If the cavity is small, fillings are an appropriate restorative option. By small, we mean that the old filling (if present) and decay must take up less than 50% of the tooth (above the gum line). If the cavity takes up more than 50% of the tooth, then a crown or cap is necessary. In other words, there must be enough teeth left to structurally support a filling. If there is not, then the top of the tooth needs to be replaced with a crown.
Fillings are commonly differentiated by their color, either silver (grayish) or white (called tooth-colored fillings). Silver fillings or amalgams are made up of an alloy comprised primarily of silver, tin, copper and mercury. Amalgams have been around for over 150 years are extremely durable and work extremely well. However, cosmetic concerns have resulted in these being phased out in favor of the more esthetically pleasing tooth-colored fillings.
Silver fillings also have a major disadvantage: They contain mercury, which is quite hazardous to the environment (because of this, some countries in Europe have banned silver fillings). However, for the vast majority of the population (>99%), silver fillings are considered to be safe in the mouth. The issue is more an environmental one: factories that process mercury generate waste that is extremely toxic to wildlife, especially birds.
Modern dental offices have therefore largely moved to tooth colored fillings and are doing fewer and fewer silver fillings. Tooth colored fillings are comprised of either composite resin or glass/resin ionomers. Composite resin fillings are more common since they can stand up to heavy chewing pressures and not break. Ionomers are better suited for non-load bearing situations—cavities between the teeth, for example.
Tooth colored fillings look great, but do have the disadvantage of costing slightly more. The white filling material usually costs more than amalgam and typically takes longer to place in the tooth (resulting in a higher fee from the dentist).
And be aware that some (not all) dental insurance companies view silver amalgam as “good enough” and only have one payment amount for a particular type of filling—regardless of whether it is silver or white. This results in the patient having to pay a slightly higher “out-of-pocket” for white fillings than for silver. If your dental insurance downgrades the fee for white fillings down to that for silver, be sure to voice your concerns to the person in human resources that buys your insurance.