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Crowns And Bridges |
Crown and Bridge refers to the fabrication and preparation for prosthetic
partially or full-coverage Indirect restorations. A crown covers a single tooth,
whereas a bridge is used to span a space between teeth, by joining to the tooth
on either side. Traditionally, the teeth are prepared by a dentist and records
given to a lab technician to create the crown or bridge to be inserted. The main
advantage of this technique allows fabrication outside the mouth, thus allowing
harder materials and fabrication techniques outside of the normal limitations of
direct restoration. As new technology and material chemistry has evolved
computers are increasingly becoming a part of crown and bridge fabrication. The
main advantages of crowning and bridging apposed to using direct restorations
are the strength, appearance and longevity. Unlike direct restorative materials,
the setting reaction can produce or use extreme heat; byproducts generated
during the reaction are not as important. This allows harder materials to be
used, that require extreme temperatures for metal casting or furnace curing.
Therefore compared to direct restorations, crown and bridge indirect fillings
technically are able to withstand greater forces and are less likely to break in
larger sections. Since Crown and bridge restorations are fabricated in a
laboratory or with cad cam technology, less time needs to be spent by the
dentist with the patient refining the shape of the filling to match the
surrounding teeth. Because indirect crowns and bridges are stronger than large
indirect fillings, they can be built up functionally, where indirect
restorations would normally fail. A damaged tooth may be difficult or impossible
to restore to correct form and function using a direct dental restorative
material such as amalgam or dental composite, since these materials are placed
in the damaged tooth and carved to shape by the dentist in the mouth, and thus
have limited strength. In such cases, the tooth may require an indirect
restoration made outside the mouth by a dental technician, who can work to
produce a customized tooth shape in the chosen material that will fit the
patient's damaged tooth exactly, somewhat like a thimble fits over a finger to
protect it. Crowns can also be used to support bridgework which replaces missing
teeth adjacent to the crowned teeth and may be required in cases of very severe
staining or where the visible form of teeth need to be realigned without the use
of orthodontics. Makeover shows such as Extreme Makeover use crowns extensively,
as the timeframe of the makeover is not long enough to allow up to 18 months for
orthodontic treatment. Finally, crowns can also provide a suitable form for a
removable partial coverage denture to link with for added denture retention.
Although no dental restoration lasts forever, the average lifespan of a crown is
around 10 years which is comparatively high, but they can last up to 30 years or
more with proper care.
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The most important factor affecting any restorative lifespan is the oral hygiene
of the patient. Other factors depend on the skill of the dentist and technician,
the material used and appropriate case selection. Root canal fillings have a
higher success rate when a crown is used as the final restoration of the tooth.
This is because the crown is fabricated as a single solid piece to be inserted
and the preparation allows a better seal and a reduced chance of structural
failure. The main disadvantages are the required extensive tooth preparation of
the abutment tooth, and the high initial cost. Preparation of a tooth for a
crown involves removal of a significant amount of tooth structure, which is an
irreversible procedure. Any restoration, compared to a natural healthy tooth has
a compromised integrity. Thus, if not necessary, crown preparation is
contraindicated. Traditionally more than one visit is required to complete crown
and bridge work, so the initial time required for the procedure can be a
disadvantage, although the increased longevity may prevent frequency of
replacements. Full restorative coverage of the tooth prevents access to for
future diagnostic testing, such as pulp testing with an electric pulp tester.
There are many types of crown like: Full coverage crown three quarter crown
implant supported crowns, and also there are types of bridge like: Crown
supported bridge Inlay supported bridge. The amount and shape of reduction to
the abutment teeth varies slightly depending on what material is going to be
used. The main requirement is that the prepared tooth has no undercuts to allow
a smooth insertion and close contact with the tooth preparation. An ideal slight
taper of 5° is normally used. The recipient of such a bridge must be careful to
clean well under this prosthesis. The main materials used are metal: Metal has
the advantage that it retains its structural integrity in thinner sections, and
so less tooth reduction is required to prepare the tooth. Metals can either be
noble metals or base metals, noble metals having higher content of gold,
platinum or palladium, Noble metals are typically more accurate when they are
cast by the lab technician and offer a better bond with porcelain. Noble alloys
in PFMs have a much lower incidence of allergic reactions as they do not contain
nickel, and porcelain: Porcelains main advantage is the color matching to
natural teeth compared to metals. All porcelain restorations can be made from
feldspathic (traditional) porcelain, lithium disilicates, aluminous porcelains,
or zirconia, and the last one is ceramic: Similarly Ceramic has high color
matching to tooth structure, with improved effects such as translucency. All
ceramic restorations typically are not as strong as those with metal
substructures, and therefore require more tooth reduction and can cause
increased wear of the opposing teeth. The materials are used alone or in
Combinations of both in the form of porcelain fused to metal (PFM). Also instead
of a bridge, a partial plate, containing a simulation of the missing tooth, may
be used. A cantilever bridge refers to a bridge that is attached to one or two
abutment teeth on one end only. | |
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