Dehydration Induces Cracking in Root Dentin Irrespective of Instrumentation: A Two-dimensional and Three-dimensional Study

Introduction: Water loss strongly affects the mechanical behavior of dentin. Micro computed tomography (ACT) studies exploring the influence of endodontic procedures on root cracking often lack information on the hydration state of the scanned samples. This study explores the relationship between dehydration and crack formation in root dentin with and without endodontic instrumentation. Methods: Fifty-three extracted teeth were used. Thirty canals were not instrumented, and 23 canals were instrumented with ProTaper files until F3. All teeth were imaged with visible light or x-rays, both moist (100% relative humidity) and after dehydration, thus allowing every tooth to serve as its own control. The presence of cracks was determined both before and after dehydration by microscopy on two-dimensional (2D) slices and in by ACT in three dimensions (3D). The ACT data were used to determine the total surface area of newly formed cracks after dehydration, which was correlated with dentin cross section. Results: Both 2D and 3D data revealed cracking with increasing dehydration. Drying led to damage in >50% of roots, with a significant number of cracks appearing within 24 hours of ambient air-drying at 35%-55% relative humidity. Some cracking was occasionally observed even within minutes. More cracks were identified in 3D by ACT as compared with 2D microscopy. A correlation was found between dentin cross section and the total newly formed crack areas. Conclusions: Dehydration may induce cracks in dentin regardless of canal instrumentation. The in vitro observed correlation between root dentin mass and newly formed cracks implies that dehydration engenders stresses that may significantly damage roots.