Influence of geometric design characteristics on primary stability of orthodontic miniscrews

Aim of the present study was to investigate the influence of geometric design characteristics on primary stability of orthodontic miniscrews.

Forty self-drilling miniscrews with different geometric design characteristics were divided into the following groups (n = 10): group I-Tomas® (Dentaurum, Germany), group II-AbsoAnchor® (Dentos, Korea), group III-HUBIT® miniscrew (HUBIT, Korea), group IV-Creative® (China). The four types were conical miniscrews with 1.6 mm diameter and 6.0 mm length. The miniscrews were manually inserted perpendicular to cow ribs until the full thread length was reached with the help of a 1.3 mm predrilled pilot hole. Each miniscrew was evaluated using scanning electron microscope. Linear and angular measurements were taken using Photoshop CS3 software. Miniscrew stability was measured by the Periotest® and pullout test.

All linear and angular measurements of the geometric characteristics showed significant differences between the four groups (p ≤ 0.001). Results of the pullout test showed significant differences between the four groups (p ≤ 0.001), while the Periotest® values showed no significant differences (p = 0.122). A multiple linear regression analysis revealed the significant predictors for higher pullout: a larger flank, a higher value for the thread angle, lead angle, and apical face angle (p ≤ 0.001).

Orthodontic miniscrews' geometric design characteristics significantly affected the primary stability. Larger pitch width, flank, thread angle, apical face angle, and/or lead angle led to higher primary stability. Smaller a thread shape factor (TSF) also improved primary stability. Varying these characteristics may enhance miniscrew design.