How Long Do Fillings Last? Composite vs. Amalgam, Honestly

When patients ask me how long do fillings last, they want a number — and I’ll give one. But the real answer is a range, because a filling is only as durable as the tooth it’s bonded into, the person biting on it, and the technique that placed it. In 20+ years of restorative work at Peninsula Dentistry in Huntington Beach, I’ve replaced 8-year-old composites and I’ve seen 40-year-old amalgams still doing their job. This post is the honest breakdown: average lifespans, what makes fillings fail, and when replacement is actually warranted.

How Long Do Fillings Last on Average?

Here are the numbers backed by the dental literature and what I see in practice week to week:

• Composite (tooth-colored) fillings: 7–10 years average, 12–15 years when well-placed in a low-stress location
• Amalgam (silver) fillings: 10–15 years average, 20–40 years for well-placed, small-to-medium restorations
• Glass ionomer fillings (used mostly on baby teeth and in specific niches): 3–5 years
• Gold inlays/onlays (rare now, still excellent): 20–30+ years

Amalgam has a longevity edge on paper. In real mouths, the gap is smaller than it looks — because most modern fillings, whichever material, get replaced not because the filling itself failed, but because new decay formed at the margin. That’s a hygiene story, not a material story. The American Dental Association’s overview of dental fillings covers the material comparison in more depth if you want the clinical-language version.

For a look at why we’ve largely moved away from silver in modern restorative work, our earlier post on tooth-colored fillings vs. amalgam walks through the material tradeoffs.

Why Composite Fillings Fail (and When)

Composite fillings fail in three predictable ways. Understanding which one is happening tells you whether it’s a material issue, a technique issue, or something you’re doing.

Marginal breakdown. The bond between the composite and the tooth weakens over years, opening a microscopic gap where new decay can start. This is the most common failure mode and usually shows up between years 7 and 12.

Bulk fracture. A large composite in a high-load location — usually a molar — can crack across the middle if the underlying tooth flexes. Grinders and clenchers see this earlier.

Wear and staining. The composite surface wears faster than enamel by a small margin each year. On a chewing surface, that shows up as a slightly recessed filling after a decade. On a front tooth, staining around the edges can make the restoration visible before it’s actually failing structurally.

The technique variable I mentioned above is real. A composite placed in a dry, well-isolated field lasts substantially longer than one placed while the tooth was contaminated by saliva. This is not about the office being expensive — it’s about the operator using a rubber dam or equivalent isolation and taking the time to layer and cure properly.

If you want to see how the material handles the aesthetic side over that same timeframe, our sibling post on whether composite fillings match your teeth over time is the honest read.

Why Amalgam Fillings Fail (and When)

Old-school amalgam failures look different because the material itself behaves differently.

Tooth fracture around the filling. Amalgam doesn’t bond to the tooth — it’s mechanically wedged in. Over decades, the wedging force plus normal chewing can crack the surrounding tooth. When I see a 25-year-old amalgam, I’m usually watching for cracks in the enamel around it, not the filling itself.

Corrosion at the margin. Amalgam corrodes very slowly and stains the surrounding tooth structure gray/black at the edge. Cosmetically ugly, but not functionally urgent unless the seal is actually compromised.

Recurrent decay. Same story as composite — new cavities form at the interface between filling and tooth when hygiene lapses. It has nothing to do with the material.

Amalgam tattoo. A cosmetic non-issue where amalgam particles get embedded in nearby gum tissue during placement, leaving a small dark spot. Harmless.

Amalgam earned its longevity reputation, but the reason we don’t place it in new patients anymore isn’t safety — it’s aesthetics and the fact that composite bonds to tooth structure, which means less healthy tooth has to be removed to place the filling.

The Habits That Extend the Life of Any Filling

Whichever material is in your mouth right now, these move the number more than most patients realize:

1. Floss around every filling every day. New decay at the margin is the #1 reason fillings get replaced. Flossing at the interface between filling and tooth is more important than flossing between untouched teeth.
2. Wear a nightguard if you grind. Grinding cracks fillings and the teeth holding them. If you wake up with a sore jaw or notice wear facets on your teeth, our post on nightguards for teeth grinding covers the fix.
3. Skip the ice-chewing and hard candy. Both crack composites and the enamel next to amalgams. Same for pen chewing.
4. Show up to cleanings twice a year. Not for the polish — for the exam. I catch failing margins with a mirror and explorer years before they’d cause pain, and small early replacements are cheaper and preserve more tooth than delayed ones.
5. Rinse with water after coffee, wine, and soda. The acid softens the composite surface temporarily and accelerates wear if brushed on immediately. Wait 30 minutes.

If your fundamental question is really about cavity prevention overall — because a filling that never needs to happen is the best filling — our approach to restorative dentistry starts with what’s already in your mouth and how to keep it that way.

When to Replace a Filling vs. Watch It

Not every old filling needs to come out. The judgment call:

Replace now — visible crack in the filling or surrounding tooth, decay confirmed at the margin on X-ray, filling is loose or has fallen out, sharp pain when biting on that specific tooth, ongoing sensitivity that doesn’t resolve within a few weeks.

Watch and monitor — cosmetic discoloration only, mild sensitivity to cold that’s stable over years, small marginal stain that hasn’t progressed on comparative X-rays. Overtreatment is a real problem in dentistry, and I’d rather monitor a filling for two more years than replace one that had five more years of life left.

The National Institute of Dental and Craniofacial Research maintains a patient overview of dental caries and restoration that reinforces this: replacement decisions should be evidence-based, not calendar-based.

Signs Your Filling Might Be Failing

Watch for these between checkups and mention them at your next visit — or come in sooner if any of them are severe:

• Sharp pain when biting down on the tooth
• Prolonged cold or hot sensitivity in one specific tooth
• A rough edge or gap you can feel with your tongue
• The filling looks darker or has a visible line around it that wasn’t there before
• Food consistently packing between the filling and the neighboring tooth
• A crack visible in the tooth around the filling

Any of these earns a look. Some resolve with a bite adjustment; others need replacement. You won’t know without an exam. Our post on why teeth get suddenly sensitive covers when sensitivity is a filling issue versus something else.

Frequently Asked Questions

How long do composite fillings last on molars specifically?

Molars are the high-stress location. A composite in a molar averages 7–10 years, with grinders and clenchers seeing shorter timelines. Well-placed composites in small molar cavities routinely reach 12+ years.

Are 30-year-old amalgam fillings safe to leave in?

If the filling is intact, sealed at the margins, and the surrounding tooth isn’t cracked — yes. There’s no medical reason to remove functioning amalgams. Replacement is only warranted if there’s evidence of failure or if you specifically want the cosmetic upgrade.

Does grinding my teeth actually shorten filling life?

Yes, meaningfully. Bruxism (grinding) can cut a filling’s expected lifespan roughly in half by fracturing the material or the tooth around it. A custom nightguard is the fix.

Will a new cavity form under my old filling?

It can, though usually at the edge (the “margin”) rather than truly underneath. This is caught on routine X-rays before it causes pain, which is one of the main reasons we take bitewings periodically.

How much does it cost to replace an old filling in Huntington Beach?

Replacement cost is the same as a new filling — roughly $180–$450 depending on size and surfaces. Insurance typically covers replacement on the same terms as the original filling if enough years have passed.

Can I get a filling replaced just because I don’t like how it looks?

Yes. Elective replacement of an intact amalgam with a composite is a reasonable cosmetic choice. I’ll always tell you honestly whether the existing filling still has useful life left before we make the swap.

Related Reading

• Tooth-Colored Fillings: Why Composite Has Replaced Silver
• Do Composite Fillings Match Your Teeth? Cost, Aesthetics, Longevity
• Do You Grind Your Teeth? How a Custom Nightguard Can Save Your Smile

Wondering if it’s time to replace an old filling — or whether that sensitivity is worth a look? Call Peninsula Dentistry in Huntington Beach at (714) 374-8800 or book a consultation online. Dr. Tran will X-ray the tooth, show you what he sees, and give you a straight answer on whether it’s a “replace now” or a “watch for another two years.” Learn more about our composite fillings approach if a swap turns out to be the right call.

Dr. Kenneth Tran, DDS

Author

Dr. Tran earned his DDS from NYU College of Dentistry and has practiced dentistry in Huntington Beach for over 20 years. He provides comprehensive care from routine cleanings to complex implant cases at Peninsula Dentistry.