Insertional torque and axial pull-out strength of mini-implants in mandibles of dogs.
BACKGROUND
The objectives of this study were to evaluate insertional torque of mini-implants (MI) for orthodontic anchorage, to compare their axial pull-out strength at 0 (T0), 15 (T15), and 60 (T60) days after placement, to determine initial and peri-implant cortical bone thickness, and to analyze the correlations among these variables.


METHODS
Sixty MI were placed in the mandibles of 10 dogs. Peak insertional torque values were recorded, and, after the animals were killed, specimens were prepared. The MI were aligned with a testing machine to register axial pull-out strength. Cortical bone thickness was measured after removal of the MI. Statistical analyses were conducted with ANOVA and Tukey HSD tests.


RESULTS
Pull-out strength and peri-implant cortical bone thickness had differences (P <0.01) at the various times. The T0 value showed the highest pull-out strength, and the smallest peri-implant cortical bone thickness was at T60. There was a regular correlation between pull-out strength and peri-implant cortical bone thickness at T0 (r = 0.44, P = 0.05). There was no correlation between insertional torque and pull-out strength, and insertional torque and initial cortical bone thickness.


CONCLUSIONS
Pull-out strength is greater immediately after placement of MI, cortical bone thickness decreases because of bone resorption, and insertional torque is not an efficient method for predicting the retention of MI.
Graduate Dentistry Program in Orthodontics, Pontifical Catholic University of Paraná, Curitiba, Brazil.
Karine Kimak
KK
Salmória
Orlando Motohiro
OM
Tanaka
Odilon
O
Guariza-Filho
Elisa Souza
ES
Camargo
Leandro Teixeira
LT
de Souza
Hiroshi
H
Maruo
D000704:Analysis of Variance; D000818:Animals; D015519:Bone Density; D003758:Dental Implantation, Endosseous; D015921:Dental Implants; D003799:Dental Stress Analysis; D004285:Dogs; D020007:Implants, Experimental; D008297:Male; D008334:Mandible / Q000033:anatomy & histology / Q000601:surgery; D008904:Miniaturization; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation*; D016348:Osseointegration; D018709:Statistics, Nonparametric; D013997:Time Factors; D019415:Torque
D015921:Dental Implants