Purpose:This prospective clinical study evaluated an experimental implant abutment made of densely sintered zirconia with respect to peri-implant hard and soft tissue reaction as well as fracture resistance over time. Materials and Methods:Twentyseven consecutively treated patients with 54 single-tooth implants were included. Zirconia abutment ingots were individually shaped and set on the implants with gold screws. All-ceramic (Empress I) crowns were cemented using a composite cement. At the 1- and 4-year examinations, reconstructions were evaluated for technical problems (fracture of abutment or crown, loosening of abutment screw). Modified Plaque and simplified Gingival Indices were recorded at implants and neighboring teeth, and periimplant bone levels were radiographically determined. Results:All but 1 of the 27 patients with 53 restorations could be evaluated at 1 year, and 36 restorations in 18 patients were evaluated 4 years after abutment and crown insertion. The median observation period for the reconstructions was 49.2 months. No abutment fractures occurred. Abutment screw loosening was reported for 2 restorations at 8 months and 27 months, respectively. Mean Plaque Index was 0.4 (SD 0.6) at abutments and 0.5 (SD 0.6) at teeth; mean Gingival Index was 0.7 (SD 0.5) at abutments and 0.9 (SD 0.5) at teeth. Mean marginal bone loss measured 1.2 mm (SD 0.5) after 4 years of functional loading. Conclusion:Zirconia abutments offered sufficient stability to support implantsupported single-tooth reconstructions in anterior and premolar regions. The soft and hard tissue reaction toward zirconia was favorable. Int J Prosthodont 2004;17:285–290.