## 4 Discussions  
Nowadays, with the development of digital technology for dental implant treatments, implant treatment planning is more precise, reliable, and efficient. The optimal position of implant fixtures can be corrected with assisted devices to improve the accuracy of the implant placement by using a computer-assisted implant system. Several articles have reported that using computer-assisted implant surgery for an implant placement was more accurate than using conventional techniques [6; 7; 8; 9; 10]. Currently, there are many software programs used for planning implant positions and designing surgical guides. However, few studies have been undertaken to compare the accuracy of each program. Therefore, in this in vitro study, we aimed to compare the accuracy of these implant planning software programs. We investigated three-dimensional implant positions by using the static surgical guides designed by three different, and widely used, software programs. These were named Program A, Program B, and Program C.  
The outcomes of this study were as follows. The implant position planning and the static surgical guide fabrication using all three different implant planning software programs provided three-dimensional implant position deviations at the implant platform, implant apex, and depth. These ranged from 0.38-0.71 mm, 0.44-1.04 mm, and 0.09-0.44 mm, respectively. There were no significant differences between the three-dimensional implant platform, implant apex, and depth deviations between all three groups. However, an important finding to note from this study was there was a significant difference between the three groups in the angular deviation of the implant placement using the static surgical guides designed by all three implant planning software programs; the mean angular deviations of Program A, Program B, and Program C were 1.72 \(\pm\) 0.88 degrees, 2.05 \(\pm\) 1.24 degrees, and 2.74 \(\pm\) 1.81 degrees, respectively. The mean angular deviation of the Program C group was greater than the Program A and Program B groups. Although the angular deviations between Program C and Program A were statistically significant, these results may not be clinically significant. According to a previous systematic review [11], the accepted clinical research indicated that the mean angular deviation ranged from 1.49 degrees to 8.54 degrees. The angular deviation of the implant axis may be caused by an impression distortion due to a greater strain of the impression material, probably because of the higher forces required for the impression removal [12]. According to the concept of a prosthetic-driven implant treatment, the proper implant position should conform to a definitive prosthesis or restorative position in order to reduce the non-axial occlusal loading force for gaining a proper loading force distribution to the implant and surrounding bone [13]. If the occlusal loading force on the restoration does not distribute to the same vector of the implant axis, a greater and more destructive stress distribution occurs between the implant fixture-supporting bone and the implant fixture abutment. This then causes marginal bone loss and the fracture of the implant abutment connection [14; 15]. The angulation of implants is one of the most important factors that influences the distribution of the occlusal loading force to the peri-implant-supported bone. To correct a deviation  
in the implant angulation to provide a path for a fixed prosthesis insertion, angulated abutments were used [16]. The use of angulated abutments could make the cantilever of the restoration or prosthesis affecting the biomechanics response more fragile due to the increase in stress concentrations on the implants and peri-implant-supported bone [17]. The vertical or depth deviations of the placed implant positions using the surgical guides designed by the three software programs ranged from 0.09-0.44 mm. From this study, most implant positions achieved were more coronal (shallower) than the planned positions.