Survival analysis of orthodontic mini-implants.
BACKGROUND
Survival analysis is useful in clinical research because it focuses on comparing the survival distributions and the identification of risk factors. Our aim in this study was to investigate the survival characteristics and risk factors of orthodontic mini-implants with survival analyses.


METHODS
One hundred forty-one orthodontic patients (treated from October 1, 2000, to November 29, 2007) were included in this survival study. A total of 260 orthodontic mini-implants that had sandblasted (large grit) and acid-etched screw parts were placed between the maxillary second premolar and the first molar. Failures of the implants were recorded as event data, whereas implants that were removed because treatment ended and those that were not removed during the study period were recorded as censored data. A nonparametric life table method was used to visualize the hazard function, and Kaplan-Meier survival curves were generated to identify the variables associated with implant failure. Prognostic variables associated with implant failure were identified with the Cox proportional hazard model.


RESULTS
Of the 260 implants, 22 failed. The hazard function for implant failure showed that the risk is highest immediately after placement. The survival function showed that the median survival time of orthodontic mini-implants is sufficient for relatively long orthodontic treatments. The Cox proportional hazard model identified that increasing age is a decisive factor for implant survival.


CONCLUSIONS
The decreasing pattern of the hazard function suggested gradual osseointegration of orthodontic mini-implants. When implants are placed in a young patient, special caution is needed to lessen the increased probability of failure, especially immediately after placement.
Department of Orthodontics, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Korea.
Shin-Jae
SJ
Lee
Sug-Joon
SJ
Ahn
Jae Won
JW
Lee
Seong-Hun
SH
Kim
Tae-Woo
TW
Kim
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D001863:Bone Screws / Q000706:statistics & numerical data*; D002648:Child; D003758:Dental Implantation, Endosseous / Q000706:statistics & numerical data*; D015921:Dental Implants / Q000706:statistics & numerical data; D019232:Dental Restoration Failure; D006801:Humans; D008875:Middle Aged; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation* / Q000706:statistics & numerical data; D016382:Orthodontic Appliance Design; D016019:Survival Analysis; D055815:Young Adult
D015921:Dental Implants