A dental filling is a restorative treatment used to repair and rebuild tooth structure damaged by decay, fracture, or wear. The procedure involves carefully removing the compromised portion of the tooth and then placing a material into the prepared space to restore the tooth’s function, shape, and integrity. Since teeth endure high forces and constant exposure to a moist, bacteria-filled environment, the material chosen for the restoration must be durable and biologically compatible. Modern dentistry offers a variety of filling materials, each possessing unique physical and chemical properties that make it suitable for different clinical situations within the mouth.
Metal-Based Fillings
Metal-based options include two of the oldest and most extensively studied materials: silver amalgam and cast gold. Silver amalgam is a mixture of metals, primarily consisting of powdered silver, tin, and copper, bound together by approximately 50% elemental mercury by weight. This combination creates a strong, inexpensive, and highly durable material used successfully for over 150 years, particularly in the non-visible back teeth where chewing forces are highest.
The controversy surrounding amalgam centers on the mercury component, a known neurotoxin. While the mercury is chemically bound within the filling, minute amounts of mercury vapor can be released during placement, removal, or heavy chewing. Major health organizations acknowledge this release but maintain that the levels are too low to pose a health risk for most people. Alternatives may be recommended for pregnant women and children.
Gold fillings, typically cast gold inlays or onlays, represent the most durable and long-lasting restoration available, often lasting 15 to 30 years or more. The material is an alloy of gold mixed with other noble metals like silver, copper, and platinum to increase hardness. Gold is highly biocompatible, does not corrode, and exhibits thermal expansion properties similar to tooth structure, which helps maintain a tight seal. Drawbacks include the high cost and the requirement for at least two appointments, as the restoration must be custom-fabricated in a dental laboratory before being cemented.
Aesthetic and Direct Bonding Fillings
Composite resin is the most common tooth-colored filling material, designed to blend seamlessly with the natural tooth structure. This material is a mixture of a plastic matrix and fine inorganic filler particles such as glass or quartz. The resin is applied directly into the prepared cavity in layers and then hardened with a high-intensity curing light, a process known as direct placement.
The material adheres to the tooth through a chemical bonding system that requires an adhesive agent after the tooth surface is prepared with an acid etch. This bonding creates a strong seal but demands a meticulously dry field during placement, making the procedure sensitive to technique and moisture contamination. Composite resin fillings are less durable and more prone to staining and wear than metal options, but they are the preferred choice for visible areas due to their superior aesthetics.
Porcelain or ceramic restorations, often fabricated as inlays or onlays, are used for larger restorations requiring a natural appearance. Unlike composite resin, these are indirect restorations, custom-made in a dental laboratory from a strong, stain-resistant ceramic material. The finished restoration is cemented into the tooth during a second appointment, providing a much stronger and longer-lasting result than a direct composite filling. These restorations are generally more costly than direct fillings but provide superior aesthetics and strength, often serving as an alternative to a full crown.
Specialized Materials for Unique Needs
Glass Ionomer Cement (GIC) and Resin Modified Glass Ionomer (RMGI) materials offer unique therapeutic advantages. GIC is formed from a reaction between a glass powder and a liquid, and it adheres chemically to the calcium ions in the tooth structure through an ion-exchange process. This chemical adhesion allows for minimal tooth preparation.
The primary benefit of GIC is its ability to release fluoride ions in a sustained manner, which helps remineralize the surrounding tooth structure and resist new decay. This property makes GIC and its hybrid, RMGI, a preferred choice for high-caries-risk patients and in pediatric dentistry. RMGI offers improved strength and wear resistance over conventional GIC, but both materials are weaker than composite or amalgam and are limited to small, low-stress areas or temporary restorations.
Key Factors Guiding Material Selection
The choice of filling material is guided by several factors related to the tooth, the patient, and the materials themselves. The location and size of the decay are primary considerations. Back molars enduring heavy chewing forces often require the robust strength of gold, amalgam, or an indirect ceramic restoration. Smaller cavities in highly visible front teeth are restored with aesthetic materials like composite resin, where appearance is prioritized over maximum durability.
Larger cavities often necessitate the superior structural support provided by indirect restorations like inlays, onlays, or cast gold. The patient’s risk for future decay may steer the decision toward GIC or RMGI due to their continuous fluoride release. Finally, cost and insurance coverage play a role, with amalgam being the least expensive option and gold or indirect ceramic restorations being the most costly.