The choice between repairing a damaged tooth with a filling or a crown depends entirely on the extent of the damage to the tooth’s structure. The decision hinges on how much healthy material remains to bear the forces of chewing. A restoration must seal out decay and provide necessary reinforcement to prevent future fracture. Understanding the functional differences between these treatments is key to making the best long-term choice.
Understanding Direct and Full Coverage Restorations
A dental filling is a direct restoration, meaning the material is placed and hardened immediately into the prepared cavity during a single appointment. The dentist removes the decayed or damaged tissue and builds up the lost tooth structure using materials like composite resin or amalgam. Direct restorations are designed to replace a small, localized section of the tooth lost to decay.
A dental crown is a full coverage restoration that completely encases the entire visible part of the tooth above the gum line. Custom-fabricated in a dental laboratory or milling unit, the crown acts like a protective cap, restoring the tooth’s original shape and function. The fundamental difference is protection: a filling supports a small area, while a crown holds the entire weakened tooth together, distributing chewing forces across its surface.
When a Filling is the Appropriate Choice
A filling is the preferred treatment when tooth decay is minimal and localized, typically a small or medium-sized cavity. The damage must not extend to areas that handle the heaviest biting pressure. This treatment is best suited when decay affects only the chewing surface or a small portion of the side surfaces.
The tooth’s cusps, the points on the biting surface, must remain intact and strong enough to withstand chewing forces. If the cavity is shallow and affects less than one-third of the tooth’s width, a direct restoration is sufficient. In these cases, the overall structural integrity of the tooth is not compromised, and a filling successfully seals the area to prevent further bacterial invasion.
Indicators That a Crown is Necessary
A crown becomes the standard of care when the tooth has suffered a significant structural compromise that a filling cannot support. One of the most common indicators is extensive decay involving multiple surfaces, or when the cavity is so large that more than half of the tooth’s original structure is lost. Placing a filling into such a large defect leaves the remaining thin walls highly susceptible to fracturing under chewing pressure.
A tooth that has undergone root canal therapy almost always requires a crown because the procedure removes the inner pulp, which slightly dehydrates the tooth and makes it brittle. Without the complete encasement of a crown, this tooth is at high risk of a catastrophic fracture down to the root. Furthermore, any tooth with a significant crack or fracture extending deep into the dentin structure needs the hoop strength provided by a full crown to keep the segments from separating. Large, failing fillings that occupy a vast portion of the tooth also signal the need for a crown, preventing irreparable structural failure.
Indirect Restoration Options
Between a standard filling and a full crown, a dentist may recommend an indirect restoration, specifically an inlay or an onlay. These restorations are fabricated outside the mouth, typically from porcelain or composite resin, and then cemented into place. They offer a balance between the conservativeness of a filling and the strength of a crown. This approach is beneficial when damage is too extensive for a direct filling but not severe enough to warrant shaving down the entire tooth for a full crown.
An inlay is used when damage is limited to the top surface, fitting neatly within the tooth cusps. An onlay is a more extensive restoration, sometimes called a partial crown, because it extends to cover and protect one or more cusps. By covering vulnerable cusps, the onlay provides superior reinforcement against fracture compared to a large filling, while preserving more healthy tooth structure than a traditional crown.