A total of 60 edentulous maxillary casts (n = 10) were distributed among six groups. Group 1 was the control group with no modification, groups 2 through 6 included a butterfly postdam preparation, groups 3 and 4 also included a 10-mm wide/4-mm deep box with addition of four round holes in group 4, and groups 5 and 6 also included a 20-mm wide/4-mm deep box with addition of four round holes in group 6.