Background <p>Orthodontic miniscrew anchorage induced a paradigm shift in orthodontics, by avoiding unwanted movement of anchoring teeth. Failure of miniscrew anchorage (premature loosening of the miniscrew) is known to be related to root proximity after insertion.</p> Objective <p>This study aimed to evaluate root proximity of orthodontic miniscrew implants using CBCT and to more precisely investigate the correlation between root proximity and miniscrew failure.</p> Materials and methods <p>CBCT images of 47 miniscrews, placed buccally between maxillary first molars and second premolars, were used in this retrospective study. In the reoriented CBCT images, presence and amount of root proximity were measured. Miniscrew failure was defined as loosening during the first month after placement. Chi-square test was used to evaluate the correlation between presence of root proximity and miniscrew failure rate. Logistic regression analysis was used to evaluate the statistical significance of correlation between the presence of miniscrew failure and the amount of root proximity area.</p> Results <p>Among the miniscrews that showed root proximity, 52.4% failed within one month after placement, whereas the failure rate of miniscrews without root proximity was 0. According to chi-square test, miniscrew failure was 2.1 times more probable with root proximity than without. Logistic regression analysis showed statistical significance between amount of root proximity and miniscrew failure.</p> Conclusions <p>This study could confirm root proximity as a major influencing factor for interradicular miniscrew failure, and present a novel approach for measuring the amount of root proximity in CBCT for preciser prediction of failure, as not every miniscrew in root proximity will fail.</p>