Pullout strengths of orthodontic palatal mini-implants tested in vitro

Abstract 

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 (2mm in diameter) of three brands (Absoanchor, Bio-Ray, and Lomas) were manually driven into artificial bone (Sawbones) to a depth of 5mm. 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.

Keywords: insertion torque, palatal mini-implant, pullout strength, skeletal anchorage