Tooth pain doesn’t go away on its own. When you’re stuck deciding between a root canal and filling, it’s tempting to go with the easier, cheaper option. But if your tooth is badly damaged, a filling could delay the inevitable and worsen things.
The Centers for Disease Control and Prevention (CDC) reports that nearly 60% of adults have had a dental cavity, and when decay reaches the nerve, root canals provide a 95% success rate in saving the tooth. This shows root canals aren’t just a last resort, they’re often the best solution for deep infections.
Figuring out if you need a root canal or a filling comes down to how deep the damage is. If your dentist says it’s more than just a surface cavity, here are 12 reasons why going with a root canal might be the better move.
1. The Decay Has Reached the Pulp
Once a cavity gets deep enough to reach the pulp, the soft inner core of the tooth that holds nerves and blood vessels, a filling won’t solve the problem.
If you try to plug it with a filling, the bacteria inside can keep growing. That can lead to infection, abscess, or eventually tooth loss. A root canal removes the damaged pulp, stops the infection, and saves the rest of your tooth.
This is usually when a dentist says, “this isn’t just a filling anymore” and they’re right.
2. There’s Too Much Tooth Structure Gone
Fillings only work well when there’s enough healthy tooth left to support the material. If the cavity is too large or the structure is too weak, a filling may crack, fall out, or not even stay in place.
In that case, you’re just patching over a bigger problem. A root canal, combined with a dental crown, gives your tooth a second life. It restores strength from the inside and gives long-term stability.
That’s often the deciding factor in the root canal vs. filling conversation.
3. You Have Lingering or Sharp Pain
If your tooth hurts randomly during the day or aches long after eating or drinking, the nerve is probably irritated or infected.
A filling might seal the hole, but it won’t fix an irritated nerve. In some cases, the pain actually gets worse. That’s a clear sign you might need a root canal instead of a filling.
With a root canal, the inflamed nerve is removed completely. No more pain. Problem solved at the source.
4. The Tooth Is Discolored
When one tooth looks darker or gray compared to the rest, it’s not just about looks. It usually means the inner tissue has died.
This is a sure sign the damage has gone deep. Fillings only touch the surface, they can’t fix a dead nerve. In this case, a root canal clears out the dead tissue and helps preserve what’s left of the tooth.
Plus, once you get a crown afterward, the tooth will look normal again.
5. You See Swelling or a Pimple on the Gums
A little bump on your gum that comes and goes? That’s likely an abscess. It’s your body trying to push out infection from the root of the tooth.
At this stage, when does a cavity need a root canal isn’t even a question anymore. A root canal is necessary to clean out the infection before it spreads.
A filling can’t touch the root, so it’s not even a temporary fix. It’s just delaying the care you really need.
6. The Tooth Already Has a Big Filling
If a tooth already had one or two fillings and is acting up again, it might not be able to handle another.
Teeth can only take so many repairs before they start to weaken. If the decay is close to the nerve, or if the nerve was never fully treated, it’s time to consider a root canal.
This happens a lot when fillings are used over and over instead of dealing with the root of the problem (literally).
7. X-Rays Show Bone Loss or Deep Infection
You might not see or feel anything yet, but your dentist might. X-rays can reveal if there’s infection around the root, widening of the root canal space, or even bone loss.
In that case, even if the tooth looks fine on the outside, it’s already failing inside. No filling is going to reverse that kind of damage.
A root canal is your only shot at saving it before it reaches the point of no return.
8. You Want Long-Term Peace of Mind
Fillings can crack, leak, or wear out, especially if they’re big or placed under pressure. That means more repairs, more visits, and more money later.
A root canal, especially when followed by a crown, gives you a much more permanent fix. Most root canal-treated teeth last well over 10–15 years when properly maintained.
So if you’re asking, deep cavity filling vs. root canal, think about whether you want to be back in the chair a year from now, or be done with it for good.
9. You’ve Had a Failed Filling Already
If you’ve had a filling placed recently and the tooth still hurts, or hurts more than before, that’s a red flag. The decay may have been deeper than expected, or the nerve was already inflamed.
A filling in that situation won’t last and might even trap more bacteria inside. That’s when switching to a root canal makes sense.
It’s frustrating, but it’s better to deal with it now than to wait until you’re in serious pain or risk losing the tooth entirely.
10. The Tooth Is Sensitive to Hot or Cold
Sensitivity to cold or heat is common, but when it lingers for more than 10 seconds, that’s usually a sign of nerve involvement.
A small filling won’t help much here. The nerve needs to be removed to stop the irritation. That’s exactly what a root canal does.
So, if that hot coffee or cold water is making you wince, don’t ignore it. The pain is your tooth telling you something deeper is wrong.
11. You Want to Avoid Tooth Loss
Sometimes people avoid root canals because they’re scared or want to save money. But avoiding a root canal when you need one often ends in extraction.
Losing a tooth leads to new problems: shifting teeth, chewing trouble, speech issues, bone loss, and the cost of replacements like implants or bridges.
A root canal keeps your natural tooth in place. And nothing beats having your own tooth.
12. You Care About Your Overall Health
Infection in your mouth doesn’t just stay there. It can affect nearby teeth, your jawbone, and even your immune system.
There’s real evidence linking chronic oral infections to heart disease, diabetes complications, and more. If you let an infected tooth sit untreated, the risks go far beyond your smile.
Choosing a root canal over a filling in these cases doesn’t just save your tooth, it protects your overall health.
Why a Root Canal May Be the Right Choice Over a Filling
Root canals get a bad rap, but they’re not the enemy, neglect is. A filling might seem like the simple fix, but it’s only right when the damage is minimal. Once a tooth starts showing deeper signs of trouble, it’s not just about getting out of pain. It’s about making a choice that protects your long-term health, your time, and your wallet.
Your teeth aren’t just chewing tools, they’re part of a much bigger system. And when one goes down, the rest eventually feel it. So if you’re weighing root canal vs. filling, think beyond today’s appointment. Sometimes the best fix is the one that goes deeper and actually lasts.