The Effect of Two Different Bar Materials Constructed with CAD/CAM Technology on Implant Retained Mandibular Overdentures: Radiographic Evaluation

Abstract

Oral rehabilitation with an overdenture on splinted or unsplinted implants is considered the standard care in cases of mandibular edentulism. Numerous studies have shown that the mandibular implant overdenture is a simple and effective solution and leads to significant improvement of patient-based outcomes as compared to conventional dentures. The use of a wide variety of attachment systems, including stud, magnet and bar attachments have proven both clinically predictable and effective results. The design of attachments should provide equal implant-tissue support and optimum force distribution around the implants to allow bone loading within physiologic levels. Implants splinted together with bars may decrease the risk of overload to each implant as a result of a greater surface area, load sharing between implants and improve biomechanical distribution (1). Bar attachments are classified according to their biomechanical behavior into rigid and resilient attachment. In comparison to resilient bar attachment, rigid anchoring of removable prostheses creates stable occlusal plane, reduces loading of denture-bearing areas, and minimizes posterior mandibular ridge resorption. One of the major drawbacks of rigid bar attachment is overloading of the abutments, however resilient bar attachment encourages torsion-free load transmission to implants dentures. The main disadvantages of bar attachments are the need for a large prosthetic space and the risk of mucositis due to an inadequate oral hygiene under the bar. With prefabricated bar designs, lack of accurate adaptation of the denture base to the bar superstructure, rotation and lateral movement of the denture are unavoidable. In order to improve the fit of the overdenture framework electrical discharge machining (EDM) and spark erosion can be used, but this procedure is costly and technique-sensitive (2). Milled bars have been suggested as a less expensive alternative to EDM. Implant-supported milled bars are bars with