MACHINED VERSUS CAST ABUTMENTS FOR SINGLE DENTAL IMPLANTS: A 3-YEAR WITHIN-PATIENT MULTICENTRE RANDOMIZED CONTROLLED TRIAL

PURPOSE. To compare clinical outcomes of machined titanium abutments (machined group) versus cast cobalt-chrome abutments (cast group). MATERIALS AND METHODS. Thirty-one partially edentulous subjects received two single non-adjacent implant-supported crowns each at three centres. Three and a half months after implant placement, implants were randomized at impression taking to receive one machined and one cast abutment according to a within-patient study design. Four patients dropped out and one patient lost one implant before randomization, so only 26 patients had their implants randomized. Outcome measures were: prosthesis and implant failures, any complications, and radiographic peri-implant marginal bone level changes. Patients were followed up for 3 years after loading. RESULTS. After randomization, three patients dropped out. One implant failed and two crowns on cast abutments were lost, but differences in implant and prosthesis failures were not statistically different (McNemar test P = 1.000; difference in proportions = 0.04 and P = 0.500; difference in proportions = 0.08, respectively). Two minor complications occurred in the cast group versus one in the machined group, the difference not being statistically different (McNemar test P = 1.000; difference in proportions = 0.04; 95% CI 0.18 to 22.06). Both groups presented statistically significant peri-implant marginal bone loss from implant placement to 3 years after loading, respectively-0.72 ± 0.90 mm (P = 0.001) for machined and-0.60 ± 0.61 mm (P <0.001) for cast abutments, with no statistically significant differences between the two groups (mean difference-0.12 mm; 95% CI-0.57 to 0.34; P = 0.624). Both groups gradually lost marginal peri-implant bone from loading (baseline) to 3 years after loading, but this was not statistically significant; machined lost-0.05 ± 0.12 mm while cast lost-0.14 ± 0.11 mm, a difference that was not statistically significant (mean difference 0.06 mm; 95% CI-0.24 to 0.35; P = 0.708). CONCLUSIONS. The present clinical data suggest that implant prognosis up to 3 years after loading is not affected by the choice of machined or cast abutments.