title: Evaluation of the stiffness characteristics of rapid palatal expander screws.
abstract: BACKGROUND
  The aim of this study is to evaluate the mechanical properties of the screws used for rapid expansion of the upper jaw.
  
  
  METHODS
  Ten types of expansion screw were assessed, seven with four arms: Lancer Philosophy 1, Dentaurum Hyrax Click Medium, Forestadent Anatomic Expander type "S", Forestadent Anatomic Expander type "S" for narrow palates, Forestadent Memory, Leone A 2620-10 with telescopic guide, and Leone A 0630-10 with orthogonal arms; and three with two arms: Dentaurum Variety S.P., Target Baby REP Veltri, and Leone A 362113. A test expander with the mean dimensions taken from measurements on a sample of 100 expanders was constructed for each screw. The test expanders were connected to the supports of an Instron 4467 (Instron Corp., USA) mechanical testing machine equipped with a 500 N load cell, and the compression force exerted after each activation was measured. The mean forces expressed by the two- and four-arm expanders were then compared.
  
  
  RESULTS
  After five activations, the forces expressed by the two-arm devices were double than those expressed by the four-arm devices on average (224 ± 59.9 N vs. 103 ± 32.9 N), and such values remained high after subsequent activations.
  
  
  CONCLUSIONS
  The expanders tested demonstrated stiffness characteristics compatible with opening of the palatine sutures in pre-adolescent patients. The stiffness of such devices can be further increased during the construction phase.
authors.affiliation: Postgraduate School of Orthodontics, University of Ferrara, Via Montebello 31, 44121, Ferrara, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Lombardo
authors.affiliation: Private Practice, Bologna, Italy.
authors.forename: Enrico
authors.initials: E
authors.lastname: Sacchi
authors.affiliation: Postgraduate School of Orthodontics, University of Ferrara, Via Montebello 31, 44121, Ferrara, Italy. dott.marialarosa@gmail.com.
authors.forename: Maria
authors.initials: M
authors.lastname: Larosa
authors.affiliation: Department of Engineering, University of Ferrara, Via Saragat 1, 44122, Ferrara, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Mollica
authors.affiliation: Department of Engineering, University of Ferrara, Via Saragat 1, 44122, Ferrara, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Mazzanti
authors.affiliation: UnipolSai Assicurazioni, Piazza della Costituzione 2, 40128, Bologna, Italy.
authors.forename: Giorgio Alfredo
authors.initials: GA
authors.lastname: Spedicato
authors.affiliation: Postgraduate School of Orthodontics, University of Ferrara, Via Montebello 31, 44121, Ferrara, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Siciliani
mesh_terms: D000293:Adolescent; D002648:Child; D003393:Cranial Sutures; D003722:Dental Alloys; D003799:Dental Stress Analysis; D005260:Female; D006801:Humans; D008297:Male; D008422:Materials Testing; D008437:Maxilla; D055595:Mechanical Phenomena; D008954:Models, Biological; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation; D016382:Orthodontic Appliance Design / Q000145:classification* / Q000295:instrumentation*; D010155:Palatal Expansion Technique / Q000145:classification* / Q000295:instrumentation*; D010159:Palate; D021362:Palate, Hard / Q000254:growth & development; D013193:Stainless Steel; D013314:Stress, Mechanical
chemical_list: D003722:Dental Alloys; D013193:Stainless Steel