Fillings, crowns and implants

Once a tooth has lost structure — to decay, a crack, a chip or years of wear — it has to be rebuilt, and the choice of how depends almost entirely on how much sound tooth is left. A small cavity takes a filling. A tooth with most of its wall gone needs something that holds it together. A tooth that has gone needs replacing, or not, which is a decision in its own right.

Fillings

A filling does two jobs: it replaces what has been lost and it seals the tooth so bacteria cannot get back in. The second matters more than most people realise, and it is why the fit at the edges is more important than the material.

Composite is now standard for most situations. A tooth-coloured resin containing glass or quartz filler, it is bonded chemically to the tooth and set with a light, placed in layers. It looks right, needs less of the tooth removed than older materials because it bonds rather than relying on a mechanical shape, and is finished in a single visit. It needs a dry working field, which is why the dentist keeps asking for the mouth to stay open.

Glass ionomer releases fluoride slowly and sticks well to tooth structure, which makes it useful at the gum margin, on root surfaces and in children's teeth. It is not as strong, so it is not a first choice for a biting surface under heavy load.

Amalgam — the silver-coloured alloy of mercury with silver, tin and copper — is extremely durable and has been used for well over a century. Its use has been declining and it is now restricted for children and during pregnancy and breastfeeding, under an international agreement to phase down mercury use generally.

Two things are worth saying about amalgam, because the subject attracts a great deal of noise. Existing sound amalgam fillings are not a reason for concern, and removing sound amalgam fillings to improve general health is not supported by evidence and is not recommended — the drilling releases more mercury vapour than leaving them alone, and it costs tooth structure every time. Replacing one because it has failed, or because a patient prefers the appearance, is a different and perfectly reasonable matter.

Inlays and onlays are laboratory-made or machine-milled restorations in ceramic or gold, fitted into or over a prepared cavity. For a large cavity they are stronger and longer-lasting than a very large direct filling, and they are often not mentioned unless asked about.

Afterwards. Sensitivity to cold for a week or two after a deep filling is normal and settles. Two things are not: pain that lingers or throbs, which may mean the pulp is involved, and a filling that feels high when biting, which needs adjusting — leaving it causes ache in the tooth and the jaw joint.

Every filling has a finite life. They wear, the edges leak, decay starts again underneath, and each replacement is larger than the last. That is the restorative cycle, and it is the reason for taking the first filling seriously: once it starts, it does not usually stop, which makes prevention the only intervention that genuinely saves tooth structure.

Crowns and onlays

A crown covers the whole visible part of a tooth. It is the answer when there is not enough sound tooth left to hold a filling, after root canal treatment on a back tooth, where a tooth has cracked, or where wear has destroyed the shape.

Current practice prefers to remove as little as possible, so an onlay — covering the biting surface and the weak walls but not encircling the tooth completely — is often chosen over a full crown where it will do. Less tooth removed means a better long-term prospect for the tooth.

The sequence is usually two appointments. The tooth is shaped under local anaesthetic, the shape is recorded — with impression material or increasingly with a digital scanner — and a temporary crown is fitted while the permanent one is made. At the second visit it is tried in, checked for fit, bite and colour, and cemented. Some practices can design and mill a ceramic crown on site in a single visit.

Materials range from all-ceramic and zirconia, which look best and are used for front teeth, through metal-ceramic, to gold — which is kinder to the opposing teeth and extremely long-lasting, and loses out mainly on appearance.

What can go wrong: sensitivity for a while afterwards; a crown that chips, particularly porcelain; and cement that gradually washes out. A crown that has come loose needs seeing promptly rather than being glued back, because bacteria get underneath and the tooth decays invisibly in the meantime. A crowned tooth is not immune to anything — decay starts at the margin where crown meets tooth, and gum disease carries on as usual, so the cleaning matters as much as before.

A missing tooth: four options, including doing nothing

Leaving the gap is a legitimate choice, and is frequently the right one for a single back tooth, particularly the last one in the row. Teeth do drift and tilt into spaces, but not always and not always significantly, and a mouth with enough teeth meeting at the front and middle can function perfectly well. Anyone being told that a gap must be filled is entitled to ask what specifically it is expected to cause.

A denture is removable, needs no surgery, can replace several teeth at once, and is the option available on the NHS. The costs are comfort, bulk, something to take out and clean, and the fact that it traps plaque against whatever it touches — so the remaining teeth need more attention, not less.

A bridge is fixed in place and does not come out. The conventional kind is supported by crowns on the teeth either side of the gap, which means preparing two sound teeth to replace one missing one — the real price of a bridge, and the reason it is not automatically the best answer. A resin-bonded bridge, cemented to the inner surface of one neighbouring tooth with a thin wing, removes almost no tooth structure and is a good option for a single front tooth.

An implant replaces the root itself and leaves the neighbouring teeth untouched, which is its real advantage over a bridge.

Implants

An implant is a screw-shaped post, almost always titanium and occasionally zirconia, placed surgically into the jawbone. Over the following weeks and months the bone grows into direct contact with its surface — osseointegration — and once that has happened a crown, bridge or denture attachment is fitted on top. The whole process commonly takes several months, and longer if bone has to be built up first with a graft.

Older writing on the subject divides implants into several types — root-form, blade, transosseous, frame designs. In practice only the root-form implant is now in general use; the others are historical.

Who they suit less well. This is the part that deserves attention before anything else:

• Smoking is the clearest risk factor for implant failure, both in healing and in the years afterwards.
• A history of gum disease raises the risk of the same process happening around the implant.
• Poorly controlled diabetes impairs healing and integration.
• Insufficient bone, which can often be grafted but adds time, cost and another procedure.
• Some bone medicines, including bisphosphonates and denosumab, carry a risk of poor healing in the jaw, which needs discussing with both the dentist and whoever prescribed them.
• A jaw still growing, which is why implants are not placed in adolescents.

What they are and are not. Implants have good long-term survival, and are a genuinely excellent solution for the right case. They are not permanent in the sense of needing nothing: the crown on top wears and is replaced in time, screws occasionally loosen, and peri-implantitis — inflammation and bone loss around an implant, the equivalent of gum disease — is a real and increasing problem. An implant has no periodontal ligament and no nerve, so it gives less warning than a tooth would, which makes the daily cleaning and the regular checks more important rather than less.

Implants are not generally available on the NHS, which provides them only in particular clinical circumstances such as after trauma or cancer treatment, or where a denture cannot be worn for medical reasons.

Questions worth asking before committing: who will place it and who will make the crown, what the total covers including the graft if one is needed, what the arrangement is if it fails, what the follow-up involves and for how long, and what happens if the person moves away.

See also tooth decay and cavities, root canal treatment, gum disease and paying for dental care.