## 1 Introduction  
At present, digital scanning technology is in common use both for teeth and implants. There are many advantages associated with intra-oral digital impressions, including: reduced distortion from impression materials and plasters, less chair time, acquisition of digital file, improved patient comfort and the ability to take passive impressions [1, 2, 3, 4]. There are two possible methods for taking a digital impression: indirect (laboratory scanner), where the lab scans either the impression or the model, or direct (intra-oral scanner) using chair-side scanning [5]. Yet many dentits continue using traditional impression methods for implants and teeth [6, 7, 8, 9]. [PERSON] et al. examined digital impressions versus conventional and showed both methods yield similar marginal fits; in the case of implants, digital impressions are more accurate for single crowns, however, cross-arch scanning for multiple unit bridges remains questionable [10].  
A digital STL file is a CAD mesh which transmits the three-dimensional scan with a high degree of accuracy, from which the final work can be designed [11]. The scan abutments for digital impressions are commonly made from polyether ether ketone (PEEK), titanium type 5 or combination of both [12]. The geometry of the scan abutment is different between the commercial companies and important for accurately conveying the position and the orientation of the implant. The data derived from the scan abutment are analyzed by the software to define the longitudinal, vertical, and rotational axis of the implant [13]. According to a study by [PERSON] et al., scan abutments attached to implants by an internal hexagon show less rotational movement than external connection [14; 15]. Moreover, they concluded that the marginal fit of the prosthetic is better than that of those with an external hexagonal design. The laboratory scanner provides a higher degree of accuracy compared to the intra-oral scanner and, therefore, serves as gold standard in comparison to intra-oral scanners [16].  
There are several terms relating to the digital files [17], between them: Value--a quantitative characterization; Trueness--Proximity between the expectation of a particular test result/measurement and the true value; Precision--Proximity between independent test results; Accuracy: the results will be close to each other and close to the target.  
It is clinically important to capture the implant axis as accurately as possible because it influences the design and manufacturing of the restoration, for example: passive fit, contact areas and occlusal contacts. In recent years, there has been a marked improvement in the impression techniques as well as in prosthetic fabrication, such that the difference in passive seating between cemented and screw-retained crowns has become an insignificant factor [18].  
To date, studies have compared the differences between digital impressions using scan abutments and conventional impressions using impression copings, and even these studies have not given unequivocal answers [19]. The purpose of this study was to evaluate the position and orientation of the implant comparing laboratory scanning (gold standard) versus intra-oral scanning with three different scan abutments. The null hypotheses were that no difference will be found between the intra-oral scanner compared to the laboratory scanner by using three different scan abutments.