# Accuracy and Wear Evaluation of the Customized Zirconia Guided Sleeves
## 4 Discussion  
The present study examined single-type surgical stents with varying CAD/CAM zirconia drill sleeve distances to determine the accuracy and wear conditions in simulated clinical positions. [PERSON] et al. [8] conducted a systematic review and reported a mean deviation of 0.9 to 1.2 mm and 3.3 deg angular deviation for partially dedentulous cases. Moreover, the results of accuracy were affected from various tooth positions; the upper right first molar exhibited the maximum horizontal deviation, and the lower left first molar exhibited the maximum vertical and angular deviations. Drill sleeve distance did not affect horizontal and vertical deviations; however, the maximum angular deviation was observed after the application of a drill sleeve distance of 0.03 mm. [PERSON] et al. [7] reported that the various quadrants of a surgical site produced varying implant deviations in a free-hand placement protocol; their results indicated that the maxilla site (first and second quadrants) was associated with a significant buccolingual angulation and apical point deviation, and the third quadrant was associated with a significant mesiodistal angulation deviation. A systematic review [21] reported a greater angular deviation of implant placement performed using a guided stent for the maxilla than the mandible. This finding can be attributable to the inadequate stability of the guided stent for placement in the fully dedentulous maxilla, thus resulting in accuracy errors. To the best of our knowledge, no study has examined single tooth-gap implantation by using a guided stent. The findings of our in vitro study partially correspond to those of previous studies. Our results indicate that the maximum horizontal deviation of the upper right first molar can be attributable to the impaction of the surgical position by the right-handed surgeon. [PERSON] et al. [22] reported that left-handed dental students found the maxilla to be more difficult to operate on than the mandible, with Quarter I being the most challenging to work on. The lower left first molar exhibited a significant difference in vertical and mesiodistal angulation deviations in our study; this could be related to the surgical habits of the right-handed surgeon who worked visually from the anterior-mesial side to the posterior-distal side, resulting in drilling deviations despite the restriction of the pathway by the static-guided stent. [PERSON] et al. [23] demonstrated that the multiple-use sleeve causes sleeve-wall attrition, thus increasing implant deviation. [PERSON] et al. [24] indicated that a higher tolerance to system components is associated with the presence of larger intrinsic errors in a system. The present study demonstrated that a distance range of 0.01 to 0.03 mm for drill sleeves did not affect horizontal and vertical deviations. A narrower sleeve (i.e., 0.01 mm) has the advantage of providing the minimal angular deviation of im-plantation; the disadvantage of a narrower sleeve is that it may produce overheating during drill-sleeve contact. However, more sleeve wear (Figure 5) was found in a bigger drill-sleeve distance (i.e., 0.03 mm); this could be relevant to the greater tolerance for deviated drill side cutting the sleeve. Drill sleeve contact during implant surgery may increase the wear debris, causing unfavorable results such as poor wound healing or osteintegration failure [25]. [PERSON] et al. [26] advised clinicians to move the drill in and out of the guide multiple times to identify the smoothest drill position and allow sufficient irrigation. [PERSON] et al. [18] demonstrated that the tolerance of surgical instruments and lateral drill movements can be significantly reduced with the application of 3D printing to achieve a decreased sleeve diameter. [PERSON] et al. [27] recommended using zirconia as the sleeve material because of better biocompatibility and less sleeve wear. The presented study examined single-type stents with a zirconia sleeve incorporated in one stent.