Root Canal or Filling: What Decides Which One You Get
Whether the decay has reached the pulp. That is the whole difference, and it is not something you can feel from the outside — but it changes the bill by an order of magnitude.
One question separates them
Has the problem reached the pulp?
The National Institute of Dental and Craniofacial Research describes how decay starts: "Tooth decay begins when bacteria in your mouth make acids that attack the tooth's surface (enamel). This can lead to a small hole in a tooth, called a cavity." A filling deals with a cavity by clearing out the damage and replacing the missing structure.
Root canal treatment deals with something further in. The AAE describes it as "a dental procedure to remove inflamed or infected pulp on the inside of the tooth which is then carefully cleaned and disinfected, then filled and sealed", where the pulp is the soft tissue "beneath the white enamel and a hard layer called dentin" containing blood vessels, nerves and connective tissue.
So the two procedures are not competing options between which you choose. They are answers to different questions about how far something has got — and the tooth decides, not you and not the dentist.
What that difference costs
A great deal, and this is where people feel it.
| What it is | Code | Pennsylvania | Montana |
|---|---|---|---|
| One-surface filling, back tooth, resin | D2391 | $50.00 | $79.04 |
| Three-surface filling, back tooth, resin | D2393 | $65.00 | $213.41 |
| Root canal, premolar | D3320 | $375.00 | $454.48 |
| Root canal, molar | D3330 | $500.00 | $553.28 |
And the canal figure is not the end of it, because every root canal line on every schedule we read is written "excluding final restoration". A filling is usually the whole job; a root canal is the beginning of one.
That gap is why the first appointment matters so much. Which of these two conversations you are having is settled by an exam and an X-ray costing $59.28 to $144.00 on these schedules, and it determines everything after it.
What makes decay cross the line
The ADA names four ways the pulp gets into trouble: "a deep cavity", "repeated dental procedures", "a cracked or fractured tooth", and "injury to the tooth". Only the first is decay doing it slowly. The others are worth knowing about because they explain teeth that need root canal treatment without ever having had much decay at all — a tooth that has been filled and refilled over decades, or one that took a knock years ago.
Why you cannot tell from the outside
Pain is a poor instrument here. A shallow cavity can be extremely sensitive; a pulp that has already died can be silent. The AAE's list of signs includes lingering sensitivity to hot or cold that outlasts the stimulus, which is the closest thing to a distinguishing symptom — and even that is not conclusive, because a pulp can be irritated in a way that settles once the decay is removed and a filling is placed.
This is a large part of why the profession measures rather than guesses. The Washington endodontic schedule prices a pulp vitality test at $74.40, which is a document telling you that "is this nerve alive?" is a question with an instrument attached to it.
What each appointment is actually like
They are not the same size of event, and it is worth knowing that before the day.
A filling is usually one visit. The decay is removed, the cavity is shaped and the material goes in, and you leave with the tooth finished.
Root canal treatment is longer and often more than one visit. The NHS page on the treatment, reviewed on 3 October 2025, says it "usually takes 2 or more appointments", and that "the appointments may last 1 to 2 hours, or sometimes longer". The American Association of Endodontists describes most root canals as one to two appointments at roughly ninety minutes each. Both describe local anaesthetic as the normal approach, and neither promises anything about how it will feel.
There is also a gap in the middle that surprises people. Between the canal work and the final restoration there is usually a temporary filling, and during that period the tooth is not finished — it is a tooth with a hole in it and a stopper. That is a stretch of weeks to think about chewing on the other side, not a completed job.
The version of this question that has a real answer
There is one place where you have genuine influence, and it is earlier than either procedure. NIDCR says that at the earliest stage, "tooth decay can be stopped or reversed at this point. Enamel can repair itself by using minerals from saliva and fluoride from toothpaste or through the application of fluoride by a dentist or dental hygienist."
That window closes. Once there is a hole, it does not heal, and the only question left is how far in the damage has got by the time somebody looks. The practical implication is dull and correct: the earlier a tooth is examined, the more likely the answer is the cheap procedure. That is covered properly in the chapter on lowering your odds of needing a root canal at all.
If you have been told you need the bigger one
Ask what the X-ray shows and ask to see it. Ask whether a filling was considered and what ruled it out. Ask whether the tooth will need a crown afterwards and what the total comes to line by line. None of that is confrontational; it is the same information the dentist used to reach the recommendation.
And if the answer is that it is borderline, that is a legitimate answer. Some teeth are genuinely on the line, and a dentist saying so is being straight with you rather than evasive. The full set of prices behind the decision is on our page pricing root canal treatment from three published fee schedules.
Questions about the two procedures
Can a filling fix a tooth that needs a root canal?
No. They treat different depths of the same problem. A filling replaces structure lost from the hard part of the tooth; root canal treatment deals with the pulp inside it once that has become inflamed or infected. If the pulp is involved, a filling put over the top does not reach it.
How does a dentist decide between them?
By examining the tooth, by X-ray, and often by testing whether the pulp is still alive — one of the schedules we read prices a pulp vitality test as its own line item. The decision is about how far the damage has reached, which is not visible from outside the mouth and is not reliably indicated by how much it hurts.
Is a root canal always more expensive than a filling?
On the two schedules here that price both, yes, by a wide margin — and the gap is wider than the table shows, because the root canal figure explicitly excludes the restoration that has to follow, while a filling is usually the whole job.
Could I get a filling now and a root canal later if it gets worse?
That is sometimes the plan, and sometimes it is not a reasonable one. It depends on what the X-ray shows about how close the decay is to the pulp. Ask directly: what happens to this tooth if we fill it and it does not settle, and how would we know?
Can early decay really reverse?
NIDCR says enamel can repair itself at the earliest stage, using minerals from saliva and fluoride from toothpaste or applied by a dentist or hygienist. That applies before there is a hole. Once a cavity has formed, it is a structural loss and reversal is off the table.
Carry on
The prices behind all of this are on what a root canal costs on three fee schedules.
Anaesthetic and Sedation for a Root Canal
Local anaesthetic is the default and is included in the procedure — it has no separate line on any schedule we read. Sedation is a different thing entirely, billed by the quarter hour, and it is worth knowing what that costs before you say yes.
Do You Need a Crown After a Root Canal?
On the schedules that price both, the crown is roughly half of the total bill — and the endodontists' own guidance says it depends mostly on which tooth it is. Back teeth generally get one; front teeth often do not.