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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.

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.