In 1836 a young dentist in nearby Winchester Illinois, known to many dentist as the father of Modern dentistry saw a need for a cheap, quick to make alternative to expensive gold cast inlays, onlays and gold foil fillings. He formulated the basic mixture of Silver, mercury, tin and later copper to control the chemical expansion of the filling. It was easy to use, cheap, quick to set and worked well in the moist oral environment. This fact makes it the best material when the decay is below the gumline when it is not possible to keep the preparation dry to place a resin composite.
Resin composite fillings are made of ceramic glass and plastic resin compounds. The blending of the resin and glass can mimic the tooth and are the closest we have when it comes to matching the natural tooth and is not only used to fill cavities but to repair mishapen and chipped teeth making them look as natural as possible. One of the biggest advantages is the fact that resin fillings actually bond to the tooth giving the dentist the ability to remove less tooth structure and forming a stronger restoration.
Dental amalgam or sometimes referred to as Silver fillings have some inherent shortcomings. The first being that they do not bond to the tooth like a resin composite or tooth colored filling. Therefore the dentist has to create undercuts to make the amalgam retentive. Over time the tooth becomes more brittle and instead of flexing it cracks and breaks which leads to the patients needing buildups and crowns to get the tooth back to its full shape and function. Even in some instances the tooth crack so severely that the nerve is effected requiring a root canal or an extraction. There is concern over whether amalgam is safe since it contains mercury. Both the American Dental Association and The Food and Drug Administration have deemed amalgam safe for use in the mouth. The amount of mercury that leeches out of a filling as it wears is minimal. We consume much more mercury consuming fish yearly. Taking out amalgam fillings just to replace them exposes the patient to many time more mercury than just leaving them in place.
Resin composites or white fillings also have their share or shortcomings too. Originally they could not tolerate high pressures and heavy wear forces of the posterior teeth. Now they have greatly improved but still wear quicker than amalgam and the natural enamel. Also cost can be a factor in resin composite too and sometime insurance will not pay the additional cost of the white filling and patient ends up paying the difference