In the present retrospective study, 14 patients (5 females and 9 males) with a mean age of 63 years (34–80 years) received Conelog® Screw-line implants (Camlog Biotechnologies, Basle, Suisse) with a length of 7 mm. In total, 30 implants were clinically and radiologically investigated after a mean loading period of 5 years (range 2–7 years).

All patients from the Department for Oral, Cranio-Maxillofacial and Facial Plastic Surgery, Medical Center of Goethe University Frankfurt who received implants of 7-mm length in the posterior maxilla to avoid a sinus augmentation procedure within the past 7 years were screened. Furthermore, the implants had to be loaded for at least 2 years. The initial residual bone height varied between 6 and 8 mm, leading to a bicortical fixation of the implants. The kind of prosthetic restoration (removable/fixed, splinted/un-splinted) was not defined as an inclusion/exclusion criteria. Patients with incomplete data collection and those who refused to participate in the study were excluded. A total of 17 patients met the inclusion criteria, 14 of whom were available for follow-up investigation and were included in the present study.

The study was approved by the ethics commission of the medical department of Goethe University in Frankfurt am Main, Germany (79/18), and it was conducted according to the fifth revision of the World Medical Association Declaration of 2000 (version, 2008). All participating patients gave informed written consent to participate in the retrospective study and for publication of the obtained data.

All implants were placed at least 3 months after the extraction of teeth in the posterior maxilla that were not able be preserved. If necessary, minor guided bone regeneration (GBR) procedures were performed simultaneously with the implant placement using a xenogenous bone substitute material (Bio-Oss®, Geistlich Biomaterials, Wolhusen, Suisse). After a mean healing period of 4 months (range 4–5 months), prosthetic rehabilitation was performed, which included fixed single-crown prosthetics in 21 implants and removable implant-retained dentures in 9 implants. Out of the 21 implants restored with single-crown prosthetics, only 4 crowns in 2 patients were splinted (patient no. 1 and patient no. 4, Fig. 1). All 9 implants retaining removable prosthetics have been restored with electroplated telescopic crowns and are therefore also not primary splinted.