The appliances used to replace missing teeth were defined in Chapter 7. Some of the terms used in bridge work are also used in relation to partial dentures.
∙An abutment is a tooth to which a bridge (of partial denture) is attached.
∙ A retainer is a crown or other rastoration that is cemented to the abutment. The terms retainer and abutment should not be confused or used interchangeably.
∙ A pontic is an artificial tooth as part of a bridge.
∙ A span is the space between natural teeth that is to be filled by the bridge.
∙ The saddle is the area of the edentulous ridge over which the pontic will lie.
∙ A pier is an abutment tooth standing between and supporting two pontics. Each pontic being attached to a further abutment tooth.
∙ A unit, when applied to bridgework, means either a retainer or a pontic. A bridge with two retainers and one pontic would therefore be a three-unit bridge.
∙ A connector (or joint) connects a pontic to a retainer, or two retainers to each other. Connectors may either be fixed or allow some movement between the components that they join.
Basic design, combinations and variations
There are four basic designs of bridge, the difference being the type of support provided at each end of the pontic. The same name is given to the design however many pontics in the span and abutment teeth splinted at one end of the span (se e Figure 85).
The four basic designs are the same whether the bridge is a conventional or a minimal- preparation type. It is possible to combine two or more of the four basic designs and to combine conventional and minimal- preparation retainers in the same bridge.
Of the four basic designs, the first three may be either conventional or minimal- preparation type. It would be unusual to have a minimal- preparation version of the spring cantilever bridge.
The four basic designs
Fixed-fixed bridge
A fixed-fixed bridge has a rigid connector at both ends of the pontic. The abutment teeth are therefore rigidly splinted together and for a conventional bridge must be prepared parallel to each other so that the bridge, which is a minimum of three units, can be cemented in one place. The retainers should have approximately the same retention as each other to reduce the risk that forces applied to the bridge will dislodge one retainer from its abutment, leaving the bridge suspended from the other abutment.
To minimize this risk it is also important for the entire occluding surface of all the abutment teeth for a conventional bridge to be co4ered by the retainers. The opposing teeth cannot then contact the surface of an abutment tooth, depress it in its socket and break the cement lute. If this should happen, the retainer will not appear loose, as it will still be held in place by the rest of the bridge. However, oral fluids will enter the space between the retainer and the abutment preparation and caries will rapidly develop (see Figure 86).
This rule does not apply to minimal- preparation bridges in which the bond between the retainer and the abutment tooth is much stronger. However, it is sometimes not strong enough and debonding sometimes occurs as a result of a mechanism similar to that shown in Figure 86. This probably partly accounts for the higher incidence of retention failure with minim，英语毕业论文，英语毕业论文 |
