The fact that the used measurement protocol is reliable has been proven in former studies [7, 8].

The use of intraoral radiographs as well as panoramic radiographs is an accepted method for the peri-implant bone evaluation [11–13]. The radiographic distortions present in panoramic imaging are well known; however, according to several studies, panoramic images are suitable to assess the crestal bone situation [14, 15]. According to Zechner et al., rotational panoramic and intraoral rectangular radiographs lead to comparable outcomes [16]. However, this is only possible on the mesial and distal sides. While the possibility to assess the bone in every dimension seems tempting, the higher exposure to radiation needs to be considered. That the mesial and distal defects can be averaged is supported by the work from Cooper et al. in 2010 [17].

Current studies rarely evaluate the peri-implant bone situation using a clearly defined measurement protocol and therefore are often sensitive to measuring errors. Due to using a clearly defined and proven measurement protocol, abnormalities were mainly caused by transcription errors and could be identified in the plotting step. There is no comparable study over such a period of time with two groups that were matched following specific criteria.

Although several studies report a better healing for immediately placed implants and a lower rate of resorption for the surrounding bone compared to delayed immediate implants or implants placed in healed sites [17–22], the results obtained in this study do not support this thesis. The differences found to the respective points of time show comparable results for both groups.

The results of Covani et al. suggest that the process of bone remodeling cannot be influenced by changing the time of implantation but merely by the implant position [19]. These results compare to the results found by Deng et al. [23]. They reported an initial bone resorption of 1.01 mm for immediate implants within the first year, which is similar to the results found in this study.