Fracture resistance, failure mode and stress concentration in a modified endocrown design

Wiam El Ghoul; Mutlu Özcan; Joao Paulo Mendes Tribst; Ziad Salameh

doi:10.1080/26415275.2020.1801348

Authors

Wiam El Ghoul a Department of Prosthodontics, Faculty of Dental Medicine, Lebanese University, Beirut, Lebanon
Mutlu Özcan b Division of Dental Biomaterials, Centre of Dental Medicine, Clinic of Reconstructive Dentistry, University of Zurich, Zurich, Switzerland
Joao Paulo Mendes Tribst c Department of Dental Materials and Prosthodontics, São Paulo State University, Institute of Science and Technology, São José dos Campos, Brazil
Ziad Salameh a Department of Prosthodontics, Faculty of Dental Medicine, Lebanese University, Beirut, Lebanon

DOI:

https://doi.org/10.1080/26415275.2020.1801348

Keywords:

Endocrown, finite element analysis, lithium disilicate, fracture resistance, failure mode

Abstract

Purpose

The purpose of this study was to assess fracture resistance, failure mode and stress concentration of a modified endocrown preparation design, under axial and lateral forces.

Materials and Methods

Forty lower molars were divided into two groups (n = 20) and were restored with lithium disilicate glass-ceramic endocrowns following 2 preparation designs: Conventional, with circumferential butt margin 2 mm above the cemento–enamel junction; and Modified, by adding 2 grooves on the mesial side of the vestibular dentinal wall and on the distal side of the lingual dentinal wall. After cementation and thermomechanical cycling loading, half of the samples (n = 10) from each group were loaded axially and the other half (n = 10) was loaded laterally. Fracture resistance and failure modes were observed and the finite element analysis (FEA) was used to identify the stress concentration. Two-way ANOVA and Chi-square tests (α = 0.05) were used for in vitro data analyzes.

Results

Fracture resistance showed a statistically significant difference between conventional and modified preparations (p < .001), and between axial and lateral loadings (p < .001). Conventional preparation recorded 2914 N under axial loading and 1516 N under lateral loading, while modified preparation recorded 3329 N under axial loading and 1871 N under lateral loading. FEA showed that retention grooves have reduced the stress concentration under both loads for the tooth and the restoration.

Conclusion

Modified endocrown design showed higher fracture resistance than conventional endocrown. Lateral loading displayed a high percentage of severe fracture but under higher load to failure than the values reported for normal masticatory forces.