title: [Geometric relationship of axial crown contour and gingiva contour of normal second mandibular premolars].
abstract: OBJECTIVE
  To investigate the relationship of axial crown contour and surrounding healthy gingiva contour.
  
  
  METHODS
  Mandibular second premolars were selected as the object of study. Three cross-sections were made through crown and gingiva of the model tooth. Curve functions of axial buccal crown and gingiva contour of each section were acquired by means of curve fitting, and the angle of emergence profile was calculated, which represents the degree of undercut.
  
  
  RESULTS
  There is unique relationship between axial crown and gingiva contour individually. This character of tooth is similar to its contralateral tooth. The emergence profile angles are in the range of 40 degrees-110 degrees, 84.1% of the angles are in range of 70 degrees-110 degrees, 15.9% in 40 degrees-70 degrees, that is to say natural teeth are inclined to be of less undercut.
  
  
  CONCLUSIONS
  The geometric relationship between crown contour and gingiva contour is so characteristic that contralateral tooth should be the only guidance to replace lost tooth.
authors.affiliation: Department of Prosthodontics, Wuxi Dental Hospital, Wuxi 214001, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Wu
authors.forename: J
authors.initials: J
authors.lastname: Xu
mesh_terms: D000328:Adult; D001641:Bicuspid / Q000033:anatomy & histology; D005881:Gingiva / Q000033:anatomy & histology*; D006801:Humans; D019228:Tooth Crown / Q000033:anatomy & histology*