Objective: To investigate the fatigue behavior of restored teeth, in particular the mechanisms of longitudinal dentinal cracking under cyclic mechanical loading, using finite element analysis (FEA) and the stress-life (S-N) approach. Methods: Ten root-filled premolars restored with resin composites were subjected to step-stress cyclic loading to produce longitudinal cracks. Fracture loads and number of cycles completed at each load level were recorded. FEA was used to predict the stress amplitude of each component under the global cyclic load. Both intact and debonded conditions were considered for the dentin-composite interface in the FEA. The predicted stress concentrations were compared with the fracture patterns to help elucidate the failure mechanisms. The S-N approach was further used to predict the lifetimes of the different components in the restored teeth. Cumulative fatigue damage was represented by the sum of the fractions of life spent under the different stress amplitudes. Results: Longitudinal cracks were seen in ~50% of the samples with a mean fracture load of 770 ± 45 N and a mean number of cycles to failure of 32,297 ± 12,624. The longitudinal dentinal cracks seemed to start near the line angle of the cavity, and propagated longitudinally towards the root. The sum of fractions of life spent for the dentin-composite interface exceeded 1 after ~7000 cycles when that for dentin was much lower than 1, indicating that interfacial debonding would occur prior to dentin fracture. This was supported by micro-CT images showing widened interfacial space in the cracked samples. In the debonded tooth, FEA showed dentinal stress concentrations at the gingival wall of the cavity, which coincided with the longitudinal cracks found in the cyclic loading test. The sum of fractions of life spent for dentin was close to 1 at ~30,000 cycles, similar to the experimental value. Significance: Debonding of the dentin-composite interface may occur prior to longitudinal cracking of dentin in root-filled teeth under cyclic loading. The approximate time of occurrence for these events could be estimated using fatigue analysis with stresses provided by FEA. This methodology can therefore be used to evaluate the longevity of restoration designs for root-filled teeth.
Bibliographical noteFunding Information:
Research reported in this paper was supported by the National Institute of Dental and Craniofacial Research of the National Institutes of Health under award number R01DE027043 . The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. This work was also supported by National Natural Science Foundation of China through a grant (No. 12102009 ) awarded to Fei Lin and a pre-K grant from the National Institutes of Health’s National Center for Advancing Translational Sciences , UL1TR002494 (CTSI-UMN), awarded to Ronald Ordinola-Zapata. Fei Lin would also like to acknowledge Minnesota Dental Research Center for Biomaterials and Biomechanics for the financial support with a Key Opinion Leaders Scholarship sponsored by 3Mgives.
© 2021 Elsevier Inc.
- Cyclic loading
- Fatigue analysis
- Finite element analysis
- Longitudinal crack
PubMed: MeSH publication types
- Journal Article
- Research Support, N.I.H., Extramural