A Method for Minimizing Rotational Errors of Implant Prostheses

Purpose: Rotational errors of implants can occur during two stages: when connecting impression copings with implants, and when connecting impression copings with analogs. The aim of this study was to determine ways to minimize these rotational errors. Materials and Methods: Three types of implants were prepared: a tissue-level implant with an internal octagon 8-degree Morse taper connection, a bone-level implant with an internal hex 11-degree Morse taper connection, and a bone-level implant with an external hex connection. Each complex (n = 10 per group) was composed of an implant, an impression coping, and an analog. Implants were embedded in resin blocks and connected with corresponding impression copings. Analogs that reproduced the position of the implants were created by means of a custom-made transfer jig, and rotational errors were measured between implants and analogs. Impression copings and analogs were connected by means of four methods: The impression coping was connected to the implant in a clockwise (CW) or a counterclockwise (CCW) direction before tightening, and the analogs were then connected with impression copings and tightened using a hemostat (Hs) or by hand (Hd). Results: The CW-Hs and CCW-Hd groups exhibited low rotational error (mean ± standard deviation 0.11 ± 0.21 and 0.19 ± 0.34 degrees, respectively), whereas the CW-Hd and CCW-Hs groups exhibited high rotational error (−1.80 ± 0.67 and 2.07 ± 0.75, respectively) in different directions. A strong association was observed between the tightening method and rotational error, and a weak association was observed between the connection type and rotational error. Conclusion: The CW-Hs method was found to be the most suitable for minimizing rotational error between implants and analogs. Keywords: clockwise, counterclockwise, implant prosthesis, impression method, rotational error, rotational freedom