A five-unit fixed partial denture spans from a single-rooted anterior abutment, across a PIER abutment, to a multi-rooted posterior abutment. Where should the NON-RIGID connector be placed?

Correct answer: A. On the DISTAL aspect of the pier abutment

• A. CORRECT. The keyway is cut into the DISTAL of the pier retainer and the key is soldered to the mesial of the posterior pontic. The reason is the direction of physiological tooth movement: teeth move mesially over time, so a mesially placed keyway would tend to separate under function, whereas a distally placed keyway is seated more firmly as the anterior segment drifts mesially. The connector allows the two segments to flex independently, so the pier no longer acts as a fulcrum for a class I lever, which would otherwise loosen the terminal retainers and stress the pier's periodontium.
• B. Two non-rigid connectors on the same prosthesis leave the intermediate segment unsupported and mechanically unstable; only one stress-breaking joint is used.
• C. The problem here is the fulcrum created by the intermediate (pier) abutment, so the connector must be at the pier, not at a terminal abutment.
• D. A connector on the MESIAL of the pier is the classic wrong answer. Mesial drift would progressively disengage the key from the keyway, opening the joint and inviting caries.

Note: ⚑ Contested across the series: one source keyed 'esthetics'. The primary purpose of a non-rigid connector is STRESS DISTRIBUTION — it prevents torquing of abutments where there is a pier abutment or divergent path of insertion. | Trigger phrase: a PIER (intermediate) abutment between two edentulous spaces plus abutments of dissimilar root support = non-rigid connector, keyway on the DISTAL of the pier. Also recall Ante's law when assessing whether the abutments can carry the span at all.