Removable partial dentures

Overview
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 bridge (a fixed partial denture) for any number of reasons, such as a lack of required teeth to serve as support for a bridge (i.e. distal abutments) or due to financial limitations.

The reason why this type of prosthesis is referred to as a removable partial denture is because patients can remove and reinsert them when required without professional help. Conversely, a "fixed" prosthesis can and should be removed only by 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 composed 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 and lower right of lower 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 category (thus making a total of six components.)


 * Base (the pink material, mimicking gingiva)


 * Teeth (plastic or porcelain formed in the shape of teeth)

Clasp Design
Direct retainers may come in various designs:
 * Cast Circumferential Clasp
 * Wrought Wire Clasp
 * I-Bar

In addition there are a couple of specific theories which include the clasp design:
 * RPI: Rest, proximal plate, I-Bar
 * Described by Kratochvil in 1963 and modified by Kroll in 1973
 * An illustration of the RPI design function
 * RPC: Rest, proximal plate, Cast Circumferential Clasp
 * So named in response to the RPI Philosophy introduced by Kratochvil and Kroll