Lais S Munari1, Walter R Bowles2, Alex S L Fok3. 1. Department of Restorative Dentistry, Faculty of Dentistry, Newton Paiva Ferreira Cultural Institute, Rua José Cláudio Rezende, 420 - Estoril, Belo Horizonte - MG, CEP 30494-230, Belo Horizonte, MG, Brazil. Electronic address: laismunari@hotmail.com. 2. Department of Restorative Sciences, School of Dentistry, University of Minnesota, Moos Health Sciences Tower, 515 Delaware Street S.E., Minneapolis, MN, 55455, USA. 3. Department of Restorative Sciences, School of Dentistry, University of Minnesota, Moos Health Sciences Tower, 515 Delaware Street S.E., Minneapolis, MN, 55455, USA; Minnesota Dental Research Center for Biomaterials and Biomechanics, School of Dentistry, University of Minnesota, Moos Health Sciences Tower, 515 Delaware Street S.E., Minneapolis, MN, 55455, USA.
Abstract
OBJECTIVE: To investigate the effect of endodontic instrumentation on fracture susceptibility of root dentin using experiments and stress analysis. METHODS: Root canals of lower premolars were enlarged with different tapers. After, teeth were cut into 2-mm sections. A metal rod of the same taper was pushed through the center of the sections using a universal test system to fracture them. The fracture load was determined from the peak load on the load-displacement curve. To determine fracture-causing stress, an axisymmetric FE model was created. An analytical solution was developed to understand the relationship between fracture load, geometrical and material parameters. RESULTS: For the same taper, increased root canal diameter did not lead to reduced fracture load. Both analytical and FE solutions showed positive linear relationship between fracture load and enlarged root canal diameter. The hoop stress was maximum at inner surface of enlarged root canal and reduced with increasing radial distance from the center. Bending of sections introduced further nonuniform stresses along the depth. Predictions for the fracture load based on the maximum hoop stress were closest to experimental values; however, account must be taken of the variation in fracture stress of dentin along the root length. Significance Our results rejected the hypothesis that fracture load of root dentin sections reduced with endodontic instrumentation size. However, the stress distributions in whole endodontically treated teeth are more complicated. Thus, caution is necessary when using thin root sections to investigate the effect of endodontic instruments on vertical root fracture.
OBJECTIVE: To investigate the effect of endodontic instrumentation on fracture susceptibility of root dentin using experiments and stress analysis. METHODS: Root canals of lower premolars were enlarged with different tapers. After, teeth were cut into 2-mm sections. A metal rod of the same taper was pushed through the center of the sections using a universal test system to fracture them. The fracture load was determined from the peak load on the load-displacement curve. To determine fracture-causing stress, an axisymmetric FE model was created. An analytical solution was developed to understand the relationship between fracture load, geometrical and material parameters. RESULTS: For the same taper, increased root canal diameter did not lead to reduced fracture load. Both analytical and FE solutions showed positive linear relationship between fracture load and enlarged root canal diameter. The hoop stress was maximum at inner surface of enlarged root canal and reduced with increasing radial distance from the center. Bending of sections introduced further nonuniform stresses along the depth. Predictions for the fracture load based on the maximum hoop stress were closest to experimental values; however, account must be taken of the variation in fracture stress of dentin along the root length. Significance Our results rejected the hypothesis that fracture load of root dentin sections reduced with endodontic instrumentation size. However, the stress distributions in whole endodontically treated teeth are more complicated. Thus, caution is necessary when using thin root sections to investigate the effect of endodontic instruments on vertical root fracture.