Effect of angled installation of orthodontic mini-implants on primary stability

ABSTRACT

AIM: The aim of this work was evaluate the insertion and removal torque for orthodontic mini-implants inserted in different inclination. Materials and methods: Ten self[drilling mini-implants from the brand SIN (Sistema de Implantes Nacional, São Paulo/SP, Brazil), and the surgical kit for their insertion were used. Two plaques of synthetic bone of 120mm x 170mm x 41,5mm were used (Sawbones, Pacific Research Laboratories Inc, Vashon, Wash), with 1,5mm height, simulating the cortical bone (density 40 pcf) and 40 mm simulating the medullary bone (density 15 pcf). In each block, five areas were demarcated for each mark, totalizing ten areas. The ten mini-implants were inserted by the same operator, previously calibrated; five of them at 900 and five at 600, using the manual key kit. After the insertion of all the mini-implants, the final threading and the reading of insertion torque value were carried out with a manual torque wrench digital Lutron TQ[8800 (Lutron Electronic Enterprise Co., Ltd, Taipei, Taiwan) until the trans-mucosal profile achieve the cortical bone. The maximum insertion torque value was registered in N/cm. After all the implants inserted, the measurement of removal torque was started, performed in the same way of insertion, but in the opposite anticlockwise. The results were submitted to the T test (parametric) and to a Mann-Whitney test (non-parametric). Results: The results demonstrated that the insertion torque was lower than the removal one in both insertion degrees, with statistically significance. Despite insertion torque at 90 degrees had been lightly higher than that inserted at 60 degrees, they were not statistically significant. Conclusion: In view of the results, it was possible conclude that insertion at 60º angulation does not offer advantages to the primary stability for orthodontic mini-implants.