Pullout strengths of orthodontic palatal mini-implants tested in vitro

Background/purpose: New modified mini-implants are used in orthodontic practice to reinforce palatal anchorage. The aim of this study was to evaluate the anchorage strengths of palatal mini-implants in terms of their vertical and horizontal pullout strengths. Materials and methods: Thirty palatal mini-implants (2 mm in diameter) of three brands (Absoanchor, Bio-Ray, and Lomas) were manually driven into artificial bone (Sawbones) to a depth of 5 mm. Their vertical and horizontal pullout strengths were measured using a material testing machine. The Kruskal-Wallis test was used to assess differences among brands (P < 0.05). Results: The pullout strengths of all the brands were significantly greater than routine orthodontic forces. The vertical pullout strength of the Absoanchor mini-implants was the lowest among the tested brands, and the horizontal pullout strengths of the Lomas and Absoanchor mini-implants were significantly higher than that of the Bio-Ray mini-implant. There was no significant relationship between the insertion torque and pullout strength in the vertical or horizontal directions. Conclusion: The pullout strengths of mini-implants were significantly greater than normal orthodontic forces. Moreover, no significant correlation was found between the insertion torque and pullout strength. Copyright (C) 2011, Association for Dental Sciences of the Republic of China. Published by Elsevier Taiwan LLC. All rights reserved.