Aim: The aim of this bench study was to provide quantitative data addressing the difference between the manual low window design and the corresponding computer-aided design and computer-aided manufacturing (CAD/CAM)-guided design. Materials and methods: Five cone-beam computed tomography (CBCT) scans of as many patients (two males and three females, age range: 61–78 years) with partially edentulous maxilla to be rehabilitated through sinus augmentation, one- or two-step implant placement, and implant-supported prostheses were used to 3D-print the corresponding five maxillary stereolithographic models. Five independent highly skilled maxillofacial surgeons, who were provided with the patients’ orthopantomographs, drew on the models the access windows for sinus augmentation according to the “high” (standard) and the low window design both by free-hand and using a surgical guide prepared by computer-guided design. Accuracy and inter-operator variability were analyzed. Results: The results of this study showed that the manual design is associated with a clinically relevant shift in the low window shape, size, and positioning compared with the CAD/CAM-based positioning. All four directions (apical, coronal, mesial, and distal) showed on average the same extent of placement error (approximately 3 mm). Overall, the intra-operator variability was very similar, and measurements were not influenced by the operator (low inter-operator variability). Conclusion: The compromised accuracy and reproducibility in the manual design may limit the advantages of the low window technique. Thus, within the limits of this study, the computer-guided approach should be preferred vs the manual approach when performing a low window sinus lift. This may limit intra- and postoperative complications, as well as patient discomfort. Clinical significance: The “best option” CAD/CAM-guided design should be chosen when performing a low window sinus lift because it reduces discrepancies in selected parameters both between and within groups. This should facilitate the achievement of better results by dentists who have insufficient experience performing implant surgery.
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