The purpose of Fillings or Inlays

Despite the aforementioned hardness of tooth enamel, it is still susceptible to tooth decay.  A tooth will decay when certain BACTERIA that reside in plaque metabolize simple SUGARS.  The metabolic by-product is ACID and that is what dissolves the enamel.  Once the acid has penetrated the enamel layer, the softer dentin layer is exposed and easily accessible for the bacteria.  Since dentin is much softer than enamel, it will decay at a faster rate.

So, the formula for decay is:

Simple Sugars  +  Bacteria  =  Acid  »  Decay

If any of the above three variables is eliminated, there will never be any decay.  It is usually easiest to eliminate the bacteria through regular brushing and flossing.

Rates of tooth decay (cavities) have been decreasing in the U.S.  The main reasons for this decline are the use of fluoride, and dental sealants in children, as well as improvements in access to dental care.  However, cavities remain an important public health problem.

Fillings or inlays are our replacement entities for the "voids" created, after the decay has been removed.  Fillings are typically made out of amalgam or composite.  Amalgam fillings are being more and more replaced by composites or ceramic inlays.  For more info on amalgams or "silver" fillings, please read the "Mercury Issue" below.  The two images below show how and old amalgam filling can be esthetically restored with composite.

An inlay resembles a filling in that it fills the space remaining after the decayed portion of a tooth has been removed. The difference is that an inlay is shaped outside the patient's mouth (usually by a laboratory technician) and then cemented into place. This, of course will require at least two appointments, however technological advances are being made in the CAD/CAM arena, that will soon allow us to cement inlays in the same appointment.  After the decay is removed and the cavity walls are shaped, the dentist takes an impression.  The laboratory technician will then create a stone copy of the prepared tooth.  He will then utilize this "copy" of your prepared tooth to make either a ceramic-type (tooth colored) or gold inlay.  Once the inlay is finished, the dentist will seal it into the tooth with dental cement or bonding agent.  Below is an image of typical gold inlays.

As we have casually mentioned above, there are generally two types of inlays available.  Gold Inlays and Ceramic-Type Inlays.  Gold Inlays have always been the "Gold Standard" against which all other inlay materials are compared against, when it comes so durability and strength.  Their tensile and compressive strength is so far unmatched, however, the do pose an esthetic challenge for many patients.  Gold can have a very shiny appearance, when polished and this can "overpower" the visual harmony of a great set of white teeth.  Many consider gold to be an excellent choice for upper molars, where visibility is not as much a factor.

If the emphasis is on a more esthetic appearance, the ceramic-type inlays may be the restoration of choice.  Durability and strength are not as good as gold, however, the esthetic advantage often outweighs the physical properties.  Below is a good example of how well a ceramic-type inlay can blend into the natural color of a tooth.

The "Mercury Issue"

In the last decade there have been many concerns about amalgam fillings because they contain mercury.  A small amount of mercury vapor is continually released into the mouth from amalgams fillings (Mackert and Berglund, 1997).  Mercury vapor released from amalgam fillings can be inhaled and absorbed into the body.  Chewing, drinking hot liquids, brushing, and grinding teeth can increase how much mercury vapor is released from amalgam fillings.  In addition to mercury vapor released from amalgams, small pieces of amalgam can break off from fillings and be swallowed.  However, mercury in amalgam particles is not easily absorbed into the body when ingested. 

It is well known that mercury vapor can cause health problems.  The extent to which a person will have health problems will depend on how much mercury the person is exposed to and how much mercury gets into their body.  Mercury vapor mainly affects the central nervous system and kidneys.  Workers exposed to mercury vapor have experienced many symptoms including physical tremors, slowed muscle responses, loss of feeling in hands and feet, emotional disturbances, personality changes, reduced kidney function, and kidney failure.  However, these workers were exposed to much higher levels of mercury than what is released from amalgam fillings. 

Although the FDA here in the U.S. maintains that no particular health problems could exclusively be linked to amalgam fillings, many countries around the world, especially in Europe, have outlawed amalgam as a filling material on a government level. The studies the FDA relies on are done on very small patient populations, which, according to many researchers, does not paint the true picture about potential long-term health hazards of amalgam fillings.