
3. ElReash AA, Hamama H, Eldars W, et al. Antimicrobial activity and pH measurement of calcium silicate cements versus new bioactive resin composite restorative material. BMC Oral Health. 2019;19:235. doi:10.1186/s12903-019-0933-z
4. Okabe T, Sakamoto M, Takeuchi H, Matsushima K. Effects of pH on mineralization ability of human dental pulp cells. J Endod. 2006;32(3):198-201.
5. Gandolfi MG, Siboni F, Taddei P, Modena E, Prati C. Apatite-forming ability of TheraCal pulp-capping material. J Dent Res. 2011;90(Spec Iss A):Abstract 2520.
6. Clinical and radiographic evaluation of indirect pulp capping with mineral trioxide aggregate and calcium hydroxide in primary molars: a systematic review and meta-analysis. https://pmc.ncbi.nlm.nih.gov/articles/pmid/40989989
7. Thomas NA, Jobe J, Thimmaiah C, Shetty K. Comparative evaluation of effectiveness of calcium hydroxide, MTA, and TheraCal LC in indirect pulp capping in primary molars: an in vivo study. 2024.
8. Li Z, Cao L, Fan M, Xu Q. Direct pulp capping with calcium hydroxide or mineral trioxide aggregate: a meta-analysis. J Endod. 2015;41(9):1412-1417. doi:10.1016/j.joen.2015.04.012
9. AAE Position Statement on Vital Pulp Therapy. J Endod. 2021;47(9):1340-1344. doi:10.1016/j.joen.2021.07.015
10. BISCO, Inc. TheraCal LC Instructions for Use. IN-192R13, Rev. 2/20.
11. Murray PE, Smith AJ, Windsor LJ, Mjör IA. Remaining dentine thickness and human pulp responses. 2003.
12. Schenkel AB, Veitz-Keenan A. Dental cavity liners for Class I and Class II resin-based composite restorations. Cochrane Database Syst Rev. 2019;(3):CD010526. doi:10.1002/14651858.CD010526.pub3

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