title: Density of dentinal tubules affects the tensile strength of root dentin.
abstract: OBJECTIVE
  The aim of this study is to count the dentinal tubules in the coronal and middle-apical third of root dentin of teeth extracted due to the progression of periodontal disease, and to compare the Ultimate Tensile Strength (UTS) of the same areas. The research hypothesis was that root dentin areas with different densities of dentinal tubules would also show different UTS values.
  
  
  METHODS
  From 10 caries free maxillary central, lateral incisors and canines, extracted for periodontal reasons from three patients, cylindrical specimens approximately 10 mm long were prepared parallel to the long axis of the root and then divided into two parts using a low speed diamond saw one from the coronal third of the root, (Group 1) and one from the middle-apical third of the root (Group 2). The density of the dentinal tubules of the specimens of the two groups was measured by means of a scanning electron microscope and the UTS of the specimens was measured by a microtensile test. One way ANOVA was used to assess the effect of specimen location (coronal specimens vs. middle-apical specimens) on UTS. The differences in the density of dentinal tubules between coronal and middle-apical specimens were also subjected to statistical analysis using one-way ANOVA.
  
  
  RESULTS
  UTS values of middle-apical specimens were found to be significantly (p < 0.05) higher than those of coronal specimens. The results of the one-way analysis of variance showed that the number of dentinal tubules of the samples from the coronal part of the root groups was significantly higher than that of samples from the middle-apical part (p < 0.05).
  
  
  CONCLUSIONS
  These results suggest that high values of tensile strength of the dentin are associated with low densities of dentinal tubules and that apical areas of root dentin are more resistant to tension than coronal ones.
authors.affiliation: Department of Restorative Dentistry, University of Siena, Italy. mannocci@sirius.pisa.it
authors.forename: Francesco
authors.initials: F
authors.lastname: Mannocci
authors.forename: Peter
authors.initials: P
authors.lastname: Pilecki
authors.forename: Egidio
authors.initials: E
authors.lastname: Bertelli
authors.forename: Timothy F
authors.initials: TF
authors.lastname: Watson
mesh_terms: D000704:Analysis of Variance; D003786:Dental Pulp Cavity / Q000648:ultrastructure; D003799:Dental Stress Analysis; D003804:Dentin / Q000648:ultrastructure*; D003806:Dentin Permeability; D006801:Humans; D008855:Microscopy, Electron, Scanning; D013718:Tensile Strength; D019227:Tooth Apex / Q000648:ultrastructure; D019228:Tooth Crown / Q000648:ultrastructure