A dental crown is a custom-made cap designed to restore the strength, shape, and function of a damaged tooth. Although it acts as a protective shield, the underlying tooth structure remains susceptible to issues that cause discomfort. Persistent pain under a crown indicates a deeper problem requiring prompt professional attention. Any lingering ache or sharp sensitivity warrants an immediate dental examination, as this is not normal wear and tear. Understanding the source of the pain is the first step toward preserving the tooth.
Internal Causes: Decay and Pulp Infection
One of the most frequent sources of pain under a crown is recurrent decay, often starting undetected at the crown’s margin. This process begins when the seal between the crown and the tooth fails, creating a microscopic gap where bacteria and food debris accumulate. Since a crown covers the tooth, this decay can progress significantly before any visual signs become apparent. As the decay deepens, it erodes the remaining dentin layer, moving closer to the tooth’s innermost soft tissue.
Once bacteria reach the dental pulp, which contains the nerves and blood vessels, the tissue becomes inflamed (pulpitis). Early pulpitis may present as sharp, temporary sensitivity to cold temperatures that lingers for a few seconds before dissipating. If the bacterial invasion continues, the pulp becomes irreversibly inflamed or necrotic, meaning the nerve tissue dies. This stage often manifests as a persistent, throbbing ache or a heightened sensitivity to heat that lasts long after the stimulus is removed.
A severe, untreated infection can eventually lead to a dental abscess, a pocket of pus that forms at the tip of the tooth’s root. An abscess can cause swelling in the gums or face and may produce a foul taste in the mouth due to pus discharge. This deep infection often results in constant pressure that does not respond well to over-the-counter pain medication. A root canal procedure is necessary at this stage to remove the infected tissue and save the tooth from extraction.
Structural Issues: Cracks and Fractures
Pain can also originate from mechanical failure within the tooth. The tooth structure beneath the crown, particularly if it was already weakened, can develop a fracture or a vertical crack. Excessive biting force, often from teeth grinding (bruxism) or biting down on hard objects, can initiate these breaks. Unlike decay, which produces a dull ache, a structural issue often causes a sharp, sudden jolt of pain.
This characteristic discomfort is often described as “cracked tooth syndrome,” where pain occurs specifically when releasing biting pressure. When the crack opens upon biting, it allows fluid movement that irritates the underlying dentin, causing sharp pain when the pressure is released. If a crack extends vertically down the root, it creates a direct pathway for oral bacteria to infect the surrounding bone and ligament. A vertical root fracture requires extraction.
External Factors: Crown Fit and Gum Irritation
Issues related to the crown’s placement and its interaction with the surrounding tissues can also be a source of pain. An improperly fitted crown that sits slightly too high can interfere with the bite alignment, causing discomfort and soreness every time the jaws close. This uneven pressure can strain the tooth and jaw joint, sometimes leading to generalized headaches or tenderness in the chewing muscles. A precise fit is necessary because any tiny gap at the crown margin allows for the leakage of oral fluids and bacteria.
The cement holding the crown in place can eventually wash out, even if the crown fit was initially correct. This cement washout compromises the marginal seal, leading to sensitivity to cold or sugary foods as the exposed dentin responds to stimuli. While this condition does not immediately cause deep decay, it creates an ideal environment for bacteria to establish decay over time. Poor oral hygiene around the crown can also lead to localized gum irritation (gingivitis), causing the gums to become red, swollen, and tender.
If the crown margin irritates the gums for an extended period, it can contribute to periodontitis. This inflammation and infection of the supporting gum and bone tissue lead to gum recession and bone loss around the tooth’s root. Symptoms include chronic gum soreness, bleeding when flossing, and sometimes an increased sensation of movement in the crowned tooth. These external factors are often treatable without removing the crown if caught early, but they must be addressed to prevent decay or bone damage.
What to Expect at the Dentist and Treatment Paths
When presenting with pain under a crown, the dentist will begin the diagnostic process with a thorough clinical examination and X-rays. Radiographs are essential for visualizing the area beneath the crown and the root tip, revealing signs of decay, bone loss, or abscess formation. The dentist will also use a specialized instrument to gently test the gums around the crown for pockets, indicating periodontal disease.
Further tests are used to assess the health of the dental pulp, including thermal testing with a cold stimulus to check the nerve’s response. A biting test, often using a special device, helps isolate a structural issue by pinpointing sharp pain when pressure is applied and released. Once the cause is identified, the treatment path is tailored to the specific problem.
If the diagnosis reveals decay that has reached the pulp, the tooth will require root canal therapy to remove the infected nerve tissue and disinfect the interior. In cases of structural damage, a minor crack may be repaired with bonding or a new crown, but a severe vertical fracture necessitates extraction. Issues related to crown fit can be resolved through a simple adjustment to the biting surface or, if the seal is compromised, removal and replacement of the crown. Timely intervention is necessary, as delaying treatment increases the risk of losing the tooth entirely.