title: The effects of ageing on the biomechanical properties of root dentine and fracture.
abstract: OBJECTIVE
  Knowledge of the mechanical behaviour of root dentine can facilitate better understanding of spontaneous vertical root fracture (VRF), an age-related disease initiated mainly at the root apex. We tested the hypothesis that the biomechanical properties of root dentine change with ageing.
  
  
  METHODS
  Sixteen human premolars were divided into "old" (17-30 years) and "young" (50-80 years) groups. The elastic modulus, nano-hardness, micro-hardness, elemental contents, tubular density/area of root dentine in cervical, middle and apical root regions were evaluated using atomic force microscopy-based nano-indentation, Knoop indentation, scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively.
  
  
  RESULTS
  The apical dentine showed a lower nano-hardness, a lower elastic modulus, a lower calcium content, a lower calcium-to-phosphorus ratio and a smaller tubular density/area than the cervical dentine in both age groups, whereas spatial differences in micro-hardness were observed only in old roots. Compared with young dentine, old dentine showed a greater hardness, a higher elastic modulus, a greater mineral content and a smaller tubular size in the cervical portion, whereas the age-induced changes in tubular density were insignificant. Finite element analysis revealed that due to its higher elastic modulus, old apical dentine has a higher stress level than young dentine.
  
  
  CONCLUSIONS
  The intrinsic material properties of root dentine have spatial variations, and they are altered by ageing. The higher stress level in old apical dentine may be one reason, if not the most important one, why spontaneous VRFs are more likely to occur in the elderly population.
authors: State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China.
authors: Haiping
authors: H
authors: Xu
authors: State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China.
authors: Qinghua
authors: Q
authors: Zheng
authors: The State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China. Electronic address: shaoyf@lnm.imech.ac.cn.
authors: Yingfeng
authors: Y
authors: Shao
authors: The State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China.
authors: Fan
authors: F
authors: Song
authors: State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China.
authors: Lan
authors: L
authors: Zhang
authors: State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China.
authors: Qian
authors: Q
authors: Wang
authors: Department of Conservative Dentistry and Endodontics, West China School of Stomatology, Sichuan University, Chengdu 610041, China. Electronic address: dingminghuang@163.com.
authors: Dingming
authors: D
authors: Huang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000378:metabolism / Q000473:pathology / Q000502:physiology*; D001696:Biomechanical Phenomena; D002118:Calcium / Q000032:analysis; D003804:Dentin / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D055119:Elastic Modulus; D020342:Finite Element Analysis; D006244:Hardness; D006801:Humans; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning; D008875:Middle Aged; D010758:Phosphorus / Q000032:analysis; D013052:Spectrometry, X-Ray Emission; D013314:Stress, Mechanical; D019227:Tooth Apex / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D019237:Tooth Cervix / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D014082:Tooth Fractures / Q000503:physiopathology*; D014092:Tooth Root / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D055815:Young Adult
chemical_list: D010758:Phosphorus; D002118:Calcium
keywords: Ageing; Biomechanics; Dentine; Finite element analysis; Nano-indentation; Root fracture