A failing dental filling usually announces itself through sensitivity, visible changes, or pain when you bite down. Some signs are obvious, like a piece of filling that chips off. Others are subtler, like food suddenly getting stuck in a spot that never trapped it before. Knowing what to look for can help you catch a problem early, before it turns into something more serious.
Pain and Sensitivity That Wasn’t There Before
The most common early warning is new sensitivity around a filled tooth. You might notice a zing when you drink something cold or hot, a sharp twinge when you bite down, or discomfort when eating sweet foods. Even sensitivity to air (like breathing in through your mouth on a cold day) can signal that the seal between your filling and tooth has broken down.
Pain specifically when biting is a strong clue. It often means the filling is interfering with how your upper and lower teeth meet, either because part of the filling has shifted, cracked, or worn unevenly. This type of bite-related pain tends to be sharp and immediate, right at the moment of pressure, and it usually doesn’t linger the way a toothache from an infection does.
A dull, throbbing ache that comes on gradually and persists is a different situation. That pattern can mean decay has worked its way underneath the filling and is reaching the nerve inside your tooth. This is a more advanced problem and typically needs attention soon.
What a Failing Filling Looks Like
You can sometimes spot trouble just by looking. A dark line along the edge of a filling, a visible crack, or an uneven surface that you don’t remember being there are all signs of breakdown. Discoloration around the margins of a tooth-colored filling can indicate that bacteria and fluids are seeping into the gap between the filling material and your tooth.
Another visual clue: the filling looks like it’s sitting lower than the surrounding tooth surface, or a small piece appears to be missing altogether. With silver (amalgam) fillings, you might see the metal looking pitted or corroded. With composite (tooth-colored) fillings, the edges may appear stained or yellowed compared to the rest of the tooth.
Not every visual change means the filling needs immediate replacement. Minor surface staining, for instance, doesn’t always indicate a structural problem. But visible cracks, gaps you can feel with your tongue, or dark shadows around the edges are worth getting checked.
Food Getting Stuck in New Places
If food starts consistently packing into the same spot around a filled tooth, and your brushing habits haven’t changed, the filling’s shape or seal has likely changed. A filling that has worn down, shifted slightly, or developed a gap at its edge creates a tiny shelf or pocket where food collects. This is more than an annoyance. Trapped food feeds bacteria right at the vulnerable margin of the filling, accelerating decay in exactly the spot where the tooth is already compromised.
How Decay Forms Under a Filling
The space between a filling and the tooth wall is where most problems start. Every filling material shrinks slightly as it hardens, and over years of chewing, the bond between filling and tooth can weaken. This creates microscopic gaps along the edges. Bacteria, saliva, and acids seep through those gaps in a process called microleakage, and new decay begins forming underneath or around the old filling.
Chewing actually makes this worse. The repeated pressure of biting pushes fluids back and forth along the filling’s edges, almost like pumping bacteria deeper into the gap. This is why fillings on your back teeth (which handle the most chewing force) tend to fail sooner than fillings on front teeth. The quality of the original bond between filling and tooth matters enormously here. A filling that was well-sealed from the start resists this process much longer.
The tricky part is that decay under a filling can grow for a while without causing any symptoms. By the time you feel pain, the decay may be extensive. This is one reason dentists use X-rays at regular visits: they can reveal dark shadows under fillings that you’d never see or feel on your own.
How Long Fillings Typically Last
No filling lasts forever, and knowing the general lifespan of yours helps you gauge when to be more vigilant. Research on filling longevity shows a wide range depending on the material, the size of the filling, and how well it was placed.
Silver amalgam fillings generally last longer. Studies in private dental practices report median survival times ranging from about 7 to 45 years, with many lasting around 13 to 23 years. Composite (tooth-colored) fillings have a somewhat shorter track record, with median survival times typically between 8 and 17 years, though larger fillings on back teeth tend to fall on the shorter end of that range. One study found amalgam fillings lasted a median of 22.5 years compared to 16.7 years for composites in patients who maintained regular dental visits.
These are averages. A small filling in a low-stress location can last decades. A large filling on a molar that takes heavy chewing force might fail in under ten years. Factors like teeth grinding, diet, and oral hygiene all shift the timeline. If your filling is approaching the 10-year mark, it’s worth paying closer attention to the signs above.
When a Filling Gets Repaired vs. Replaced
Not every imperfect filling needs to come out entirely. Dentists weigh several factors when deciding whether to replace a filling or simply repair its edges. The key criteria include the filling’s age, whether there are cracks or defects along the margins, whether decay is visible, and whether the tooth is causing pain.
A filling with minor edge imperfections but no evidence of decay underneath can sometimes be repaired by smoothing or adding material to the affected margin. This is a more conservative approach that preserves more of your natural tooth structure. However, if there are signs that bacteria have gotten underneath (dark shadows on an X-ray, persistent sensitivity, visible decay at the margins), the filling typically needs to come out completely so the dentist can remove the new decay and place a fresh restoration.
Older fillings with marginal cracks deserve careful evaluation. The combination of high age plus visible edge defects is one of the strongest indicators that decay may be hiding underneath. Multi-surface amalgam fillings (those that cover more than one side of the tooth) also warrant extra scrutiny, since larger fillings have more edge length where problems can develop.
What Happens If You Wait Too Long
A failing filling that goes unaddressed doesn’t just stay a filling problem. Once bacteria reach the inner chamber of your tooth (the pulp, where the nerve lives), the infection has nowhere to go in that tight space. Pressure builds, and you get the kind of intense, throbbing toothache that’s hard to ignore.
From there, the infection can track down through the root and into the jawbone, forming a dental abscess. At that point, treatment escalates significantly. What could have been a straightforward filling replacement may now require a root canal or, in severe cases, extraction of the tooth. People who seek treatment early when a filling first shows signs of failure have a much better outcome than those who delay until an abscess develops.
The progression from “slightly sensitive tooth” to “serious infection” doesn’t happen overnight. You typically have weeks to months of warning signs. But decay under a filling can be painless for a surprisingly long time before suddenly becoming urgent, which is why the visual and functional signs (food trapping, visible cracks, changes in how the filling feels against your tongue) matter just as much as pain.