Do Deeper Fillings Really Need Liners?

I held this assumption for years without examining it: a deep cavity gets a liner. Not a question, a clinical commandment: calcium hydroxide, glass ionomer, one of the newer bioactive pastes, it didn't matter which, you just did it.

So I went back to the literature to see if that's actually true, or a habit left over from the amalgam era that adhesive dentistry quietly made unnecessary. Feeling like you're doing something extra for the patient and actually improving their outcome aren't the same thing, and the only way to tell them apart is to read the trials.

The question#

In a permanent tooth receiving a Class I or Class II direct resin composite restoration, with a sound bonding protocol and no pulp exposure, does placing a cavity liner beneath the composite (calcium hydroxide, resin-modified glass ionomer, or a newer bioactive material) reduce post-operative hypersensitivity or improve restoration survival, compared with bonding directly onto the prepared dentin? A meaningful difference is a real, reproducible gap in sensitivity incidence or failure rate over at least a year, not one small trial's noise.

The mechanism#

The case for liners rests on the hydrodynamic theory of dentin pain: fluid movement inside the dentinal tubules stimulates nerve endings, producing that sharp response to cold or air. The old logic was that covering exposed tubules with a liner stops that movement and insulates the pulp from thermal change. It's intuitive, but it assumes the composite and its bonding agent aren't already doing that job.

They're built to. A properly placed modern dentin bonding agent infiltrates the collagen network and forms a hybrid layer that seals the tubules directly; if that seal is intact, there's no fluid movement left to stimulate a nerve. So the real question was never "does this tooth need insulation," it's "does a liner seal better than the bonding agent already does", and separately, whether a soft, low-modulus liner acts as a shock absorber for polymerization shrinkage stress, flexing so the composite doesn't pull away from the cavity walls. That second argument is really about the composite, not the liner. See the research on bulk-fill versus incremental layering for how much of that shrinkage-stress problem the resin's own chemistry already solves. Both are testable. Here's what testing them against clinical outcomes shows.

What the evidence says#

Schenkel & Veitz-Keenan, 2019: Cochrane systematic review#

What they did. An update of Cochrane's review on dental cavity liners, searching five databases through November 2018 for randomized trials comparing Class I and Class II composite restorations placed with a liner versus without one. Eight studies, over 700 participants, met inclusion.

What they found. Evidence on postoperative hypersensitivity was inconsistent: a benefit appeared at some follow-up points but not others, and all eight studies carried unclear or high risk of bias (low-quality evidence). Four trials measuring restoration failure found no difference at one year; three of four had zero failures in either arm, and three studies followed to two years found the same 1.

Why it matters. The closest thing liners have to a definitive clinical test, and the honest read is "inconsistent, low-quality evidence for a sensitivity benefit, none at all for survival", not the clean "liners don't work" some retellings compress it to, but not the confident case the old teaching assumed either.

Strober, Veitz-Keenan, Barna, Matthews, Vena, Craig, Curro & Thompson, 2013: randomized controlled trial#

What they did. A practice-based research network trial (341 participants) randomized patients with hypersensitive posterior lesions to a Class I or Class II composite restoration with or without a resin-modified glass ionomer liner, all placed with a one-step self-etch bonding agent, and measured sensitivity clinically and by patient report at one and four weeks.

What they found. Restorations with and without the RMGI liner had the same postoperative sensitivity outcomes at both time points, by both measures 2.

Why it matters. A large, independent RCT testing the exact liner most of us were taught was standard for moderate-depth preps, under real-world practice conditions, and it found nothing. The authors' own conclusion was blunt: the time, effort, and expense of placing it may be unnecessary.

da Rosa, Lima, Moraes, Piva & da Silva, 2019: systematic review and meta-analysis#

What they did. A review specifically of deep caries lesions, pooling 17 studies (15 in primary teeth, 2 in permanent teeth) comparing clinical success with and without a calcium hydroxide liner, using trials with at least 12 months of follow-up.

What they found. Risk difference for calcium hydroxide versus a bonding agent alone was 0.06 (95% CI −0.01 to 0.13); versus glass ionomer, 0.10 (95% CI −0.01 to 0.22), neither significant. The liner did not influence clinical success in primary or permanent teeth 3.

Why it matters. The deep-lesion answer to "but what about when I'm close to the pulp," and it lands the same place as the routine-depth evidence. Worth flagging precisely: 15 of the 17 studies are in primary teeth, so the permanent-tooth evidence specifically is thinner than the headline number suggests.

Pereira, Santos-Júnior, Tavares, Oliveira, Leal, Takeshita, Barbosa-Júnior, Bertassoni & Faria-E-Silva, 2017: randomized controlled trial#

What they did. Ninety-eight patients with a deep posterior lesion underwent stepwise caries removal, then were randomized to a provisional RMGI restoration with or without a calcium hydroxide liner. The primary outcome was tooth vitality at 90 days.

What they found. No significant difference in tooth vitality between groups; dentin got darker, harder, drier, and less contaminated in both groups regardless of liner use 4.

Why it matters. A direct test in exactly the scenario liners are supposed to matter most (deep, stepwise-managed caries), and the liner added nothing measurable over the provisional restoration's own seal.

Ahmed, Wafaie, Hamama & Mahmoud, 2024: randomized controlled trial#

What they did. A split-mouth trial in 20 patients, each with two deep lesions treated by selective caries removal, one lined with a bioactive ionic resin liner and the other with a resin-modified glass ionomer liner, both restored with the same composite and followed three years by FDI criteria.

What they found. Both liner types showed 100% clinical success at three years, with no significant difference between them at any interval 5.

Why it matters. Genuinely fresh, longer-follow-up data, but with no liner-free control arm, it proves the two materials perform the same as each other, not that either outperforms skipping the liner. The newer bioactive material isn't beating the older one, which, per the studies above, isn't clearly beating nothing.

Evidence at a glance#

Study	Design	Sample	Follow-up	Finding	Weight
Schenkel & Veitz-Keenan, 2019 1	Cochrane systematic review	8 trials, 700+ participants	1–2 years	Inconsistent sensitivity evidence; no difference in failure	High
Strober et al., 2013 2	RCT	341 participants	1 & 4 weeks	Same sensitivity outcomes, liner vs. none	High
da Rosa et al., 2019 3	Systematic review & meta-analysis	17 studies	≥12 months	CH liner did not improve deep-caries success	Moderate
Pereira et al., 2017 4	RCT	98 patients	90 days	No difference in tooth vitality	Moderate
Ahmed et al., 2024 5	RCT (split-mouth)	20 patients, 40 restorations	3 years	Both liner types 100% success, no difference	Low

Risk difference in clinical success, calcium hydroxide liner versus comparator, deep caries lesions (mostly primary teeth). A bar crossing zero means no reliable benefit. Data from da Rosa et al., 2019 3.

Where the evidence is thin#

• Cochrane's founding review is 8 studies and roughly 700 participants, all at unclear or high risk of bias. "Inconsistent, low-quality evidence" is the accurate description of the sensitivity finding, not a confident null result, and not a confident positive one either.
• Most deep-caries calcium hydroxide evidence is in primary teeth: 15 of da Rosa's 17 included studies. Extending that finding fully to permanent teeth is a reasonable clinical read, not a directly proven one.
• No trial here follows past three years, and Ahmed's 2024 RCT compares two liner materials to each other, not to no liner. It cannot itself prove a liner is unnecessary, only that which one you pick barely matters.
• The elastic-layer, shock-absorber argument for liners is a plausible mechanical hypothesis none of these trials test directly against clinical failure. It remains theory.
• A 2025 systematic review and meta-analysis on liners was named in the source script but could not be verified under the cited author name after repeated database searches. It is not cited here; the claim it made is covered instead by the verified studies above, which point the same direction.

What this means Monday morning#

1. Stop defaulting to a liner for shallow-to-moderate Class I/II preps with adequate remaining dentin. Put that effort into the bonding protocol: selective-etch on enamel, scrub the adhesive into dentin rather than painting it on, and evaporate the solvent until the surface is shiny and immobile.
2. For a genuinely deep lesion, do selective caries removal and seal it well rather than reaching for a liner as reassurance: the evidence keeps crediting the seal, not the material under it, for the outcome.
3. Reserve MTA or a bioceramic material for an actual or near pulp exposure. That's a direct pulp cap aimed at inducing a dentin bridge: a different biological goal from lining a routine deep prep, and this evidence base doesn't speak to that decision.
4. If a patient calls back with sensitivity, troubleshoot the bonding technique and the bite before assuming you needed a liner: check occlusion, margin integrity, and curing light output; a weak or misaimed light undercuring the composite is its own well-documented problem, covered in the research on curing light output.
5. Simplify your inventory. One reliable bonding system and one composite cover routine restorative days (by Ryan's own estimate, Class I and Class II composites make up the large majority of a typical restorative schedule), and the 3 to 5 minutes saved per tooth by skipping a liner step adds up across a full day. Run your own material and time numbers through the overhead diagnostic. If you keep a bioactive base on hand for the rare deep case, that's reasonable, just don't expect it to do the sensitivity-prevention job the marketing implies; the same "the chemistry helps something, just maybe not what you assumed" theme runs through whether glass ionomers actually remineralize dentin.

The bottom line#

For most Class I and Class II composites, a liner adds an interface, a material cost, and a few minutes of chair time without a measurable return on sensitivity or survival: a Cochrane review and a 341-patient independent RCT both say so. Even in the deep-caries scenario where the instinct to line feels strongest, the studies that isolate the liner keep landing on the same answer: the seal did the work, not the paste underneath it. Spend the saved time on the bonding protocol, and save the liner conversation for a genuine near-exposure.

References#

1. Schenkel AB, Veitz-Keenan A. Dental cavity liners for Class I and Class II resin-based composite restorations. Cochrane Database of Systematic Reviews. 2019;3(3):CD010526. DOIPubMed
2. Strober B, Veitz-Keenan A, Barna JA, Matthews AG, Vena D, Craig RG, Curro FA, Thompson VP. Effectiveness of a resin-modified glass ionomer liner in reducing hypersensitivity in posterior restorations: a study from the Practitioners Engaged in Applied Research and Learning Network. Journal of the American Dental Association. 2013;144(8):886-897. DOIPubMed
3. da Rosa WLO, Lima VP, Moraes RR, Piva E, da Silva AF. Is a calcium hydroxide liner necessary in the treatment of deep caries lesions? A systematic review and meta-analysis. International Endodontic Journal. 2019;52(5):588-603. DOIPubMed
4. Pereira MA, Santos-Júnior RBD, Tavares JA, Oliveira AH, Leal PC, Takeshita WM, Barbosa-Júnior AM, Bertassoni LEB, Faria-E-Silva AL. No additional benefit of using a calcium hydroxide liner during stepwise caries removal: a randomized clinical trial. Journal of the American Dental Association. 2017;148(6):369-376. DOIPubMed
5. Ahmed B, Wafaie RA, Hamama HH, Mahmoud SH. 3-year randomized clinical trial to evaluate the performance of posterior composite restorations lined with ion-releasing materials. Scientific Reports. 2024;14(1):4942. DOIPubMed

This article summarises published research for clinicians. It is not a substitute for your own reading of the studies or your clinical judgment.