Original article
Effect of screw diameter on orthodontic skeletal anchorage

https://doi.org/10.1016/j.ajodo.2007.07.031Get rights and content

Introduction

Many case reports have documented the successful use of titanium miniscrews for orthodontic anchorage. However, the literature lacks a well-controlled study examining the effect of miniscrew diameter on anchorage force resistance. The purpose of this in-vitro study was to compare the force resistance of larger-diameter monocortical miniscrews to smaller-diameter monocortical miniscrews; and to compare the force resistance of larger-diameter monocortical miniscrews to smaller-diameter bicortical miniscrews.

Methods

Ninety-six titanium alloy screws were placed into 24 hemisected maxillary and 24 hemisected mandibular specimens between the first and second premolars. Specimens were randomly and evenly divided into 2 groups. In the first group, 24 large-diameter screws (2.5 × 17 mm) and with 24 small-diameter screws (1.5 × 15 mm) were placed monocortically. In the second group, 24 large-diameter screws (2.5 × 17 mm) were placed monocortically and 24 small-diameter screws (1.5 × 15 mm) were placed bicortically. All screws were subjected to tangential force loading perpendicular to the miniscrew with lateral displacement of 0.6 mm. Statistical analyses, including the paired-samples t test and the 2-samples t test, were used to quantify screw force-deflection characteristics. One-way analysis of variance (ANOVA) with the post-hoc Tukey studentized range test was used to determine any significant differences, and the order of those differences, in force anchorage values among the 3 screw types at maxillary and mandibular sites.

Results

Mean mandibular and maxillary anchorage force values of the 2.5-mm monocortical screws were significantly greater than those of the 1.5-mm monocortical screws (P <0.01). No statistically significant differences in mean mandibular anchorage force values were found between the 2.5-mm monocortical screws and the 1.5-mm bicortical screws. However, mean maxillary anchorage force values of the 1.5-mm bicortical screws were significantly greater than those of the 2.5-mm monocortical screws (P <0.01). Data analyzed with 1-way ANOVA with the post-hoc Tukey studentized range tests indicated that the mean mandibular and maxillary force values of the 2.5-mm monocortical screws and the 1.5-mm bicortical screws were significantly greater than those of the 1.5-mm monocortical screws (P <0.01). Based on the 2-samples t test, mean anchorage force values at mandibular sites were significantly greater than at maxillary sites for the 2.5-mm monocortical screws and the 1.5-mm monocortical screws. There were no statistically significant differences in mean anchorage force values between maxillary and mandibular sites for the 1.5-mm bicortical screws.

Conclusions

In vitro, larger-diameter (2.5 mm) monocortical screws provide greater anchorage force resistance than do smaller-diameter (1.5 mm) monocortical screws in both the mandible and the maxilla. Smaller-diameter (1.5 mm) bicortical screws provide anchorage force resistance at least equal to larger-diameter (2.5 mm) monocortical screws. An alternative to placing a larger-diameter miniscrew for additional anchorage is a narrower bicortical screw.

Section snippets

Material and methods

The maxillae and mandibles of human cadavers were obtained from the Department of Anatomy and Cell Biology Deeded Body Program at the University of Iowa. Fully dentate and partially dentate specimens were considered acceptable. Fully edentulous or partially dentate specimens with visible, severely atrophic alveolar ridges were excluded. Maxillary specimens were dissected superior to the maxillary sinus to avoid damage to the maxillary alveolar bone and tooth roots and extended distally to the

Results

Data analysis showed (Fig 3, Fig 4) that the mean mandibular anchorage force values of the 2.5-mm monocortical screws were significantly greater than those of the 1.5-mm monocortical screws when the deflection increased from 0.04 to 0.6 mm (P <0.01). Moreover, the mean maxillary anchorage force values of the 2.5-mm monocortical screws were significantly greater than those for the 1.5-mm monocortical screws when the deflection increased from 0.14 to 0.6 mm (P <0.01).

No statistically significant

Discussion

Two principal findings resulted from this in-vitro study. The first was that larger-diameter monocortical screws provide increased anchorage force resistance compared with smaller-diameter monocortical screws. As illustrated in Figure 3, the mean anchorage force values of the 2.5-mm monocortical screws exceeded those of the 1.5-mm monocortical screws in both the mandible and the maxilla (P <0.01). The second finding was that smaller-diameter bicortical screws can provide anchorage resistance

Conclusions

  • 1.

    In vitro, larger-diameter (2.5 mm) monocortical screws provide increased anchorage force resistance compared with smaller-diameter (1.5 mm) monocortical screws in both the mandible and the maxilla.

  • 2.

    Smaller-diameter (1.5 mm) bicortical screws provide anchorage force resistance at least equal to larger-diameter (2.5 mm) monocortical screws.

  • 3.

    Miniscrew anchorage force resistance is independent of the side of either the maxilla or the mandible. Force resistance is independent of apical or coronal site

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Supported by the Dr. George Andreasen Memorial Fund.

The authors report no commercial, proprietary, or financial interest in the products or companies described in this article.

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