Dental implant placement has shown high survival and success rates [1, 2]. According to one study, the overall 5-year prosthetic survival rate for implant treatment has increased from 93.5 to 97.1% during the past 10 years [1]. Despite the high survival rate of implants, technical complications, such as screw loosening, are frequently reported [1,2,3]. The 5-year complication rate for screw loosening in studies after the year 2000 is 8.7%. Screw loosening can cause a misfit of the implant-abutment connection [4] which may lead to a gap, increasing bacterial accumulation, and possible peri-implant tissue inflammation. Moreover, using an implant prosthesis with a loose screw can result in abutment screw fracture [5]. One of the key factors in the success of dental implant treatment is the implant-abutment connection [6]. One such connection is the internal cone connection which has been reported to improve the biomechanical properties of implant-abutment assemblies [7]. If the contacting angle of the cone connection is 2° to 8°, the connection is called a Morse taper connection [8]. The Octatorx-cone connection is a combination of a Morse taper connection with a 6° tapered angle and star-shaped “octalobules” indices with eight rounded points [9] (Fig. 1). This Octatorx-cone connection provides an anti-rotational characteristic and surface frictional resistance at the implant-abutment interface, which may prevent micromovement and screw loosening during function.

The stability of the implant-abutment connection comes from both the screw function and the frictional resistance between the conical, contacting metallic surfaces of the connection [10]. An abutment screw provides stability via a clamping force [11, 12]. When rotational torque is applied to the screw, the screw elongates and causes stress on the stem and threads. After that, elastic recovery of the screw occurs, the stem and threads of the screw are in tension and a clamping force is created, pulling the abutment and the implant together. This clamping force is parallel to the axis of the implant and is also known as preload. The preload value is directly proportional to screw elongation. The more screw elongation remains after elastic recovery, the greater is the preload value.