title: Mineral densities and elemental content in different layers of healthy human enamel with varying teeth age.
abstract: OBJECTIVE
  This study aims to evaluate the mineral density, calcium (Ca), and phosphorus (P) weight percent of healthy human enamel of varying human teeth age and enamel layers.
  
  
  METHODS
  Twenty human teeth were divided into "young" (18-24 years) and "old" (55 ≤ years) age groups. From each tooth, one enamel slab (approximately 8 mm × 2 mm × 1.5 mm) was obtained. All enamel slabs were embedded and scanned by micro-computed tomography. The scanned slices were reconstructed into a 3D image and regions of interest (ROIs) were defined. Then, the mineral density for each ROI was calculated. The Ca and P weight percent in the outer, middle, and inner enamel layers were quantified by scanning electron microscopy with energy dispersive spectroscopy. Finally, the data were analysed using one-way ANOVA and Student's t-test.
  
  
  RESULTS
  In the two age groups, the mineral density, Ca and P weight percent decreased from outer to the inner enamel layer. The mineral density, Ca and P weight percent in the outer enamel layer in the old age group were significantly higher than those in the young age group (P<0.05); however, no age-dependent differences were observed for these properties in the middle and inner enamel layers (P>0.05).
  
  
  CONCLUSIONS
  The mineral density, Ca and P weight percent decreased from the outer to the inner enamel layers in the two age groups. In the outer enamel layer, the differences in these properties between the two age groups were significantly different; however, no region-dependent differences were observed in the middle and inner enamel layers.
authors.affiliation: State Key Laboratory of Oral Diseases, Sichuan University, Chengdu 610041, China.
authors.forename: Bing
authors.initials: B
authors.lastname: He
authors.forename: Shengbin
authors.initials: S
authors.lastname: Huang
authors.forename: Chaoliang
authors.initials: C
authors.lastname: Zhang
authors.forename: Junjun
authors.initials: J
authors.lastname: Jing
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Hao
authors.forename: Liying
authors.initials: L
authors.lastname: Xiao
authors.forename: Xuedong
authors.initials: X
authors.lastname: Zhou
mesh_terms: D000293:Adolescent; D000367:Age Factors; D002118:Calcium / Q000032:analysis*; D003743:Dental Enamel / Q000737:chemistry / Q000648:ultrastructure*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008855:Microscopy, Electron, Scanning; D008875:Middle Aged; D008903:Minerals / Q000737:chemistry*; D008964:Molar, Third / Q000737:chemistry / Q000648:ultrastructure; D010758:Phosphorus / Q000032:analysis*; D013052:Spectrometry, X-Ray Emission; D055114:X-Ray Microtomography / Q000379:methods; D055815:Young Adult
chemical_list: D008903:Minerals; D010758:Phosphorus; D002118:Calcium