title: The labial aging process: a surface analysis-based three-dimensional evaluation.
abstract: BACKGROUND
  With increasing age, the smile becomes elongated and less appealing. Currently, several methods are proposed for analysis of lip morphology including lateral cephalograms, profile and frontal photographs, video images, and three-dimensional systems. Despite several descriptions of morphologic and histologic age-related changes in the literature, no scientific well-supported model of the labial aging process is reported.
  
  
  METHODS
  For this study, 33 healthy volunteers were selected and divided into two groups according to age: a youthful group (ages 21-34 years) and an aged group (ages 45-65 years). Their dental and labial stone casts were obtained, digitized, and virtually reproduced using a computerized electromechanical digitizer and applying nonuniform rational B-spline geometry. To obtain a synthetic parameter describing local surface deformation, average curvature and curvature variability indexes were computed and compared.
  
  
  RESULTS
  No significant age- or sex-related differences in the average curvature were detected. In contrast, the curvature variability was significantly greater in the young than in the aged subjects.
  
  
  CONCLUSIONS
  The labial arch surface remains macroscopically constant between the third and the sixth decades of life, but with local modifications that influence the standard deviation of its curvature. A high standard deviation described the protruding labial appearance of the young subjects, whereas a reduced one described the flat lips of the aged subjects.
  
  
  METHODS
  This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .
authors.affiliation: Dipartimento di Scienze Biomediche per la Salute, Università degli Studi di Milano, via Mangiagalli 31, 20133, Milan, Italy.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Rosati
authors.affiliation: Dipartimento di Scienze Biomediche per la Salute, Università degli Studi di Milano, via Mangiagalli 31, 20133, Milan, Italy.|Dipartimento di Elettronica, Informazione e Bioingegneria (DEIB), Politecnico di Milano, Milan, Italy.
authors.forename: Marina
authors.initials: M
authors.lastname: Codari
authors.affiliation: Centro Cardiologico Monzino IRCCS, Milan, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Maffessanti
authors.affiliation: Dipartimento di Scienze Biomediche per la Salute, Università degli Studi di Milano, via Mangiagalli 31, 20133, Milan, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Dolci
authors.affiliation: Dipartimento di Scienze Biomediche per la Salute, Università degli Studi di Milano, via Mangiagalli 31, 20133, Milan, Italy.
authors.forename: Virgilio F
authors.initials: VF
authors.lastname: Ferrario
authors.affiliation: Dipartimento di Scienze Biomediche per la Salute, Università degli Studi di Milano, via Mangiagalli 31, 20133, Milan, Italy. chiarella.sforza@unimi.it.
authors.forename: Chiarella
authors.initials: C
authors.lastname: Sforza
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging; D005260:Female; D006801:Humans; D008046:Lip / Q000033:anatomy & histology* / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D055815:Young Adult