Implant-Retained Overdenture vs Fixed Prosthesis in a Patient with a Shallow Anterior Mandible
A 67-year-old woman with a completely edentulous mandible has worn a conventional denture for 20 years. She has severe resorption: the anterior mandible shows 7 mm of bone height above the mental foramina and a knife-edge ridge. She has a history of two denture fractures in the last 3 years. She is healthy, takes only a statin, and is a non-smoker. She wants a stable lower prosthesis and asks about 'the fixed teeth.' Her maxillary arch has a well-functioning complete denture.
1. Compare an implant-retained overdenture (two implants) with a fixed implant prosthesis in this patient, and recommend one with reasoning.
Read the worked answer
Fixed prosthesis: Requires substantially more bone volume and often grafting. With 7 mm of anterior height and a knife-edge ridge, a fixed full-arch prosthesis would likely need extensive grafting or a more complex surgical approach, and the knife-edge ridge increases the risk of implant malposition and buccal plate perforation. It also demands high hygiene compliance and is more costly.
Two-implant overdenture: Well-supported by the literature for the severely resorbed mandible. Two implants in the anterior mandible (between the mental foramina) with 7 mm of height are feasible if primary stability can be achieved; the knife-edge ridge may require ridge reduction or a slightly more apical placement. The overdenture improves retention, stability, and function, and reduces the denture fracture risk she has already experienced.
Recommendation: Two-implant overdenture with a resilient attachment (e.g., locator or ball) and a reinforced denture base. It addresses her chief complaint (stability), is less invasive than a fixed prosthesis, and is appropriate for her bone volume. If primary stability is questionable, consider a staged approach or additional grafting.
Key caveat: confirm bone width and the position of the mental foramina on CBCT before committing.
2. She has fractured two dentures. How does that change your material and design choices?
Read the worked answer
Repeated denture fractures indicate high occlusal loads, an ill-fitting base, or a thin/weak base - all of which must be addressed.
Design and material changes:
- Reinforce the base - use a metal (cast or wrought) framework or a high-impact acrylic with a reinforcing mesh, especially in the midline where fractures commonly occur.
- Improve fit - a new, well-extended impression and a properly relieved palate/lingual flange reduce flexural stress.
- Occlusal scheme - balanced occlusion to distribute load and avoid tipping forces; check for interferences.
- Attachment choice - resilient attachments reduce torque on the implants and the base compared with rigid ones.
- Consider the opposing arch - the maxillary denture is well functioning, so maintain balanced contacts.
If fractures continue despite reinforcement, reconsider whether the prosthesis is being overloaded (e.g., parafunction) or whether the implants are not sharing load adequately.