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d be replaced by means of an inlay or other conventional retainer. The other abutment tooth is unrestored or the restoration does not involve the surfaces to be covered by a minimal- preparation retainer. These circumstances occur surprisingly commonly and so this design of bridge is being used increasing.
Variations
Removable bridges
All the designs described so far are permanently cemented in the patient ' s mouth. With large bridges there are disadvantages in permanent cementation in that the maintenance and further endodontic or periodontal treatment of abutment teeth is difficult, and if something goes wrong with one part of the bridge or with one of the abutment teeth, usually the whole bridge has to be sacrificed. For this reason larger bridges, including full arch bridges, are sometimes made so that the dentist without being destroyed can remove them. Cementing individual cast gold copings to each of the abutment teeth does this. Some of the copings have threaded sleeves soldered into them, and the bridge is then cemented to these copings with weak cement. It is held in place with line screws that pas through holes in. the retainers of the bridge into the threaded sleeves.

Figure 88
A large splint/bridge with cantilevered pontics.
a The working dies.

Figure 88
b The metal framework showing two cantilevered pontics on the right of the picture.
In other cases the bridge is removable by the patient and has no cement or screws. The advantage of this is that cleaning around the abutment teeth and under the pontics is much easier. The bridge has to withstand handling by the patient and so it is usually made in a base metal with acrylic facings. The base metal is more rigid than a precious metal framework and the acrylic facings are less liable to chip if the bridge is dropped. They can also be replaced without the risk of distorting the framework.
Advantages and disadvantage of the four basic designs
A comparison of conventional fixed-fixed, fixed-moveable and cantilever bridges is shown on page 240 -241 Spring cantilever bridges are discussed separately.
Spring cantilever bridge
These are dealt with separately because they are used only to replace upper incisor teeth, usually when there are spaces between the incisor teeth and the adjacent potential abutment teeth are sound. They should not be used to replace lower incisors as the shape of the ridge and the resilience of the soft tissues are not suited to absorbing part of the occlusal loading.
The advantages of the design are: the pontic not being attached to adjacent teeth, spaces can be preserved both sides of it, and the sound natural anterior teeth do not need to be prepared as abutments.
Disadvantages: some patients find the permanent bar running across the palate intolerable.
Although most get used to this surprisingly well, it is very difficult to predict those who will not become accustomed to it. It has on occasion been necessary to remove a perfectly sound spring cantilever bridge for no other reason than that the patient could not tolerate the feeling of the bar.
A more common problem is the difficulty of cleaning under the bar, particularly at its connector with the retainer. The effective way of cleaning the area is to pass dental floss, superfloss, or other thread material over the pontic and along the bar and t