Using CAD-Designed Cast Frameworks to Reinforce Overdentures

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Incorporating a cast framework is one option for increasing the strength of the prosthesis.3-5 Traditionally, these frameworks are designed and waxed on the model, then cast and finished. Today's CAD/CAM systems, such as Sensable and 3Shape, allow the technician to scan the master model and then virtually design the framework, including establishing the finish line, blocking out undercuts and encasing the attachment housings. Once the design work is completed, the framework is printed, cast and finished. The framework can then be incorporated into the acrylic base of the bite block or trial denture and processed into the definitive prosthesis.

The clinical techniques used in the overdenture cases that follow demonstrate how cast frameworks can be virtually designed and fabricated for a Locator® Implant Overdenture (Zest Anchors; Escondido, Calif.), a Locator CAD/CAM Milled Bar Overdenture and a partial overdenture.

Case 1: Locator® Implant Overdenture
For this case, the clinician requested a palateless overdenture retained by four Locator Attachments. The cast framework is designed to have struts over the tops of the attachment housings to prevent the housings from breaking through the acrylic of the final prosthesis. The framework will provide strength as well as partial palatal coverage and support. The thin palatal apron is designed for patient comfort, with a smooth transition to the acrylic. A small bead is incorporated into the framework design to provide a palatal seal.

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Case 2: Locator CAD/CAM Milled Bar Overdenture
Having sufficient space for adequate acrylic thickness can be even more challenging with bar overdentures. A cast framework can provide strength in cases with limited vertical space.

Case 2 Photos
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Case 3: Partial Overdenture
Implant attachments can also be incorporated into partial framework designs. Two Locator Attachments will be utilized in this case to retain and stabilize bilateral distal extensions.

Case 3 Photos
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Conclusion
Overdenture repairs can be a practice disruption and a source of frustration for the patient. For cases with limited vertical space that would result in an inadequate thickness of acrylic, a cast framework can provide the needed strength. Utilizing Computer-Aided Design and printing technologies to fabricate the framework enables a precise and predictable prosthetic outcome to be achieved.

1. Sposetti VJ, Gibbs CH, Alderson TH, Jaggers JH, Richmond A, Conlon M, Nickerson DM. Bite force and muscle activity in overdenture wearers before and after attachment placement. J Prosthet Dent. 1986;55(2):265-73.
2. Prats LM, Roberson MJ. Preventing fractures in implant-supported removable dentures. Dent Today. 2010;29(12):100-02.
3. Finley JM. Restoring the edentulous maxilla using an implant-supported, matrix-assisted secondary casting. J Prosthodont. 1998;7(1):35-9.
4. Cheng AC, Wee AG, Maxymiw W, Morrison D. The management of implant-retained overdenture treatment with custom-made metallic attachment housing. J Prosthodont. 1998;7(2):79-83.
5. Rodrigues AH. Metal reinforcement for implant-supported mandibular overdentures. J Prosthet Dent. 2000 May;83(5):511-13.