Finite element analysis of the effects of three preparation techniques on stresses within roots having curved canals.

Aim: To compare stress distribution within roots having curved canals prepared by three preparation techniques when subjected to occlusal loads and condensation loads as a consequence of different filling techniques.
Methodology: Three preparation techniques (crown-down, step-back and reverse-flaring) were compared by finite element analysis (FEA). Based on an established FEA model within curved canal, three modified models prepared by different preparation techniques were established by replacing original canal with prepared ones. FEA was performed to investigate the stress distribution under occlusal forces, which were simulated by loads of 500 N in four directions (buccal, lingual, mesial and distal), at 0 (vertical), 30, 45 and 60 degrees to the longitudinal axis of the tooth. In addition, vertical and lateral condensation processes at the curvature were simulated to determine the influence of different canal filling techniques on stress distribution.
Results: When the occlusal and the filling loads were applied, stress distribution around the curvature and the orifice had little change on the three modified prepared models. The reverse-flaring technique resulted in the least stress with the lateral condensation process. In the case of vertical condensation, the maximum von Mises stress (46.205 MPa) occurred near the loading site. The model also revealed a tendency for stress concentration (30.635 MPa) just below the compacting level.
Conclusions: The study confirms that appropriate canal preparation techniques in simulated curved canals have little influence on stress distribution around the curvature or the orifice. However, vertical compaction induced high stress in the region just below the loading site.