Teeth occupy a neutral position in the
dental arches, maintained by a delicate balance of forces from the cheek, tongue,
and lip muscles – and by each other. When a tooth is lost,
adjacent teeth may drift into its former position, the opposing teeth begin to
extrude, and forces on the remaining teeth are increased. Those that have been
weakened with decay and fillings can break. One option for replacing missing
teeth is a fixed partial denture or “bridge.” Bridges can be made of several
different materials, including metal – usually an alloy of gold, platinum, and
palladium, which do not corrode in the mouth. Other metals can be used, with
greater potential for corrosion or allergy. Visible teeth can be partly
covered to avoid showing metal, or any visible surfaces can be covered with
tooth colored porcelain or resin. Depending on how many teeth are visible
in the smile, it may be necessary to have multiple teeth veneered with ceramic. Porcelain-fused-to-metal is a common
option for bridges covering back teeth, having a metal core that strengthens the
porcelain during fabrication and provides it with a rigid backbone. To
hide darker metals, however, the porcelain can look opaque. Porcelain fused to white ceramometals
like zirconium maybe an option. Here, masking a dark metal framework is
not necessary, so the porcelain can be made more
naturally translucent for a superb cosmetic result. The structural
properties of these materials have greatly improved in recent years.
Depending on which teeth are lost bridges can be designed many ways. A pier
abutment can support a long-span bridge where teeth are missing on both sides.
Often these have a stress-breaking hinge or a “keyway” joining two segments. Teeth
of different sizes don’t move equally in the jaws. Keyways allow the bridge
elements to flex independently so they won’t loosen from the abutment teeth.
They also allow the bridgework to be completed in segments so the patient can
better plan for the expense. A cantilever bridge can be used near the front of the
mouth if carefully designed to prevent excess forces. Cantilevers require only
the reduction of a single tooth to anchor the retainer crown. That tooth
must be structurally capable of withstanding the chewing forces that
will be placed upon it. Bonded bridges allow replacement teeth
to be inserted with little or no reduction of the abutment teeth. The
retainers can be made of metal or ceramic. It’s critical to maintain
excellent oral hygiene around bridge abutments to prevent undermining decay.
Your dental professional can recommend specific hygiene aides for this purpose.