well-healed, a conventional RPD is constructed.
In-mediate partial dentures are usually fabricated
completely of a resin base and denture teeth.
These prostheses include complete, partial, and
immediate overdentures. A complete overdenture
replaces the entire dentition and is constructed for
insertion over one or more remaining prepared teeth,
roots, or dental implants. A partial overdenture
replaces the partially missing dentition and is
constructed for insertion over one or more remaining
prepared teeth or roots. If the overdenture is
constructed for insertion immediately following the
surgical removal of natural teeth, leaving no strategic
teeth to support the denture, the prosthesis is
considered an immediate prosthesis.
Many dental materials are unique to prosthodontic
procedures. The improper use of any of these materials
could cause a delay in the treatment and an
inconvenience to the patient. You should be familiar
with the use, handling, reaction time, and storing
procedures for these materials. This knowledge is
necessary for your successful performance as a
Although you do not make dental prostheses as a
basic dental assistant, you must know enough about the
materials used in their construction to document
properly the treatment patients receive. When a
patients prosthesis is given to a dental lab for repair or
change, they need to know its history to do the work
properly, or a tragic result may follow. You should
document al I laboratory requests and patient dental
records with information, such as alloy type used,
solder type, and tooth shade if applicable.
Dental alloys can be classified as precious,
semiprecious, and nonprecious. For the purpose of
training and clarification, we will classify them as
noble metal or base metal alloys.
Noble Metal Alloys
Noble metals resist oxidation and corrosion. The
four noble metals used primarily in dentistry are silver,
platinum, palladium, and gold. Gold is very useful for
dental put-poses. Although too soft for use alone, it can
be combined with other metals in varying proportions
to produce alloys of almost any desired properties.
Other noble metals are used in most dental labs to
fabricate crowns and FPDs because of the high cost of
Base Metal Alloys
Since base metal alloys do not contain noble
metals, they are much stiffer and harder. Thus, they are
useful for constructing RPDs and certain types of
Many types of impression materials are used in the
dental clinic. However, no one material fulfills all
requirements for making a perfect negative
reproduction of the oral structures. The dentist will
determine which material will best meet the
requirements for each case. The two commonly used
impression materials are alginate hydrocolloids and
Hydrocolloids that change state because of
thermal changes are known as reversible
hydrocolloids because the process can be changed
back and forth by altering the temperature. Those that
are altered through a chemical change are known as
irreversible hydrocolloids. Once the chemical change
has taken place, it cannot be reversed or turned back to
the previous state.
Irreversible hydrocolloids, more commonly
known as alginates, were developed from seaweed
during World War II. Alginate impression material has
largely replaced the reversible type for impressions.
The advantages of alginate material are that it is easy to
prepare and handle, it does not require excess
equipment and advanced preparation, it is comfortable
for the patient, and it is inexpensive. Alginate is used
in making preliminary impressions for all study casts
and most final impressions for RPD working casts.
According to the American Dental Association
(ADA) specifications, alginate materials are divided
into two types based on gelling time:
Type IFast set material, must gel in 1 to 2
Type IIRegular set material, must gel in 2 to
4.5 minutes after the beginning of the mix.