The aim of this retrospective study was to compare the amount of marginal bone loss between upper anterior area and upper posterior area with 71 upper single-tooth restorations on 2 stage machined $Br{{aa}}nemark$ implants since Jan 1995. The second aim was to compare the bone defect group which had dehiscence and fenetration and the others in the upper anterior region. The results were as follows. 1. The most frequent reason of missing tooth in the upper anterior region was trauma by 61%. While upper posterior region showed various reasons such as congenital missing, advanced periodontitis, trauma. 2. Peri-implantitis with fistula occurred 1 of 41 implants in the upper anterior group in 1 year after loading and 2 of 32 implants in the upper posterior group failed before loading. The 1 year success rate of upper anterior group was 97.56 %, and 93.75 % for upper posterior group. 3. The mean marginal bone loss in the upper anterior group was 0.44${pm}$0.25 mm, while 0.57${pm}$0.32 mm in the upper posterior group. There was statistically significant difference in the amount of mean marginal bone loss (P<O.05). 4. The mean marginal bone loss of bone defect group was 0.40${pm}$0.10 mm at one year, and 0.48${pm}$0.26 mm for the control group. No statistically significant difference of mean marginal bone loss was showen between bone defect group and the others at implantation. According to the results, the upper anterior region showed less marginal bone loss than the upper posterior region. In case of missing single upper tooth, careful consideration on recipient residual ridge to determine proper implant diameter and length, sufficient healing time, proper loading would lead to implant success. Single tooth implants in the maxilla seemed to be an alternative to fixed partial dentures without damage to adjacent teeth.