After 4 months, the animals were anaesthetised and then euthanised with an overdose of pentobarbital sodium and subsequently perfused with 10% formalin. The maxilla was retrieved en bloc, trimmed, and immersed in formalin solution.

All histological procedures were performed in the Laboratorio de Histologıa de la Facultad de Odontologıa de la Universidad de Ciencia Medica in Havana, Cuba. Bilateral maxillary block sections, each containing one sinus, were obtained and maintained in a 4% formaldehyde solution. The blocks were then cut in a buccolingual plane at the level of the landmark reference, using a diamond band saw fitted in a precision slicing machine (Exakt; Apparatebau, Norderstedt, Germany). One hemiblock was dehydrated in a series of graded ethanol and subsequently embedded in resin (Technovit® 7200 VLC; Kulzer, Friedrichsdorf, Germany). One section was obtained and reduced to a thickness of approximately 60 μm using a cutting-grinding device (Exakt®; Apparatebau, Norderstedt, Germany). Subsequently, the histological slides were stained with Stevenel’s blue and alizarin red and examined under a light microscope for histometric analysis.

The histological measurements were performed using an Eclipse Ci microscope (Nikon Corporation, Tokyo, Japan), equipped with a digital video camera (Digital Sight DS-2Mv, Nikon Corporation, Tokyo, Japan), connected to a computer and using the software NIS-Elements D 4.10 (Laboratory Imaging, Nikon Corporation, Tokyo, Japan).

Histological measurements within the augmented sinus were performed in four different regions: (i) subjacent to the sinus elevated mucosa (submucosa), (ii) centre of the grafted area (middle), (iii) the original base of the sinus (base), and (iv) immediately under the replaced bone window or the membrane (sub-window) (Fig. 3a).

In the antrostomy area, histology was performed in two regions: (i) the bony window or membrane area (centre) and (ii) the osteotomy regions on the maxilla (edges) (Fig. 3b).

A point counting procedure [21] was performed to identify the tissue composition within the described regions. A lattice, with squares of 75 μm in dimensions, was superposed over the tissues at a magnification of × 100.