The effect of anchor volume on the mechanical strengths of orthodontic micro-implants

Anchor volume (AV) might be an important factor affecting mechanical strengths of micro-implant. To investigate the correlation between AV and three mechanical strengths (IT: insertion torque; RF: resonance frequency; HPS: horizontal pullout strength), 55 micro-implants (diameter 1.5 mm: Type A, B, C; diameter 1.3 mm: Type D and E) were driven into the artificial bones at a 7-mm depth. The RF, IT, HPS and AV were measured. One-way analysis of variance (ANOVA) with Tukey Honestly Significant Difference (HSD) post comparison and Pearson’s correlation were used to detect significant differences. Null hypothesis states that there was no statistically significant correlation between AV and these three forces (IT, RF, and HPS). Type A and Type D had the lowest IT (4.2 Ncm). Type C had the highest RF (9.9 KHz) in the stability test, and Type B had the greatest HPS (190.9 Ncm) in the resistance test. There was significant correlation between the IT and HPS. AV was significantly correlated with RF, IT, and HPS. The null hypothesis was rejected. In this study, each of these brands had its distinct advantages in the RF, IT, and HPS. Moreover, inner diameter/outer diameter ratio and AV affect the magnitude of HPS.