A cavity, or dental caries, represents a breakdown of the tooth structure caused by acid-producing bacteria that erode the enamel and underlying dentin. While small to moderate cavities are routinely repaired with a direct filling, extensive decay presents a complex structural challenge. When the volume of lost tooth structure is significant, simple filling materials like composite resin or amalgam lack the necessary durability to withstand the forces of chewing and grinding. Fortunately, restorative dentistry offers several alternatives beyond a standard filling to restore and protect a severely damaged tooth.
When Standard Fillings Are Not Viable
A conventional filling is placed directly into the prepared tooth cavity and hardens in place, but this material does not inherently strengthen the surrounding natural tooth structure. If decay has compromised a substantial portion of the tooth, typically exceeding one-third of the chewing surface width, the remaining walls become structurally weak. Placing a large filling in this compromised tooth can create a wedging effect, which increases the risk of the surrounding tooth walls fracturing under normal biting pressure. Therefore, the dentist must assess the remaining healthy tooth structure, particularly the thickness of the cusps, before determining if a direct filling is a suitable long-term solution.
Partial Coverage Restorations
When the decay is too extensive for a simple filling but does not require the complete coverage of a crown, a partial coverage restoration offers a conservative and structurally sound compromise. These restorations, known as inlays and onlays, are fabricated outside of the mouth in a dental laboratory or sometimes chairside using Computer-Aided Design and Manufacturing (CAD/CAM) technology. Because they are milled or cast as a single, solid piece, they offer superior resistance to fracture compared to a large, directly placed filling.
An inlay restores the chewing surface between the cusps, similar to a traditional filling, but is precisely bonded for greater strength. Conversely, an onlay, sometimes referred to as a partial crown, extends over and covers one or more of the tooth’s cusps. This cuspal coverage holds the weak tooth walls together and prevents them from flexing outward and breaking under pressure. Common materials include ceramics, such as color-matched porcelain for aesthetics, or gold alloy, which provides exceptional durability for back teeth. The fabrication process typically requires two appointments: one for preparation and impression-taking, and the second for final bonding.
Full Coverage Restorations
For teeth with the most extensive loss of structure, widespread cracking, or severe existing fractures, a dental crown is the definitive treatment. It encases the entire visible portion of the tooth above the gum line, acting as a full-coverage helmet that distributes chewing forces evenly to prevent future breakage. The procedure involves shaping the existing tooth, often requiring the removal of 1 to 2 millimeters of material from all surfaces to create enough space for the crown material to be thick and durable.
Crowns are available in various materials, each offering a different balance of strength, aesthetics, and required tooth reduction. Full ceramic crowns, especially those made from high-strength zirconia, are favored for their natural appearance and biocompatibility, offering an excellent solution for both front and back teeth. Porcelain-Fused-to-Metal (PFM) crowns use a metal alloy base for strength, which is then veneered with porcelain, but they require significant tooth reduction and can sometimes show a dark line at the gum margin. Gold alloy crowns, while not aesthetic, require the least amount of tooth reduction and are highly resistant to wear, making them a long-lasting choice for molars, especially in patients who grind their teeth heavily.
When Decay Reaches the Tooth Pulp
When a cavity is so large and deep that the bacterial infection penetrates the dentin and reaches the pulp—the soft tissue containing the tooth’s nerve and blood vessels—the treatment shifts to endodontic therapy. This scenario, often indicated by spontaneous or lingering pain, means the pulp tissue is irreversibly inflamed or infected and must be removed to save the tooth from extraction. The initial step is a root canal treatment, which involves cleaning out the infected pulp and sealing the internal root canals with a rubber-like material.
This endodontic process, while saving the tooth, can further compromise its structural integrity due to the loss of internal tissue and the access opening required for the procedure. Therefore, after the root canal therapy is complete, the tooth requires a definitive restoration to protect it from fracture and seal out bacteria. For posterior teeth that bear heavy chewing loads, a full-coverage crown is almost always necessary to reinforce the weakened tooth structure and ensure its long-term survival.