Purpose: The aim of this randomised clinical trial was to evaluate the influence of restoration on marginal bone loss (MBL) using immediately definitive abutments (one abutment-one time concept) versus provisional abutments later replaced by definitive abutments. Materials and methods: In three private clinics, 32 patients with 32 hopeless maxillary premolars were selected for post-extractive implant-supported immediate restoration and randomised to provisional abutment (PA) and definitive abutment (DA) groups, 16 sites in each group. After tooth extraction, 7 patients had to be excluded for buccal wall fracture at tooth extraction or lack of sufficient primary implant stability ( 35 Ncm). The remaining 25 patients (10 PA, 15 DA) received a post-extractive wide-diameter implant. Immediately after insertion, the PA group were immediately restored using a platform-switched provisional titanium abutment. In the DA group, definitive platform-switched titanium abutments were tightened. In both groups, provisional crowns were adapted, avoiding occlusal contacts. All implants were definitively restored after 3 months. In the PA group, a traditional impression technique with coping transfer was adopted, dis/reconnecting abutments several times; in the DA group, metal prefabricated copings were used and final restorations were seated, avoiding abutment disconnection. Digital standardised periapical radiographs using a customised film holder were recorded at baseline (T0 = implant insertion), final restoration (T1 = 3 months later), and at 18-month (T2) and 3-year (T3) follow-ups. The MBL was evaluated with a computerised measuring technique and digital subtraction radiography (DSR) software was used to evaluate radiographic density. Results: At the 3-year follow-up a success rate of 100% in both groups was reported. In the PA group, peri-implant bone resorption was 0.36 mm at T1, 0.43 mm at T2, and 0.55 mm at T3. In the DA group, peri-implant bone resorption was 0.35 mm at T1, 0.33 mm at T2, and 0.34 mm at T3. Statistically significant lower bone losses were found at T2 (0.1 mm) and T3 (0.2 mm) for the DA group. At T3, significantly higher DSR values around implant necks were recorded in the DA group (72 ± 5.0) when compared with the PA group (52 ± 9.5). Conclusions: The current trial suggests that the 'one abutment-one time' concept might be a possible additional strategy in post-extraction immediately restored platform-switched single implants to further minimise peri-implant crestal bone resorption, although a 0.2 mm difference may not have any clinical effect. Additional clinical trials with larger groups of patients should be performed to better investigate this hypothesis. Keywords: bone preservation, definitive abutment, dental implant, immediate loading, platform switching