Definitions and Descriptions

When for any reason it's impossible to substitute the patient's teeth with a permanently fixed solution, mainly because there are no teeth avilable to construct a bridge and/or there's a bone deficiency in order to perform an implantology, the only available option is the so called removable prosthetics.

Removable prosthetics in general, is defined such because it's possible to insert it and remove it from the patient's mouth. Whatever kind it is, it has a general characteristic: at least one part of the teeth it is replacing, has to be rested upon the gum.

This fact is obviously a biological compromise because the gum is not structured to directly support the chewing charge, and is also the reason why removable prosthetics is usually much more problematic than the fixed one, in regards to comfort for the patient and management by the dentist.

This kind of removable prosthesis implies the presence of a sufficient number of teeth in the patient's mouth, allowing to anchor the removable part. The number and position of these teeth may vary, but in the prosthetic design, a correct balance between added parts and pillar teeth must be reached. Sometimes, in order to offer more grip to the mobile part, the residual teeth must be covered, sometimes also connecting more than one with a bridge. In this case the partial prosthesis is called "combined".

A removable partial denture consists of various parts that have to be perfectly combined to reach the result.

Saddle or base - With this term, the most delicate part of the prosthesis is indicated, the one that goes into direct contact with the edentuolous ridge, that is. Even if recently some new materials have been introcuced, the great majority of the saddles is built of acrylic resin, a pink colored plastic material.

On top of the saddle, the teeth, also made of resin are fixed, deputated to the chewing function. More seldom, ceramic teeth are used on the saddles also.

Connector or Bar - This component of the removable prosthesis has the function to connect the right side to the left one. It can be made of acrylic resin or it can be a metal element.

This part of the partial denture is sadly always necessary to stabilze the device. Even if partial dentures covering just one side of the mouth do exist, these are quite complicated to build, so the preferred solution is to anchor the teeth on one side to the opposite one with a connector.

Clasp - It's the most used anchorage system for partial dentures on natural teeth. It practically consists in a small metal extension starting from a saddle or one of the connectors, protruding towards the outer part of the dentition, embracing the external part of the pillar tooth. When the prosthesis is inserted, the clasp should theorically excerpt a small friction, and having passed that, the denture positions itself with a click in its prefixed site, while the clasp offers the necessary retention for it not to move.

Of course, being built of flexible metal, with the rising frequency of denture wearing, they tend to loosen themselves, and the dentist must periodically tighten them. It is never advisable to attempt this maintainance with improvised tools, because of the risk of breaking the clasp itself.

Connector - As an alternative to clasps, a more esthetic solution can be used. It substantially is a male/female connector that links the mobile part precisely to a structure based on natural teeth. The only way of constructing it, is to build one of the two parts on one or more teeth: to do so, a crown or a bridge is usually necessary to mold the connector itself.

This kind of prosthesis is used when the patient has no natural tooth and is not going to insert any implant, so the only way to provide him with a dentition, is to build a dental arch entirely based on the gingiva. It must be clear at this point that the main problem to solve will be the device's stability.
The total denture, relies entirely on the so called "suction cup" effect. The resin base that goes into gingival contact is built in a way to tightly adhere to the tissue and its borders are designed to follow the mucosal parts and seal the covered area.
When positioning the denture into the mouth, air is compressed out of the covered area creating the negative pressure effect and the prosthesis stabilizes in site. Many are the factors that influence this simple principle. First of all, the gingiva has not the same consistency in all of its parts, so that more elastic areas may rebound the prosthetic rest and sadly keep the device rather unstable.
It's understandable that the upper denture will be more easy to stabilize because it has a bigger resting area, while the inferior (mandibular) denture must run around the tongue. The tongue itself, with its movements is another instability source.

A periodic control (at least annual) on any removable denture is practically mandatory. The bone under the resin saddles tends to reabsorb as a consequence of the continuous chewing poressure, so that slowly, an eccessive space between the base and the resting surface is created.

In this situation, the denture becomes unstable. In the case of a total denture, it'll lead to moving or falling off site, while, speaking of partial or combined dentures, the chewing effort will be excerpted too much on the dental pillars, damaging them sometimes in a severe way.

Connectors and clasps are subject to wear out or to get loose, and some even have parts that have to be changed periodically.

The general health of the pillar teeth must be verified rigorously.

Relining - This procedure consists in regaining the lost contact between the saddle or the base and the gingiva, by filling up the space with new resin. The relining techniques are various.

a) Direct or cold relining. The dentist uses an acrylic resin that is mixed directly by the dental chair, put on the saddle base and conformed to the gum by positioning the denture in the mouth. This technique is quite gross, because the cold cured resin doesn't have the same characteristics of the one used in the lab, and should be reserved to very small or non permanent relinings.

The same technique can be implemented heating the just applied resin under pressure.

b) Indirect relining. The dentist records the thickness of the volume to fill with an imprint paste and then extracts the denture with the aid of a total impression into which the denture finds place. The lab then restores contact with the gingiva by filling the empty space.

A second variant of this technique consists in inserting on the prosthetical base a soft paste and asking the patient to use the denture for 4-5 days. The paste records not only the thickness variations, but also all those functional movements induced by the mouth's muscles. After this phase, the prosthesis is given to the lab to complete the base.