title: The role of organic tissue on the punch shear strength of human dentin.
abstract: OBJECTIVE
  The tendency to fracture of human teeth has been attributed to numerous reasons, including pulpless tooth dehydration, tooth structure degeneration, and excessive spreader loading. To date, however, no consistent data has been gathered to ascertain the effect of organic tissue on the biomechanical properties of human dentin. This study explored the influences of organic tissue removal on the morphological changes and punch shear strength by means of low vacuum wet scanning electron microscope (Wet-SEM) and punch shear apparatus.
  
  
  METHODS
  The crown dentin slices with a thickness of 0.45-0.50 mm were prepared from extracted human molars. These specimens were immersed in 5% NaOCl for 1, 3, and 6 h to remove the organic tissue. The dynamic morphological changes of these dentin slices after immersion were observed using Wet-SEM. In addition, the punch shear strength and stiffness of specimens were measured.
  
  
  RESULTS
  The removal of organic tissue by 5% sodium hypochlorite treatment caused many cracks on the specimen surfaces. Intertubular and peritubular dentin were also affected, causing an abnormal configuration of dentinal tubule orifices. The 5% sodium hypochlorite treatment for 1, 3, and 6 h significantly reduced the punch shear strength of dentin. As the immersion time increased, the values of punch shear strength also diminished.
  
  
  CONCLUSIONS
  The organic tissue loss of human dentin would affect the structure of intertubular and peritubular dentin and cause many cracks on the dentin surface. The punch shear strength of human dentin also reduced after removal of organic tissue.
authors.affiliation: Graduate Institute of Clinical Dentistry, College of Medicine, National Taiwan University and National Taiwan University Hospital, No. 1, Chang-Te Street, 10016, ROC, Taipei, Taiwan.
authors.forename: Bor-Shiunn
authors.initials: BS
authors.lastname: Lee
authors.forename: Tseng-Ting
authors.initials: TT
authors.lastname: Hsieh
authors.forename: Danny Chia-Hsiang
authors.initials: DC
authors.lastname: Chi
authors.forename: Wan-Hong
authors.initials: WH
authors.lastname: Lan
authors.forename: Chun-Pin
authors.initials: CP
authors.lastname: Lin
mesh_terms: D002809:Chondroitin Sulfates / Q000502:physiology; D024042:Collagen Type I / Q000502:physiology; D003799:Dental Stress Analysis; D003804:Dentin / Q000737:chemistry* / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D006025:Glycosaminoglycans / Q000502:physiology; D006801:Humans; D016014:Linear Models; D008855:Microscopy, Electron, Scanning / Q000379:methods; D008963:Molar; D033081:Shear Strength; D016369:Smear Layer; D012973:Sodium Hypochlorite / Q000494:pharmacology
chemical_list: D024042:Collagen Type I; D006025:Glycosaminoglycans; D002809:Chondroitin Sulfates; D012973:Sodium Hypochlorite