A deep cavity does not automatically mean a root canal. If the nerve inside the tooth is still healthy, or only mildly irritated, a dentist can often remove the decay, cover the deepest point with a protective material and let the pulp recover. This is pulp capping, and its aim is to keep the tooth alive rather than replace its nerve with a root filling.
The nerve has to be healthy enough to heal
The pulp is the soft core of the tooth, carrying nerves and blood vessels. Decay that creeps towards it causes inflammation. Mild inflammation, known as reversible pulpitis, usually produces short, sharp twinges to cold or sweet that fade within seconds. A pulp in that state has a fair chance of settling once the bacteria are removed and the cavity is sealed.
Capping is far less likely to work when the pulp is badly inflamed or already dying. Clues include pain that arrives without a trigger, aching that lingers for minutes after a hot or cold drink, pain that keeps you awake, swelling, or a tooth that has turned darker. Those signs usually point towards root canal treatment, and our article on the signs of a dead or dying tooth explains them in more detail. Depth of decay on an X-ray matters, but how the pulp is behaving matters more.
Two ways to cap a pulp
The choice depends on whether the nerve ends up exposed during treatment.
| Indirect pulp capping | Direct pulp capping | |
|---|---|---|
| Situation | Decay reaches very close to the nerve, but the pulp is not opened | A small exposure of healthy pulp appears while the decay is removed |
| What is left over the pulp | A thin layer of dentine, sometimes slightly softened, is deliberately left in place | Nothing, so the material sits right on the exposed tissue |
| What the dentist places | A protective liner, then a sealed filling | A bioactive cement on the exposure, then a sealed filling |
Current thinking favours leaving a little dentine over the pulp where it is safe to do so, because avoiding an exposure in the first place protects the nerve. The European Society of Endodontology's 2019 position statement on deep caries and the exposed pulp puts keeping the pulp alive, using minimally invasive methods, at the centre of modern care.
Modern cements have better results than calcium hydroxide
For decades the usual capping material was calcium hydroxide. It has largely been overtaken by hydraulic calcium silicate cements, a group that includes MTA and Biodentine. A 2025 systematic review in the International Endodontic Journal (Herbst and colleagues), carried out for a clinical guideline, pooled five randomised trials of direct capping in teeth with healthy or reversibly inflamed pulps. Calcium silicate cements were significantly more likely to succeed than calcium hydroxide, with moderate certainty in the evidence, and the differences between individual calcium silicate products were small.
Another review, by Pinto and colleagues in Restorative Dentistry and Endodontics (2024), found success rates for direct capping with MTA or Biodentine ranging from 80 to 100 per cent in the included trials, even after three years. The authors rated the certainty of that evidence as low, so the figures are encouraging rather than a guarantee for any single tooth.
At Lumi Dental we use bioceramic materials, including Biodentine, for pulp protection when a tooth is suitable for capping.
The months after capping
The procedure itself is done under local anaesthetic. Some sensitivity to cold or biting for a few weeks is common while the pulp settles. Depending on the tooth, the dentist may place the final filling straight away or review the tooth first, checking how it responds to testing and, when needed, taking a follow-up X-ray.
Signs that the pulp is not recovering include pain that gets worse rather than better, toothache at night, pain without a trigger, and swelling of the gum or face. Contact your dentist promptly if any of these appear. A capped tooth that does not settle can usually still have root canal treatment, so trying to keep the nerve alive first does not close off that option.
Questions we are often asked
Why not just do a root canal straight away?
A tooth with a living pulp keeps its blood supply and its ability to sense problems, and the procedure removes less of the tooth. Root canal treatment is a reliable option when the pulp is too damaged to heal, but when the signs are favourable, keeping the nerve alive is the more conservative choice.
How will I know whether capping has worked?
Most people simply notice the tooth settling down over the following weeks. Your dentist will usually check it at later visits with sensitivity testing and, from time to time, an X-ray, because a pulp can occasionally die quietly without much pain.
Can every deep cavity be capped?
No. The decision rests on the health of the pulp, the size of any exposure and whether bleeding from it can be controlled. Teeth with signs of irreversible pulpitis are usually better managed another way.
A deep cavity treated early gives the nerve its best chance of recovery. You can book a check and see current offers on our current deals page, or, if a tooth is already badly broken down, read our comparison of root canal versus extraction.
