A Comparison of the Mechanical Measures Used for Assessing Orthodontic Mini-Implant Stability

Purpose: Mechanical loosening remains a common complication associated with mini-implant failure. The purpose of this study was to compare common mechanical measures of mini-implant stability to determine their association and reliability. Materials and Methods: Ninety self-drilling orthodontic mini-implants from 6 manufacturers were inserted into artificial bone blocks. Insertion torques (ITs) and Periotest values (PVs) were measured. Subsequently, mini-implants underwent pull-out testing for measures of pull-out load (POL) and screw displacement (ScrD). Stability measurements were compared using one-way ANOVA, associations among them were assessed using correlation analyses, and reliability was evaluated using coefficients of variation (COVs). Results: Variations in stability of mini-implants were found, specific to the mechanical measure used for assessment (P < 0.05). The strongest correlations were found between IT and PV (r =-0.68) and between IT and POL (r = 0.66). Overall, PV showed the greatest variability (COV: 11%-100%) compared with IT (≤11%), POL (≤4%), and ScrD (≤19%). Conclusions: IT, PV, and POLs only agreed moderately in their assessment of mini-implant stability, and Periotest showed the least reliability in predicting mini-implant stability. As such, independent and interchangeable use of these stability measures should be avoided.