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al- preparation bridges than with conventional bridge.
At one time it was thought that the support for the abutment teeth at each end of a fixed-fixed bridge should be similar. In other words, the root surface area of the abutments should be approximately the same. Today this is not considered necessary.
A fixed-moveable bridge has a rigid connector, usually at the distal end of the pontic and a moveable connector that allows some vertical movement of the mesial abutment tooth. The moveable connector should resist both separation of the pontic from the retainer and lateral movement of the pontic (see Figure 87).

Figure 85
Four basic bridge designs of conventional bridges.
a Fixed-fixed design Both upper and lower bridge will be fixed-fixed, the lower retained by full crowns on the canine tooth and central incisor. The upper bridge will be retained by the canine teeth only.
Fixed-moveable bridge
Occasionally the fixed and moveable connectors are reversed but this has a number of disadvantages. The retainer with the moveable connector (the minor retainer) is smaller and less visible and so is better in the more anterior abutment tooth. Mesial drift tends to unseat distal moveable connectors, but is resisted by mesial ones.
The moveable connector can be separated before the bridge is cemented and so the two parts of the bridge can be cemented separately. The abutment teeth do not therefore have to be prepared parallel to each other and the retention for the minor retainer does not need to be as extensive as for the major retainer. Neither does it need full occlusal protection. (occlusal forces applied to the tooth surface not covered by the retainer will depress the tooth in its socket and there will be movement at The moveable joint rather than rupturing of the cement lute(see Figure 86).

b Fixed-moveable design with Do inlay in the lower seen premolar and full crown on the molar tooth. This bridge has been present for twenty years, in feet so long that the occlusal surface of the crown has worn through (see Chapter 13). The moveable Joint can be seen between the pontic and the minor retainer. It would not normally be as obvious as this.

c Cantilever design Both lateral incisors are pontics supported by crowns on the canine teeth. Both bridges are all-porcelain and the right one has been present for fourteen years. The left one fractured fater seven years and was replaced with another all porcelain bridge, which is still present.

d Spring cantilever design with first molar tooth as abutment. There is a midline diastema and a diastema between the lateral incisor and canine on the side of the missing central incisor. Any other bridge design would have involved closing one or both of these specs.
A fixed-moveable minimal- preparation bridge cannot have the moveable joint within the contour of the original abutment tooth, as this is not prepared sufficiently for the moveable connector. This means that the moveable connector is in the pontic of the bridge and is usually a through and through tube and pin arrangement. This means that the two parts of the bridge are connected but if either debonds then it can be removed without disturbing the other part of the bridge and recemented.
However, this design of moveable joint is cumbersome and the undersurface, which approximates the ridge, is