No abstract

No abstract

The flexural strength of Type I collagen, the major organic component of human dentin, increases with heat. We hypothesized that human dentin can be strengthened by heating, which may help prevent fracture of non-vital teeth after restoration. Beam-shaped dentin specimens were obtained from the crowns of human third molars. The dentinal tubular orientations were arranged to run parallel or perpendicular to loading surfaces. The flexural and microtensile strengths of dentin in the parallel specimens were 2- to 2.4-fold greater after being heated between 110 degrees C and 140 degrees C for 1 hr. The stress intensity factors at fracture also increased after specimens were heated. The x-ray diffraction analyses suggested that shrinking of the lateral packing of the collagen triple-helices from 14 A to 11 A was the probable cause of the strengthening of heated dentin. We conclude that heat treatment strengthens human dentin.

A B S T R A C T Damage accumulation is investigated in the early stage of fatigue life in a ferritic martensitic dual phase steel. Microcrack initiation and propagation are influenced by microstructure, such as grain boundaries, grain orientation and/or phase distribution morphology.The dominant crack initiation pattern is one in which microcracks are generated in a ferrite grain along slip bands inclined at a certain angle with respect to the loading direction. Subsurface observation with a focused ion beam (FIB) device and additional crystallographic characterization by means of the electron backscatter diffraction (EBSD) technique show that a slip system having a high Schmid factor value is activated and results in a crack nucleus. The FIB tomography technique with the help of EBSD measurement allows a three-dimensional investigation of small crack behaviour to be performed.