Bridges: the choice of abutments matters more than the quality of the framework

The conventional bridge has lost ground to implants, but remains indicated in many situations: abutments already crowned, insufficient bone without willingness to graft, or simply cost.

Assessment of the abutments is the decision that determines the outcome, and it is still often made by looking at the radiograph without measuring anything.

Ante's law provides a reference: the root surface of the abutments should equal or exceed that of the teeth replaced. It is not a proven rule, but remains a useful order of magnitude for recognising borderline cases.

Its limitation is that it considers only surface, not the quality of support. An abutment with a broad root but fifty per cent attachment loss offers less than one with a modest root and intact periodontium.

Mobility must always be assessed, and distinguished. Grade 1 mobility on a reduced but stable periodontium is compatible with an abutment; increasing mobility over time indicates an active process and contraindicates the bridge until stabilised.

The crown-root ratio is the second parameter. The ideal value is 1 to 2, the acceptable 1 to 1: above that ratio the lever on the abutment grows and load concentrates on the coronal portion of the ligament.

The connector between units is where bridges break, and minimum dimensions depend on the material. Zirconia requires at least 9 square millimetres of cross-section in posterior sectors; lithium disilicate requires more, which limits its use to short anterior bridges.

Connector shape matters as much as area. A sharp angle at the base concentrates stress and initiates fracture; a rounded fillet of adequate radius distributes tension, and it is the detail the technician knows but which the clinical design must permit.

Space for an adequate connector is created during preparation, not in the laboratory. If the interdental space is reduced and the preparation did not allow for it, the technician must choose between a thin connector and a wrong emergence profile.

The cantilever bridge — with one unit suspended beyond the last abutment — has narrow indications. The extension creates a lever transmitting tensile forces to the adjacent abutment, and the literature reports higher complication rates.

Where unavoidable, the cantilever should be limited to one unit, preferably reduced in occlusal dimension, with at least two splinted abutments on the other side and no lateral contact on the suspended unit.

The pontic must rest on the ridge without compressing it. The saddle design, wrapping the ridge, is impossible to clean and produces chronic inflammation; the ovate design, with a slight concavity resting on the buccal aspect, is aesthetic and cleansable provided the patient uses floss.

In summary: assess abutments for real support rather than number, size the connector at the preparation stage, avoid cantilevers where alternatives exist, and choose a pontic the patient can clean. A bridge almost always fails from one abutment, and that abutment was identifiable beforehand.