How Cavities Get Treated: From First Filling to Root Canal

What are the stages of cavity treatment?

Cavity treatment is a ladder, not a single procedure. Each rung matches the repair to how deep the decay has reached and whether the tooth's living pulp is still healthy. The rungs run from arresting a tiny lesion, to a filling, to an inlay or crown for larger damage, to a root canal when the nerve is involved, and finally to extraction with replacement when nothing else will hold. Cavities are common enough that most adults meet this ladder eventually: about one in five adults aged 20 to 64 in the United States has at least one untreated cavity 1Ref 1Centers for Disease Control and Prevention (2024).Cavity Facts.About one in five (21%) adults aged 20 to 64 in the United States has at least one untreated cavity, and untreated decay is a leading cause of tooth loss.. Where a specific tooth lands depends on depth, symptoms, and how much sound structure remains.

This cavity treatment ladder is what dentists mean when they say a tooth caught early is simpler and cheaper to fix. The same principle — the least invasive option that will actually work, escalating only as far as the damage forces — also shapes the periodontitis treatment ladder for gum disease. The sections below take the cavity version one rung at a time, and defer the dollar figures to the dedicated cost guides for each procedure.

Does every cavity need a filling?

Not every cavity needs a filling. The earliest decay shows up as a chalky white or brown spot where the enamel has started to lose minerals but has not yet collapsed into a hole. At that stage the surface can sometimes be remineralized with fluoride and more thorough daily cleaning, or simply watched at follow-up visits to see whether it stabilizes or advances. Watching an early cavity is a legitimate, evidence-based plan rather than neglect — but it depends on a dentist actually monitoring the spot over time, not on hoping.

For active decay where drilling is difficult — very young children, frail older adults, people with dry mouth, or teeth that are hard to reach — dentists increasingly use silver diamine fluoride, a liquid brushed onto the tooth that can stop a cavity from progressing without any drill or anesthetic 2Ref 2American Academy of Pediatric Dentistry (2021).Silver Diamine Fluoride Policy and Fact Summary.Silver diamine fluoride is a liquid that can arrest active caries without drilling, and it permanently stains the treated lesion dark.. The trade-off is cosmetic and permanent: silver diamine fluoride stains the arrested decay dark brown or black where it is applied 2Ref 2American Academy of Pediatric Dentistry (2021).Silver Diamine Fluoride Policy and Fact Summary.Silver diamine fluoride is a liquid that can arrest active caries without drilling, and it permanently stains the treated lesion dark.. The evidence for it is promising but honest about its limits — a 2024 Cochrane review found that silver diamine fluoride may arrest existing cavities and may prevent new ones, though the certainty of that evidence is low, and the review could not confirm it works better than other active treatments 3Ref 3Worthington HV, et al. (2024).Topical silver diamine fluoride (SDF) for preventing and managing dental caries in children and adults.A 2024 Cochrane review found silver diamine fluoride may arrest and may prevent caries at low certainty and could not confirm it is superior to other active treatments..

The honest answer to when cavities need filling is roughly the point where decay has broken through the enamel into the softer dentin beneath and formed a cavity that traps bacteria a toothbrush cannot reach. Past that line the tooth cannot reliably repair itself, and a restoration has to replace what the decay has destroyed.

When a filling is the right repair

A filling is the standard repair once a cavity has reached the dentin but has not undermined too much of the tooth. The dentist numbs the area, removes the softened and infected tooth structure, cleans the space, and rebuilds the missing part with a bonded material — most often a tooth-colored composite resin, and sometimes silver amalgam. Crucially, the tooth keeps its own root and living nerve; only the decayed portion is replaced, and the tooth goes on functioning normally.

Which material a dentist recommends depends on where the tooth sits and how much force it takes when you chew. Front teeth almost always get composite for appearance; large cavities in the back molars are sometimes still restored with amalgam for its durability. How a filling is priced, and how tooth-colored composite stacks up against amalgam on cost and longevity, is a decision in its own right and is covered in the filling-cost guides rather than here.

A filling done early is the least invasive and least expensive rung on the ladder, which is the whole argument for catching decay before it deepens. Fillings do not last forever, though. Decay can start again at the edge of an old filling, and a very large or repeatedly repaired filling eventually weakens the tooth enough that the next repair has to be something sturdier.

When decay is too big for a filling: inlays, onlays, and crowns

When a cavity is too large for a filling to hold, the repair moves up to a lab-made restoration that covers more of the tooth than a filling can. An inlay fits inside the chewing surface between the cusps; an onlay extends over one or more cusps; a crown, or cap, covers the entire visible tooth down to the gumline. The more of the tooth the decay has taken, the more coverage the restoration provides.

Dentists reach for a crown when a tooth carries a very large filling, is cracked or otherwise weakened, or has just had a root canal and needs protection against fracture 4Ref 4American Dental Association (2024).Crowns.Crowns strengthen a tooth with a large filling, protect a weak, cracked, or broken tooth, anchor a bridge, cover an implant, and restore a discolored or misshapen tooth.. Crowns also do other jobs on the same tooth: they anchor a bridge, cover a dental implant, and restore the shape and color of a badly broken or discolored tooth 4Ref 4American Dental Association (2024).Crowns.Crowns strengthen a tooth with a large filling, protect a weak, cracked, or broken tooth, anchor a bridge, cover an implant, and restore a discolored or misshapen tooth.. Because a crown is fabricated to fit precisely, it usually takes an impression or scan and either a second visit or a same-day milling machine.

The reason a large cavity cannot simply take a bigger filling is structural. Once the surrounding walls of enamel are thin, a filling wedged inside them can act like a splitting wedge under chewing force and crack the tooth. Wrapping the tooth in an onlay or crown redistributes that force instead. The cost of these indirect restorations runs higher than a filling and is covered in the inlay, onlay, and crown cost guides.

When decay reaches the nerve: root canal

Once decay reaches the pulp — the living nerve and blood supply at the core of the tooth — a filling can no longer solve the problem, because the inside of the tooth is now inflamed or infected. A root canal treats exactly this situation: a dentist or endodontist removes the inflamed or infected pulp, cleans and shapes the narrow canals inside the roots, then fills and seals them to relieve the pain and keep the natural tooth in place 5Ref 5American Association of Endodontists (2024).Root Canal Treatment.A root canal removes inflamed or infected pulp, cleans and shapes the canals, then fills and seals the tooth to relieve pain and save the natural tooth, which is preferred when feasible.. With modern anesthetics, most people are comfortable during the procedure.

A root canal becomes necessary because pulp damage does not reverse. When decay lets bacteria into the pulp, the tissue can die and the infection can build into a dental abscess — a pocket of infection at the root tip that can spread into the surrounding bone 6Ref 6American Dental Association (2024).Abscess.A dental abscess is an infection that forms when decay lets bacteria into the pulp, which can die; the infection can spread into surrounding tissue and bone.. That is why a tooth that was aching intensely can suddenly go quiet: the nerve has died, but the infection has not gone away. The quiet is not recovery.

After the pulp is removed, the tooth is usually more brittle and, especially on a back tooth, is typically protected with a crown so it can take chewing force again without splitting. A root canal followed by a crown is a larger commitment than a filling, but it lets a person keep a tooth that would otherwise be lost.

When a tooth can't be saved: extraction and replacement

Extraction is the last rung, reached when so much of the tooth has been destroyed by decay or fracture that no restoration can hold, or when the supporting bone around it is too far gone. Endodontists and dentists generally favor saving the natural tooth whenever it is feasible, because a natural tooth preserves the bite and the jawbone in a way no artificial replacement fully reproduces 5Ref 5American Association of Endodontists (2024).Root Canal Treatment.A root canal removes inflamed or infected pulp, cleans and shapes the canals, then fills and seals the tooth to relieve pain and save the natural tooth, which is preferred when feasible.. Removal is the option of last resort, not a first convenience.

When a tooth does have to come out, the gap is usually restored with a bridge, a dental implant, or a partial denture. Replacement matters for more than appearance: an empty space lets the neighboring teeth tip and the opposing tooth drift, and the jawbone under the gap gradually shrinks once it no longer has a root to support. Those downstream effects, and the cost of each replacement option, are covered in the extraction and tooth-replacement guides.

Deciding between saving a tooth with a root canal and removing it is a genuine judgment call that weighs how much healthy tooth is left, the condition of the roots and bone, and the cost and durability of each path. It is a conversation worth having with the dentist rather than a decision to make from a search result.

What decides which treatment you need

Three things put a tooth on a particular rung of the ladder: how deep the decay has reached, whether the pulp is inflamed or infected, and how much sound tooth is left to build on. A dentist reads these from an examination, an X-ray, and your symptoms — a brief twinge with cold usually points to reversible irritation, while pain that lingers, throbs, or wakes you at night suggests the pulp itself is involved and a filling will not be enough.

This is why the same word, cavity, can mean a five-minute fluoride varnish for one person and a root canal with a crown for another. It is the same disease at different depths. Because decay generally advances rather than retreats, the earliest rungs are both the least invasive and the least expensive, which is the practical case for regular checkups: they catch cavities while they are still small 1Ref 1Centers for Disease Control and Prevention (2024).Cavity Facts.About one in five (21%) adults aged 20 to 64 in the United States has at least one untreated cavity, and untreated decay is a leading cause of tooth loss..

None of this replaces an in-person diagnosis. A guide can describe what each rung of treatment does and why a dentist might choose it, but only an exam and X-ray can locate a specific tooth on the ladder. The most useful thing this page can do is help you walk into that appointment already understanding the options, so the conversation is about which repair fits your tooth rather than what the words mean.