Replacing Bilateral Mandibular Free-End Saddle: Implants, RPD, or Nothing
A 64-year-old woman requests replacement of her missing mandibular molars and reports difficulty chewing steak and nuts. She has teeth #20 through #29 remaining; #19 and #30 and all posterior teeth distal to them are missing bilaterally, and the posterior ridges are knife-edged with 4 mm of keratinized tissue. The remaining teeth are sound except for a large MOD amalgam on #20 and a mesio-occlusal composite on #29. She is healthy, takes no medications, does not smoke, and shows no signs of bruxism. Probing depths are 3 mm throughout with no bleeding. She says cost matters but she wants 'the best long-term answer.'
1. Compare the realistic options for this patient's chief complaint and identify which specific findings in the history drive the choice.
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Three realistic options:
- Implant-supported fixed prostheses bilaterally. Best function and no removable component, but it requires adequate bone width, which the knife-edged ridges call into question, and it may need grafting with a healing delay and a higher cost. It also commits her to hygiene access around implants in the posterior mandible, close to the lingual nerve and the inferior alveolar canal.
- Implant-assisted or implant-retained removable partial denture. Converts a Class I lever on the abutment teeth into a supported situation at much lower cost than multiple implants, and it is the option most of these patients actually complete. The trade-off is a removable prosthesis and a denture base.
- Conventional mandibular RPD. Lowest cost and quickest, but this is a Kennedy Class I - the worst-case RPD design, because the free-end saddles rotate around the abutments. The two large restorations on #20 and #29 are precisely the teeth that would be loaded.
Driving findings: the knife-edged ridges (bone volume, and a grafting decision that changes cost and timeline), the 4 mm of keratinized tissue (adequate for an RPD base and for implant hygiene, but not generous), sound periodontium and no bruxism (good prognosis for either abutments or implants), her health and non-smoking status (favourable for implants), and 'cost matters' combined with 'best long-term answer' - two requests that may conflict, and the conflict should be presented rather than resolved silently.
2. If she chooses a conventional RPD, describe the design decisions and the biomechanical reasoning behind each.
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Design for a Kennedy Class I is a lever problem, and every decision should reduce torque on #20 and #29.
- Major connector: lingual plate rather than a lingual bar. She has a full anterior dentition and the teeth are periodontally sound, so a plate can be used, and it adds cross-arch stabilization and rigidity. Rigidity is the whole point - a flexible connector transfers the free-end rotation directly to the abutments.
- Rests: mesial on #20 and distal on #29, placed in prepared rest seats, not on unprepared marginal ridges. The rest converts the vertical load into a force directed down the long axis of the abutment. A rest on a composite or amalgam margin will fail.
- No clasps on the canines if it can be avoided - use the rests and the plate for retention where possible; a wrought-wire or I-bar clasp on the terminal abutments adds retention without adding torque.
- Maximum extension of the denture bases to the retromolar pad and the buccal shelf, with a functional impression of the extension areas. Coverage is retention: every millimetre of tissue-borne area reduces the load per unit area and reduces the rotational force on #20 and #29.
- Replace the large restorations on #20 and #29 first and consider full-coverage or onlay restorations that incorporate the rest seats, so the abutment is not dependent on a failing intracoronal restoration.
- Because the two abutment restorations are the weak link, tell her the design works only if she wears it and returns for maintenance.
3. She asks what you would do if she were your family member, and what maintenance she should expect. How do you answer, and how do you handle the cost-versus-longevity conflict?
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Answer honestly and with a preference, not a menu. If cost were not the issue, the most predictable long-term answer is implant support posteriorly - either two implants per side supporting a fixed prosthesis, or, more realistically in a knife-edged ridge, two implants supporting an implant-retained RPD. That converts the Class I lever into a tooth-and-implant-supported situation and spares #20 and #29.
But cost is the issue, and it should change the plan, not the explanation. Present the staged path: conventional RPD now with well-prepared rest seats and maximum base extension, then convert to implant support later if she chooses. That is not a lesser plan - it is a sequenced one, and it keeps her options open. What she should not do is leave it untreated: the unopposed maxillary posteriors will continue to erupt, and drifting and loss of the remaining mandibular teeth are a real risk in a Class I situation.
Maintenance expectations: 6-month recalls with denture-base and abutment review, reline or rebase as the ridges resorb (expect measurable resorption in the first year), and prompt repair or remake of restorations on #20 and #29 if they fail - those teeth carry the design. Give her the numbers in writing, including the cost of the RPD, the cost of the implant conversion, and the fact that the RPD will need replacement eventually. Then record which option she chose and what she was told.