Abstract
Primary fixation is one of the most important factors in establishing adequate osseointegration between bone and fixture. The present study is an attempt to investigate the necessary removal torque of titanium alloy screws (d: 3.2 mm, l: 8 mm) inserted in the rabbit tibia with cortical and bicortical support. After 4, 8, and 16 weeks, the titanium alloy screws in nine animals were removed with a Tohnichi model 15 BTG-N torque gauge instrument. The torque necessary for removal of the implants was measured.
Then implants in the tibia were cut out in bloc with the surrounding cortical bone. They were fixed in formalin, dehydrated in alcohol, which embedded in acrylic resin. The samples were cut by a sawing machine, and investigated by SEM.
Sixteen weeks after implant placement, the average removal torque of the bicortical group was 24.9 Ncm (range 18 to 30 Ncm, SD 5.0). The average removal torque for the bicortical group was 11.7 Ncm (range 7 to 19.5 Ncm, SD 4.5). There was a highly significant difference (P＜0.001) between the advantage of the bicortical group (Mann-Whitney's U test).
From a qualitative histologic aspect, mature bone was observed around the implants in the cortical region, however, there was little contact in the cancellous region.
It can be concluded that bicortical suppore is From these results, stable and a higher degree of bone-to-metal contact than cortical support.
