## 4 Discussion
In another study that investigated the effect of drilling distance, sleeve length, and sleeve height, it has been shown that the length of the sleeve had no influence on accuracy, but rather the drilling distance below the sleeve had a significant effect on the accuracy of implant placement [17]. The VARO guide has adopted the latter design of reduced sleeve length rather than the open-sleeve design, which should produce greater accuracy according to these indications in the literature. The four cases included in this study exhibited a variation of deviation values. Case 1 showed the greatest deviation in the angle and horizontal aspects at the platform and apex. This result could be owed to Case 1 having the least remaining ridge height among all of the cases. In contrast, Case 4, having the tallest remaining ridge height, revealed the most accurate result. There was also a correlation between the remaining ridge height and the initial stability of the implants, as Case 1 was the least stable and Case 4 was the most stable. Taking this into consideration, it could be deduced that shorter ridge height can lead to less implant stability and less accurate implant placement. Another possible explanation for the variation among the data might be the influence of the learning curve. The four cases were performed in chronological order; therefore, the skill of the surgeon at using the VARO guide would have improved after each case. This was evident in the data, as there was a trend of decrease in error from Case 1 through to Case 4. However, due to the small number of subjects in this pilot study, it is difficult to draw a conclusion based on statistics. In the authors' knowledge, there has not been a prospective trial up-to-date on the accuracy of guided implant placement with simultaneous crestal sinus graft. It is necessary, therefore, to perform a randomized controlled trial to verify the effect of the simultaneous Hapless approach on the accuracy of guided implant placement. It is also possible that other sources of error might have contributed toward the deviation data in this study. Inaccuracies in VARO-guided surgery can be attributed to factors that are intrinsic and extrinsic to the surgical guide. Intrinsic errors can arise from the inaccuracy of the composite resin impression using the pre-guide and incorrect seating of the pre-guide during CBCT taking. Polymerization shrinkage is an inherent drawback of resin composite [18], and since the inner surfaces of the pre-guide had been cured extraorally, shrinkage of the fitting surfaces can be a possibility. Extrinsic errors can result from the movement of the VARO guide during implant placement and the experience of the surgeon in the VARO guide protocol. In regards to the latter, however, a recent in vitro study has reported similar outcomes in terms of time and accuracy when VARO guide surgery was performed by expert and novice users [11]. In the same study, when the VARO guide was compared to a 3D-printed surgical guide, the VARO guide required less time to prepare, although the surgical time was similar. Since the evolution of implant dentistry toward minimally invasive procedures, flapless surgery has been shown to provide many benefits. These include preservation of blood circulation and soft tissue architecture [19], prevention of marginal bone loss by avoiding bone denudation during flap elevation [20; 21; 22], and considerably less postoperative mor bidity and discomfort in terms of the patient-reported outcome [23; 24; 25]. However, it can be disadvantageous to perform flapless surgery freehanded as the true outline of the underlying bone cannot be detected by palpation alone [26]. Furthermore, in the vertically atrophic ridge, as in this study, accurate implant placement may seem like a challenging task. In the VARO guide sinus kit, a soft tissue punch is included, and it has become possible to access the sinus floor without raising a flap and place the implant fixture according to the virtual plan.