Reversible Sensitivity or Irreversible Pulpitis? How We Tell After a Filling

By Dr. Boris Zusin · Published September 5, 2026

Most post-restorative sensitivity is reversible: a short, sharp pain provoked by cold, air, or sweets that doesn't linger, reflecting polymerization-shrinkage gaps, incomplete sealing of the microscopic tubules in the dentin, or minor microleakage rather than true nerve damage. The pivotal clinical question, when sensitivity sticks around, is whether the pain is stimulus-provoked and fleeting, or spontaneous and lingering. Only the latter — or frank nerve death — actually calls for a root canal.

How We Characterize the Pain

Reversible pulpitis / dentinal sensitivity: transient, sharp pain to cold, sweets, or air that resolves within seconds of removing the stimulus, with no pain occurring spontaneously on its own.

Irreversible pulpitis: spontaneous pain (it happens without any trigger at all), sharp pain that lingers — often 30 seconds or more, sometimes several minutes — after a thermal stimulus is removed, pain that's referred or hard to pinpoint to one specific tooth, pain that gets worse lying down or bending over, and pain that over-the-counter analgesics typically don't touch.

How We Evaluate It Clinically

Cold testing against a control tooth. We compare the response on the tooth in question to a sound, unrestored tooth on the other side of your mouth. A normal, fleeting response supports a recoverable pulp; a prolonged, lingering response suggests deeper inflammation — and the longer that lingering response lasts, the more advanced the inflammation tends to be.

Percussion and palpation. Irreversible pulpitis on its own usually isn't tender to percussion (a gentle tap on the tooth). Pain specifically with percussion or biting more often points toward either the inflammation extending past the root tip, or — very commonly after a new restoration — a simple hyperocclusion, meaning the filling is sitting a fraction too high. That's a readily reversible cause of tenderness that resolves with a quick occlusal adjustment, not a sign of nerve damage.

Radiographs. An X-ray lets us assess how close the restoration sits to the pulp, check for secondary decay or voids underneath it, and look for a periapical radiolucency — a dark shadow at the root tip that would indicate the nerve has actually died and inflammation has spread into the surrounding bone.

Timing and depth. Sensitivity that's steadily improving over days to a few weeks favors an ordinary, settling, reversible process. Fillings deeper than roughly 3mm, and larger fillings generally, are more predictive of some postoperative sensitivity in the first place — which is useful context but not, on its own, a red flag.

Managing Reversible Sensitivity

Most cases genuinely just need reassurance and a monitoring interval, since the pulp-dentin complex typically recovers on its own. When it doesn't settle fast enough on its own, desensitizing agents — glutaraldehyde/HEMA-based products or oxalate/calcium-phosphate formulations — work by occluding the exposed dentinal tubules; glutaraldehyde-based agents have performed best in head-to-head trials, though none work as well in very deep cavities. If the restoration is simply sitting high, an occlusal adjustment is one of the most common and easiest fixes for what feels like persistent discomfort. And if we find microleakage, an open or defective margin, a void, or secondary decay on exam, the restoration itself needs to be repaired or replaced — no amount of waiting fixes a leaking margin.

When It Points to Irreversible Pulpitis

• Spontaneous, unprovoked pain, or cold/heat pain that lingers well after the stimulus is gone.
• Pain that over-the-counter analgesics don't relieve, that disturbs sleep, or that's clearly worse with postural changes like lying down.
• Pain specifically triggered by heat with relief from cold — a classic (though not universal) marker of advancing pulpal breakdown, especially alongside a periapical radiolucency on X-ray.

The revised FDI restoration criteria are direct about this distinction: transient postoperative hypersensitivity can simply be monitored, but true irreversible pulpitis or pulp necrosis needs endodontic treatment rather than more time.

An Honest Caveat, and a Newer Option

The reversible/irreversible split is a clinical framework, not a perfect one — it correlates imperfectly with what's actually happening at the tissue level, and there's no single chairside test that separates the two with certainty every time. That imperfection matters practically: in mature permanent teeth diagnosed with symptomatic irreversible pulpitis, vital pulp therapy (a full or partial pulpotomy, removing only the inflamed portion of the nerve rather than the whole thing) is an increasingly evidence-supported alternative to a full root canal, with better than 90% success at one year in some published series. It's relevant precisely because the pulp in a "irreversible" diagnosis may, in some cases, be only partially and recoverably inflamed rather than uniformly dead — a conversation worth having with your endodontist if root canal treatment is on the table.

If sensitivity after a filling isn't settling the way it should, or you're noticing any of the lingering, spontaneous, or heat-triggered patterns above, it's worth an exam rather than waiting to see which way it goes. See our companion guide on what to expect after a filling for the normal timeline this is being compared against, or learn more about root canal treatment if that's where this is heading.