Implant drilling procedures were carried out using the drill sequence recommended by the manufacturer. The drill speed was set at 700 rpm under continuous sterile saline solution irrigation (stored at + 4 °C).

Implants were inserted with an insertion torque peak between 28 and 34 Ncm. Each animal received three implants of each group.

The suture of deep muscle planes was performed with polyglycolic acid Dexon II (Kendall Company, MA, USA), while the superficial soft tissues were sutured with a non-absorbable suture (Codisan S.p.A., Belpasso, Italy).

The surgical site underwent to topical antibiotic therapy (Gellini-Intervet, Milan, Italy). Finally, each animal was subjected to systemic antibiotic postoperative therapy with 20 mg/kg of intravenous ampicillin every 12 h for 3 days after surgery.

Two animals were sacrificed by intravenous injection of Tanax (Intervet - Boxmeer, Netherlands) after 15 days, while the other two animals after 30 days.

All bone specimens were immediately rinsed in saline solution, fixed in 10% neutral buffered formalin and finally processed to obtain thin ground sections.

Afterwards, the samples were included in resin (LR White EM, TAAB Laboratories Equipment Ltd., England) and sectioned along the longitudinal plane with a microtome (Micromet, Bologna, Italy). From each sample, approximately four sections were obtained with a 300 μm thickness; the slides were then reduced in thickness to about 90 μm, using a lapping machine (Micromet, Bologna, Italy). Subsequently, the sections were stained with toluidine blue and magenta acid and analyzed under an optical microscopy (Laborlux Leitz, Leica Microsystems, Wetzlar, Germany) equipped with a digital camera (3CCD JVC KY-F55B, JVC, Yokohama, Japan).

The resulting images have undergone a histological qualitative and quantitative morphometric analysis by means of dedicated software (Image J 1.32j. Wayne Rasband, National Institutes of Health, USA) to calculate the BIC% values. On each image (× 9 magnification), a midline parallel to the long axis of the fixture was traced using a software for graphic processing (Corel Photo Paint, Corel Corporation, USA) to divide the image into two halves. The two different slices were then treated separately during the intermediate steps of BIC% measurement, according to the following order: