16 Clinical evidence and Science Fig. 10_Occlusal view of the five tested implant connections with their characteristic position indices: (A) ITI implant with conical-joint and octagonal positional index, (B) Steri-Oss implant with standard butt-joint and hexagonal positional index, (C) CAMLOG® implant with butt-joint and cam positional index, (D) Astra Tech implant with conical-joint and dodecagram positional index, and (E) Replace Select implant with butt-joint and polygonal positional index. (Semper et al. 2010, reproduced with kind permission of Quintessence Publishing co, Inc, USA) Effect of the connection design on the accuracy of repositioning The theoretical calculations described above (13–15) were also tested in an experimental study. Positional stability of five different implant systems (ITI, Steri-Oss, CAMLOG®, Astra Tech, and Replace Select: Fig. 10) was compared after multiple manual disassembly and reassembly (Semper et al., 2010) (16). Five implants were arranged with varying angles in a stainless-steel model to simulate a typical clinical situation. Abutments were assembled and reassembled manually by three test people for each implant system 20 times by using system-specific screwdrivers. Any rotational, vertical, and canting deviation from the initially determined position was monitored using a coordinate reading machine. Rotational freedom ranged from 0.92 to 4.92 degrees. CAMLOG® connections showed significantly smaller rotational discrepancy than the other systems tested (Fig. 11A). The systems with a horizontal butt-joint displayed significantly lower vertical alterations in position than beveled implant-abutment connections (Fig. 11B). Regarding canting discrepancies, the implant systems did not differ significantly (Fig. 11C). The authors concluded that reposition of rotation-safe abutments on the implants leads to a three-dimensional deviation compared to the initial position and that the accuracy of repositioning is influenced by the geometric design of the implant-abutment interface. SCIENCE BEHIND THE IMPLANT-ABUTMENT CONNECTIONS
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