Clinical evidence and Science 13 SCIENCE BEHIND THE IMPLANT-ABUTMENT CONNECTIONS Positional stability of the implant-abutment connection Stability of the implant-abutment connection influences the manufacturing of the superstructure as well as the long-term success of implant-based prosthetic reconstructions. To ensure a precise fit of an implant-supported restoration, the reproduction of the exact abutment position in the patient’s mouth and the laboratory is of fundamental importance. During superstructure fabrication, multiple repositioning of the implant and laboratory components is required. An imprecise connection may impair screw joint stability and result in unfavorable load transmission to the components of the reconstruction. Connection stability depends on the precision of fit, which is influenced by the design of the connection as well as by manufacturing tolerances. Numerous studies have been performed to analyze the connection stability of the CAMLOG® and CONELOG® Implant Systems and to compare both to other implant systems. Rotational fit of the cam-groove index design: mathematical considerations Positional stability of the abutment connected to the implant is ensured by the positional index that functions as an anti-rotation mechanism. Different geometric designs of positional indices are used in various implant systems. One main factor influencing the horizontal stability of the implant-abutment connection is the rotational freedom. A rotational displacement of the abutment may impair the fit of the prosthetic superstructure. A research group at the Charité hospital in Berlin, Germany, evaluated the influence of the geometric design of positional indices on the horizontal position stability of the abutment (Semper et al., 2009) (13). The group performed mathematical analyses for three common geometric designs: regular polygon interface of different vertices (Steri Oss, Astra Tech, Straumann); rounded polygonal patterns (Replace Select implant system), and the cam-groove connection which is used in Camlog’s implant systems. The calculations clearly showed that the geometric design as well as the size of the positional index influence the rotational freedom and thereby the horizontal stability of the abutment. The clearance between the implant wall and the abutment has a major influence on the positional stability emphasizing the importance of the manufacturing tolerances. Based on above findings, Semper et al. (2009) used mathematical analyses and 3D-simulations to directly compare the rotational freedom of the three common positional index designs described above, i.e., regular polygon, rounded polygon as well as the cam-groove pattern (14). They hypothesized that the manufacturing tolerances, geometric pattern and dimensions of the index do not influence the positional stability. The study demonstrated that with an assumed clearance of 20 µm between implant and abutment the bidirectional rotation observed varied depending on the positional index design of the implant system. The largest positional freedom, i.e. worst rotational fit, was calculated for the regular polygonal positional index (varying from 3.0° to 3.7°). A better positional stability was determined with the rounded polygonal pattern (1.9°) (Fig. 9). However, the highest positional accuracy was calculated for the cam-groove design of the CAMLOG® Implant System (1.4°).
RkJQdWJsaXNoZXIy MTE0MzMw