Cone-beam computed tomography evaluation of mini-implants after placement: Is root proximity a major risk factor for failure?

INTRODUCTION: The purposes of this study were to determine factors favoring successful mini-implant placement and to evaluate root proximity as a possible risk factor for failure of osseointegration-based mini-implants during orthodontic treatment. METHODS: Three-dimensional cone-beam computed tomography images were used to examine 50 sandblasted, large-grit, and acid-etched surface-treated mini-implants (C-implant, Seoul, Korea) placed in 25 patients. The images were analyzed for 3-dimensional position of the mini-implant (placement angle and depth) and any contact with root surfaces or maxillary sinuses. RESULTS: There were no remarkable differences in horizontal placement angles in the axial plane and placement depths of the mini-implants, but the vertical placement angle was significantly higher on the left side (24.5 degrees +/- 11.0 degrees ) compared with the right side (11.8 degrees +/- 11.6 degrees ). The horizontal mini-implant placement angle had a greater inclination tendency toward the maxillary first molar, and 11 mini-implants with root proximity showed mesiobuccal contact with the maxillary first molar root. Only 1 failure in 15 mini-implants with root proximity and 1 failure in 35 without root proximity were observed on the images. CONCLUSIONS: Root proximity alone was not considered a major risk factor for osseointegration-based mini-implant failure.

Nanoscale bonding between human bone and titanium surfaces: osseohybridization.

Until now, the chemical bonding between titanium and bone has been examined only through a few mechanical detachment tests. Therefore, in this study, a sandblasted and acid-etched titanium mini-implant was removed from a human patient after 2 months of placement in order to identify the chemical integration mechanism for nanoscale osseointegration of titanium implants. To prepare a transmission electron microscopy (TEM) specimen, the natural state was preserved as much as possible by cryofixation and scanning electron microscope/focused ion beam (SEM-FIB) milling without any chemical treatment. High-resolution TEM (HRTEM), energy dispersive X-ray spectroscopy (EDS), and scanning TEM (STEM)/electron energy loss spectroscopic analysis (EELS) were used to investigate the chemical composition and structure at the interface between the titanium and bone tissue. HRTEM and EDS data showed evidence of crystalline hydroxyapatite and intermixing of bone with the oxide layer of the implant. The STEM/EELS experiment provided particularly interesting results: carbon existed in polysaccharides, calcium and phosphorus existed as tricalcium phosphate (TCP), and titanium existed as oxidized titanium. In addition, the oxygen energy loss near edge structures (ELNESs) showed a possibility of the presence of CaTiO3. These STEM/EELS results can be explained by structures either with or without a chemical reaction layer. The possible existence of the osseohybridization area and the form of the carbon suggest that reconsideration of the standard definition of osseointegration is necessary.