The combined effects of undersized drilling and implant macrogeometry on bone healing around dental implants: an experimental study

This study investigated the effect of undersized preparations with two different implant macrogeometries. There were four experimental groups: group 1, conical implant with an undersized osteotomy of 3.2 mm; group 2, conical implant with an undersized osteotomy of 3.5 mm; group 3, cylindrical implant with an undersized osteotomy of 3.2 mm; group 4, cylindrical implant with an undersized osteotomy of 3.5 mm. Implants were placed in one side of the sheep mandible (n = 6). After 3 weeks, the same procedure was conducted on the other side; 3 weeks later, euthanasia was performed. All implants were 4 mm × 10 mm. Insertion torque was recorded for all implants during implantation. Retrieved samples were subjected to histological sectioning and histomorphometry. Implants of groups 1 and 2 presented significantly higher insertion torque than those of groups 3 and 4 (P < 0.001). No differences in bone-to-implant contact or bone area fraction occupied were observed between the groups at 3 weeks (P > 0.24, and P > 0.25, respectively), whereas significant differences were observed at 6 weeks between groups 1 and 2, and between groups 3 and 4 (P < 0.01). Undersized drilling affected the biological establishment of bone formation around both dental implant macrogeometries.