Three-dimensional evaluation of bone void induced in the cortical bone upon insertion of an orthodontic anchor screw

Abstract

Purpose

The present study evaluated the relationship between the bone void induced in the surrounding cortical bone upon screw insertion, and insertion torque. 3D bone morphometry was analyzed using micro-computed tomography (micro-CT) with different screw diameters and cortical bone thicknesses.

Materials and methods

Titanium alloy miniscrews with different diameters were used. Specimens were collected from porcine pelvic bones and divided by cortical bone thickness into 48 regions per cm². Screws were inserted into 32 regions by self-drilling, and maximum insertion torque was recorded. The remaining 16 regions were part of the control group. Specimens were partitioned into regions and micro-CT was used to measure the void volume in bone, including the microdamage surrounding the screw. The proportion of void volume in cortical bone (Vv/Cv) for each region was calculated and compared between the groups.

Results

Compared with the control group, characteristic microdamage distribution was observed in the group with screws inserted, and a particularly high Vv/Cv was noted on the bone marrow side. In the screw insertion groups, both insertion torque and Vv/Cv were significantly higher in areas with thicker cortical bone. There were no significant differences in the Vv/Cv for different screw diameters, but the influence of the insertion torque was apparent.

Conclusion

These results suggest that to reduce the bone void to the cortical bone surrounding the screw, it is important to use appropriate insertion torque in accordance with cortical bone thickness.

Keywords:

• 3D evaluation
• Cortical bone thickness
• Miniscrew
• Microdamage