Morphological and structural characteristics of orthodontic mini-implants

The purpose of this study was to investigate the geometric characteristics, composition, microstructure, and pullout strength of commercially available orthodontic mini-implants.

The mini-implants used were AbsoAnchor®, Dual-Top™ JA, Spider Screws® K1, and Vector-TAS™. The geometric features were measured by optical microscopy. Surface texture and elemental composition were examined by scanning electron microscopy and energy dispersive X-ray microanalysis. Surface 3D roughness was estimated by optical profilometry, and pullout strength measured in artificial bone blocks with two bone densities.

The AbsoAnchor® showed the highest intra-osseous surface area, followed by the Dual-Top™, Spider Screw®, and Vector-TAS™. The mini-implants were composed of a Ti6Al4V alloy. The Vector-TAS™ had the highest oxygen and phosphorus content with the most homogeneous surface texture. No significant differences were detected in amplitude surface roughness parameters (Sa, Sz) between the implants. However, differences existed in hybrid (Sdr, Sds) and functional (Sci) parameters. AbsoAnchor® achieved the highest pullout strength, followed by the Dual-Top™, Spider Screw®, and Vector-TAS™, with highest values in the high density group. The intra-osseous surface area of mini-implants showed a positive correlation with pullout strength, especially in the high density group.

All the mini-implants tested were made of Ti6Al4V alloy. Significant differences were found in the surface area of the threaded parts. The significant differences documented in 3D surface roughness parameters (hybrid and functional) and pullout strength may anticipate variations in their clinical performance.