Overlapping calibrated digital images of the tissues were recorded with Leica Applications Suite version 4.4.0 software from a bright field Leica DM4000 B microscope (Leica Microsystems GmbH, Wëtzlar, Germany) equipped with a 5× lens and DFC420 digital camera. Single images were pasted and merged to compose each elevated sinus using the program Photoshop (Adobe Photoshop CC 2015.0.0).

The histomorphometric measurements were taken by an expert assessor (JM) using a lattice with squares of 75 μm. The following different areas were assessed within the grafted regions (Fig. 2): (i) close to the bone walls (Bone walls region), (ii) center of the augmented region (middle region), (iii) subjacent to the sinus mucosa (sub-mucosa region), (iv) and close to the antrostomy (close-to-window region). Moreover, the antrostomy (antrostomy region) was also evaluated in three different areas: adjacent to the medial and lateral edges, and the middle of the access window (Fig. 2). The tissues evaluated were newly formed bone, graft material, and soft tissues. Percentages were subsequently calculated.

The sites that received autogenous bone in the antrostomy and the subjacent regions (close-to-window) were considered as a test (treated sites) while the sites that did not receive the autogenous bone were considered as control (untreated sites).

The primary variable was the new bone percentage in the region of major interest that was the antrostomy and close-to-window areas. The mean new bone within the augmented sinus was considered as a secondary variable. Mean values and standard deviations were calculated for each outcome variable. The results were calculated using the software Excel 2013 (Microsoft Corporation, Redmond, WA, USA), while the statistical analyses were performed with the IBM SPSS Statistics software v.19 (IBM Inc., Chicago, IL, USA). In the text are reported only mean values and standard deviations while the tables were complemented with 25th, 50th (median), and 75th percentiles were also added. The Wilcoxon test was used to evaluate differences between the two sites with a level of significance set at 5%.