Abstract
This paper aims to compare, in vitro, the biomechanical properties of an overdenture retained by two bar-retained implants and an overdenture retained by two bar-retained implants with ball attachments. An edentulous mandible model was prepared for the study based on the FRASACO mold with two implants. In the first system, the “rider” type (PRECI-HORIX, CEKA) retention structure and the complete mandibular denture with the matrix were made. In the second system, the “rider” type retention suprastructure was also used. In the distal part, (CEKA) clips were placed symmetrically, and a complete mandibular denture, together with the matrix on the bar, and the clip patrices were made. A numerical model was developed for each system where all elements were positioned and related to geometric relations, as in reality. The FEA analysis (finite element analysis) was carried out for seven types of loads: with vertical forces of 20, 50, and 100 N and oblique forces of 20 and 50 N acting on individual teeth of the denture, namely central incisor, canine, and first molar. Displacements, stresses, and deformations within the systems were investigated. Maximum denture displacement in the first system was 0.7 mm. Maximum bar stress amounted to 27.528 MPa, and implant stress to 23.16 MPa. Maximum denture displacement in the second system was 0.6 mm. Maximum bar stress amounted to 578.6 MPa, that of clips was 136.99 MPa, and that of implants was 51.418 MPa. Clips cause smaller displacement of the overdenture when it is loaded but generate higher stress within the precision elements and implants compared to a denture retained only by a bar. Regardless of the shape of the precision element, small deformations occur that mainly affect the mucosa and the matrix.
Highlights
Overdentures are one of the recognized methods of prosthetic treatment of the mandible
Contour maps show places where the greatest stress is concentrated within the bar retention and clips, as well as around the implants (Figure 6)
When a denture retained by a “rider” bar is loaded with a Greater dislocations of the denture were recorded in the first system, where the maximuGmrevaatleuredwisalosc0a.t7iomnms o(fFtihgeudreen8t)u
Summary
Overdentures are one of the recognized methods of prosthetic treatment of the mandible. Reasonable costs and uncomplicated clinical management with a significant improvement in retention and stabilization make this type of restoration an attractive treatment option for both patients and dentists [1,2,3]. Precision elements, such as bars, ball or locator clips, telescopic crowns, and magnets [4,5,6,7], limit denture mobility both vertically and horizontally. Precision attachments used with implant-retained overdenture counteract free rotation, so a greater occlusal force may be exerted because of the perceived better denture stability. Along with other manufacturing errors or lack of follow-up care, unexpected and uncontrolled rotation of the denture, rapid wear, damage to its components, or implant overloading may happen [9]
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