Fillings are the most common type of dental treatment, with about 175 million done each year in the United States. The dentist’s term for a filling is “restoration” because its purpose is to restore a tooth to its healthy shape, structure, and performance. The usual reason restoration is needed is tooth decay, the erosion of the hard enamel which in time results in caries (cavities). The treatment involves removing the diseased parts of the tooth and filling the resulting space with a restorative material replacing the part of the tooth lost to decay.
The practice of restorative dentistry appears to date back as far as 9,500 years ago, as evidenced by skeletal remains from that period found in Pakistan. A 6,500-year-old skeleton found in Italy had a molar with a beeswax filling. It’s unlikely that these ancient fillings were very effective.
The art and science of restorative dentistry made rapid progress during the 1800s, with the introduction of metal fillings early on and then, as the 20th century approached, a great leap forward with the development of filling material made from a mixture of four metals: mercury, tin, silver, mercury, and copper.
This mixture is widely used today. This is amalgam, one of the standard restorative materials in modern dentistry. The amalgam used today consists of about 50% elemental (liquid)mercury, which is combined with a powdered mix of tin, silver, and copper to produce the restorative material applied by the dentist.
After numbing the area around the affected tooth, the dentist uses a high-speed drill or a laser device to remove the decayed material around the cavity and form a space in which the amalgam filling can sit solidly.
The next step is mixing the amalgam. Nowadays, most manufacturers supply dental amalgam ingredients in a sealed capsule with two isolated compartments. The liquid mercury is in one compartment, the tin, silver, and copper powder in the other. A purpose-built machine breaks the membrane separating the two compartments and mixes all the ingredients together.
The amalgam is then ready for immediate application as a thick paste the dentist can press into the space shaped by grinding away the decay. The amalgam quickly hardens into a solid filling.
During the 1960s dentists introduced a new type of restorative material, a mixture of synthetic resins which became known as composite. The 1990s saw significant improvements in terms of bonding strength.
The composite filling procedure begins with removal of decay but then goes on to further prepare the tooth for application of the composite material. The surface area that’s going to be in contact with the composite filling is etched, or roughened a little, by applying an acidic gel for 15 seconds or more, then rinsing it off. The textured surface offers a better “grip” to the filling.
Some manufacturers have eliminated the need for this conditioning step by combining the etching with the bonding agent, the next material applied by the dentist to the entire surface area of the space to be filled. This thin layer is hardened with a special curing lamp and serves as the foundation for successive layers of composite material the dentist applies and cures until the space is filled and the overall form of the tooth is restored.
The dentist then uses polishing stones and the drill to carefully sculpt the filling so it more precisely conforms to the original shape of the healthy tooth. Special attention is given to molars so that the patient’s bite is natural and comfortable.
AMALGAM VS. COMPOSITE: PATIENT PERSPECTIVE
Composite filling materials and procedure are the newer and more “modern” dental technology but have not replaced the older amalgam alternative. Each approach has relative advantages and disadvantages, which patients and dentists evaluate in relation to the specifics of each case.
For many patients, the main issues are cost and cosmetics. Composite fillings cost more than amalgam, though sometimes dental insurance does cover them. Composite fillings are popularly known as “white” fillings, as opposed to “silver fillings” as amalgams are termed. Even when composites increase the patients’ out-of-pocket expenses some consider the cosmetic advantage well worth it. The color of a composite filling can be matched by the dentist to the surrounding tooth so that the filling is virtually invisible. Amalgam fillings are metallic and conspicuous against the surrounding enamel.
Durability is a practical consideration. In general, amalgam fillings appear in the research to be more durable than composite, but there’s a lot of variability depending on factors like the size, shape, and location of the fillings.
Safety concerns are a factor for some patients who are troubled by the presence of mercury in amalgam. Elemental mercury, liquid at room temperature, is unique in its ability to bind the particles of tin, silver, and copper into a mixture that’s easy for the dentist to work with and hardens to a strong and durable filling. Liquid mercury is not itself toxic. If swallowed, it passes through a healthy digestive system without being absorbed. The safety issue is related to tiny amounts of mercury vapor, a gas, which if inhaled enter the bloodstream.
The FDA estimates that about 1 billion amalgam fillings were put in between 1988 and 2008, and finds no clinical evidence of mercury poisoning in patients with these fillings. The American Dental Association Council on Scientific Affairs agrees, stating that “the scientific evidence supports the position that amalgam is a valuable, viable and safe choice for dental patients”. The FDA does not recommend replacement of sound amalgam fillings with other materials.
The scientific consensus notwithstanding, patients who feel uncomfortable with the idea of having mercury in their mouths have recourse to the composite option. Some concerns have been raised about the presence of BPA in composite filling materials. Here, again, the FDA and the American Dental Association agree that the evidence indicates this concern is hypothetical. BPA is approved by the FDA for use in manufacturing hard plastic bottles and widely-used packaging materials, and in fact, is not used in the manufacture of dental composite materials. Any trace amounts of BPA found in dental composite ingredients are there as a by-product of the chemical reactions involved in manufacture.
AMALGAM VS. COMPOSITE: DENTIST PERSPECTIVE
Dentists consider the size, shape, location, and the type of tooth in weighing the pros and cons of the two types of filling material.
Small cavities may better be addressed with composite, which can get a better “grip” and be less likely to fall out than amalgam fillings would be. Amalgam fillings require the dentist to craft a space in which an amalgam filling will be stable, which may be limited by the amount and shape of the surrounding healthy tooth. Composite fillings bond to the tooth and so work well in smaller spaces of any shape.
Grinding teeth, like molars, may encourage a preference for amalgam, which is better able to withstand the intense pressures there.
The composite filling procedure is more complex, and success depends more on the skill of the dentist and the cooperation of the patient. It is critical to keep the tooth completely dry before and during the application of bonding agents and resin. On the other hand, the dentist has more control during a composite procedure. Amalgam starts to set as soon as it’s mixed, on its own schedule. Composite cures only when the dentist irradiates it with the lamp.
Amalgam and composite restorative materials are both safe and effective treatment options. Evaluation of the pros and cons in any given case may be simple or may be complex. Patients and dentists have preferences and constraints to consider but readily reach consensus. The choice is not a burden, it’s a benefit of the continuing advances in dentistry.