You might think a dental filling means the end of your cavity worries—but what if decay starts hiding beneath it? Many people are surprised to learn that tooth pain or sensitivity years after a filling isn’t always “normal.” So, is it possible to get a cavity under a filling? The answer might change how you look at old dental work and your next checkup.
See a Dentist for Cavity Under Filling Today!
TL;DR
Yes, it’s possible to get a cavity under a filling. This occurs when small gaps, cracks, or worn edges allow bacteria and plaque to enter between the filling and tooth. The bacteria feed on sugars, producing acids that weaken enamel and dentin, leading to hidden decay. If left untreated, the damage can progress to the pulp, causing pain or infection. Visible defects or recurrent decay may require filling repair or full replacement to restore protection and prevent future problems.
How Does a Cavity Develop Under a Dental Filling?
A cavity that forms beneath or beside an existing filling is known as secondary or recurrent caries. Unlike a new cavity that appears on an untouched area of the tooth, this type of decay develops at the margin or underneath a filling—where the restoration meets the natural tooth surface.
This process begins when the seal between the filling and the tooth weakens or breaks down. Even tiny gaps can allow bacteria, plaque, and food particles to collect in hard-to-clean areas. As bacteria feed on sugars, they produce acids that gradually erode the surrounding tooth structure, especially where the seal has failed.
The acids penetrate deeper over time, compromising the integrity of both the filler and the tooth. The result is a hidden pocket of decay that continues to spread unnoticed beneath the restoration. Regular dental checkups and attention to changes in tooth sensitivity are essential for detecting these problems early.
Bacteria Enter the Tooth Through Gaps or Cracks
Over time, even well-placed fillings can develop tiny openings between it and the natural tooth, a process known as microleakage. These microscopic gaps or cracks can occur from normal wear, chewing forces, temperature changes from hot or cold foods, or slight shrinkage of the filling material, especially with composites. Once the gap widens beyond a very small threshold (around 50 micrometers), it becomes large enough for bacteria, saliva, and fluids to seep in.
In some cases, the material itself deteriorates or cracks due to long-term mechanical stress, grinding, or minor trauma. The adhesive layer that bonds the filling to the tooth may also weaken with age, creating additional entry points for bacteria. Once microbes find their way between the tooth and filling, they begin colonizing those hidden spaces, setting the stage for new decay to form underneath.
Sometimes the problem starts even earlier—during the initial placement of the filling. If all decayed tooth material wasn’t completely removed, or if the seal between it and tooth wasn’t perfect, bacteria can remain trapped inside or re-enter later. These imperfections act as starting points for decay to progress unseen beneath the restoration over time.
Acid-Producing Bacteria Begin to Decay the Tooth
Once bacteria enter small gaps or margins around a filling, they begin feeding on sugars and starches in the mouth. This triggers acid production that slowly breaks down the tooth from the inside out.
- Bacterial colonization: Decay-causing (cariogenic) bacteria settle along the filling’s edge or under it, feeding on sugars and producing acids such as lactic acid.
- Acid attack: These acids dissolve minerals in the tooth, starting with enamel and progressing into dentin.
- Demineralization and weakening: Repeated acid exposure removes calcium and phosphate, weakening the tooth structure. Without enough remineralization from saliva or fluoride, decay continues to spread beneath the filling.
Plaque and Food Particles Accumulate
Plaque naturally forms on teeth every day, but it becomes a problem when it builds up around fillings—especially if the edges have gaps, ledges, or rough surfaces. Over time, this buildup creates an environment where bacteria thrive and damage the tooth.
- Plaque formation: Dental plaque is a sticky biofilm made of bacteria, food particles, saliva, and bacterial byproducts. It tends to collect around imperfect filling margins, where cleaning is more difficult.
- Bacteria feeding on sugars: When sugary or starchy foods and drinks are consumed, bacteria in plaque metabolize them and produce acids that attack the tooth surface. Frequent snacking or sweet beverages increase these acid challenges.
- Disrupted protection balance: Normally, saliva and fluoride help neutralize acids and repair enamel. But when plaque remains and acid attacks occur often, the tooth’s natural defenses weaken allowing decay to take hold.
The Decay Continues to Spread if Left Untreated
Once decay begins beneath or around a filling, it doesn’t stop on its own—it continues to advance deeper into the tooth. When demineralization breaks through the enamel, the decay reaches the dentin, a softer and less mineralized layer. Because dentin is more vulnerable, the damage progresses more rapidly, often spreading under the filling floor or along its walls where it can remain hidden until it’s quite advanced.
As the decay spreads, it can form wall lesions or surface lesions that occur on nearby tooth surfaces. These lesions may start at or below the margin and gradually extend sideways or downward, weakening the surrounding tooth structure.
If left untreated, the decay can move close to the pulp, the inner part of the tooth containing nerves and blood vessels. At this stage, it may cause increased sensitivity, pain, or infection. In severe cases, root canal treatment might be required to save the tooth, and if the cavity grows too large, it can undermine the tooth’s remaining structure, leading to cracks or fractures.
The Filling May Need to Be Replaced
Over time, a dental filling can wear down, chip, or develop gaps that allow bacteria to enter. Visible defects such as cracks, rough or discolored edges, or margin openings are clear signs that a filling may need attention. In many cases, recurrent decay can also be detected through clinical examination, probing, or X-rays, prompting the need for repair or full replacement.
Sometimes, a localized defect can be corrected with a simple repair, where only the affected portion of the filling is replaced. Nevertheless, when decay is more extensive or the margins are compromised, a full replacement is usually necessary to restore function and prevent further damage.
When replacing it, the goal is to remove all decayed tissue, create a smooth, well-sealed margin, and select a restorative material that bonds effectively to the tooth. Preventing recurrence depends not only on the dentist’s technique but also on good oral hygiene, a balanced diet, and the use of fluoride treatments to strengthen enamel.
Key Takeaways
- Cavities can form under fillings: Known as secondary or recurrent caries, these cavities develop at the margin or underneath a filling when the seal between the filling and tooth breaks down.
- Microleakage allows bacteria entry: Tiny gaps or cracks caused by wear, chewing forces, thermal changes, or material shrinkage let bacteria, saliva, and food particles seep beneath the filling.
- Acid-producing bacteria cause decay: Once inside, bacteria feed on sugars and produce acids that dissolve minerals from enamel and dentin, weakening the tooth structure over time.
- Plaque buildup accelerates damage: Plaque tends to accumulate around uneven or rough filling edges. Frequent acid exposure from bacterial activity and sugary foods disrupts the balance between demineralization and natural repair.
- Decay spreads if untreated: Once it reaches dentin, decay advances quickly beneath the filling or along its walls. If it nears the pulp, pain, infection, or the need for root canal treatment may occur.
- Filling replacement may be necessary: Cracks, chips, margin gaps, or recurrent decay often require repair or full replacement. Proper sealing, removal of decay, and smooth margins are key to preventing future problems.
- Prevention depends on maintenance: Good oral hygiene, fluoride use, and regular dental checkups help detect early issues and protect both the filling and natural tooth from recurring decay.
Sources.
Askar, H., Krois, J., Göstemeyer, G., & Schwendicke, F. (2021). Secondary caries risk of different adhesive strategies and restorative materials in permanent teeth: Systematic review and network meta-analysis. Journal of dentistry, 104, 103541. https://doi.org/10.1016/j.jdent.2020.103541
InformedHealth.org [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. Overview: Tooth decay. [Updated 2023 Sep 5]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK279514/