A minor, but statistically significant, radiographic bone loss occurred from baseline to the final follow-up at the neighbouring tooth surfaces in both groups. Moreover, both groups experienced a minor recession of the marginal gingiva from baseline to the final follow-up, but the change was not significant. Recession and the bone level of the neighbouring tooth surfaces to implants placed in autogenous bone grafts have not been assessed previously, but preservation of the marginal bone level of the neighbouring tooth surfaces is important to preserve the vertical position of the papillae [43]. Obviously, recession around the teeth has a clinically and aesthetically adverse effect [44].

Some complications were registered in the process from the primary bone augmentation to implant placement, including a loss of one bone block and a minor change of intra- and extraoral sensitivity. Also, at the time of implant placement, simultaneous bone augmentation was necessary due to bone resorption of the primary augmented bone block in two patients (one patient in each group). This finding is consistent with previously described complications after bone block augmentation [10, 45], and in both patients, no further complications were registered. Despite these observed complications, the rating of the patient questionnaire revealed an overall high satisfaction with treatment at baseline and at the follow-up.

The prospective study design involving randomisation as well as a standardised surgical technique and systematic postoperative follow-up is an important strength of this study. Some weaknesses should also be acknowledged. First, it is important to bear in mind the potential bias associated with taking a biopsy from a relatively narrow bone block on the long-term results for implant treatment. It is possible that the clinical result of losing two implants is associated with the mechanical force applied on the bone block when retrieving the bone biopsy. This should be considered in future scientific work involving bone biopsy from a narrow bone block. Another limitation of the present study is the small sample of participants and the distribution of different recipient sites. The results should therefore be interpreted with caution.

Although the current study is based on a small sample of participants, the findings suggest that the methodology of the PRF and the control group approach can both be used for bone augmentation with a similar outcome. A significant, but clinically irrelevant, higher peri-implant marginal bone level was registered in the PRF group than in the control group. Patients in both groups were highly satisfied with the treatment.