title: Mini-Implant Screws for Bone-Borne Anchorage: A Biomechanical In Vitro Study Comparing Three Diameters.
abstract: OBJECTIVE
  To evaluate the maximum strength and the maximum aperture supported by mini-implant screws of three different diameters in an in vitro rapid maxillary expander model.
  
  
  METHODS
  Fifteen appliances were mounted in artificial bone polyurethane blocks. In each appliance, a Hyrax expander anchored by four mini-implant screw sets of three different diameters were divided into: group 1 (n = 5), 1.8-mm-diameter screws; group 2 (n = 5), 2.0-mm-diameter screws; and group 3 (n = 5), 2.2-mm-diameter screws. All sets (bone blocks + expander + four mini-implants) were inserted into a customized and standardized device that simulated a mid-palate disjunction. The expanders were activated to mechanically test the insertion of the mini-implant into the devices until breakage or deflection of screws occurred. The number of activations, the maximum supported strength, and the maximum expander aperture values until failure were recorded for each group. Data were subjected to a Student t test at a significance level of 5%.
  
  
  RESULTS
  There were no significant differences between the groups regarding the number of activations up to the maximum supported strength. The expander achieved aperture values where differences were slightly significant just between groups 1 and 2 (P = .048). There was a significant difference between groups 1 and 3 regarding the maximum supported load (P = .039).
  
  
  CONCLUSIONS
  Regardless of the mini-implant screw diameters, the expander device used in this anchorage system model withstood strengths and aperture rates beyond those that may be required during clinical rapid maxillary expansion.
authors.forename: Angélica Castro
authors.initials: AC
authors.lastname: Pimentel
authors.forename: Marcello Roberto
authors.initials: MR
authors.lastname: Manzi
authors.forename: Alex Juliano
authors.initials: AJ
authors.lastname: Prado Barbosa
authors.forename: Flávio Augusto
authors.initials: FA
authors.lastname: Cotrim-Ferreira
authors.forename: Paulo Eduardo
authors.initials: PE
authors.lastname: Guedes Carvalho
authors.forename: Gleison Fábio
authors.initials: GF
authors.lastname: de Lima
authors.forename: Maria Cristina
authors.initials: MC
authors.lastname: Zindel Deboni
mesh_terms: D001696:Biomechanical Phenomena; D001863:Bone Screws; D003799:Dental Stress Analysis; D006801:Humans; D008422:Materials Testing; D008954:Models, Biological; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation*; D016382:Orthodontic Appliance Design; D010155:Palatal Expansion Technique / Q000295:instrumentation*