The manuscript was written following STROBE (Strengthening the Reporting of Observational studies in Epidemiology) guidelines. All described data and treatments were obtained from a single dental clinic in Vitoria, Spain. The time period of the study was between December 2014 and April 2016. Patients’ records were retrospectively reviewed to identify patients that fulfilled the following inclusion criteria:

Male and female patients older than 18 years old.

Transalveolar sinus floor augmentation.

The insertion of dental implants.

Patients/implants were excluded if not completed with all these criteria. Patients with incomplete data were also excluded. An exemption from IRB approval of the study protocol was granted by the author’s institution as it was a retrospective study, and the evaluated medical devise had already been approved for clinical use. This study was performed following the Helsinki declaration regarding the investigation with human subjects.

The principal outcome was the marginal bone loss. The experimental group was composed of the dental implants with Ca²⁺ ions (UnicCa® surface), and the control group was composed of the implants having the same surface as the UnicCa® but without the calcium ion modification (known as Optima® surface). The surface is acid-etched to generate a multi-scale roughness at the different parts of the implant (neck, valleys, and threads) in adaptation to the different biological needs: homogenous and attenuated roughness at the neck to avoid the risk of bacterial colonization, micro-roughness at the valleys to enhance the osseointegration, and micro-roughness + pores at the threads to enhance anchorage.

Data about patients’ age and sex were collected. Cone-beam CT scans were visualized in BTI Scan III (Biotechnology Institute, Vitoria, Spain) to measure the residual bone height and the bone density at the surgical site. The sequence of bone drilling was determined according to the bone density [14].

Implant survival determined whether the implant was still physically in the mouth or lost at the time of evaluation. To assess the marginal bone stability, the distance between the uppermost point of the implant platform and the most coronal bone-implant contact was measured mesial and distal to the implant by a computer software (Sidexis, Sirona, USA). Implant length was used to calibrate the linear measurements on the radiograph.