A lot of people wearing dentures find them difficult to manage, because often they are not well supported or retained by gums which have shrunk, and therefore they tend to move about too much during chewing. Some people even give up and manage by eating entirely soft foods which is certainly not ideal for their health and is also aging because the jaws have a tendency to over close to try to get the gums to meet together instead of the teeth, and give the face a “scrunched up” appearance.
If there are a few teeth remaining, even just two or three, then this can make a tremendous difference to the situation by using these teeth for anchorage.
This can be achieved in suitable cases by means of an overdenture, or denture that fits over the top of suitably reduced natural teeth where a few are still present, to give support and retention. Where there are no teeth standing at all the concept can sometimes still be used by providing implants and using these for support of the denture.
The degree of stabilisation can often be remarkable, giving significant improvement in chewing ability and consequent better health, plus the benefits of improved appearance, speech, and general self-confidence.
Sometimes an existing denture can be converted to an overdenture but most often it is necessary to make a new one to fit to the supporting abutment teeth.
When natural teeth are used as abutments for an overdenture they are usually devitalised and root-filled first because the considerable reshaping and reduction would otherwise damage the pulp, and then they are either simply reduced in size and shaped as a cone, or else used to carry some kind of attachment such as a stud or bar depending on the number of teeth available and their distribution. A simple fitting over of the under-surface of the denture on to some natural teeth helps prevent lateral movement of the denture during chewing and also prevents the denture sinking into the gums under load. A pop-over stud will give more secure retention whilst still allowing the denture to be easily removed for cleaning. Strong magnets have also been used on occasion to secure a denture to underlying prepared teeth.
When impressions are taken to provide for the fit of the underside of the denture to teeth and gums, opinions vary as to whether the best type of impression should displace the gum tissues under load or not. It is for the dentist to decide in any given case. If precision attachments are used then the procedure is more complicated and the process has to be done stage by stage.
Muco-displacing impression materials such as dental compound and some elastomeric products are fairly viscous and these record an impression of the mucosa under load. This can result in a wider distribution of load during function, making it more stable. It may also reduce the risk of denture fracture from flexing because of the differing compressibility of the hard and soft denture bearing areas. Since the soft tissues of the mouth will try to regain their resting position though, they may tend to cause denture displacement.
Some impression materials are muco-static and hardly displace the tissues resulting in better general denture retention because of the better adaptation, except during function. Low viscosity elastomers, alginates, and zinc oxide materials come into this category.
If a patient has no remaining teeth and resorbed ridges giving little retention for full dentures then implants can sometimes be used to provide that retention and support. This depends however on there being sufficient bone tissue present, (although bone grafts might be considered), and will take time to complete since it is usual to place the implants first and wait for osseo-integration to occur before the loading can occur. The top of the implants might carry stud retainers, although commonly two lower jaw implants in the canine region are joined by a solid metal bar between them in order to provide sound location and help prevent lateral displacements of the denture.
The provision of an overdenture can work well provided there is some thought given to the most appropriate design and that the whole construction process is carried out in a careful stepwise manner.