In the present study, the iliac crest of the sheep was chosen as a model because the site is characterized by a cancellous bone rich in marrow spaces, similar for quality to D4 density. This bone model appears superimposable to postero-lateral sectors of the human upper jaw that often represents a hard challenge for implant osseointegration due to low bone density.

Bone quality, in fact, is a key factor in dental implant rehabilitations because it could significantly influence the bone percentage of implant osseointegration [17]. In D4 bone type, it could be difficult to achieve a sufficient primary and secondary implant stability, and it is important to achieve high and fast, as much as possible, bone apposition onto titanium surface. The present analysis focused its attention on the bone affinity of different implant surfaces, evaluating the speed of bone formation and the amount of newly formed tissue.

For this reason, the sampling procedure was performed in short term (15 and 30 days) to be able to better investigate the differences on bone apposition speed onto different titanium implant surfaces.

The speed of bone apposition onto titanium surface could improve implant stability during the crucial initial healing phase allowing immediate or early loading protocol. It is important to underline that the new bone formation process, onto the implant surface, represents the transition between the initial primary implant mechanical stability to the functional secondary implant stability [18]. Once the osseointegration and the subsequent secondary stability are achieved, the implant may undergo to the occlusal loads with success [19].

The BIC%, observed by the present analysis, after 15 and 30 days of the machined surface group was very low if compared to the other groups. This fact strongly suggests the existence of more rapid integration phenomena in sandblasted and acid-etched surfaces and in laser-treated ones.

Moreover, it was observed a BIC% increase in both groups A and B between 15 and 30 days while in the machined group (group C), the BIC% decreased. This is because a slow physiological process of reabsorption of the fractured bone trabeculae (due to implant drilling procedures) characterizes the bone tissue in contact with any surface, but in group C, the newly formed bone apposition seems to be subsequent. In groups A and B instead, the micro-geometry of the surface could enhance the adhesion and proliferation of the bone-forming cells, and the new bone formation phase seems to start from the first days concurrently with the remodeling of the old bone trabeculae.