title: Short-term effects of strain produced on a split palatal screw-type hyrax appliance after rapid maxillary expansion: A clinical trial.
abstract: BACKGROUND
  The aim of this study was to establish an accumulated strain pattern in different parts of rapid maxillary expansion appliances and relate them to different vertical growth patterns. A clinical study was conducted of 40 patients with posterior crossbite who required rapid palatal expansion.
  
  
  METHODS
  Patients (mean age, 8.48 years) were recruited and treated at the Dental Hospital of Bellvitge, Hospitalet de Llobregat, Barcelona, Spain. Strain gauges were placed on the arms of the RME hyrax screw appliance to record deformation (strain) during the expansion and the retention phases for 75 days. A finite element model was used to place the gauge at the point where the strain was most expressed. The vertical coefficient of variation was used to classify the patients by their vertical growth pattern. P = 0.05 was considered to be statistically significant.
  
  
  RESULTS
  During the expansion phase, the highest values of accumulated strain were measured in the posterior part of the appliance for all facial biotypes, but these values passed to the anterior area at the end of the retention phase of the mesocephalic and brachycephalic patients. There was statistically significant difference in the strain of the posterior arms in accordance with the vertical growth pattern (P = 0.05) during the retention phase. At 75 days of retention, 61.25% of the arms had already begun to have strain dissipation.
  
  
  CONCLUSIONS
  The accumulated strain pattern in the rapid maxillary expansion appliance can vary depending on the facial biotype. In the future, orthodontists should try to tailor the activation and retention protocol based on each patient's characteristics.
authors.affiliation: Graduate student, Orthodontic Graduate Program, Orthodontics Unit, Department of Odontostomatology, Health University of Barcelona campus, University of Barcelona, Barcelona, Spain. Electronic address: valentingarcia2@gmail.com.
authors.forename: Valentin Javier
authors.initials: VJ
authors.lastname: Garcia
authors.affiliation: Professor, Applied Physics Unit, Department of Materials Engineering, University of Vigo, Vigo, Spain.
authors.forename: Rafael
authors.initials: R
authors.lastname: Comesaña
authors.affiliation: Graduate student, Orthodontic Graduate Program, Orthodontics Unit, Department of Odontostomatology, Health University of Barcelona campus, University of Barcelona, Barcelona, Spain.
authors.forename: Khaled
authors.initials: K
authors.lastname: Kasem
authors.affiliation: Professsor, Orthodontics Unit, Department of Odontostomatology, Health University of Barcelona campus, University of Barcelona, Barcelona, Spain.
authors.forename: Josep Maria
authors.initials: JM
authors.lastname: Usrtell-Torrent
authors.affiliation: Professor, Applied Physics Unit, Department of Materials Engineering, University of Vigo, Vigo, Spain.
authors.forename: Aida
authors.initials: A
authors.lastname: Badaoui
authors.affiliation: Professor, Human Anatomy and Embryology Unit, Department of Pathology and Experimental Therapy, Health University of Barcelona campus, University of Barcelona, Barcelona, Spain.
authors.forename: Maria Cristina
authors.initials: MC
authors.lastname: Manzanares-Céspedes
authors.affiliation: Associate professor, Human Anatomy and Embryology Unit, Department of Pathology and Experimental Therapy, Health University of Barcelona campus, University of Barcelona, Barcelona, Spain.
authors.forename: Patricia
authors.initials: P
authors.lastname: Carvalho-Lobato
mesh_terms: D000365:Age Determination by Skeleton / Q000379:methods; D002574:Cervical Vertebrae / Q000254:growth & development; D002648:Child; D003799:Dental Stress Analysis / Q000295:instrumentation; D003818:Dentition, Mixed; D055119:Elastic Modulus; D005260:Female; D020342:Finite Element Analysis; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008310:Malocclusion / Q000628:therapy; D008437:Maxilla / Q000254:growth & development; D008445:Maxillofacial Development / Q000502:physiology; D016382:Orthodontic Appliance Design; D018704:Orthodontic Retainers; D010155:Palatal Expansion Technique / Q000295:instrumentation*; D013314:Stress, Mechanical; D013499:Surface Properties; D014716:Vertical Dimension