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Hayashi M.,Osaka University | Furuya Y.,Osaka University | Minoshima K.,Osaka University | Saito M.,Jikei University School of Medicine | And 6 more authors.
Dental Materials | Year: 2012

Objectives: We had previously discovered that the flexural and tensile strengths of human dentin were 2-2.4 times greater after being heated to 140 °C, and deduced that the generation of higher-density structures and therefore dehydration probably promoted the increased strength. Our test hypotheses were that intertubular dentin, which constitutes a major part of organic components, was selectively affected by heating, and such changes could happen without critical damages to the basic structure of dentin type I collagen. Methods: Micro-mechanical changes of human dentin by heating at 140 °C were investigated by nano-indentation. Chemical changes in dentin collagen after heating were also investigated by X-ray diffraction study, a microscopic Fourier transform infrared (micro-FTIR) and a laser Raman spectroscopic analyses, and a cross-linking analysis by high-performance liquid chromatography. Results: The results of nano-indentation showed that the micro-hardness of intertubular dentin increased after heating at 140 °C to 1.8 times more than unheated dentin; on the other hand, peritubular dentin was unchanged. Results of X-ray diffraction showed that the lateral packing of collagen molecules shrank from 13.6 ± 0.3 to 10.6 ± 0.1 after heating, but the shrinkage reversed to the original after rehydration for seven days. After heating, no substantial chemical changes in the collagen molecules were detected in tests by micro-FTIR or Raman analyses, or by cross-linking analysis. Significance: These results suggest that intertubular dentin, which contains most of the type I collagen, was selectively affected by heating at 140 °C without critical damage to its collagen. © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

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