Pier (intermediate) bridge abutments

In bridge design, a pier abutment is where there is a tooth in the middle of a bridge span. i.e a Fixed fixed bridge between the 17 and 13 with the with 14 included as an abutment (Figure 1). The issue with this design is that there are physiologic tooth movements in function and this design is generally used in long span bridges around the dental arch. Due to the shape of the arch, the physiologic movements are in different directions which will have unfavourable forces on the bond strength of the restoration. Anterior teeth will tend to be displaced labially and posterior teeth will tend to tilt mesially. In a fixed bridge situation, the abutment will always fail at the weakest interface which will lead to leakage and recurrent decay. This splinting effect may be beneficial in periodontally compromised teeth but with sound teeth it will often lead to a loss of restorative seal.

Figure 1: An example of a pier abutment

Alternatives to this design are dental implants, multiple cantilever bridges (Figure 2), removable partial dentures or a fixed free design with a semiprecision attachment. As posterior teeth will tend to tilt mesially, the female portion of the attachment would be best placed on the distal surface of the more anterior tooth (Figure 3). This allows the male portion of the posterior tooth to seat into the female portion in function. On the other hand if the female portion is placed on the mesial surface of the posterior tooth, the attachment will tend to unseat in function (Figure 4). Non rigid connectors should only be used for short span bridges replacing one tooth. They lack the support to function over a long span. If used over a long span, what you are essentially providing is a very long span cantilever bridge. They should not be used in cases of significant mobility and a rigid connector should be used instead.

Figure 2: Alternative design- Multiple cantilever bridges will remove the splinting effect of the fixed-fixed bridge design and allow independant movement around the arch. It will also assist in retrievability i.e if the 15 becomes carious then the bridge of the 16 can be left intact

Figure 3: Asemi-precision attachment slot on the distal of the 15 will allow independant micromovement of the teeth around the arch. Function on the molars will result in mesial movement of the molar which will seat further into the attachment slow for support

Figure 4: If the semiprecision attachment is placed on the mesial of the 17. The mesial tilt of the tooth will tend to unseat the attachment relative to the 16 pontic