title: Laypeople's perceptions of frontal smile esthetics: A systematic review.
abstract: BACKGROUND
  The emphasis on dental esthetics has increased in recent years. There are, however, differences in esthetic perceptions among professional and lay groups. The aim of this comprehensive review was to update previous reviews and answer the following research question: Can lay thresholds for acceptance of smile esthetic anomalies be defined?
  
  
  METHODS
  A systematic search in the medical literature (PubMed, PMC, NLM, Embase, Cochrane Central Register of Controlled Clinical trials, Web of Knowledge, Scopus, Google Scholar, and LILACs) was performed to identify all peer-reviewed articles reporting data regarding evaluations of laypeople's perceptions of dental esthetic factors.
  
  
  RESULTS
  Of the 6032 analyzed articles, 66 studies were selected for the final review process. Among the selected articles investigated perceptions of diastema, 15 analyzed modifications in tooth size and shape, 8 considered incisor positions, 15 evaluated midline discrepancies, 16 investigated buccal corridors, 26 analyzed gingival display and design, 3 considered lip height, and 20 investigated miscellaneous factors. Threshold values were identified for the following features: diastema (0-2 mm), tooth size and shape of incisor position, midline discrepancy (0-3 mm), buccal corridors (5-16 mm), gingival exposure (1.5-4 mm), occlusal canting (0°-4°), and overbite (2-5 mm). Furthermore, few other smile characteristics were found to be significantly associated with perception of smile aesthetics, even though any threshold could be detected.
  
  
  CONCLUSIONS
  On the basis of the obtained results, threshold values for the main features of smile and dental esthetics could be identified. Limitations of the present study were the heterogeneity of data which made it impossible to perform a meta-analysis, and the lack of information about sample selection and selective outcome reporting.
authors.affiliation: Resident, Department of Orthodontics, Dental School, University of Turin, Turin, Italy. Electronic address: dr.simone.parrini@gmail.com.
authors.forename: Simone
authors.initials: S
authors.lastname: Parrini
authors.affiliation: Resident, Department of Orthodontics, Dental School, University of Turin, Turin, Italy.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Rossini
authors.affiliation: Visiting professor, Department of Orthodontics, Dental School, University of Turin, Turin, Italy.
authors.forename: Tommaso
authors.initials: T
authors.lastname: Castroflorio
authors.affiliation: Visiting professor, Department of Orthodontics, University of Cagliari, Cagliari, Italy.
authors.forename: Arturo
authors.initials: A
authors.lastname: Fortini
authors.affiliation: Adjunct professor, Department of Orthodontics, Dental School, University of Turin, Turin, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Deregibus
authors.affiliation: Professor, Department of Orthodontics, Dental School, University of Turin, Turin, Italy.
authors.forename: Cesare
authors.initials: C
authors.lastname: Debernardi
mesh_terms: D001294:Attitude to Health; D004955:Esthetics, Dental / Q000523:psychology / Q000706:statistics & numerical data; D005149:Facial Expression; D006801:Humans; D009055:Mouth / Q000033:anatomy & histology; D014070:Tooth / Q000033:anatomy & histology