Analysis of time to failure of orthodontic mini-implants after insertion or loading

OBJECTIVES: This study was performed to evaluate patterns of failure time after insertion, failure rate according to loading time after insertion, and the patterns of failure after loading. MATERIALS AND METHODS: A total of 331 mini-implants were classified into the non-failure group (NFG) and failure group (FG), which was divided into failed group before loading (FGB) and failed group after loading (FGA). Orthodontic force was applied to both the NFG and FGA. Failed mini-implants after insertion, ratio of FGA to NFG according to loading time after insertion, and failed mini-implants according to failed time after loading were analyzed. RESULTS: Percentages of failed mini-implants after insertion were 15.79%, 36.84%, 12.28%, and 10.53% at 4, 8, 12, and 16 weeks, respectively. Mini-implant failure demonstrated a peak from 4 to 5 weeks after insertion. The failure rates according to loading time after insertion were 13.56%, 8.97%, 11.32%, and 5.00% at 4, 8, 12, and 16 weeks, respectively. Percentages of failed mini-implants after loading were 13.79%, 24.14%, 20.69%, and 6.9% at 4, 8, 12, and 16 weeks, respectively. CONCLUSION: Mini-implant stability is typically acquired 12 to 16 weeks after insertion, and immediate loading can cause failure of the mini-implant. Failure after loading was observed during the first 12 weeks.

Effect of rotation bump on removal torque of orthodontic mini-implants

OBJECTIVES: This study is designed to evaluate the mechanical stability of orthodontic mini-implants with vertical grooves in rabbits. MATERIALS AND METHODS: This study was done from March 2011 to February 2012 in Dental Research Institute of Seoul National University. Thirty-two mini-implants in the control group and 32 in the rotation bump (RB) group were inserted in the tibias of 16 rabbits and were removed after two weeks and four weeks, respectively. The maximum insertion torque (MIT), maximum removal torque (MRT), torque ratio (TR) of MRT to MIT and removal angular momentum (RAM) were all measured at the time of removal. RESULTS: There were no significant differences between the two groups in MIT and MRT at two weeks or four weeks. However, TR and RAM at four weeks in the RB group were significantly higher than in the control group (P<0.05). TR of the RB group was significantly increased at four weeks (P<0.05). In both groups, RAM at four weeks was significantly higher than at two weeks (P<0.05). CONCLUSION: These results suggest that RB of the mini-implant could provide resistance to the removal rotation, although it did not increase the MRT.