Randomized controlled clinical trial comparing one-piece and two-piece dental implants supporting fixed and removable dental prostheses: 4-to 6-year observations

ObjectivesTo test whether or not a one- (S1) and a two-piece (S2) dental implant systems render the same biological, technical, and esthetic outcomes regarding implants and implant-supported reconstructions over an observation period of 4 to 6years. Materials and methodsSixty patients were randomly assigned to receive S1 or S2 implants. The implants were restored with either fixed or removable prostheses. The insertion of the final reconstruction was chosen as baseline. One-year and 4- to 6-year (FU-5) measurements included biological (e.g. marginal bone level, probing pocket depth, peri-implant mucositis, and peri-implantitis), technical (e.g. fracture or loosening of prosthetic screws, fracture or loosening of abutments, fracture of framework, and/or veneering ceramic (minor, major), loss of retention for cemented restorations), and esthetic parameters (visibility of the crown margin, shimmering of the implant through the mucosa, the level of the facial margo mucosae compared to the contralateral tooth or implant site and the modified papilla index) for implants and reconstructions. Survival and success rates of implants and reconstructions were calculated. Because of the asymmetric data distributions, nonparametric statistical methods were applied. ResultsThe implant-based analysis revealed a cumulative implant survival rate of 97.9% (S1: 96.6%; S2: 98.9%) at FU-5. The median marginal bone level for group S1 changed from 0.51mm at baseline to 0.49mm at FU-5 and for group S2 from 1.02mm to 1.35mm (P<0.001). Patient-level analyses demonstrated a frequency of peri-implant mucositis of 7.7% (S1) and 10.0% (S2) and for peri-implantitis of 7.7% (S1) and 13.3% (S2) at FU-5. The patient-based cumulative implant survival rate was 94.6% (S1: 92.3%; S2: 96.7%). The overall patient-based biological complication rate amounted to 15.4% (S1) and to 23.3% (S2) (P=0.517), whereas the overall technical complication rates were 30.8% (S1) and 13.3% (S2) (P=0.349). The prosthetic survival rates were 93.1% for S1 and 100% for S2 (P>0.05). ConclusionsBoth implant systems reveal high survival rates on the implant and prosthetic level. Apart from marginal bone-level changes, biological and technical outcomes did not reveal significant differences between the two implant systems.