Effect of platform switching on peri-implant bone levels: a randomized clinical trial

Objective: The concept of platform switching has been introduced to implant dentistry based on observations of reduced peri-implant bone loss. However, randomized clinical trials are still lacking. This study aimed to test the hypothesis that platform switching has a positive impact on crestal bone-level changes. Material and methods: Two implants with diameters of 4mm were inserted epicrestally into one side of the posterior mandibles of 25 subjects. After 3 months of submerged healing, the reentry surgery was performed. On the randomly placed test implant, an abutment 3.3mm in diameter was mounted, resulting in a horizontal circular step of 0.35mm (platform switching). The control implant was straight, with an abutment 4mm in diameter. Single-tooth crowns were cemented provisionally. All patients were monitored at short intervals over the course of 1 year. Standardized radiographs and microbiological samples from the implants' inner spaces were obtained at baseline (implant surgery), and after 3, 4, and 12 months. Results: After 1 year, the mean radiographic vertical bone loss at the test implants was 0.53 +/- 0.35mm and at the control implants, it was 0.58 +/- 0.55 mm. The mean intraindividual difference was 0.05 +/- 0.56 mm, which is significantly <0.35mm (P = 0.0093, post hoc power 79.9%). The crestal bone-level changes depended on time (P<0.001), but not on platform switching (P = 0.4). The implants' internal spaces were contaminated by bacteria, with no significant differences in the total counts between the test and the control at any time point (P = 0.98). Conclusions: The present randomized clinical trial could not confirm the hypothesis of a reduced peri-implant bone loss at implants restored according to the concept of platform switching.