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Screw Restoration Essay

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screw, with an increase of cohesive and adhesive failure in the bond between ceramic and framework(8)and can disrupt the normal occlusal contacts (8,11).Because the occlusal restoration's durability of the screw-retained prosthesis, such as amalgam or composite, which cover the screw access channel is inferior to an intact full coverage crown particularly when the size of the implant is increased ,the screw access hole is increased too, thus leading to a large occlusal restoration, which may compromise the long-term durability(66),so the selection of screw retention or cement retention as an attachment mechanism impacts significantly on the occlusion. Implants ideally placed under the central fossa or stamp cusps of posterior teeth…show more content…
It was further noted that the implants lost were mainly short and posteriorly positioned implants(37)and the necessity for the use of the shorter implant lengths to avoid anatomic structures such as sinuses or inferior alveolar nerves(40). As this was the main concern with the traditional hexagonal implant systems, the incidence is greatly reduced with the advent of newer implant systems (e.g., internal connections with a geometric lock, larger abutments, and screws designs (66)Moreover, the patient does not perceive the occlusal overload on an implant structure with painful symptoms because of the lack of the natural teeth and its mechanical receptors in the periodontal ligament.(32) As a consequence to implant's periodontal ligament lack, higher forces are exerted on implant crowns, then porcelain fracture is a frequently occurred (66)However, nerve fibers in the bone,mucosa,periosteum and muscle trigger a compensatory mechanism defined ‘bone perception’ that can only partially compensate the mechanical negative feedback of the periodontal ligament. For this reason, every prosthetic implant system is exposed to a greater risk of biomechanical overload(32). Nevertheless, the use of screw retention, with all of its disadvantages, still remains the retention mechanism of choice for many practitioners as evidenced by the product lines of implant manufacturers.
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