Effects of acid etching and calcium chloride immersion on removal torque and bone-cutting ability of orthodontic...

The 2-fold purpose of this study was to evaluate the effects of acid etching and calcium chloride immersion on removal torque and the bone-cutting ability of orthodontic mini-implants (OMIs).

For the removal torque part of the study, 3 types of OMIs (titanium alloy) were evaluated in a rabbit model: OMIs with acid surface etching with and without calcium chloride immersion (ECG and EG, respectively) and a control group (CG), in which the OMIs had an untreated, machined surface. We inserted 126 OMIs (42 OMIs per type) into both tibias of 21 male rabbits (5 months of age) with body weights of 3.0 to 3.5 kg. Removal torque was evaluated after 1, 4, and 7 weeks. To determine the OMIs' bone-cutting ability, total insertion time to place an OMI 6 mm into artificial bone was measured (6 OMIs per group).

Removal torque values for the EG (3.97 ± 0.52 Ncm) and ECG (4.21 ± 0.44 Ncm) were statistically and significantly higher than those of the CG (3.02 ± 0.53 Ncm) 1 week after implantation (P <0.05). The ECG (6.54 ± 0.50, 6.61 ± 0.66 Ncm) showed the highest removal torque value followed by the EG (5.68 ± 0.58, 5.89 ± 0.70 Ncm) and CG (3.43 ± 0.62, 3.38 ± 0.54 Ncm) at 4 and 7 weeks after implantation (P <0.05). Removal torque did not change over time with the CG, but with the ECG and EG, it was significantly higher in weeks 4 and 7 than in week 1 (P <0.05). Total insertion time was significantly greater for the EG than for the ECG and CG (P <0.05).

Treating OMIs with a calcium chloride solution improved the initial bone reaction by preventing contamination of the implant surface, and increasing the surface roughness of OMIs by acid etching enhanced their stability without decreasing the bone-cutting ability compared with OMIs without surface treatment.