Editorial Type:
Article Category: Research Article
 | 
Online Publication Date: 16 Feb 2023

Abutment-Bar Structure Connection Geometry: An Important Design Parameter for Implant-Supported Bar-Retained Overdentures With Cantilever Extension

PhD and
PhD
Page Range: 330 – 339
DOI: 10.1563/aaid-joi-D-22-00055
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When extended distally due to higher loading in the posterior region, implant-supported bar-retained overdentures with cantilever bar extension exhibit greater bending moments on the implants closest to the cantilever bar and increased stresses in the overdenture components. In this study, a new abutment-bar structure connection was introduced to minimize undesired bending moments and reduce the resulting stresses by increasing the rotational mobility of the bar structure on the abutments. Copings of the bar structure were modified to have 2 spherical surfaces, sharing the same center, located at the centroid of the top surface of the coping screw head. The new connection design was applied to a 4 implant-supported mandibular overdenture to create a modified overdenture. Both the classical and modified models had bar structures with cantilever extensions in the first and second molar areas and were analyzed for deformation and stress distribution using finite element analysis, which was also conducted for both the overdenture models without cantilever bar extensions. Real-scale prototypes of both models with cantilever extensions were manufactured, assembled on implants embedded in polyurethane blocks, and subjected to fatigue testing. Both models' implants were subjected to pullout testing. The new connection design increased the rotational mobility of the bar structure, minimized the bending moment effects, and reduced the stress levels in the peri-implant bone and overdenture components, whether cantilevered or not. Our results verify the effects of rotational mobility of the bar structure on the abutments and validate the importance of the abutment-bar connection geometry as a design parameter.

Figure 1.
Figure 1.

Main components of the overdenture models: coping, coping screw, abutment, and implant (from left to right). (a) Astra Tech Classic (model 1-T1). (b) Astra Tech Modified (model 2-T1).


Figure 2.
Figure 2.

Cross-sectional views of the assembled overdenture components with cantilever extension. (a) Astra Tech Classic (model 1-T1). (b) Astra Tech Modified (model 2-T1).


Figure 3.
Figure 3.

Three-dimensional solid models of the assembled overdenture components with cantilever extension. (a) Astra Tech Classic (model 1-T1). (b) Astra Tech Modified (model 2-T1). Soft tissue was excluded from the models.


Figure 4.
Figure 4.

Half finite element models of the assembled overdenture components with cantilever extension. (a) Astra Tech Classic (model 1-T1). (b) Astra Tech Modified (Model 2-T1). Soft tissue was excluded from the models.


Figure 5.
Figure 5.

Representative photographs of the real-scale prototypes. (a) The implants embedded in the polyurethane foam block. (b) The assembled bar structure with cantilever extension.


Figure 6.
Figure 6.

Representative photographs for the pullout testing of the implants embedded in the polyurethane foam blocks.


Figure 7.
Figure 7.

Representative photograph for the fatigue testing of the bar structure with cantilever extension assembled on the implants.


Figure 8.
Figure 8.

von Mises stress distribution for the bar structure and posterior components. (a, b) Bar structure. (c, d) Abutment. (e, f) Implant. (g, h) Peri-implant cortical bone.


Figure 9.
Figure 9.

von Mises stress distribution for the anterior components. (a, b) Abutment. (c, d) Implant. (e, f) Peri-implant cortical bone.


Figure 10.
Figure 10.

Boxplots with error bars for the pullout forces of the testing groups.


Contributor Notes

Corresponding author, e-mail: ramazankayacan@sdu.edu.tr
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