The effects of cortical bone thickness and miniscrew implant root proximity on the success rate of miniscrew implant: A retrospective study

Objective To investigate the effects of cortical bone thickness (CBT), miniscrew implant root proximity (MRP) and other related factors on the success rate of miniscrew implant (MSI). Materials and Methods Four hundred and five MSIs placed in 171 patients were analysed in this retrospective study. The primary predictor variables were CBT and MRP at MSI insertion sites. The predictor variables also included patient, location, MSI design and procedure related factors. The outcome variable was the survival of MSI. The differences in measurement data between success group and failed group were evaluated by the analysis of variance and independent samples t tests. Patient, location, MSI design and procedure related factors associated with the MSI prognosis were analysed by survival analysis with Cox proportional hazard regression model. The P value was set at .05. And the survival curves of independent factors were plotted. Results The overall success rate of MSI was 82.7%. The age of MSI host, CBT, interdental root distance (IRD) and MRP at MSI sites showed no significant differences between failed group and success group. CBT and insertion jaws were independent prognosis factors screened out by Cox proportional hazard regression model. Failure risk (hazard ratio) of MSI with CBT <1 mm was 4.72. The failure risk in the mandible was 3.80 times as high as that in the maxilla. Conclusion Inadequate CBT (<1 mm) contributed to the failure of MSI. MSI placed in the maxilla showed better prognosis compared to the mandible. MRP had no significant effect on the prognosis.