Silver fillings, formally known as dental amalgam, have been a common restorative material for over 150 years. This long history is due to their strength and durability in repairing teeth damaged by decay. The question of when a silver filling should be replaced is a frequent topic of discussion, often involving a conflict between structural integrity and patient concern. Ultimately, the decision to replace a filling involves weighing clinical necessity against personal preference and the potential risks of the procedure.
Understanding Dental Amalgam
Dental amalgam is a metallic mixture composed of approximately 50% elemental mercury, which is combined with a powdered alloy of silver, tin, and copper. The mercury acts as a binder, allowing the mixture to be pliable for placement before it hardens into a strong, wear-resistant restoration. Amalgam’s primary benefits include its high resistance to the forces of chewing and its cost-effectiveness compared to other materials, making it a reliable option for posterior teeth.
The durability of amalgam is one of its most notable characteristics, with an average lifespan ranging from 10 to 15 years, and often longer in favorable conditions. This longevity results from its capacity to withstand heavy occlusal forces, especially in molars.
Criteria for Medically Necessary Replacement
The primary reason a dentist recommends replacing an amalgam filling is based on demonstrable structural or pathological failure. One of the most common issues is recurrent decay, also called secondary caries, which occurs when bacteria infiltrate the space between the filling and the tooth structure. This new decay weakens the tooth from within, often necessitating the removal of the old filling to eliminate the infection.
Another frequent failure involves marginal breakdown, where a gap forms at the junction between the filling and the surrounding tooth. This gap allows for microleakage of oral fluids and bacteria. Fractures of the restoration itself, or of the adjacent tooth structure, are also definitive indicators for replacement.
Large amalgam restorations are particularly susceptible to fracture, as the material does not bond to the tooth like modern composites do, which can weaken the tooth cusp. A visible crack in the filling, a fracture in the surrounding enamel, or a loss of anatomical form that compromises chewing function all qualify as clinical reasons for replacement. Replacement is a necessary medical intervention to prevent infection, tooth loss, or the need for more complex treatment like a crown or root canal.
Safety Concerns and Elective Removal
Patient concerns about the mercury content drive many inquiries regarding elective replacement, even for structurally sound fillings. Dental amalgam does release minute amounts of elemental mercury vapor, a process that can be slightly increased by actions like chewing or teeth grinding. However, for the general population, the majority of evidence indicates that the exposure level from amalgam does not lead to harmful health effects.
The Food and Drug Administration (FDA) maintains that amalgam is safe for most people, but they recommend that certain high-risk groups avoid receiving new amalgam fillings. These groups include pregnant women, nursing mothers, children, people with neurological diseases, and those with impaired kidney function. For those with existing, intact amalgam fillings, the FDA does not recommend removal unless it is medically necessary, such as in cases of a documented mercury allergy.
Elective removal, replacing a filling for aesthetic preference or health anxiety, carries its own set of risks. The drilling process required for removal can temporarily increase the patient’s exposure to mercury vapor, necessitating the use of safety protocols. Furthermore, removing an intact filling always results in the loss of some healthy tooth structure. Therefore, a balanced discussion with a dental professional is important to weigh the potential, low-level risk of a sound amalgam against the immediate risks of the removal procedure.
Modern Alternatives to Amalgam
Several modern materials are available when replacing a silver filling or choosing a new restoration. Composite resin, often referred to as a tooth-colored filling, is a popular alternative composed of a plastic resin and fine glass particles. Composite resins offer excellent aesthetics because they can be matched to the natural tooth color, but they may be less durable than amalgam, especially in large restorations subject to heavy chewing forces.
Glass ionomer cement is another option, made from a mixture of acrylic and a specific type of glass. This material is particularly valued because it releases fluoride, which may help protect the tooth from further decay. Glass ionomers are less durable and are often reserved for smaller, non-stress-bearing restorations or as temporary solutions.
For cases requiring maximum strength and longevity, porcelain or ceramic inlays and onlays are used. These restorations are custom-made in a dental laboratory and then bonded to the tooth, offering both superior aesthetics and a durability that can rival or exceed amalgam. However, ceramic materials are generally more expensive and require more than one dental visit for placement.