A dental crown is a custom-made cap placed over a damaged or weakened tooth to restore its original shape, size, strength, and appearance. It entirely covers the visible part of the tooth above the gum line, functioning as the new outer surface. Crowns are fixed in place using specialized dental cement, creating a strong adhesive bond between the restoration and the prepared natural tooth structure. Despite this secure placement, a crown can come off because the bond is subject to degradation over time. The structural integrity of the cement and the health of the underlying tooth determine the crown’s long-term security.
Common Reasons Crowns Detach
One of the most frequent causes of detachment is the gradual breakdown or washout of the luting cement used to secure the crown. Dental cements are designed to resist the constant moisture, temperature changes, and chemical environment of the mouth, but they are not impervious to degradation over time. Over many years, the cement at the crown margins can slowly dissolve due to oral fluids, causing the crown to lose its tight seal. This loss of marginal integrity and adhesion means that even normal chewing or biting forces can eventually cause the restoration to dislodge.
New decay forming underneath the crown margin is another leading cause of failure, representing a structural issue rather than a purely adhesive one. When oral bacteria penetrate the crown’s seal, they create decay on the underlying prepared tooth structure, leading to the compromise of the remaining support. As the decay progresses, the prepared tooth shrinks and changes its geometry, meaning the rigid crown no longer fits snugly against the remaining dental tissue. This change in underlying morphology removes the necessary frictional and mechanical retention designed to hold the crown securely in place.
Sometimes, the original crown may detach due to issues related to the initial tooth preparation or the seating process itself. If the underlying tooth was not shaped with sufficient wall height or a minimally aggressive taper, the crown may inherently lack adequate mechanical retention to resist dislodging forces. Similarly, if the cement was contaminated by saliva or blood during the initial bonding procedure, it may never have achieved its full chemical bonding strength. A crown that was not fully seated on the first attempt, leaving an open margin, is also significantly more prone to premature failure and subsequent detachment.
Physical trauma or excessive stress placed on the restoration can lead to an abrupt and unexpected detachment. Biting down on hard or resistant objects, such as ice, un-popped popcorn kernels, or hard candies, can exert a pulling force that exceeds the cement’s tensile strength. Patients who experience bruxism, or habitual teeth grinding, apply constant, heavy, non-axial forces that cause fatigue and weakening of the adhesive bond over extended periods. These intense, repetitive physical stresses introduce microscopic fractures in the cement that eventually culminate in a complete failure of the bond.
Immediate Steps When a Crown Comes Loose
The moment a crown feels loose or comes entirely off, the first action should be to safely retrieve the restoration from the mouth to prevent accidental swallowing. After retrieval, gently clean the inside of the crown and the underlying prepared tooth structure with water to remove any debris or old cement. Inspect the crown to ensure it is intact and to see if a piece of the original tooth may have broken off with it.
Immediately contact your dental office to explain the situation and schedule an emergency appointment. The underlying tooth tissue is now exposed and highly sensitive to temperature changes and pressure, necessitating prompt professional attention. Leaving the prepared tooth exposed increases the risk of further decay, fracture, or irritation to the pulp tissue, making the eventual repair more complicated.
While waiting for the dental appointment, temporary measures can be taken to protect the exposed tooth and relieve sensitivity. Over-the-counter dental cement, available at most pharmacies, can be placed inside the crown before gently seating it back onto the tooth. If commercial cement is unavailable, a thick layer of petroleum jelly or even toothpaste can act as a temporary, non-damaging adhesive to hold the crown in place for a short time.
When attempting to temporarily re-seat the crown, it is imperative to ensure the crown is facing the correct direction and seated fully without forcing it. Never use household adhesives like super glue or model glue, as these materials are toxic, can permanently damage the crown or surrounding tissue, and will prevent successful professional re-cementation. Once the crown is temporarily secured, avoid chewing on that side of the mouth until you can be seen by the dentist.
Ensuring Crown Longevity
Maintaining specific dietary habits can significantly reduce the risk of mechanical failure or detachment. Avoid biting directly into extremely hard items, such as hard candies or ice cubes, which can cause the crown material or the underlying tooth to fracture. Sticky foods like taffy or caramels should also be avoided because they exert a strong pulling force that compromises the cement bond.
Diligent oral hygiene practices are important for ensuring the long-term success of the restoration. Brushing twice daily and flossing around the margins of the crown helps prevent plaque accumulation and subsequent decay at the tooth-crown interface. Preventing decay at this margin eliminates the primary biological reason for long-term crown failure and detachment.
Regular dental check-ups allow the dentist to monitor the crown’s margins and the surrounding gum tissue for any signs of cement washout or leakage. Early detection of a compromised seal allows for prompt intervention before the crown fully detaches or the underlying tooth is damaged. These appointments are also important for addressing parafunctional habits, such as bruxism.
If a patient clenches or grinds their teeth, the dentist may recommend a custom-fitted night guard to absorb the intense nocturnal forces. This protective appliance shields the crown and its cement bond from excessive lateral stress that can otherwise lead to premature adhesive fatigue. Minimizing these destructive forces is an effective strategy for maximizing the restoration’s lifespan.