Introduction: Dentin is a calcified and hydrated biological composite that forms the major bulk of tooth structure. Understanding the biomechanical response of dentin structure to forces is key to develop treatment strategies to restore the compromised mechanical integrity associated with both pathologic and iatrogenic dentin loss[1]. Digital Moiré Interferometry (DMI) is an optical interferometry technique which provides a whole field strain information in real-time with high sensitivity. They can be applied to study the biomechanical response in dental hard tissues under clinically realistic loading conditions, distinctly different to traditional mechanical testing[2],[3].
The aim of this study is to conduct a DMI analysis to evaluate (1) the degree and pattern of microstrain distributions in dentin after iatrogenic dentin removal, and (2) the influence of nanoparticle based conditioning on the mechanical microstrain distribution in dentin, qualitatively.
Materials and Methods: Thirty extracted human upper anterior teeth were collected and decoronated with the root lengths being standardized at 16mm. The root canals of the specimens were enlarged with K files (K-Flexofiles, Dentsply®) to size #10(n=6), #30(n=12) and #50(n=12) followed with/without naoparticles conditioning. Chitosan nanoparticle was found to be biocompatible, antimicrobial with excellent film forming properties[4]-[6]. Dentin collagen treated with them was reported of increasing the resistance of dentin enzymatic degradation to enhance the mechanical properties of dentin as well[7],[8].
The tooth specimens were prepared by grinding the mesial and distal surfaces to reach slab shaped, parallel-sided, facio-lingual section with uniform thickness of 2.5mm. A high frequency grating of 1200 lines /mm were replicated on the specimens which were subsequently loaded in a custom made loading jig, compressively from 10 to 50N. Moiré fringes were recorded and analyzed at specific regions of interest to determine the in-plane deformation in dentin that perpendicular (U-field) and parallel to the dentinal tubules (V-field).
Results and Discussion: The U-field and V-field moiré analyses showed that the compressive loads resulted in a distinct strain distribution along the axial and lateral directions in dentin. The strain distribution gradually increased in the direction perpendicular to the dentinal tubules, while it remained constant in the direction parallel to the tubules during compressive loadings. The strain values were higher in the group with #50 canal sizes enlargement compared with the values from #10 and #30 canal sizes enlargement. The root dentin conditioned with nanoparticles had lesser microstrain increase with increase in compressive loads.
The results obtained from strain analysis showed that the specimens with minimal dentin removal during canal enlargement and the root dentin conditioned with nanoparticle demonstrated lesser deformation with increase in loads.
Conclusion: The functional strain distribution in dentin gradually increased in the direction perpendicular to the dentinal tubules, while it remained constant in the direction parallel to the tubules during compressive loadings. The root dentin, which was conditioned with the nanoparticles, displayed markedly less microstrain increase with loads. The current photomechanical experiment highlighted the significance of nanoparticle conditioning to improve the mechanical integrity of dentin.
Natural Sciences and Engineering Research Council, Discovery grant; Canadian Foundation of Innovation; University of Toronto
References:
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