A dental filling is a restorative material used to repair a tooth damaged by decay, restoring its original shape and function. While these restorations are designed for durability, they are not intended to last forever. The sudden onset of pain around an old filling signals that the restoration or the underlying tooth has developed a problem. This discomfort usually points to a specific issue requiring professional evaluation, ranging from a simple mechanical failure to a deep biological concern. A comprehensive check-up, often involving X-rays, is necessary to diagnose and treat the source of the discomfort.
When the Filling or Tooth Structure Fractures
Years of constant pressure from chewing (mastication) and the daily thermal cycling of hot and cold foods place immense stress on dental restorations. This mechanical fatigue can eventually lead to the physical breakdown of the filling material, especially with older generations of amalgam or composite resin. A fracture may appear as a small chip or a larger break, exposing the underlying tooth structure.
A more concerning mechanical failure is the fracture of the surrounding tooth structure, often seen in teeth with large fillings. The filling material, particularly stiff amalgam, can act as a wedge, transferring internal stresses and eventually causing a cusp fracture. A cusp is a pointed projection on the chewing surface; when it cracks, pain often occurs specifically when biting down and quickly releasing the pressure.
Even a hairline crack or a loose margin, where the filling meets the tooth, constitutes a structural failure that can cause discomfort. This loss of a tight seal allows for micro-leakage, where oral fluids and bacteria penetrate the space between the tooth and the restoration. This micro-leakage can cause sensitivity to temperature and pressure by allowing irritants direct access to the underlying dentin.
Recurrent Decay and Marginal Breakdown
The most frequent biological reason for pain is the development of secondary or recurrent caries—a new area of decay forming beneath or around the restoration. This process begins with marginal breakdown, which is the formation of a microscopic gap at the interface between the filling and the natural tooth structure. Over time, the bond weakens due to wear, temperature fluctuations, and biting forces.
Once the marginal seal is compromised, bacteria and plaque colonize the exposed area and migrate into the tooth. These microbes produce acid that demineralizes the dentin, the softer layer beneath the enamel, leading to a cavity hidden beneath the existing filling. The decay can progress silently, often going undetected until it is deep enough to cause noticeable pain or sensitivity.
Factors such as poor oral hygiene, a diet high in fermentable carbohydrates, and reduced salivary flow accelerate this failure. Saliva normally helps neutralize acid and wash away food debris. If these protective mechanisms are insufficient, marginal breakdown progresses quickly into deep recurrent decay. Older restorations may also degrade, making the tooth more susceptible to bacterial invasion.
Deep Pain From Nerve Inflammation
When decay or a fracture progresses deep into the tooth, it can irritate the dental pulp (the soft tissue containing the nerve and blood vessels), leading to pulpitis. This inflammation often causes severe, persistent pain described as a constant ache or throbbing. Pulpitis can be reversible (mild nerve irritation) or irreversible (severe, lasting damage to the pulp tissue).
In reversible pulpitis, the pain is usually sharp but brief, occurring only when the tooth is exposed to a stimulus like cold air or sweet foods, and quickly subsiding. Irreversible pulpitis is characterized by lingering pain that persists for a minute or more after exposure to hot or cold, or spontaneous, unprovoked pain, often waking the person at night. This throbbing response signals that the inflammation is too severe for the pulp to heal.
Pain can sometimes manifest years after a deep filling procedure due to delayed onset nerve damage. Even if the initial procedure was successful, the filling’s proximity to the pulp chamber may have caused chronic, low-grade trauma to the nerve. Over time, this chronic irritation, combined with factors like teeth grinding (bruxism) or small recurrent decay, culminates in irreversible pulpitis, often necessitating root canal therapy.
Pain Originating Outside the Filled Tooth
Not all pain felt near an old filling originates from the filled tooth; sometimes, the discomfort is referred from a different source. Referred pain occurs because the nerve pathways transmitting sensation from the teeth, jaw, and surrounding structures (particularly the trigeminal nerve) converge as they travel toward the brain. This convergence makes it difficult to pinpoint the source of the signal.
An infection or inflammation in the maxillary sinuses, located directly above the roots of the upper back teeth, can mimic a toothache. Similarly, temporomandibular joint (TMJ) disorders or chronic teeth grinding can cause muscle tension that radiates into the jaw and teeth, leading to the mistaken belief that the pain originates from an old restoration.
Another common cause of localized sensitivity is gum recession, which exposes the root surface near the filling margin. Unlike the crown, the root surface is covered by cementum, which is easily worn away, exposing the underlying dentin tubules. This exposure causes sharp sensitivity to cold or touch at the gum line, separate from any filling failure. A professional examination and diagnostic tools like X-rays are necessary to identify the true cause and determine appropriate treatment.