title: Generational differences in tooth size in the Japanese population: analysis of cohorts with a generation gap of four to five decades.
abstract: OBJECTIVE
  Since early modern times, tooth size has reportedly been increasing in each successive generation. A detailed analysis of these trends can provide meaningful information for elucidating the origin of various problems caused by larger teeth, such as an abnormal dentition and occlusion. By using data from most recent generations, this study aimed to clarify the time course of changes in tooth size in the Japanese.
  
  
  METHODS
  The dentitions of two Japanese cohorts comprising young individuals born in the 1980s and the 1990s were compared with those of another cohort of Japanese individuals born in the 1940s, approximately half a century earlier. The mesiodistal diameter of the tooth crowns was measured on plaster models and subjected to statistical analyses.
  
  
  RESULTS
  A mean difference test revealed that each recent generation showed positive generational differences in the size of more than 50% of the tooth types. In addition, a deviation graph analysis indicated that the degree of change in tooth size varied with the tooth type or sampling site. Principal component analysis clearly showed an increase in tooth size on an individual basis in the more recent generations.
  
  
  CONCLUSIONS
  This study revealed positive generational differences in tooth size in the Japanese population. The results may aid in understanding the development of abnormal dentitions and occlusion in recent Japanese populations.
authors.forename: Koji
authors.initials: K
authors.lastname: Sumi
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kawakubo
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Yamashita
authors.forename: Masaaki
authors.initials: M
authors.lastname: Goto
authors.forename: Akio
authors.initials: A
authors.lastname: Kuraoka
mesh_terms: D000293:Adolescent; D000367:Age Factors; D044466:Asian People; D002648:Child; D015331:Cohort Studies; D005260:Female; D006801:Humans; D013997:Time Factors; D014070:Tooth / Q000033:anatomy & histology*; D055815:Young Adult