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Objective: This study was designed to investigate the effect of certain pathological alterations of the dental structures (diminishing bone support, internal resorption, root perforation, periapical lesion) on stress distribution during root canal filling procedures by the warm vertical compaction technique., Design: The computer stress analyses were done for a maxillary canine tooth model which was based on dimensions recovered from a human cadaveric maxilla scanned by CT., Methods: The finite element method was used to calculate the stresses generated during root canal filling procedures by warm vertical compaction technique. Patterns of stress distribution associated with various alterations in dental structures were investigated. For this purpose 60 cases were simulated. The hypothetical force of 10 N is taken as a unit representation. For other magnitudes of applied force, the corresponding stresses would be scaled directly because the calculations were made for linear materials., Results and Conclusion: It is found that, when diminishing bone support and internal resorption are concurrently simulated, a marked increase in stress magnitudes occur (maximum von Mises stress 5.37 N/mm2). However, these values still remain much below the most frequently reported tensile strength of dentine (50-100 N/mm2). If dentist's handwork is transformed into equivalent edge tractions on gutta-percha, then stresses in dentine, even when they are corrected for 3-kg applied force, appear to remain below fracture strengths of this material. This result leads us to conclude that when warm vertical compaction technique is skillfully performed and inadvertent undue force is not applied, a premature root fracture in a large rooted maxillary anterior tooth with straight root canal anatomy is not likely to occur, even for the unfavourable conditions simulated in our model. This result, like all results derived from modelling applications, is of course contingent upon agreement between the way in which the clinical operations are performed and the way in which they are mirrored for computer representation. We believe that the approach described here avoids the spurious stresses that have been reported in similar investigations.

Objective: To investigate the distribution of stresses that occur in a maxillary canine tooth during vertical and lateral condensation of gutta-percha in the root canal., Design: An elaborate three-dimensional finite element model of a maxillary canine tooth was developed for the purposes of stress analysis. A sample stress analysis was also performed to demonstrate the variations in stress values that occur between different solutions of the same problem., Methods: A 3D finite element analysis was performed on a maxillary canine tooth model which was created using the dimensions of computer tomographic scans of a cadaveric maxilla as reference., Results: If the manual operations of the endodontist are transcribed to the software by considering the finite size of the plugger or the spreader, then the maximum stresses generated in the dentine are much smaller than the reported tensile strength of this material., Conclusion: The causes of the fractures in the dentine reported by previous investigators must be traced to conditions which were not considered in this study. These include aspects of modelling, which is the most important single parameter on which the final results depend. Stresses calculated by means of the complicated 3D model appear to agree with those recovered from a simpler 2D idealisation.

The finite element method was used to calculate the stresses in a maxillary canine tooth produced during lateral and vertical condensation. Description of the biological domain to be analyzed, and conversion of the manual operations of the endodontist to realistic load representation are intricate problems which must be overcome before stresses are recovered and plotted. The stresses in dentin are in general of comparable magnitudes during lateral or vertical condensation, but these magnitudes generally remain much below those presented in a previous study. From these calculations it appears that root fractures reported by some investigators may be explained in terms of stress concentrations and local irregularities of the samples tested.