MACHINED VERSUS CAST ABUTMENTS FOR SINGLE DENTAL IMPLANTS: A 5-YEAR WITHIN-PATIENT MULTICENTRE RANDOMISED CONTROLLED TRIAL

PURPOSE. To compare clinical outcomes of titanium machined abutments (machined group) versus cobalt-chrome cast abutments (cast group).

MATERIALS AND METHODS. Thirty-one partially edentulous subjects received two single non-adjacent implant-supported crowns at three centres. Three months and half after implant placement, at impression taking, implants were randomised to receive a machined and a 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 randomised. Outcome measures were: prosthesis and implant failures, any complications, and radiographic peri-implant marginal bone level changes. Patients were followed to 5-year after loading.

RESULTS. After randomization, five patients dropped out. Two implants failed and three crowns on cast abutments were lost. Differences for implant and prosthetic failures were not statistically different (difference in proportions = 0.095, McNemar test P = 0.4795 and difference in proportions = 0.143, P = 0.248; respectively). Three complications occurred in the cast group versus one in the machined group, the difference being not statistically different (difference in proportions = 0.095; 95% CI -0.077 to 0.259, McNemar test P = 0.480). Both groups presented a statistically significant peri-implant marginal bone loss from implant placement to 5 years after loading, respectively -0.76 ± 1.09 mm (P = 0.001) for machined and -0.56 ± 0.77 mm (P <0.001) for cast abutments, with no statistically significant differences between the two groups (mean difference -0.19 mm; 95% CI -0.54 to 0.25; P = 0.454). Both groups gradually lost marginal peri-implant bone from loading (baseline) to 5 years after loading, but this was not statistically significant, respectively -0.001 ± 0.86 mm for machined compared with -0.12 ± 0.65 mm for cast abutments, with no statistically significant differences between the two groups (mean difference 0.11 mm; 95% CI -0.31 to 0.50; P = 0.629).

CONCLUSIONS. The present clinical data suggests that up to 5 years after loading implant prognosis may not be affected by using machined or cast abutments.