Factors Affecting Fracture Susceptibility of Tooth Root: A Laboratory and Finite Element Analysis (FEA) Study

From a fracture mechanics viewpoint, structural defects, cracks or canal irregularities are likely to play a major role in fracture susceptibility of the roots, because stresses can be exponentially amplified at these sites. By incorporating defects into a smooth round canal using rotary NiTi, theoretically the roots could be strengthened. The aims of the study were to determine whether rotary NiTi canal preparation strengthens roots, and whether the fracture pattern can be predicted by finite element analysis (FEA) models. 25 teeth were prepared using hand file and another 25 using rotary NiTi. After obturation, all teeth were subject to loading until fracture; load and patterns were recorded. Four FEA models were created from fractured roots. No significant difference of fracture load between the two techniques was found. Mesio-distal fracture occurred more often in the rotary NiTi group. Stress patterns in three of the four FEA models correlated well with the observed fracture patterns. The aim of the subsequent study was to determine the extent to which canal size, radius of curvature and proximal root concavity influence fracture susceptibility and pattern. A standardized cross-section of the mid-root region of a mandibular incisor was created by averaging the dimensions of ten extracted teeth, and the basic FEA model was created. By varying canal diameter, shape and proximal concavity, these factors could be examined for roles in fracture susceptibility and pattern. The factors all interact in influencing fracture susceptibility and pattern, with dentine thickness not the iii only determining factor. The removal of dentine does not always result in increased fracture susceptibility. iv Declaration This is to certify that the thesis comprises only my original work except where indicated in the preface; due acknowledgement has been made in the text to all other material used; the thesis is 12,858 words in length, inclusive of footnotes, but exclusive of tables, maps, appendices and bibliography.