All patients within this study were treated at the Dental School of the Eberhard Karls University in Tübingen between the 22nd of February in 1991 and the 24th of October in 2005. Every patient received at least one Frialit implant. The study protocol of the study was approved by the German Society of Research (Sonderforschungsbereich 175 Implantologie). Informed consent was obtained from all patients. The study evaluates the Frialit implants (Friadent, 68221 Mannheim, Germany) shown in Fig. 1, right side.

Patient selection criteria:

This study includes patients matching the following criteria:

Patients need to agree to take part in this study as well as being part of a regular recall system.

Patients must have a need for dental implants, such as edentulous ridge, distal-extension situation, tooth bound gap, or a single tooth replacement. This includes patients with tooth loss due to traumata, excessive internal tooth resorption, endodontic failure, root resorption after replantation, or retained primary teeth (in case of agenesis) as well as patients with tooth loss because of excessive caries or advanced periodontitis.

Implants that were inserted immediately and a matched control group of implants that were inserted after a healing period of at least 3 months after tooth extraction (non-immediate implants).

The matching criteria: implant length, diameter, site of the implant, and the patient’s gender.

Radiographs from either the time of insertion and/or the time patients received their restorations as well as follow-up radiographs had to be available.

Patients were ineligible if one of the following criteria was matched:

Irradiation of the implant area

Pathologic changes of the receptor site (cysts, tumors, osteomyelitis, etc.)

Insufficient bone volume

Acute periapical pathology (tooth sensitive to percussion)

Existence of non-treated generalized progressive periodontitis

Chronic acute systematic disorders (e.g., uncontrolled diabetes, hemorrhagic diatheses, general or auto immunodeficiency)

Patients refusing to give their consent for the use of their data