Which Tooth Decay Treatment Fits the Damage? Filling, Inlay, Crown or Root Canal

The X-ray goes up on the screen and the dentist leans in with a pen. “See this shadow? That is the decay. It has gone under your old filling.” You nod, because nodding is what you do in that chair, but the question that actually matters stays stuck behind your teeth: so what now? A bigger filling? One of those caps? Something with the word “root” in it?

Anyone weighing a filling or crown for cavity damage is really asking one thing: how much of my tooth is still worth building on, and how much has to be replaced with something artificial? That question has a reasonably clear, evidence-based answer, even if the internet makes it sound like a coin toss.

This explainer walks through the four main repairs for a decayed tooth, what each one actually involves, who is usually offered which, and why “it doesn’t hurt yet” is the least reliable guide you could use. The decision belongs to you and your dental team. The job here is to make sure you walk into that conversation knowing what the pen is pointing at.

How does a dentist decide between a filling or crown for cavity damage?

Picture a tooth as a small house with a roof (the chewing surface), four walls (the sides) and a living room in the middle (the pulp, which is the soft tissue holding the nerve and blood supply). Decay is water damage. A patch on one wall is a filling. Rebuilding a roof is an onlay. Wrapping the whole structure in a new shell is a crown. When the water has reached the living room, you are into root canal territory.

Dentists work through roughly the same questions every time, whatever words they use at the chair:

• How deep is the decay, and how close is it to the pulp? Dental X-rays show this better than eyes do, which is why they are part of a routine exam (Mayo Clinic).
• How many surfaces are involved? A cavity on one side of a molar behaves very differently from one that has hollowed out the middle and undercut two walls.
• How thick are the remaining walls? Enamel and dentin that are left standing too thin tend to fracture under chewing forces.
• Is there an existing filling, and how big is it? A tooth that is mostly filling material with a rim of natural tooth has little left to anchor another patch.
• Is the tooth alive and settled, or inflamed? Lingering pain to hot or cold, or pain that wakes you at night, points toward the pulp.

The answers sort the tooth into a treatment tier. Small to moderate decay in a tooth with strong walls: filling. Moderate to large decay where a filling would leave the tooth too weak: inlay, onlay or crown. Pulp involvement: root canal first, and very often a crown afterward to protect the hollowed tooth (NHS).

Notice that pain is not on the list as a deciding factor. Decay in enamel and the outer dentin is frequently painless, which is exactly why cavities get caught on X-rays rather than by symptoms (Mayo Clinic).

What actually happens during a filling?

A filling is the simplest repair: remove the decayed tooth material, then replace it with a durable substitute that restores the shape and seals out bacteria. Most are done in a single visit.

After local anesthetic numbs the tooth and surrounding gum, the dentist uses a small drill, and sometimes hand instruments, to clear away softened, infected dentin until only firm, healthy tooth remains. The cavity is shaped so the filling material will lock in and resist being pulled out by sticky food. The tooth is dried and the material is placed.

Two families of material dominate (NHS, Mayo Clinic):

• Composite resin: a tooth-colored plastic and glass mixture, placed soft and hardened in layers with a blue light. It bonds chemically to enamel, which lets the dentist remove less healthy tooth.
• Dental amalgam: a silver-colored metal alloy, pressed into the cavity and left to set. It is strong under heavy chewing but needs a slightly different cavity shape to stay in. Several health systems, including the NHS, no longer use amalgam routinely for children under 15 or for people who are pregnant or breastfeeding, as a precaution rather than because of proven harm (NHS).

Glass ionomer, a material that slowly releases fluoride, is sometimes used near the gumline, on baby teeth, or as a temporary measure (NHS).

The dentist then checks your bite with colored marking paper and trims any high spots, because a filling that is even a fraction of a millimeter too tall will feel like a pebble and can leave the tooth sore for days.

What a filling cannot do is hold a tooth together. It sits inside the tooth, relying on the walls around it. Once those walls are thin, every chewing stroke flexes them against a rigid block of material. That is the mechanical reason large fillings and cusp fractures travel together, and the point at which the conversation turns to inlays, onlays and crowns.

Inlay vs onlay vs crown: what is the difference?

These three are often lumped together as “indirect restorations,” meaning they are made outside the mouth and cemented in, rather than packed directly into the cavity. The difference is how much of the tooth each one covers.

An inlay is a custom-made piece that fits inside the chewing surface between the pointed tips of the tooth (the cusps). Think of it as a precision-milled filling, usually in porcelain or a strong composite, for a cavity that is too wide for a conventional filling to be reliable but has not weakened the cusps.

An onlay does the same job but also extends up and over one or more cusps. It replaces a damaged corner of the roof rather than just patching the middle. Onlays are sometimes called “partial crowns” for that reason.

A crown covers the entire visible tooth above the gumline. The tooth is reshaped into a smaller core and the crown fits over it like a thimble, taking the chewing load and spreading it across the whole tooth (Cleveland Clinic).

Why would anyone choose an onlay over a crown? Tooth structure. Preparing a tooth for a crown means trimming healthy enamel from every surface. An onlay preserves the walls that are still sound and replaces only what is lost. Many dentists favor the most conservative option that will still be strong enough, because tooth you keep today is tooth you can still work with in twenty years.

Why would anyone choose a crown over an onlay? Strength and coverage. When walls are thin on several sides, when a tooth has had a root canal and is brittle, or when a crack runs toward the root, wrapping the whole tooth is the more predictable way to stop it splitting.

All three typically need two visits, with a temporary restoration in between while a dental laboratory makes the final piece, although some practices use chairside scanning and milling to finish in one appointment (Cleveland Clinic).

When is a crown needed after a cavity?

A crown is the treatment of choice when a tooth has lost too much structure to be safely rebuilt with a filling, or when it needs protection from splitting. Common triggers include (Cleveland Clinic, NHS):

• decay that has spread across most of the chewing surface and undermined the cusps
• a large, failing old filling with recurrent decay around its edges, where replacing it would leave paper-thin walls
• a cracked tooth, where the crown holds the pieces together under load
• a tooth that has had root canal treatment, especially a molar or premolar, because removing the pulp and widening the inner chamber leaves it more brittle
• a tooth that is badly worn or misshapen, when a filling cannot restore a workable bite

The appointment itself unfolds in a predictable order. After numbing, the dentist removes all decay and any old filling. If the remaining core is small, it is built up with filling material so the crown has something to grip. The tooth is then shaped: a uniform layer is trimmed from the top and sides so the finished crown will be strong without making the tooth look bulky. An impression or digital scan records the shape, and a temporary crown is fitted.

At the second visit, usually a week or two later, the temporary comes off, the final crown is tried in, adjusted for fit and bite, and cemented (Cleveland Clinic).

Crowns come in several materials: all-ceramic or porcelain for front teeth where appearance matters most; porcelain fused to a metal core for a balance of strength and color; metal alloys, including gold, for back teeth that take heavy forces; and zirconia, a very strong ceramic now widely used for molars. Each has trade-offs in wear, chipping and translucency, which is a conversation for your dentist rather than a ranking.

Crowns do not last forever. Cleveland Clinic gives a typical range of 5 to 15 years, with longevity depending heavily on oral hygiene, grinding habits and the condition of the tooth beneath (Cleveland Clinic).

When does a cavity need a root canal instead?

Root canal treatment steps in when the problem is no longer only the hard shell of the tooth but the living tissue inside it. The pulp, the soft core of nerves and blood vessels, can become inflamed or infected when decay reaches it, when a deep filling sits very close to it, or when a crack lets bacteria in (NHS, Cleveland Clinic).

Once bacteria are inside the pulp, a filling or crown on its own will not help. Sealing the top of the tooth over infected tissue is like painting over damp; the problem continues underneath and can spread through the root tip into the jawbone, forming an abscess.

The procedure is methodical rather than dramatic. Under local anesthetic, the dentist opens the top of the tooth, removes the inflamed or infected pulp, and cleans and shapes the fine canals running down each root. The canals are disinfected, dried and sealed with a rubbery filling material, and the opening is closed with a temporary or permanent filling (NHS). Cleveland Clinic puts a typical appointment at 30 to 60 minutes, with complex teeth taking up to around 90 minutes, and the NHS notes that treatment may be spread over more than one visit, with a temporary filling in between (Cleveland Clinic, NHS).

Modern root canals are generally no more uncomfortable than a large filling. The old reputation for pain comes from the toothache that leads people to the chair, not from the treatment that relieves it (NHS).

Afterward, a tooth without its pulp is still a tooth: you chew on it, floss around it, and it stays in your jaw. What it has lost is internal moisture and a fair amount of structure, so back teeth that have had root canals are usually crowned to stop them fracturing (NHS). Front teeth with little structural loss may sometimes be restored with a filling alone, a judgment your dentist will make based on how much tooth remains.

The alternative to a root canal for a dead or infected tooth is extraction. Both resolve the infection; only one keeps the tooth.

Filling, inlay, crown or root canal: how the options compare

The table pulls together what has been covered so far. It describes typical patterns, not rules; an individual tooth can sit between categories, and the dentist’s view of the remaining structure trumps any chart.

Treatment	Usually chosen when	What is removed	Typical visits	Main trade-off
Filling	Small to moderate decay; walls still strong	Decay only	One	Cannot reinforce a weakened tooth
Inlay	Wide cavity within the chewing surface; cusps intact	Decay only, precise shaping	Usually two; one with chairside milling	More complex than a filling, less coverage than a crown
Onlay	Decay or fracture involving one or more cusps	Decay plus damaged cusps	Usually two	Preserves sound walls but needs skilled fit
Crown	Extensive loss, cracks, or after root canal on back teeth	Decay plus a layer from every surface	Usually two	Most protective; removes the most healthy enamel
Root canal	Decay or infection has reached the pulp	Pulp tissue inside the tooth	One to several	Saves the tooth but usually needs a crown afterward

Two points deserve underlining. First, these are not rungs on a ladder you must climb in order. A tooth can go straight from “never treated” to “crown” if the first cavity is large enough, and a root canal is sometimes needed in a tooth that has only ever had one small filling, because a crack let bacteria in.

Second, the most conservative treatment that will be reliably strong is generally the goal. Dentists talk about the “restorative cycle”: each time a repair is replaced, a little more natural tooth goes with it, and the tooth moves one step closer to needing a crown, then a root canal, then possibly extraction. Choosing the smallest adequate repair, and looking after it, slows that cycle. Choosing one that is too small for the damage speeds it up when it fails.

Who is usually offered which option, and who is asked to wait?

Not every spot a dentist finds gets drilled. Decay is a process, not an event, and the earliest stage can stall or even reverse.

When acid from bacteria first dissolves minerals from enamel, it leaves a chalky white patch without a hole. At this stage the enamel can take minerals back from saliva and from fluoride, a process called remineralization. Mayo Clinic lists professional fluoride treatments among the options for very early decay, and the NHS describes monitoring early lesions and improving fluoride exposure rather than filling them (Mayo Clinic, NHS). So the first group “asked to wait” is anyone whose cavity has not yet broken through the enamel surface; the plan is watchful waiting with X-rays at review, not neglect.

A second group is children and teenagers with decay in baby teeth. Depending on how close the tooth is to falling out naturally, options range from fluoride varnish and sealants to small fillings, stainless-steel crowns for badly broken-down molars, or a form of pulp treatment designed for primary teeth. Dentists aim to keep baby molars in place until the adult tooth is ready, because early loss can crowd the permanent teeth.

Pregnancy is a reason to adjust timing rather than avoid care. Routine fillings and emergency treatment are considered safe during pregnancy, and untreated infection is the greater risk; dentists often prefer the second trimester for elective work and avoid amalgam as a precaution (NHS).

People with heavy tooth grinding, called bruxism, are more likely to be steered toward onlays or crowns on back teeth, because large fillings fracture under those forces. Those with a high rate of new cavities, often linked to dry mouth, frequent sugar intake or certain medications, may be advised to stabilize the underlying cause before investing in extensive crown work, since new decay at the crown margin would undo the effort.

Finally, a tooth with a poor long-term outlook, such as a fractured root or severe gum disease around it, may not be a candidate for any of these repairs. Extraction, and a discussion about replacement, becomes the honest option.

Can a cavity wait, and what happens if you leave it?

“Can I wait two years to fill a cavity?” is one of the most searched questions on this topic, and the honest answer is: it depends entirely on what kind of cavity, and nobody can tell you from a search bar.

An early enamel lesion with no break in the surface may well be stable for years with good fluoride exposure and a lower-sugar diet. Your dentist will often say so and schedule a check. The NHS sets routine check-up intervals anywhere from 3 months to 2 years depending on individual risk, which is itself a signal that “wait and see” is a legitimate clinical plan for low-risk situations (NHS).

A cavity that has reached the dentin, the softer layer under enamel, is a different animal. Dentin is less mineralized and has tiny tubes running toward the pulp, so decay spreads through it faster and wider than it did through enamel. This is why a small dark spot on an X-ray can hide a large hollow underneath. Left alone, the sequence is predictable (Mayo Clinic, Cleveland Clinic):

• the enamel over the hollow thins and collapses, often while eating something unremarkable
• sensitivity to sweet, hot or cold appears as the pulp starts to react
• bacteria reach the pulp, causing inflammation that can become constant, throbbing pain
• the pulp dies and infection spreads through the root tip into the bone, forming an abscess, which can cause swelling of the face or gum and, rarely, spread further

Each step moves the treatment up a tier. A filling becomes a crown; a crown becomes a root canal plus a crown; a root canal becomes an extraction. Waiting rarely saves anything except the appointment, and it tends to trade a short, simple visit for a longer, more complex one.

None of this means every cavity is an emergency. It means that “wait” is a decision your dentist should make with you, with an X-ray in hand and a review date in the diary, rather than one made by default because the tooth is quiet.

Will a tooth rot under a crown?

Yes, it can, and understanding why is the best protection against it.

A crown is made of porcelain, metal or zirconia. None of those decay. But the crown sits on natural tooth, and where the edge of the crown meets the tooth, the margin, there is a thin line of cement and a change in surface. That line is usually at or just below the gumline, which is precisely where plaque collects when brushing is rushed and flossing is skipped. Bacteria at the margin produce acid, the acid dissolves the tooth just under the crown edge, and decay creeps under the crown where you cannot see it and where a toothbrush cannot reach (Cleveland Clinic).

The result is a crown that looks perfect from the outside while the tooth beneath it softens. Often the first sign is on a routine X-ray, or a feeling that the crown is slightly loose, or sensitivity returning in a tooth that had been quiet. In a tooth that has had a root canal, there is no nerve to warn you at all, so the problem can advance silently until the crown comes off or the tooth fractures.

Several things raise the risk:

• a margin that does not fit snugly, leaving a step where plaque sticks
• receding gums that expose new root surface below the crown edge
• dry mouth, which removes the buffering and washing effect of saliva
• frequent sugary or acidic snacks and drinks
• skipping floss or interdental brushes, which are the only tools that clean the margin between teeth

And several things lower it: cleaning along the gumline daily with a fluoride toothpaste, flossing or using interdental brushes around every crown, keeping to the review schedule your dentist sets so margins are checked and X-rayed, and asking for a bite check if the crown feels high, since excess force can open a margin over time.

A crown protects a tooth from fracture. It does not protect it from your diet or exempt it from cleaning. Treat it as the tooth it covers.

What do the days and weeks after treatment look like?

Recovery from any of these procedures is usually undramatic, but it has a rhythm worth knowing so you can tell normal from not.

The first few hours. Numbness from the local anesthetic lingers after you leave. Chewing or sipping hot drinks while numb risks biting your cheek or tongue, so most dentists advise waiting until feeling returns before eating on that side. Composite fillings are fully hardened by the light and can be used immediately; amalgam continues to set and dentists often suggest avoiding hard chewing on it for the rest of the day (NHS).

The first week. Some sensitivity to cold, pressure or sweetness is common after a filling or crown preparation, especially if the decay was deep and the pulp was close. It typically settles over days to a few weeks (Cleveland Clinic). Sensitivity that is improving is reassuring; sensitivity that is worsening or lasts more than a few seconds after the trigger is removed is worth reporting. A bite that feels “high” should be adjusted promptly rather than tolerated.

Between crown visits. A temporary crown is held with weak cement by design. Sticky or very hard foods can pull it off, and flossing is done by sliding the floss out sideways rather than lifting it up. If a temporary comes off, keep it and call the practice; the exposed tooth can be sensitive and may shift slightly, affecting the final fit (Cleveland Clinic).

After a root canal. Mild soreness, particularly when biting, is common for a few days as the tissues around the root tip settle. The NHS advises avoiding hard chewing on the tooth until the final restoration is placed, because a root-treated tooth with only a temporary filling is vulnerable to fracture (NHS). Any pain relief is a matter for your dentist’s advice based on your medical history.

Weeks to months. Deep decay sometimes leaves a pulp that seemed healthy at the time but later becomes inflamed. If a filled or crowned tooth develops lingering ache, night pain or swelling months on, it is not a sign the work failed; it is a sign the pulp did not recover, and root canal treatment can usually be done through the existing restoration.

What are the risks and alternatives?

Every restoration carries trade-offs, and a good consent conversation names them plainly.

Fillings. Postoperative sensitivity is the most common complaint. Fillings can chip, wear or develop recurrent decay at their edges over time, and very deep fillings carry a chance that the pulp will later need root canal treatment because the decay was already close to it. Composite can stain and may wear faster under heavy forces; amalgam can expand slightly and is visible (NHS, Mayo Clinic).

Inlays, onlays and crowns. Preparing a tooth removes healthy structure that does not grow back. Ceramic can chip; porcelain fused to metal can show a dark line at the gum as gums recede; cements can wash out over years, loosening the restoration. Decay at the margin remains possible. A small proportion of crowned teeth later need root canal treatment because the preparation and the earlier decay together stress the pulp (Cleveland Clinic).

Root canal. Treatment may not fully clear infection if canals are unusually curved or narrow, and a second procedure, or a small surgical procedure at the root tip, is sometimes needed. Instruments can rarely fracture inside a canal. A root-treated tooth is more brittle and relies on a good final restoration (NHS, Cleveland Clinic).

Alternatives exist at each level:

• For early enamel decay: fluoride varnish, sealants and dietary change instead of a filling (Mayo Clinic).
• For deep decay near a healthy pulp: some dentists leave a thin layer of softened dentin and place a protective lining, a technique called indirect pulp capping, to avoid exposing the nerve. Evidence supports it in selected cases, and it is not suitable for every tooth.
• For young children or people who cannot tolerate conventional treatment: silver diamine fluoride, a liquid that arrests decay but stains it black, is used in some settings to stabilize cavities.
• For a tooth needing a root canal: extraction, followed by a discussion of a bridge, implant or denture, or leaving the space.

Which risks matter most depends on the tooth, your health, your habits and your priorities. That weighing-up is the treating team’s job, done with you.

What people often get wrong about filling or crown for cavity choices

A few beliefs come up so often that they deserve direct correction.

“If it doesn’t hurt, it doesn’t need treating.” Decay in enamel and outer dentin is usually painless, and a tooth that has had a root canal has no nerve to hurt at all. Pain arrives late in the process, typically once the pulp is involved and the simpler options are already off the table (Mayo Clinic).

“A crown is always the stronger choice, so I should just get the crown.” A crown is stronger for a weakened tooth. On a tooth with sound walls, cutting them down to fit a crown removes healthy enamel for no benefit and starts the restorative cycle earlier than necessary. More coverage is not automatically better.

“Brushing harder will fix a cavity.” Enamel can remineralize before a hole forms. Once dentin is exposed, no amount of brushing removes bacteria from inside the tooth; the softened tissue has to be cleaned out by a dentist. Brushing matters enormously for preventing the next one.

“Root canals cause illness elsewhere in the body.” This idea traces back to research from a century ago that has been thoroughly discredited. Mainstream health bodies describe root canal treatment as a safe, effective way to treat infection and keep a tooth (NHS, Cleveland Clinic). Leaving an abscess untreated is the genuine health risk.

“Crowns are permanent.” They are durable, with Cleveland Clinic citing a typical lifespan of 5 to 15 years, but they are not immune to wear, chipping, loosening or decay at the margin, and they need the same cleaning and reviews as any tooth (Cleveland Clinic).

“Is this a lot to pay for a crown?” Fees vary so widely by region, material and funding system that no general figure is meaningful, and this magazine does not publish prices. The more useful question is why a crown rather than a smaller restoration is being recommended for this tooth, and what the expected consequences of each option are. Ask it directly.

“Silver fillings should all be replaced.” Sound amalgam fillings do not need removing for health reasons; replacing them unnecessarily removes more tooth (NHS). Replace a filling when it fails, not because of its color.

Questions to ask your care team

Dentists make these judgments many times a day and can forget how opaque the reasoning looks from the chair. A handful of specific questions turns a verdict into a conversation.

• How deep is the decay, and how close is it to the nerve? Can you show me on the X-ray?
• How much healthy tooth will be left after the decay is removed, and is that enough to support a filling?
• If you are recommending a crown, what would happen if we tried a filling or an onlay instead? What is the realistic risk of fracture?
• Is an inlay or onlay an option for this tooth, and if not, why?
• Is the pulp healthy right now? What is the chance this tooth will need a root canal later, even after the filling or crown?
• Which materials are you suggesting, and what are the trade-offs for a tooth in this position?
• If this tooth needs a root canal, will it need a crown afterward, and how soon?
• Are there any teeth on the X-rays that you are choosing to monitor rather than treat, and what would change that decision?
• How many visits will this take, and what should I expect between them?
• What should I do if the temporary comes off, or if sensitivity does not settle?
• What is the single biggest thing I can change to reduce the chance of new decay around this restoration?
• When would you like to review this tooth, and what are you looking for at that visit?

Write the answers down. A plan that made sense in the chair can blur by the time you are deciding whether to book, and having the dentist’s own words in front of you makes a second opinion, if you want one, far more productive.

One more worth asking yourself: do I understand why this option and not the next one up or down? If the answer is no, the appointment is not finished.

When to call your doctor

Most discomfort after dental treatment is mild and fades. Some signs mean the tooth, or the infection around it, needs prompt attention. Contact your dental practice without delay, or an urgent dental service or emergency department out of hours, if you notice any of the following (NHS, Mayo Clinic):

• swelling of the face, jaw, cheek or neck, especially if it is spreading or making it hard to open your mouth
• difficulty swallowing or breathing, or a feeling that your throat is tightening; this is an emergency and needs immediate medical care
• fever alongside a toothache or swelling
• severe, throbbing pain that is not controlled by the measures your dentist advised, or pain that wakes you repeatedly at night
• a bad taste or pus draining from the gum near the tooth
• a filled or crowned tooth that becomes increasingly sensitive over days rather than less, or pain that lingers long after hot or cold is removed
• a crown, temporary or permanent, that comes off, or a filling that falls out, leaving a sharp edge or an exposed tooth
• a tooth that cracks or breaks after treatment
• numbness or altered sensation in the lip, chin or tongue that has not resolved by the following day
• bleeding from the gum around the tooth that does not stop with gentle pressure

Before any treatment, seek a dental appointment rather than waiting for a routine check if you have a tooth that hurts spontaneously, a visible hole or dark spot, sensitivity that is new and persistent, or a gum boil near a tooth. These are the signs that a cavity may already be beyond the filling stage.

None of the information in this article replaces an examination. Only the clinician who has seen the tooth and the X-rays can say whether a filling, inlay, onlay, crown or root canal fits the damage in front of them, and every decision about treatment, timing and materials rests with you and that team.

Frequently asked questions

Crown vs filling for cavity: which is better?

Neither is better in the abstract; each suits a different amount of damage. A filling is appropriate when the decay is small to moderate and the surrounding tooth walls are strong enough to support it. A crown is appropriate when so much tooth has been lost, or the tooth is cracked or root-treated, that a filling would leave it likely to fracture. Your dentist judges this from the exam and X-rays.

Can a cavity wait if it does not hurt?

Sometimes, but only when a dentist has confirmed the decay is early and has set a review date. Enamel-only lesions can stay stable or remineralize with fluoride. Once decay reaches dentin, it tends to spread faster and more widely than it appears on the surface, so waiting usually moves the tooth toward a larger repair. Pain is a late sign and is not a safe guide for timing.

When is a crown needed after a filling?

A crown is usually recommended when a filling has grown so large that little natural tooth surrounds it, when decay has returned around a filling’s edges and undermined the walls, when a cusp has fractured, or after root canal treatment on a back tooth. In each case the aim is to hold the remaining tooth together under chewing forces that a filling alone cannot withstand.

What is the difference between an inlay, an onlay and a crown?

All three are custom-made outside the mouth and cemented in. An inlay fits inside the chewing surface between the cusps. An onlay also covers one or more cusps, replacing a damaged corner of the tooth. A crown covers the entire visible tooth above the gumline. Inlays and onlays preserve more natural tooth; crowns give the most protection against splitting.

Will a tooth rot under a crown?

It can. The crown material itself does not decay, but the natural tooth at the crown’s edge, usually at the gumline, can. Plaque that collects there produces acid that dissolves tooth beneath the margin, often without pain, especially if the tooth has had a root canal. Daily cleaning along the gumline, flossing around the crown and regular X-rays at check-ups are the main safeguards.

Does every cavity need a filling?

No. Very early decay that has not broken through the enamel surface can often be managed with fluoride treatments, sealants and changes to diet and brushing, with the dentist monitoring it over time. Once there is a hole into dentin, bacteria cannot be removed by brushing and the softened tissue needs to be cleaned out and restored, most commonly with a filling.

Why would I need a root canal and then a crown?

Root canal treatment removes infected pulp from inside the tooth and seals the canals, which resolves the infection. It also leaves the tooth hollower and more brittle. Back teeth take heavy chewing forces, so a crown is usually placed over a root-treated molar or premolar to stop it cracking. Front teeth with little structural loss can sometimes be restored with a filling instead.

How long does sensitivity last after a filling or crown?

Some sensitivity to cold, sweet or pressure is common and usually fades over days to a few weeks as the tooth settles, according to Cleveland Clinic. Sensitivity that is gradually improving is reassuring. Sensitivity that is worsening, pain that lingers long after the trigger is removed, or a bite that feels high should be reported to your dentist so the tooth can be checked and adjusted.

Is a root canal painful?

Modern root canal treatment is done under local anesthetic and is generally described as no more uncomfortable than having a large filling. The pain people associate with it usually comes from the infected tooth beforehand, which the treatment relieves. Mild soreness when biting is common for a few days afterward. Your dentist will advise on comfort measures based on your medical history.

Can an old silver filling just be replaced with a bigger filling?

Sometimes. If removing the old amalgam and any new decay leaves thick, sound walls, a new filling can work. If the remaining tooth is thin or a cusp is cracked, a larger filling is likely to fail and an onlay or crown is usually advised. Sound amalgam fillings do not need replacing for health reasons alone; doing so removes more healthy tooth.

References

• Tooth decay (NHS)
• Root canal treatment (NHS)
• Dental crowns (Cleveland Clinic)
• Root canal (Cleveland Clinic)

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.