This prospective study was designed to assess the safety and effectiveness of the N.A.B.E technique in the rehabilitation of the atrophic posterior maxilla. As for all implant placements, the N.A.B.E technique requires high precision to prevent complications. The literature demonstrates lesser / reduced accuracy when implants are placed free hand versus guided (static guidance and /or dynamic navigation). Vercruyssen et al. (2014) [
25] reported on a randomized, prospective study comparing the accuracy obtained when placing implants using static guidance from several providers (Materialise Universal, Facilitate) with that obtained from free-hand (“mental navigation”) and pilot-drill templates in 72 fully edentulous jaws. The mean deviations (SD) for those implants placed with static guidance were 1.4 (0.7) mm at the entry point; 1.6 (0.7) mm at the apex and 3.0 (2.0) degrees from the angular standpoint. In comparison, mean deviations (SD) measured with free-hand (“mental navigation”/ unguided) were: 2.8 (1.5) mm at entry point, 2.9 (1.5) mm at the apex and 9.9 (6.0)° for angle deviations. The above demonstrated the significant difference in deviation encountered when comparing static guidance to both the pilot guide and free hand, confirming superior accuracy with static guidance. With this kind of deviation (2.9 mm at apex and 9.9 degrees as angular error), and given the high sensitivity of the technique /method presented, attempting a free hand method could represent a high risk of sinus perforations and implant failure due to inadequate initial implant stability. Although using static guidance has been demonstrated to be significantly more accurate than free hand, using the N.A.B.E technique with static guides would require the fabrication of two guides, one for the initial osteotomy and one to direct the corrected angle preparation and implant placement, which could be very costly. Dynamic Navigation not only eliminates the need to fabricate static guides but allows for real time verification of the osteotomy and real time visualization of the adjunct anatomical structures. These are two critical advantages of the N.A.B.E technique. The accuracy of dynamic navigation is easily verified throughout the procedure by touching fixed points with the drill tip and verifying the virtual image representation with the actual patient. The accuracy of dynamic navigation has been reported in the literature. Block et al. (2017) [
22] treated, in a multicentre study (3 clinicians), 100 partially edentulous patients using the X-guide dynamic navigation system and reported the following accuracy: 0.87 (0.42) mm at the coronal point, 1.56 (0.69) mm at the apex (3D) and 3.62° (2.73°) for angle deviations when the surgeries were guided. For the non-guided surgeries, the accuracy reported were 1.15 (0.59) mm as coronal deviation, 2.51 (0.86) mm as apex deviation, and 7.69° (4.92°) as angle discrepancy. A separate study by Block et al. (2017) [
22] reported on the accuracy of implant placement using dynamic Navigation both fully guided and partially guided when compared to free hand. In this prospective cohort study of 478 patients with a total of 714 implants placed, Dynamic Navigation proved again to be more accurate than free hand. For fully guided navigational surgery, the mean deviation at entry point was 1.16 mm, at the apical point was 1.29 mm, and the mean angle discrepancy was 2.97 degrees. The mean deviations for implants placed free-hand/unguided were 1.78 mm at the entry point and 2.27 mm at the apical point, with a mean angle discrepancy of 6.5degrees. Their accuracy data support the conclusion that implant placement using dynamic surgical navigation is at least as good as to, if not more accurate than, static guides and substantially superior to non-guided/freehand implant surgery. Stefanelli et al. [
20], reported in a retrospective observational study on 231 implants (89 arches) an error of 0.71 mm at the entry point, 1 mm at the apex, and a mean angular error of 2.26 degrees. The combined data obtained from Block et al. (2017) [
24] (2017) [
25] and Stefanelli et al. (2019) [
20] demonstrates the increased accuracy of Dynamic Navigation when compared to both analog fabricated or fully digitally made [
26] static guidance and its superior performance over free hand surgery. In this prospective study, the technique presented was done in combination with a dynamic navigation system. The residual native bone of the posterior atrophic maxilla was used to expand the bone in the ideal prosthetic position followed by the placement of implants in the absence of a bone graft. Parameters evaluated with the N.A.B.E technique included the bone gain using this technique, the implant osseointegration rate, the range of the angular value correction from the initial osteotomy to the implant insertion, the percentage of cases in which screw-retained versus cemented-retained restorations were placed and the complications occurred. The literature has reported on the same parameters evaluated using several techniques when a posterior atrophic maxilla was treated. Nedir R [
27]., et al., placed 37 implants into atrophic sinuses with or without grafting for the osteotome mediated sinus elevation. The success rate reported was 91.9% (94.1% without grafting, 90.0% with graft). All implants had gained antral bone of 3.8 mm without grafting and 4.8 mm with graft. Santoro M, et al., [
28] in a systematic review of the literature, reported that there were no statistically significant differences between an osteotome mediated transcrestal sinus augmentation simultaneous with implant placement whether or not bone grafting materials were used. The mean intrasinus bone gain at 3 years after surgery was 2.99 mm in cases where no grafting material was used and 4.24 mm in cases in which grafting materials were used. The mean percentage of crestal height increase at the implant site at 3 years after surgery, referring to a selection of studies with initial bone height > 4 mm, was 47.28% in procedures without grafting material and 62.68% in procedures with grafting material. A different dimensional behavior of the newly formed bone during the first 3 years after surgery was found: a slight volumetric shrinkage in grafting procedures and a slight bone increase in procedures without grafting material. No statistically significant difference in implant survival rate was found. Nedir R. et al. [
29] inserted 25 implants using the osteotome sinus floor elevation technique without grafting on sites with a mean residual bone height of 5.4 mm. The reported mean sinus bone gain was 2.5 mm after the first year of follow up. In a meta- analysis evaluating the most effective method of rehabilitation of the posterior maxilla (RBH 4-8 mm) with implant-supported prostheses, Al-Moraissi EA et al. [
30] analyzedthe following techniques: short implants (SI) (SIs; ≤8 mm) alone, SIs in conjunction with osteotome sinus floor elevation (OSFE) with or without bone grafting, long implants (LIs) in conjunction with OSFE with and without bone grafting, and LIs combined with lateral sinus floor elevation (LSFE) with bone grafting. They reported that moderate-quality evidence demonstrate that OSFE, combined with SI or LI placement with or without bone grafting or SI placement alone, is superior to LI placement combined with LSFE and bone grafting when used for patients with intermediate maxillary residual bone height (RBH) of 4 to 8 mm. Pjetursson BE [
31] et al., reported a cumulative survival rate of 97.4% of 252 implants placed on osteotome mediated sinus augmentations on a mean 3.2 years of follow-up post-placement. According to the residual bone height, the survival rate was 91.3% for implant sites with < or = 4 mm, and 90% for sites with 4 mm and 5 mm, compared to 100% in sites with RBH bone height greater than 5 mm. According to the implant length, the survival rates were 100% for 12 mm, 98.7% for 10 mm, 98.7% for 8 mm and only 47.6% for 6 mm implants. Pesce et al. [
32], evaluated the implant survival and peri-implant bone resorption around long vs normal length implants in maxillary, full-arch, immediate-loading rehabilitation of low bone quality (D4). A total of 45 patients received two mesial normal-length (10 to 15 mm) or longer (18 to 20 mm) implants and two long (18 to 20 mm) distally tilted implants. At 24 months, the use of long implants provided favorable survival and bone maintenance results in the immediate loading rehabilitation of low-quality maxillary arches. Yang J. et al. [
33], in a systematic review and meta-analysis based on randomized controlled trials of maxillary sinus floor augmentations with or without grafts in the atrophic maxilla, reported no significant differences between the two groups in implant survival (
P = 0.94), marginal bone loss (
P = 0.73) and new bone density (
P = 0.54). There was a significant gain in antral bone in the group that received bone grafting (
P = 0.02). Essam Al-Moraissi [
34], reported in a systematic review of the literature that there is a statistically significant correlation between Schneiderian membrane perforations and implant failure rate. In the present study, patients included in the analysis presented at the base-line with a residual bone height ranging from 4.10 to 6.90 mm (mean 5.89 ± 0.68 mm), demonstrated with linear measurements on CBCT. The bone height after the N.A.B.E ranged from 7.70 to 11.50 mm (mean 9.85 ± 1.10 mm). The mean bone gain was 3.96 mm (67.2%). The survival rate was 94.6%. When comparing the results reported in the current study, similar survival rates were encountered to those reported in the literature that employed other techniques. Using the N.A.B.E technique, 67.2% bone gain was obtained, which is consistent with transcrestal sinus augmentations in combination with bone grafting, and much greater than those reported in the literature without grafting materials. A mean angular value correction of 25.17 degrees was obtained. A total of 32 out of 35 implants received screw-retained restorations. The 3 remaining implants received cemented-retained, custom implant supported restorations due to their angles. Perforations of the sinus membrane were not encountered. Two cases were aborted due to fracture of the palatal alveolar process, which occurred while using the bone expanders for the correction of the axis. It is with no doubt that dynamic navigation is crucial in the application of the Antral Bone Expansion (N.A.B.E) technique due to the precision required in the atrophic posterior maxilla. The limitation of this study was the short observational time after the implant loading (4 months). Longer follow-up and a larger sample are needed to better understand the predictability of this technique and to draw more reliable conclusions.