Prosthodontics

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Prosthodontics is the art of making artificial substitutes for teeth. There are two types: removable prostheses (false teeth), and fixed prostheses which are permanently cemented onto existing teeth or metal implants and cannot be removed.

Removable prostheses are either full dentures used when all teeth have been lost, or partial dentures which are attached by spring clasps to remaining teeth when only some teeth have been lost. Full dentures are made on a plaster model which is an exact copy of the patient's mouth, and consist of a pink acrylic resin base, to which are attached porcelain or acrylic resin teeth. Upper dentures are held in mainly by suction, and lower dentures mainly by muscle control. Partial dentures are similar, but are held in place by small wire springs which grip the remaining teeth. The best partial dentures are made from a cast chrome-cobalt metal or gold framework, to which the teeth are attached by acrylic resin.

It is now possible, where supporting teeth have been lost, to use a titanium implant to hold a denture. A hole is drilled into the jaw bone and a small cylinder of sterile titanium is dropped into place and sewn over. After some weeks, the surrounding bone attaches itself to the titanium. The gum is then cut back again and a small titanium extension is screwed into the implant. A denture can then be attached to the extension. It is very specialised work.

It is possible to provide very natural-looking teeth with the facilities now available. A common technique is to make a denture with an exact copy of teeth that need extracting, and place it in the mouth immediately the natural ones are removed. Some months later, when bone shrinkage has ceased, the dentures are re-lined with acrylic to make them fit very accurately once again. In this way the patient is never without teeth.

Fixed prostheses are crowns and bridges. To make a crown, the existing tooth is cut down to a cone shape, and the artificial crown (made from gold, acrylic resin, porcelain, or a combination of these) is cemented over the top. A bridge is a series of crowns linked together to bridge the gap made by missing teeth. It is cemented onto the remaining teeth and can only be removed with difficulty. It can also be attached to an implant of titanium or other metal.

A new type of bridge which is made of metal with teeth attached is simply cemented onto existing teeth without cutting them down to a cone shape. It uses a system of etching the enamel with an acid to allow a very strong cement bond to hold the bridge in place. It can only be used in favourable situations. A variation on this etching technique involves the use of thin baked porcelain veneers, which are cemented in the same way over the visible surfaces of ugly or stained teeth to give a perfect appearance.

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