Effect of Dehydration on Mechanical Properties of Human Dentin

Objective: Tooth fracture encountered in clinical practice is a problem urgently needed to address. Better understanding of fracture mechanisms of dentin is a significant approach to prevent tooth fracture. The purpose of this study was to investigate the effect of dehydration on flexural and micro-tensile strength of human dentin with different dentinal tubule orientations. Methods: Beam-shaped specimens (0.9x1.7x7.0mm) were obtained from the coronal part of freshly extracted human third molars. Specimens with the dentinal tubules running either parallel or perpendicular to their longitudinal surfaces were prepared. The specimens were kept in one of the following environmental conditions; wet (kept in saline or Hank's balanced salt solution), dry (put into a desiccator for 7 days), or heat (put into an oven at 110ºC for 1 hour). Flexural and micro-tensile strengths were measured with a universal testing machine and fractured surfaces were observed with a scanning electron microscopy. Results among the groups with different tubule orientations and different environmental conditions were compared by means of ANOVA and Scheffe's F test at a 95% level of confidence. Results: Both flexural and micro-tensile strengths increased in the heat groups. The increase was significant in specimens with parallel tubule orientations. Desiccation did not show significant effects on both mechanical strengths. According to the fractographic observations, in perpendicular specimens, peritubular and intertubular dentin were clearly distinguishable in the wet and dry groups, while the boundaries between peritubular and intertubular dentin were difficult to identify in the heat group. Conclusion: Regardless of the tubule orientations, flexural and tensile strength of human dentin increased by heating at 110ºC for 1 hour. (This study was supported in part by Grant-in-Aid for Scientific Research (No. 1639054) from the Japan Society for Promotion of Science and by the 21st century COE program at Osaka University Graduate School of Dentistry.)