On vertical root fracture from condensation of gutta-percha
Herzl Chai (Tel-Aviv University), Aviad Tamse (Tel Aviv University)
Crack initiation and growth: methods, applications, and challenges
Tue 2:40 - 4:00
Sayles Auditorium
Vertical root fracture (VRF) is a major complication in endodontically treated teeth that often leads to tooth extraction. VRF is attributed to such factors as occlusal forces, post placement and use of excessive forces during root canal obturation. It is the latter type which is of concern here. The apical force applied to gutta-percha ("gp"), the most common root canal filling material, causes a pressure in the gp. This leads to circumferential tensile stresses on the canal surface, which may enlarge existing surface defects to cause VRF. We aim at predicting analytically the apical force needed to cause VRF. The fracture problem at hand encompasses a formidable 3D geometry and material variables whose mechanical properties are not fully understood. Given these complexities, some bold simplifications are invoked, the main one being the treatment of VRF as a 2D fracture problem. The morphology of the root canal cross section is systematically explored. The resulting analytic relation for apical load causing VRF agrees well with major trends reported in in-vitro tests on roots subjected to vertical condensation of gp. This analysis is then discussed in relation to the more clinically relevant case of cyclic condensation. The model explicitly exposes the role of root canal morphology and dentin fracture toughness on VRF. Ovoid and irregular canals are prone to fracture while the effect of mean root canal radius is quite modest. Canal taper and instrumentation details may affect VRF only marginally and indirectly. The model predicts dentinal cracks to occur following root canal instrumentation and obturation, which may pose long-term threats to tooth integrity.