Stresses under warm vertical compaction

Key Points

• This article deals with the question: 'What would happen to the stresses in a tooth under warm vertical compaction forces if it contains different forms of defects that would weaken it and its supporting structures?'

• The results show that, the warm vertical compaction technique when performed skilfully, is not likely to create premature root fracture in a large rooted maxillary anterior tooth with straight root canal anatomy even in the presence of severe weaknesses that are assumed to exist.

• Skilful performance means the avoidance of application of undue force through the tip of the plugger to the root canal wall.

Abstract

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 skilfully 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.

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