## 4 Discussion  
This study focused on determining a suitable methodology for assessing trueness and precision by considering the error in the diameter of 3 DP full-arch surgical guides. The diameters of each plane hole and their accuracy are crucial for implant placement to avoid damage to any anatomical structures such as the maxillary sinus and inferior alveolar nerve [25]. A strength of this study was the method to measure error; to ensure accurate measurement, a CMM with direct profilometric measurements was acquired and analysed using inspection software to compare the measurements to the reference STL files. This approach minimises the measurement errors arising from optic scanning. It is followed by iterative closest point superimposition (best-fit alignment or registration) used by other studies that  
Figure 5: Confidence interval and mean demonstrating trueness (mean) and precision (IQR) in a box plot. Note: handwashing without nitrogen (HH wo N), handwashing for 2.5 min (HH 2.5), handwashing for 5 min (HH 5.0), handwashing and sonication (H_US), sonication (US_US). All measurements are in millimetres. tend to over- or under-estimate measurement deviation [1; 26; 27]. Moreover, to minimise printing errors, a high-accuracy DLP printer was selected for manufacturing the surgical guides with a reported accuracy of \(-16\)\(\upmu\)m [8]. Additionally, the choice of the controlled variables of print orientation and print layer thickness in this study having been determined based on existing evidence proved to be a strength, as the print orientation affects dimensional and mechanical properties [22]. A study [28] investigated the fracture toughness for additive layer manufacturing (ALM) techniques similar to the DLP used in this study, and found that printing of composite double cantilever beams in a vertical direction had a 217% increased toughness compared to a horizontal direction for the same configuration. However, in terms of print orientation used for dental implications, a horizontal (0\({}^{\circ}\)) build angle is most commonly used with proven superior accuracy, although a 45\({}^{\circ}\) inclination has also been reported to have a high fit rate [6; 11]. Nevertheless, [PERSON] et al. [7] reported that a 0\({}^{\circ}\) build angle required the shortest printing time of (hour: minute) 1.26 \(\pm\) 0.03 (\(p\)! 0.001) and had a reported accuracy of 0.048 mm \(\pm\) 0.007, whilst a 90\({}^{\circ}\) build angle required the longest printing time of 2.52 \(\pm\) 0.06 (\(p\)! 0.001) and had a 0.097 mm \(\pm\) 0.017 accuracy. Another study looking at additive manufacturing 3 DP [29] assessed the effect of print orientation on strength in terms of elastic modulus and tensile strength. It was found that a print orientation of 0\({}^{\circ}\) had higher strengths than those at 90\({}^{\circ}\). As a result of the aforementioned literature, this study utilised a horizontal 0\({}^{\circ}\) build angle for all prints. The layer thickness can equally influence the accuracy of the implant surgical guide. [PERSON] et al. [30] and [PERSON] et al. [31] assessed layer thickness for DLP printers, and demonstrated that the range of 25 to 150 \(\upmu\)m layer thickness achieved clinically acceptable results. Similarly, [PERSON] et al. [8] reported that a layer thickness of 100 \(\upmu\)m proved optimal to ensure accuracy and reduce printing time, compared to 25 and 50 \(\upmu\)m thicknesses. In this study, varying parameters were investigated, including resin type, arch location, and post-processing methods. Regarding the type of resin, both tested resins were propriety, validated, and photosensitive polymer resins from the 3D printer's manufacturer (Asiga) and indicated for implant surgical guides' manufacturing. As a result of this, it was appropriate for this study to print implant surgical guides.