Dehydration-induced shrinkage of dentin as a potential cause of vertical root fractures

Vertical root fractures (VRF) of endodontically treated teeth constitute a severe clinical condition frequently requiring removal of the affected tooth. Numerous attempts have been made to find the cause for VRF without reaching definitive conclusions. As changes in moisture content have been reported to appear as a consequence of root canal therapy, it is the goal of this paper to evaluate associated volume changes as a possible cause for VRF. Considering disk shaped horizontal cross sections of endodontically treated teeth with a moisture content of dentin decreasing from the root surface towards the root canal, both relative circumferential and relative radial stresses resulting from volume changes of dentin were calculated. It could be shown that the presence of a root canal itself increases radial and circumferential stresses acting on root dentin by a factor of two. Reduction in moisture content of dentin at the wall of the root canal results in shrinkage of the tooth structure and tensile stress. On the outer surface of the root, compressive stresses occur. Thus, VRF would start at the canal wall and propagate to the root surface. The theory presented appears to be consistent with previous reports on stress development as a consequence of dehydration of dentin and finite element analysis on root fractures. It may be concluded that dehydration of dentin induces cracks at the walls of a root canal which subsequently grow as a result of cyclic loading or traumatic overload.