Aim: to assess clinical and radiographical outcomes of single tooth posterior implants with a dehiscence defect treated with or without guided bone regeneration (GBR). Methods: In a randomized clinical trial of 59 patients, single-tooth posterior implants were placed. For the subanalysis of 16 patients with a buccal dehiscence defect (≤ 5mm), the implants were randomly assigned to GBR or spontaneous healing (SH). In 8 patients, the implants were surrounded by native bone (Native bone). A transmucosal healing approach was chosen for all sites. Patients were examined at restoration delivery (RD) and at one year (1y). Measurements included: soft tissue thickness (STT), bone tissue thickness (BTT) and buccal contour, based on cone-beam computed tomography (CBCT), optical scans, clinical parameters. All data were analyzed descriptively. Results: The mean STT at implant shoulder (IS) showed a gain of 0.15 mm (Q1: - 0.16, Q3: 0.49) for the GBR group and 0.03 mm (Q1: -0.49, Q3: 0.13) for the SH group. The mean BBT 1 mm below IS showed a loss of 0.25 mm (Q1: -0.85, Q3: -0.09) for the GBR group and 0.04 mm (Q1: -0.14, Q3: 0.17) for the SH group. All peri-implant soft tissue parameters indicated healthy peri-implant tissues with no clinically relevant differences between the groups. Patient-reported outcomes regarding pain one day after surgery were similar among the study groups. Conclusions: The present sub-analysis resulted in a similar buccal contour and similar radiographic outcomes as well as peri-implant health for sites treated with or without GBR.