Much controversy surrounds dental amalgam as a result of the Mercury content in the material. In short, study after study has been conducted on the possible harm to patients with amalgam fillings over decades, all of which have concluded that amalgam is safe. The reason is that once the filling is set, the mercury remains chemically bound to the silver, preventing leakage of the mercury out of the filling in a statistically significant amount.
What is Amalgam?
Amalgam, or “silver” fillings have long been a staple of restorative/operative dentistry. Amalgam is a combination of numerous metals, the greatest percentages of which are Mercury and Silver. The liquid mercury is mixed with the Silver/metal filler particles, which initiates the setting process. The material is condensed into the cavity preparation, compressing the filler particles together and expelling excess Mercury in between them, which is then removed. It is classified as spherical, lathe cute, or admix, each of which describes the shape of the filler particles and how they are produced. The filler particles of spherical amalgam are formed by “dripping” the metal in its liquid phase, forming a spherical droplet, which is then cooled to its solid form to incorporate in the mixture. Lathe cut fillers are formed when a lathe is used to grind a large amount of the metal to form the proper sized particles. Admix refers to amalgam consisting of a combination of lathe cut and spherical fillers.
How is an Amalgam filling placed?
When an amalgam filling is placed the capsules are vibrated to initiate the setting reaction. Liquid mercury is mixed with the silver/metal filler particles during this process. The material is placed in a viscous form and condensed into the cavity preparation. This condensation optimizes the structure of the amalgam filling as the condensing packs the filler particles close together, reducing the amount of mercury between each particle, causing the excess mercury to rise to the top of the filling, which is then removed. As it sets the filling is carved to restore form and function (appearance/tooth anatomy) of the tooth in question. Patients should not eat within one hour of placement of the fillings, after which the amalgam is sufficiently set to withstand chewing forces. However, the material does not completely set for approximately 24 hours so caution should be used.
When and why is Amalgam used?
Amalgam is typically used in the posterior/“back” region of the mouth to restore teeth typically used for chewing/grinding food. The benefits of the material are numerous. For example, the material has thermal coefficient and wear resistance properties similar to that of natural tooth structure. This means that amalgam expands and contracts similarly to natural tooth structure when exposed to hot/cold temperatures, such as ice water or coffee, preventing breakdown at the filling/tooth interface caused by the resulting stresses. Wear resistance refers to the material’s ability to withstand chewing forces without breaking down or wearing away. Other benefits include the corrosion of the material at the margins of the filling, which is where the filling meets the tooth structure. This prevents recurrent decay around and underneath the filling by sealing the margins, thereby reducing the leakage of saliva, bacteria, etc. down the walls of the restoration. Marginal corrosion, wear resistance, and thermal expansion contributes to the material’s longevity, often lasting 10+ years without need of replacement. Finally, amalgam has withstood the clinical test of time having been used and studied as a dental restorative material for centuries.