title: Effects of variable attachment shapes and aligner material on aligner retention.
abstract: OBJECTIVE
  To evaluate the retention of four types of aligners on a dental arch with various attachments.
  
  
  METHODS
  For this study, three casts were manufactured, two of which contained attachments (ellipsoid and beveled), and one without any attachments to serve as a control. Four types of aligners were thermoformed: Clear-Aligner (CA)-soft, CA-medium, and CA-hard, with various thicknesses, and Essix ACE. Measurements of vertical displacement force during aligner removal were performed with the Gabo Qualimeter Eplexor. Means and standard deviations were next compared between different aligner thicknesses and attachment shapes.
  
  
  RESULTS
  CA-soft, CA-medium, and CA-hard did not present a significant increase in retention, except when used in the presence of attachments. Additionally, CA-medium and CA-hard required significantly more force for removal. Essix ACE demonstrated a significant decrease in retention when used with ellipsoid attachments. The force value for Essix ACE removal from the cast with beveled attachments was comparable to that of CA-medium. Forces for aligner removal from the model without attachments showed a linear trend. Essix ACE did not show a continuous increase in retention for each model. Overall, ellipsoid attachments did not present a significant change in retention. In contrast, beveled attachments improved retention.
  
  
  CONCLUSIONS
  Ellipsoid attachments had no significant influence on the force required for aligner removal and hence on aligner retention. Essix ACE showed significantly less retention than CA-hard on the models with attachments. Furthermore, beveled attachments were observed to increase retention significantly, compared with ellipsoid attachments and when using no attachments.
authors.affiliation: a   Postgraduate Student, Section of Orthodontics, School of Dentistry, University of California, Los Angeles, Calif.
authors.forename: Hiltrud
authors.initials: H
authors.lastname: Dasy
authors.affiliation: a   Postgraduate Student, Section of Orthodontics, School of Dentistry, University of California, Los Angeles, Calif.
authors.forename: Andreas
authors.initials: A
authors.lastname: Dasy
authors.affiliation: b   Dental Student, School of Dentistry, University of California, Los Angeles, Calif.
authors.forename: Greg
authors.initials: G
authors.lastname: Asatrian
authors.affiliation: c   Associate Professor, Department for Paediatric Dentistry and Orthodontics, Faculty for Dentistry, Semmelweis University, Budapest, Hungary.
authors.forename: Noémi
authors.initials: N
authors.lastname: Rózsa
authors.affiliation: d   Instructor, Section of Orthodontics, School of Dentistry, University of California, Los Angeles, Calif.
authors.forename: Hao-Fu
authors.initials: HF
authors.lastname: Lee
authors.affiliation: e   Assistant Professor, Section of Orthodontics, School of Dentistry, University of California, Los Angeles, Calif.
authors.forename: Jin Hee
authors.initials: JH
authors.lastname: Kwak
mesh_terms: D004868:Equipment Failure; D008310:Malocclusion / Q000628:therapy*; D018704:Orthodontic Retainers
keywords: Aligner therapy; Attachment shapes; Retention; Thermoplastic appliances