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Prosthodontic treatment for edentulous maxillae with severe bone loss is a challenge to clinicians. Although implant-supported, fixed maxillary complete dentures are increasingly common, they are not always able to provide adequate lip support without a buccal overextension in patients with bone loss. The overextended buccal flange makes it difficult for patients to clean under the prosthesis. This case report describes rehabilitation of an atrophic maxilla through an implant-supported double-bar overdenture designed to resolve difficulties in oral hygiene maintenance that were caused by the buccal overextension of the prosthetic flange in a previous implant-supported fixed complete denture. In addition to reestablishing lip support, overdentures with a double-bar system provide retention and stability, because the prosthesis is only removed for cleaning by the patient with the help of a specific key. Implant-supported double-bar overdentures represent a viable and versatile option for rehabilitation of atrophic maxillae., Competing Interests: Disclaimer: The authors report no conflicts of interest pertaining to any of the products or companies discussed in this article.

In this in vitro study, 2 implants were embedded in the interforaminal region of an acrylic model. Two kinds of retention mechanisms were used to construct complete overdentures: ball type and direct abutment (Locator). The ball-type retention mechanism models included 3 different collar heights (1, 2, and 3 mm) with 15 mm occlusal plane height, and 3 different occlusal plane heights (9, 12, and 15 mm) with 1 mm collar height. The direct abutment models included 3 different occlusal plane heights (9, 12, and 15 mm) with 1 mm cuff height. Vertical unilateral and bilateral loads of 150 N were applied to the central fossa of the first molar. The stress of the bone around the implant was analyzed by finite element analysis. The results showed that by increasing vertical restorative space, the maximum stress values around implants were decreased in both unilateral and bilateral loading models. The results also showed that the increase in maximum stress values around implants correlated with the ball attachment collar height. The Locator attachment with a 1 mm cuff height and 9 mm occlusal plane height demonstrated 6.147 and 3.914 MPa in unilateral and bilateral loading conditions, respectively. While a reduction in the collar height of a ball-type retention mechanism and an increase in the vertical restorative space in direct abutment retention mechanisms are both biomechanically favorable, and may result in reduced stress in peri-implant bone, a ball attachment seems to be more favorable in the stress distribution around an implant than a Locator attachment.