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Received Mar 12, 2018; Accepted May 9, 2018
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1. Introduction
High precision in transfer of clinical conditions to dental laboratory is one of the most important factors in fabrication of the prosthesis with excellent fit for either natural teeth or implants [1]. Therefore, the essential first step for fabrication of a successful implant-supported prosthesis is accurate transfer of three-dimensional implant position and angulation from the mouth to the master cast via impression [1, 2]. Inaccurate position of the implant in the master cast makes it impossible to fabricate a well-fitting prosthesis, and the resultant misfit can lead to biomechanical complications such as screw loosening [3], bone loss [4], and ceramic veneer fracture as a result of increasing stress within the prosthesis or at the interface of the implant and bone. Accuracy of the master cast is influenced by several factors including the impression technique, type of the tray [5, 6], manipulation of the dental stone, and its compatibility with the impression material [7]. Each step could have a potential error related to inherent materials or humans which is inevitable. Moreover, other factors involved in the precision of implant impression could be the impression technique (direct versus indirect), splinting, machining tolerance of components, number and angle of implants, depth of implants, and type of connection [8–14]. Multiple implants with different angulations can cause distortion of the impression material on removal [11]. In a review by Lee et al. [15], it has been reported that when the implants are more than three, angulation of implants may affect the accuracy. However, when the implants are limited to 2 or 3, no effect was reported on the impression accuracy [10]. Also, many articles studied the accuracy of different implant impression techniques [16–20]. For situations in which there were 4 or more implants, studies showed more accurate impressions with the direct technique than the transfer technique [8, 15, 18, 19].
The advent of intraoral scanners (IOSs) has led to a change in implant dentistry. Although the first IOSs became commercially available two decades ago, their popularity in recent years has...