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If you are missing only a few teeth scattered over either arch (upper or lower teeth), or even if you have a minimum of two teeth on both sides of the arch, then you can most inexpensively replace the missing teeth with a removable partial denture (RPD). There are several types of RPD’s. All of them use standard plastic denture teeth as replacements for the missing natural teeth. The differences between them are the materials that are used to support the denture teeth and retain the RPD in the mouth.
The Treatment RPD (flippers)
Affectionately known in dentistry as a “flipper”, this is the least expensive of all the removable partial dentures. The one pictured on the left replaces 4 missing upper teeth, leaving spaces for 7 natural teeth. Two of the natural teeth are clasped with wrought wire clasps which are cured into the structure of the denture base.
When a flipper is intended for temporary use while replacing one or more front teeth, it is often termed a “stayplate”. Most frequently, these are intended to be used only for several months while awaiting healing during the various phases of implant placement.
The pink plastic of the denture base is brittle acrylic, the same material used to make standard full dentures. The largest single advantage to this type of RPD (aside from the cost) is that new teeth and new denture base can easily be added to an existing treatment RPD. These are frequently fabricated even if the remaining teeth have existing decay or periodontal disease and their prognosis is doubtful. If later in the course of treatment some of the existing natural teeth are extracted for any reason, new false teeth can be added quickly to the partial, maintaining the patient’s appearance. In spite of the fact that they are considered a temporary solution, many people keep this type of appliance for many, many years, because as long as they are properly maintained, they look outwardly as good as the more expensive permanent appliances described below.
One of the neatest tricks that a flipper can do is to act as an “immediate partial denture”. This means that the appliance can be made before the teeth are removed, and inserted immediately after the extraction of the offending teeth. If the patient is presently wearing one of these inexpensive appliances, and needs to have an existing natural tooth extracted, an impression can be taken with the flipper in place. The impression with the flipper embedded in it is sent to the lab and a new denture tooth put in place of the one to be extracted. This can be done in the course of a single day, so a patient can come in with a bad tooth and walk out with a good false tooth in its position.
Flippers do have a number of disadvantages, however.
- The acrylic denture base is somewhat brittle, and due to their irregular shape, these partials tend to break frequently, especially those made for the lower arch. (Full dentures are more regular in shape and tend to be fairly strong as a result.)
- In order to counteract their tendency to break, the acrylic is usually built fairly thick which can take some “getting used to”.
- The denture base rests only on the gums, and even though they are much more stable than full dentures, they are much less stable than the more permanent RPD’s which are “tooth born”.
- As the gums resorb, The false teeth tend to sink below their original level making it necessary to reline them frequently, and sometimes even to reset the teeth which adds to their expense.
- Flippers are most frequently retained with wire clasps (shown in image above). These are frequently unsightly due to the limitations that pertain to their placement (they can’t interfere with the way you bite).
Cast Metal RPD’s
Removable Partial Dentures with cast metal frameworks are probably one of the oldest forms of dentistry. Originally, the frameworks (an example seen on the right) were made out of wrought (hammered) silver. One of the most famous American dentists was Paul Revere who was a silversmith when he wasn’t fighting redcoats.
This type of partial denture offers numerous advantages over the treatment partial described above. A close look at the pictures above will show you that these frameworks are cast to fit the teeth. Since they sit on the teeth, as well as being attached to them, they are extremely stable and retentive. The teeth have been altered slightly beforehand in order that the partial denture can rest upon them without interfering with the way the patient bites the teeth together.
The metal framework does not contact the gums. Thus, as the gums resorb, this type of partial does not sink with them and rarely requires relines. Because the teeth are altered by the dentist beforehand, there are fewer limitations in the placement of clasps, and they are less likely to be seen than the wrought wire clasps of the treatment partial. Modern frameworks are cast from an extremely strong alloy called chrome cobalt which can be cast very thin and are much less likely to break than the all plastic variety. They are also much less noticeable to the tongue.
The largest single advantage that cast metal framework partial dentures have over the newer flexible framework partials (covered below) is that sore spots are almost never an issue since neither the framework, nor the plastic extensions contact the soft oral tissues with any force! Patients who exhibit the symptoms ofTMJ, or who are known bruxers are much better off with cast metal partials than with flexible framework partials.
The flexible framework RPD’s
The most recent advance in dental materials has been the application of nylon to the fabrication of dental appliances. Nylon generally replaces the metal, and the pink acrylic denture material used to build the framework for standard removable partial dentures. Nylon is similar to the material used to build those fluorescent orange traffic cones you sometimes see on highways. It is nearly unbreakable, is colored pink like the gums, can be built quite thin, and can form not only the denture base, but the clasps as well. Since the clasps are built to curl around the necks of the teeth, they are practically indistinguishable from the gums that normally surround the teeth. Finally, the entire framework is flexible, yet stiff enough to maintain its shape indefinitely.
A second type of flexible partial denture base uses a vinyl composite instead of nylon. The most commonly sold brand is Flexite. This material is also flexible and can be built with tooth or gum colored clasps. Unlike nylon partial dentures, they are much easier for the dentist to adjust making them a much more “user friendly” denture base.
Even though this type of denture does not rest on the natural teeth like the metal framework variety, the clasps rest on the gums surrounding the natural teeth. This tissue, unlike the gums over extraction sites, is stable and changes very little over time which keeps these RPD’s stable and unchanging similar to the cast metal variety. The clasps can be seen (if you look hard) on the image on the right below just under my thumb and index fingers. This type of partial denture is extremely stable and retentive, and the elasticity of the flexible plastic clasps keeps them that way indefinitely.
A lower Nylon based partial denture
The Vitallium/Nylon Partial denture
A good alternative to the all-nylon partial denture is one made with a combination cast metal framework with nylon clasps. This has the advantage of being tooth supported (like the cast metal framework partial denture discussed above) and also having gum colored plastic clasps like the nylon partial.
This combination of metal framework and plastic clasp eliminates most of the difficulty of recurrent sore spots, since the framework resists movement and pressure from the clasps, while having the benefit of nearly invisible clasps.
The Nesbit RPD
The flexible framework RPD can replace any number of teeth in a dental arch, similar to the flipper and cast metal RPD. There is, however, one type of removable tooth replacement device that can (legally) be built ONLY out of the flexible framework variety of material. This is the single tooth RPD that we refer to as a NESBIT.
Dentists used to build Nesbits for their patients all the time. They were composed of a single denture tooth (usually a back tooth) between two cast metal clasps which attached onto the teeth on either side of the missing one. They looked a little like spiders when out of the mouth. Patients tended to like them, but they came to an abrupt end in the 1970’s. Prior to that time, in the rare event that a patient swallowed his appliance, he either waited for it to pass, or sought medical help on his own assuming that the accident was his own fault. In rare instances, the metal clasps were sharp enough to cause damage to the digestive system. After that time, tort lawyers discovered that it was a law suit made in Heaven, (or Hell depending on your point of view) and it didn’t take the dental profession long to abandon this service.
The design of the new flexible plastic framework takes the danger out of an accidental swallowing of the appliance. In the event that someone did swallow one, it is unlikely that any damage could be done to the lining of the digestive system. This is a series of pictures that show the form and function of a nylon Nesbit.
The Cu-sil * partial denture
If you have read my page on full dentures, you will realize that they tend to be unstable and difficult to retain in the mouth. However, even the presence of a single remaining tooth in an arch can make the denture much more stable and retentive. A new kind of appliance is now available to allow a patient to retain one or more teeth and still wear a “full denture”. A Cu-sil * partial denture is essentially a full denture with holes allowing the remaining natural teeth to protrude through. Normally, the key to retaining a full denture is the suction that is obtained by fitting the plastic closely to the gum tissue, but a hole allowing a tooth to protrude through would ordinarily break the suction. The Cu-sil * partial denture is unique because the holes that surround the natural teeth are lined with a Silicone rubber gasket which snugly holds the teeth while allowing a natural suction to form under the denture. For a more complete discussion of the Cu-sil * partial denture, click the image below.