”one abutment-one time”: optimizing platform-switching concept. 3-year controlled prospective study

Background: The “platform-switching” concept showed better peri-implant crestal bone preservation in post-extraction immediately restored implants when compared to matching diameter abutment configuration. However repeated abutment dis/reconnections during restorative procedures from provisional to final crown could produce apical shifting of peri-implant tissues. Aim: Aim of this controlled prospective study was to evaluate on bone levels (MBL) the influence of restoration using immediately definitive abutments (one abutment-one time concept) versus provisional abutment later replaced by a definitive abutment. Materials and methods: 26 patients with 26 hopeless maxillary premolars received a post-extraction wide diameter implant. Immediately after insertion, 11 patients (Control Group, CG) were immediately restored using a platform-switched provisional titanium abutment. In 15 patients (Test Group, TG), 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: for the final impression, in CG, traditional impression technique with coping transfer was adopted, dis/reconnecting abutments several times; in TG, metal prefabricated coping was used and final restoration was seated avoiding abutment disconnection. Digital standardized periapical radiographs using a customized film holder were recorded at baseline (T 0 = implant insertion), final restoration (T1=3 months after), 18 (T2) and 36 months (T3) follow-ups. The MBL was evaluated with a computerized measuring technique applied to radiographs. Digital subtraction radiography software was used to evaluate radiographic density of bone tissue around implants. The Student’s t-Test (confidence level: P<0.05) was selected to identify differences between test and control groups at different follow-ups concerning MBL values. Results: In the CG peri-implant bone resorption was 0.41mm (SD=0.15mm) at T1, 0.38mm (SD=0.12mm) at T2, 0.53mm (SD = 0.13mm) at T3. In the TG, on average, peri-implant bone resorption was 0.59 mm (SD=0.19mm) at T1, 0.31mm (SD=0.11mm) at T2, 0.32mm (SD = 0.16mm) at T3. Statistically significant difference between groups was only found at T3. At the same follow-up period, higher density in radiographic bone appearance around implant neck was recorded in the TG compared to CG. Conclusions and clinical implications: The implant/abutment stability following the minimally invasive prosthetic strategy adopted (“platform-switching” and “one abutment- one time”) could longitudinally produce additional hard tissue preservation compared to implants restored according to “platform-switching” only. Despite of the encouraging data reported, however, controlled clinical studies on larger patient sample and histologic investigations are required to confirm this hypothesis, analyzing biologic mechanism.