Free Water Loss-induced Heterogeneous Residual Strain and Reduced Fatigue Resistance in Root Dentin: A 3-dimensional Digital Image Correlation Analysis

Bobby Nadeau; Zhenning Chen; Anil Kishen

doi:10.1016/j.joen.2019.03.012

Free Water Loss-induced Heterogeneous Residual Strain and Reduced Fatigue Resistance in Root Dentin: A 3-dimensional Digital Image Correlation Analysis

J Endod. 2019 Jun;45(6):742-749. doi: 10.1016/j.joen.2019.03.012. Epub 2019 May 2.

Authors

Bobby Nadeau¹, Zhenning Chen², Anil Kishen³

Affiliations

¹ Graduate Endodontics Program, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
² State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing, China.
³ Dental Research Institute, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada; Department of Dentistry, Mount Sinai Hospital, Sinai Health System, Toronto, Ontario, Canada. Electronic address: anil.kishen@utoronto.ca.

PMID: 31056299
DOI: 10.1016/j.joen.2019.03.012

Abstract

Introduction: This study evaluated free water loss-induced residual strain with and without axial compressive loading and assessed the mechanical effect of cyclic loading in fully hydrated and partially dehydrated root dentin.

Methods: Root dentin sections prepared from freshly extracted human premolars were used. Customized 3-dimensional digital image correlation was used to qualitatively and quantitatively analyze the residual strain induced by 2 hours of free water loss in different regions of root dentin. Residual strain in partially dehydrated root dentin during axial compressive loading was also analyzed using 3-dimensional digital image correlation. The effect of cyclic loading on load to fracture in fully hydrated and partially dehydrated dentin and their fractography were analyzed using micro-computed tomographic imaging.

Results: Free water loss resulted in a heterogeneous distribution of residual strain and an overall formation of residual compressive strain with areas of tensile strain localized to the root canal and outer dentin. More residual compressive strain was observed in the apical dentin compared with the cervical dentin (P < .05), and more residual shear strain was observed in outer dentin compared with inner dentin (P < .05). Axial loading resulted in an increase in the load-induced compressive strain in the direction perpendicular to dentinal tubules (P < .05). Fully hydrated roots displayed a higher mean (P < .05) and median (P < .05) number of cycles to fracture with microcracks characteristic of toughness.

Conclusions: After free water loss, root dentin displayed an increased formation of heterogenous residual strain, which resulted in increased axial compressive load-induced strain and a decreased resistance to fatigue failure. The effect of free water loss in the loss of mechanical integrity of root-filled teeth needs further investigation.

Keywords: Free water; digital image correlation; residual strain.

MeSH terms

Bicuspid
Dentin
Humans
Root Canal Therapy*
Tooth Root* / physiology
Water* / physiology

Substances

Water