Do we need abutments at immediately loaded implants supporting cross-arch fixed prostheses? Results from a 5-year randomised controlled trial.

Purpose: To compare the clinical outcome (in particular of marginal peri-implant bone level changes) between immediately loaded straight implants which had definitive abutments placed at implant placement and never removed versus implants which had no intermediate abutments.

Materials and methods: Thirty-two edentulous patients had one of their jaws rehabilitated with a provisional screw-retained resin reinforced cross-arch fixed prosthesis supported by four immediately loaded implants: two central straight implants and two either tilted or straight distal implants. The two central straight implants were randomly allocated in two equal groups to receive or not an intermediate abutment (Multi-Unit Abutment, MUA) according to a parallel group design. To be immediately loaded implants had to be inserted with a minimum torque of 30 Ncm, which was achieved by all implants. After 4 months, definitive screw-retained metal-ceramic prostheses were delivered and patients were followed-up to 5 years after loading. Prostheses were removed every 8 months to facilitate professionally delivered maintenance. Outcome measures were prosthesis and implant failures, complications, peri-implant marginal bone level changes and bleeding on probing (BoP).

Results: Five-years after loading one patient dropped out from each group. No implant or prosthetic failure occurred. Three patients of the abutment group versus one of the no-abutment group were affected by complications (risk difference = 0.125; 95% CI: -0.13 to 0.37; Fisher exact test, P = 0.600). At 5 years, both groups lost marginal bone in a statistically significant way (0.32 ± 0.40 mm for patients of the abutment group and 0.35 ± 0.29 mm for patients of the no-abutment group), with no difference in bone loss between groups at patient levels (difference = 0.03 mm; 95% CI: -0.23 to 0.29 mm; P = 0.809). At 5 years, BoP was significantly higher in the no-abutment group than in the abutment group (difference between medians = 25%; 95% CI: 12.5% to 25%; P < 0.001). By considering only the average of the two central study implants per patient with and without intermediate abutments, there were no differences in bone loss (difference: -0.05 mm; 95% CI: -0.41 to 0.31 mm; P = 0.763), while marginal bleeding was significantly higher in the no-abutment group (difference between medians = 25%; 95% CI: 0% to 50%; P = 0.004).

Conclusions: The present results suggest that intermediate abutments may not be needed at immediately loaded cross-arch screw-retained prostheses, unless there is the necessity to correct implant angulation.