Dentures -
Removable partial denture
Occlusal view of a mandibular
partial denure.
All seven parts
of an RPD are visible on this example.
A Removable partial
denture (RPD) is for a partially edentulous
dental patient who desires to have replacement teeth for
functional or esthetic reasons, and who cannot have a fixed
partial denture (crown and bridge) for any number of reasons,
such as a lack of required teeth to serve as support for
a bridge (i.e. distal abutments) or because of financial
limitations.
The reason why these prostheses are
referred to as removable partial dentures is because patients
can remove and reinsert them when required without professional
help. Conversely, a "fixed" prosthesis can and
should be removed only with the help of a dental professional.
Partially edentulous conditions
Depending on where in the mouth teeth
are missing, edentulous situations can be grouped under
four different categories, as defined by Dr. Edward Kennedy
in his classification of partially edentulous arches.
Class I (bilateral
free ended partially edentulous)
Class II (unilateral free ended partially
edentulous)
Class III (unilateral bounded partially
edentulous)
Class IV (bilateral bounded anterior partially
edentulous)
Class I RPD's are fabricated for people
who are missing some or all of their posterior teeth on
both sides (left and right) in a single arch (either mandibular
or maxillary), and there are no teeth behind the edentulous
area. Thus, Class I RPD's clasp onto teeth that are more
towards the front of the mouth, while replacing the missing
more-back-of-the-mouth teeth on both sides with false denture
teeth, themselves made out of either plastic or porcelain.
Class II RPD's are
fabricated for people who are missing some or all of their
posterior teeth on one side (left or right) in a single
arch, and there are no teeth behind the edentulous area.
Thus, Class II RPD's clasp onto teeth that are more towards
the front of the mouth, as well as on teeth that are more
towards the back of the mouth of the side on which teeth
are not missing, while replacing the missing more-back-of-the-mouth
teeth on one side with false denture teeth.
Class III RPD's
are fabricated for people who are missing some teeth such
that the edentulous area has teeth remaining both behind
and in front of it. Unlike Class I and Class II RPD's which
are both tooth-and-tissue-borne (meaning they both clasp
onto teeth and rest on the posterior edentulous area for
support), Class III RPD's are strictly tooth-borne, which
means they only clasp onto teeth and do not need to rest
on the tissue for added support. This makes Class III RPD's
exceedingly more secure as per the three rules of removable
prostheses that will be mentioned later, namely, support,
stability and retention. (See the article on dentures for
a more thorough review of these three fundamentals of removable
prosthodontics.)
However, is the edentulous area described
in the previous paragraph crosses the anterior midline (that
is, at least both central incisors are missing), the RPD
is classified as a Class IV RPD.
Class I, II and III RPD's
that have other edentulous areas in which to replace teeth
are further classified with modification states that were
defined by Oliver C Applegate.
Components of an RPD
Rather than lying entirely on the edentulous ridge like
complete dentures, removable partial dentures possess clasps
of metal or plastic that "clip" onto the remaining
teeth, making the RPD more stable and retentive.
The parts of an RPD can be listed
as follows (and are exemplified by the picture above):
Major Connector (the thick metal
"U" in the RPD above is a lingual bar, a type
of major connector)
Minor Connector (the small struts
protruding from the lingual bar at roughly 90 degree angles)
Direct Retainer (examples are in
the upper left of upper photo; the clasp arms act to hug
the teeth and keep the RPD in place. The metal clasp and
rest immediately adjacent to the fake teeth is also a direct
retainer.)
Indirect Retainer (example is the little metal piece coming
off the "U" at a 90 degree angle near the top
of the upper photo, which is a cingulum rest on a canine.)
Physical Retainer (this is a mesh
of metal that allows the pink base material to connect to
the metal framework of the RPD. Some consider physical retainers
their own component (making a total of seven), while others
consider them within the indirect retainer catergory (thus
making a total of six components.)
Base (the pink material, mimicking
gingiva)
Teeth (plastic or porcelain formed
in the shape of teeth)
.....................................................................
FIXED
PARTIAL DENTURES
What are fixed
partial dentures?
As the name suggests, fixed partial dentures or FPD are
tooth replacements that are fixed permanently in the mouth
and cannot be removed for routine cleaning by the patient.
These dentures are made to take support from adjacent natural
teeth. Unfortunately these dentures can replace only a few
missing teeth. When a large number of teeth are missing
one has to go in for a removable partial denture or RPD.
What are the types of fixed partial dentures?
Fixed partial dentures
are of various types. They can be made of porcelain or metallic
alloys. The metallic FPD's are made of either gold alloys
or chrome cobalt alloys.
What is a
crown?
A crown is a restoration
that covers the entire tooth like a cap. It can be made
of porcelain or acrylic. Crowns are used to restore teeth
that are discolored, have multiple decays or are fractured.
What is a bridge?
A bridge is a prosthetic
appliance that replaces missing teeth by permanently getting
attached to the adjacent remaining teeth.
What are metallic FPD's?
Metallic FPD's are
fixed partial dentures that are made of metal alloys such
as gold alloy or chrome cobalt alloy. The metallic FPD's
are used mostly in the back teeth, as they are not esthetic
in appearance. In case esthetics is important the metal
crowns can be given an acrylic or porcelain facing over
the areas that are visible to the exterior so as to make
them esthetically acceptable.
Can metallic bridges be made to look more esthetic?
The metallic FPD's
can be given an acrylic or porcelain facing over the areas
that are visible to the exterior so as to make them esthetically
acceptable.
Is it pure
gold that is used?
Earlier pure gold
was used in the fabrication of FPD's. The higher cost of
gold and its softness led to the introduction of the gold
alloys, which have some % of gold along with other metals
such as platinum, palladium, silver, copper, zinc, etc.
These additions to the gold made the alloy cheaper and also
improved its mechanical properties. A number of different
gold-based alloys are available with differing contents
of gold that are used for different dental applications.
How many teeth
can be replaced by a bridge?
The maximum number
of teeth that can be replaced by a bridge is two to three.
Much depends upon the health of the remaining teeth and
in which area the teeth are missing.
What is a
cantilever bridge?
Unlike a normal bridge
that is attached to teeth on both sides, a cantilever bridge
is one that is attached only on one side to the remaining
teeth. The other side is free or unattached. These cantilever
bridges are indicated when the tooth to be replaced is the
last one and does not have remaining teeth beyond it. These
bridges have poor prognosis in the long run.
What are bonded bridges?
The resin bonded fixed
partial dentures are those that are bonded to adjacent teeth
using acrylic resins. Unlike the conventional bridges these
resin bonded ones need less reduction of the adjacent remaining
teeth and are therefore more conservative.
Can a root be used to give support for a bridge?
Sometimes we come
across patients who have some roots remaining. These roots
can be used to give support for prosthesis. These roots
are first endodontically treated and then strengthened by
inserting a post into their root canals. Over these posts
a core is built up and this core can be used to give support
for the prosthesis. These are called post and cores.
Why is the teeth cut to make a crown or bridge?
The fixed partial
dentures are made in such a way that they are fixed on the
teeth on either side of the lost teeth that are being replaced.
These teeth are reduced a little to accommodate the bridge.
COSMETIC DENTISTRY - DENTURES
