Pitch and longitudinal fluting effects on the primary stability of miniscrew implants

Abstract

Objective: To test the hypotheses that pitch and fluting have no effect on the primary stability ofminiscrew implants (MSIs). Materials and Methods: Maximum placement torque and pullout strength of experimental MSIswere compared with those of control MSIs with the use of synthetic and cadaver bone. MSIs with1.00 mm pitch were compared with those with 1.25 mm and 0.75 mm ptch; MSIs with threelongitudinal flutes were compared with the same MSIs without flutes. A total of 60 MSIs (15 ofeach design) were evaluated with synthetic bone; a split-mouth cadaver model was used to comparethe three experimental designs against the 1 mm control MSIs (total of 90 MSIs).Results: The synthetic bone model showed higher placement torque and pullout strength for the 0.75 pitch than for the 1.0 mm and 1.25 mm pitch MSIs, but differences were significant (P < .05) only for pullout strength. The cadaver model showed no significant differences in placementtorque or pullout strength associated with pitch. Both synthetic and cadaver bone models showedthat MSIs with flutes had significantly (P < .05) higher placement torque and pullout strength.Spearman correlations between placement torque and pullout strength were statistically significantfor both synthetic (r = .504) and cadaver (r = .502) bone. Conclusion: Within limits, decreasing MSI pitch increases pullout strength, and fluting increasesboth placement torque and pullout strength. (Angle Orthod. 2009;79:1156-1161.