title: Effect of screw diameter on orthodontic skeletal anchorage.
abstract: BACKGROUND
  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 x 17 mm) and with 24 small-diameter screws (1.5 x 15 mm) were placed monocortically. In the second group, 24 large-diameter screws (2.5 x 17 mm) were placed monocortically and 24 small-diameter screws (1.5 x 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.
authors: Department of Preventive and Community Dentistry, College of Dentistry, University of Iowa, Iowa City 52242, USA.
authors: Chad
authors: C
authors: Morarend
authors: Fang
authors: F
authors: Qian
authors: Steve D
authors: SD
authors: Marshall
authors: Karin A
authors: KA
authors: Southard
authors: Nicole M
authors: NM
authors: Grosland
authors: Teresa A
authors: TA
authors: Morgan
authors: Michelle
authors: M
authors: McManus
authors: Thomas E
authors: TE
authors: Southard
mesh_terms: D000539:Alveolar Process / Q000601:surgery; D001863:Bone Screws; D002102:Cadaver; D003758:Dental Implantation, Endosseous / Q000379:methods; D003799:Dental Stress Analysis; D006801:Humans; D008904:Miniaturization; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation* / Q000379:methods*; D016382:Orthodontic Appliance Design