title: Effect of aging on the microstructure, hardness and chemical composition of dentin.
abstract: OBJECTIVE
  Understanding the effects of biological aging on human tissues has been a topic of extensive research. With the increase in healthy seniors and quality of life that topic is becoming increasingly important. In this investigation the effects of aging on the microstructure, chemical composition and hardness of human coronal dentin was studied from a comparison of teeth within "young" and "old" age groups.
  
  
  METHODS
  The microstructure of dentin within three regions (i.e., inner, middle and outer) was analyzed using electron and optical microscopy. The mineral-to-collagen ratio in these three regions was estimated using Raman spectroscopy and the hardness was evaluated using microindentation.
  
  
  RESULTS
  Results showed that there were significant differences in tubule density, tubule diameter and peritubular cuff diameter with depth. Although there was no difference in tubule density and diameter of the tubules between the age groups, there was a significant difference in the occlusion ratio. A significant increase in hardness between young and old patients was found for middle and outer dentin. An increase in mineral-to-collagen ratio from inner to outer dentin was also found for both groups. In old patients, an increase in mineral content was found in outer coronal dentin as a consequence of tubule occlusion.
  
  
  CONCLUSIONS
  An increase in occlusion ratio, hardness, and mineral content was found in the dentin of adult patients with age. This increase is most evident in the outer coronal dentin.
authors.affiliation: Materials Engineering Research Group, School of Engineering, Universidad Eafit, Medellín, Colombia.
authors.forename: C
authors.initials: C
authors.lastname: Montoya
authors.affiliation: Faculty of Dentistry, Universidad Cooperativa de Colombia, Envigado, Colombia.
authors.forename: S
authors.initials: S
authors.lastname: Arango-Santander
authors.affiliation: Faculty of Dentistry, Universidad Cooperativa de Colombia, Envigado, Colombia.
authors.forename: A
authors.initials: A
authors.lastname: Peláez-Vargas
authors.affiliation: Department of Materials Science & Engineering, University of Washington, Seattle, WA, USA.
authors.forename: D
authors.initials: D
authors.lastname: Arola
authors.affiliation: Materials Engineering Research Group, School of Engineering, Universidad Eafit, Medellín, Colombia. Electronic address: eossa@eafit.edu.co.
authors.forename: E A
authors.initials: EA
authors.lastname: Ossa
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging; D003804:Dentin / Q000737:chemistry* / Q000648:ultrastructure*; D005260:Female; D006244:Hardness; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008855:Microscopy, Electron, Scanning; D008875:Middle Aged; D008964:Molar, Third; D013059:Spectrum Analysis, Raman; D013499:Surface Properties
keywords: Chemical composition; Dentin; Dentinal tubules; Hardness