Platform switching and marginal bone-level alterations: the results of a randomized-controlled trial.

This randomized-controlled trial aimed to evaluate marginal bone level alterations at implants restored according to the platform-switching concept, using different implant/abutment mismatching. Eighty implants were divided according to the platform diameter in four groups: 3.8 mm (control), 4.3 mm (test group(1)), 4.8 mm (test group(2)) and 5.5 mm (test group(3)), and randomly placed in the posterior maxilla of 31 patients. After 3 months, implants were connected to a 3.8-mm-diameter abutment and final restorations were performed. Radiographic bone height was measured by two independent examiners at the time of implant placement (baseline), and after 9, 15, 21 and 33 months. After 21 months, all 80 implants were clinically osseointegrated in the 31 patients treated. A total of 69 implants were available for analysis, as 11 implants had to be excluded from the study due to early unintentional cover screw exposure. Radiographic evaluation showed a mean bone loss of 0.99 mm (SD = 0.42 mm) for test group(1), 0.82 mm (SD = 0.36 mm) for test group(2) and 0.56 mm (SD = 0.31 mm) for test group(3). These values were statistically significantly lower (P<0.005) compared with control (1.49 mm, SD = 0.54 mm). After 33 months, five patients were lost to follow-up. Evaluation of the remaining 60 implants showed no difference compared with 21 months data except for test group(2) (0.87 mm) and test group(3) (0.64 mm). There was an inverse correlation between the extent of mismatching and the amount of bone loss. This study suggested that marginal bone level alterations could be related to the extent of implant/abutment mismatching. Marginal bone levels were better maintained at implants restored according to the platform-switching concept.