Kennedy Class II modification 1 with a borderline terminal abutment
55-year-old man requests a new mandibular removable partial denture; his previous two fractured. He is missing 36, 37 and 46 (Kennedy Class II, modification 1). Tooth 45 has a 4 mm mesial pocket, grade I mobility and a 1:1 crown-to-root ratio; teeth 44 and 34 are sound with 5 mm of attached gingiva. He has a high smile line and refuses visible clasps. The buccal vestibule at 45 is 3 mm deep. He bruxes at night. Teeth 31 and 41 have 40% bone loss and grade I mobility. He asks for a "flexible" partial because he has heard they contain no metal.
1. Which teeth would you use as abutments, and how do you justify including or excluding tooth 45?
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Primary abutments: 34 and 44. Both are sound, have attached gingiva and a favourable crown-to-root ratio, and they bracket the arch.
Tooth 45 is the judgement call.
- Against: 4 mm mesial pocket, grade I mobility, 1:1 crown-to-root ratio, shallow vestibule. A rigid clasp engaging it on a distal-extension side converts it into a torque-bearing terminal abutment.
- For: excluding it creates a longer, more cantilevered distal extension and leaves the 44 as the sole support on that side, which increases load on 44 and on the ridge.
- Resolution: treat and reassess the periodontium first. If the pocket responds and mobility is stable, use 45 with a mesial rest and a stress-releasing design so that functional load is directed axially and the distal extension is not torqued.
Avoid 31 and 41 as primary abutments given 40% bone loss; a lingual plate can provide indirect retention with light, broad contact rather than point loading.
2. How do you respond to his request for a flexible partial, given his history of fracture?
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Explain the mismatch between the request and the clinical situation:
- Flexible (thermoplastic) frameworks cannot provide the rigidity and tissue support needed for a distal-extension base. Under load they flex, transmitting force to the abutment teeth and compressing the ridge.
- They are difficult to reline or repair, and the all-polymer major connector tends to cover more gingival margin than a cast framework.
- His two previous fractures are a warning sign, not a reason to choose a less rigid material.
Reframe the goal: what he actually wants is no visible metal. That can be achieved with:
- a cast metal framework with lingual reciprocation and minimal buccal display (e.g. mesial rests, lingual plate, wrought-wire or aesthetic clasp on 44),
- or a metal framework with composite-veneered clasps.
Do not trade structural rigidity for aesthetics in a bruxer with a distal extension.
3. List the design features you would use specifically to reduce fracture risk.
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- Rigid cast major connector (lingual plate) rather than a flexible resin connector; rigidity spreads load and prevents flexural fatigue.
- Rest seats on every abutment, placed to direct force along the long axis; mesial rests on terminal abutments of the distal extension.
- Broad, well-adapted denture base with accurate tissue support so the framework is not load-bearing on its own.
- Avoid thin, unsupported connector cross-sections; keep minor connectors bulky enough at the junction with the base.
- Occlusal scheme: balanced contacts, no working-side interference, and consider reduced cusp angles in a bruxer.
- Occlusal splint for nocturnal bruxism, and a documented review interval - the previous failures suggest the cause was design or parafunction, not bad luck.