Machine-driven versus manual insertion mode: influence on primary stability of orthodontic mini-implants.
OBJECTIVE
The study aimed to explore the effect of the insertion method on maximal insertion torque as a measure of primary stability while controlling for the effect of cortical bone thickness, mini-implant length and diameter, and vertical insertion force on insertion torque.


METHODS
Six types of mini-implants (Dual Top; Jeil Medical, Corp.) with diameters of 1.4, 1.6, and 2.0 mm and lengths of 6 and 8 mm were inserted manually and in a machine-driven mode into pig rib bone samples, and experiments were repeated 10 times, which totaled 120 tested implants in 120 pig rib samples. Cortical bone thickness was measured with a sliding caliper, whereas insertion torque and vertical insertion forces were recorded with a specially designed device.


RESULTS
Significant predictors of better primary stability are thicker cortical bone (explaining 24.2% of variability), wider diameter (20.6%), manual insertion (9.9%), greater length (3.7%), higher maximal vertical insertion force (2.2%), and lower vertical force at maximal insertion torque (1.4%).


CONCLUSIONS
Manual insertion is associated with higher primary stability of orthodontic mini-implants than mechanical insertion, but thicker cortical bone and larger implant diameter seem to be stronger predictors of primary stability.
*Intern, Public Health Center Rijeka, Rijeka, Croatia. †Research Assistant, Department of Orthodontics, School of Medicine, University of Rijeka, Rijeka, Croatia. ‡Assistant Professor, Department of Orthodontics, School of Medicine, University of Rijeka, Rijeka, Croatia.
Domen
D
Novsak
Magda
M
Trinajstic Zrinski
Stjepan
S
Spalj
D000818:Animals; D001863:Bone Screws; D003758:Dental Implantation, Endosseous / Q000379:methods*; D003799:Dental Stress Analysis; D052280:Orthodontic Anchorage Procedures / Q000379:methods*; D012272:Ribs; D013314:Stress, Mechanical; D013552:Swine; D019415:Torque