What’s
wrong with silver fillings?
Silver fillings are actually a mixture of
silver and mercury. It is the mercury content that
causes concern. Mercury is a heavy metal like lead.
When animals are exposed to mercury it can accumulate
in the brain and cause altered personality and learning
disabilities. The expression “Mad Hatter”
stems from the use of a mercury compound to process
hat making materials. The “hatters” began
to exhibit personality changes after working with
the mercury compound for several years and their odd
behavior caused them to be labeled as mad.
It takes high levels of mercury in the body to cause
problems for the majority of people and mercury fillings
do not cause a large increase in mercury content in
the body. There are other properties of this material
which cause even more concern.
Mercury is a metal but is liquid at room temperature.
Metals often have a very large change in dimension
with temperature change. These properties make mercury
great for filling thermometers but questionable for
filling teeth. When you have some ice cream for dessert
the metal filling contracts and may allow bacteria
to invade the space between the filling and the tooth.
This can allow decay to start up around the filling.
When you wash down your ice cream with a nice hot
cup of coffee the metal expands and bends the tooth.
Over time the tooth can develop cracks, this will
lead to portions of the tooth breaking off. Sometimes
root canal therapy or extraction is necessary when
a tooth breaks.
The metal filling material does not adhere or “bond”
to the tooth and requires the tooth to support the
filling. When there is a big cavity the huge filling
requires what is left of the tooth to support it.
Doesn’t that seem backwards?
So what can be done instead? When there is a small
cavity or filling and the tooth has good strength
remaining a bondable tooth colored filling may be
placed. Because this material is adhesive it can actually
give strength back to the tooth. It does not promote
fractures and the bond resists bacterial invasion.
This material will not last forever but it is kinder
to the tooth. When these fillings fail the bond breaks
down and there is a visible sign that something needs
to be done. Often these fillings can actually be repaired
versus stressing the tooth by removing the entire
filling. This characteristic is referred to as a “soft”
failure mode and it is obvious that the metal fillings
have a “hard” failure mode taking part
or all of the tooth with them. An additional advantage
of the bonded materials is the more natural appearance.
Gold has been used to replace missing tooth structure
or to make full crowns. Gold is an excellent material
and can be very long lasting but is less acceptable
to many due to its esthetics.
Porcelain has been used for many years but recent
technical improvements now have made new high strength
porcelain a very nearly ideal material to repair teeth.
The new materials are stronger than teeth and can
be bonded to the tooth with such bond strength that
the repaired tooth is stronger than it has ever been.
Porcelain can be nearly difficult to detect from natural
tooth structure. The preparation of the tooth for
these inlay/onlay restorations is less traumatic than
crown preparation. In most cases these teeth will
not need further treatment. When considered from this
perspective these restorations are a bargain.
