Effect of cortical bone thickness and implant placement torque on stability of orthodontic mini-implants.
OBJECTIVE
To examine the relationship between cortical bone thickness, inter-root distance (horizontal space), distance from alveolar crest to the bottom of maxillary sinus (vertical space) at the prepared site, and implant placement torque and the success rate of mini-implants placed for orthodontic anchorage.


METHODS
After computerized tomography examination, mini-implants 1.6 mm wide and 8 mm long were placed in the posterior alveolar bone. The mini-implant was judged a success when orthodontic force could be applied for at least 6 months without pain or clinically detectable mobility. The unpaired t test was performed to examine differences between the success and failure groups. The chi-square analysis or Fisher exact probability test was used to compare the implant success according to placement torque, location, and patient gender. P values less than .05 were considered significant.


RESULTS
The subjects included 4 males (11 implants) and 28 females (76 implants) who ranged in age from 14.6 to 42.8 years. The success rate of the 87 implants was 87.4%. Cortical bone thickness was significantly greater in the success group (1.42 +/- 0.59 mm vs 0.97 +/- 0.31 mm, P = .015). The success rate was significantly higher in the group with an implant placement torque of 8 to 10 Ncm (100%) as compared to implants with higher or lower placement torques. The odds ratio for failure of the mini-implant was 6.93 (P = .047) when the cortical bone thickness was less than 1.0 mm relative to 1.0 mm or more.


CONCLUSIONS
A relationship between stability after implant placement and the width and height of the peri-implant bone was not demonstrated. The prepared site should have a cortical bone thickness of at least 1.0 mm, and the placement torque should be controlled up to 10 Ncm.
Motoyoshi
Mitsuru
M
Department of Orthodontics, Nihon University School of Dentistry, Tokyo, Japan. motoyoshi@dent.nihon-u.ac.jp
Yoshida
Tohru
T
Ono
Akiko
A
Shimizu
Noriyoshi
N
D000293:Adolescent; D000328:Adult; D000539:Alveolar Process / Q000033:anatomy & histology / Q000601:surgery; D003724:Dental Arch / Q000033:anatomy & histology / Q000601:surgery; D015921:Dental Implants; D003764:Dental Materials; D005260:Female; D006801:Humans; D008297:Male; D008334:Mandible / Q000033:anatomy & histology* / Q000601:surgery; D008437:Maxilla / Q000033:anatomy & histology* / Q000601:surgery; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation*; D016382:Orthodontic Appliance Design; D012737:Sex Factors; D013314:Stress, Mechanical; D014025:Titanium; D014057:Tomography, X-Ray Computed; D014087:Tooth Movement Techniques / Q000295:instrumentation; D019415:Torque; D016896:Treatment Outcome
D015921:Dental Implants; D003764:Dental Materials; D014025:Titanium