Publications by authors named "Mobin Yahyazadehfar"

9 Publications

  • Page 1 of 1

Durability of self-healing dental composites: A comparison of performance under monotonic and cyclic loading.

Mater Sci Eng C Mater Biol Appl 2018 Dec 30;93:1020-1026. Epub 2018 Aug 30.

Dr. Anthony Volpe Research Center, American Dental Association Foundation, Gaithersburg, MD, USA. Electronic address:

Durability is an important quality of dental restorative materials, and the ability to autonomously heal damage incurred during their oral function is highly desirable.

Objective: The objective was to evaluate the improvement in durability of self-healing dental composites (SHDCs) in terms of their resistance to fracture and capacity for healing of damage under monotonic and cyclic loading.

Methods: SHDCs were prepared by incorporating dental resin composites with microcapsules containing healing liquid. Control specimens with the same mass fraction (5% and 25%) of microcapsules filled with water were also evaluated. Two sets of SHDCs were distinguished by the silane coupling agents that functionalized and bonded the microcapsules to resin network. One set used a methacrylate silane (MA-silane) that connected resin network through covalent bonds, and the other used a H-bonding forming hydroxyl silane (OH-silane). The fatigue crack growth resistance was assessed in terms of the threshold stress intensity range and the conventional Paris Law parameters. Cyclic loading was conducted at 5 Hz with maximum cyclic load ranged between approximately 1 N and 5 N. The efficiency of the autonomous healing was determined per the recovering of the fracture toughness and the extension of fatigue life.

Results: The SHDCs with 5 wt% of healing microcapsules exhibited a larger fracture toughness than those with 25 wt% microcapsules. MA-silane SHDCs had approximately five times more responsive microcapsules triggered by fracturing of the composites. Consequently, the MA-silane SHDCs with 5 wt% of microcapsules achieved the best performance in terms of fracture toughness and healing efficiency. In regards to the fatigue crack growth behavior, there was a significant increase in the resistance to fatigue crack growth and 580 ± 15% improvement in the fatigue life.

Significance: Strong silanization is vital in SHDCs to simultaneously achieve clinically applicable mechanical performance and substantial healing capability. Moreover, the evaluation of self-healing under cyclic loading is a promising tool in quantifying the degree of fracture-induced healing.
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http://dx.doi.org/10.1016/j.msec.2018.08.057DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6192528PMC
December 2018

Durability of adhesive bonds to tooth structure involving the DEJ.

J Mech Behav Biomed Mater 2018 01 2;77:557-565. Epub 2017 Oct 2.

Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA; Department of Restorative Dentistry, School of Dentistry, University of Washington, Seattle, WA, USA; Department of Oral Health, School of Dentistry, University of Washington, Seattle, WA, USA. Electronic address:

The importance of the Dentin Enamel Junction (DEJ) to the durability of adhesive bonds to tooth structure is unclear. In fact, no investigation has been reported on contributions of the DEJ to the fatigue resistance of the bonded interface. In this study, the durability of adhesive bonds to tooth structure involving the DEJ was quantified and compared to that of adhesive bonds to enamel only, not including the DEJ. Two different configurations of enamel bonding were considered, including when tensile stress is focused on the outer enamel (occlusal configuration) or the inner decussated enamel (decussated configuration). The resistance to failure for all bonded interfaces was assessed under both static and cyclic loading to failure. Results showed that the durability of the bonded interfaces was primarily a function of their resistance to crack initiation and growth. The bonded interface strength involving the DEJ was significantly (p ≤ 0.05) greater than that of bonds to enamel only with occlusal configuration, under both static and cyclic loading. While the fatigue strength of bonds involving the DEJ was approximately 20% greater than that for enamel bonds with occlusal configuration (7.7MPa) it was lower than that of enamel with the decussated configuration. The DEJ deterred cracks from extending readily into the dentin but it did not prevent fatigue failure. These results suggest that the durability of bonds to enamel are most dependent on the enamel rod decussation and that the DEJ plays a minor role.
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http://dx.doi.org/10.1016/j.jmbbm.2017.10.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5837065PMC
January 2018

Effects of polar solvents on the mechanical behavior of fish scales.

Mater Sci Eng C Mater Biol Appl 2016 Apr 10;61:23-31. Epub 2015 Dec 10.

Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA. Electronic address:

Fish scales are unique structural materials that serve as a form of natural armor. In this investigation the mechanical behavior of scales from the Cyprinus carpio was evaluated after exposure to a polar solvent. Uniaxial tensile and tear tests were conducted on specimens prepared from the scales of multiple fish extracted from near the head, middle and tail regions, and after exposure to ethanol for periods from 0 to 24h. Submersion in ethanol caused instantaneous changes in the tensile properties regardless of anatomical site, with increases in the elastic modulus, strength and modulus of toughness exceeding 100%. The largest increase in properties overall occurred in the elastic modulus of scales from the tail region and exceeded 200%. Although ethanol treatment had significant effect on the tensile properties, it had limited influence on the tear resistance. The contribution of ethanol to the mechanical behavior appears to be derived from an increase in the degree of interpeptide hydrogen-bonding of the collagen molecules. Spatial variations in the effects of ethanol exposure on the mechanical behavior arise from the differences in degree of mineralization and lower mineral content in scales of the tail region.
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http://dx.doi.org/10.1016/j.msec.2015.12.007DOI Listing
April 2016

On the importance of aging to the crack growth resistance of human enamel.

Acta Biomater 2016 Mar 31;32:264-274. Epub 2015 Dec 31.

Department of Material Science and Engineering, University of Washington, Seattle, WA, USA; Department of Restorative Dentistry, School of Dentistry, University of Washington, Seattle, WA, USA; Department of Oral Health Sciences, School of Dentistry, University of Washington, Seattle, WA, USA. Electronic address:

Unlabelled: With improvements in oral health and an overall increase in quality of life, the percentage of fully or largely dentate seniors is increasing. Understanding the effects of aging on the mechanical properties of teeth is essential to the maintenance of lifelong oral health. In this investigation the effects of aging on the fracture toughness of human enamel were evaluated from incremental crack growth experiments performed on tissue of donor teeth representing "young" (17 ⩽ age ⩽ 25) and "old" (age ⩾ 55) age groups. Results showed that the old enamel exhibited significantly lower resistance to fracture than that of the young tissue in two orthogonal directions of crack growth. For crack growth transverse to the enamel rods, the fracture toughness of the old enamel (0.37 ± 0.15 MPa m(0.5)) was nearly 70% lower than that of tissue from the young teeth (1.23 ± 0.20 MPa m(0.5)). Based on results from a mechanistic analysis of crack growth, the reduction in fracture resistance is attributed to a decrease in the degree of extrinsic toughening. The practice of restorative dentistry should account for these changes in tooth tissues in the treatment of senior patients.

Statement Of Significance: The mechanical behavior of enamel has been studied for over 3 decades. Due to the limited volume of tissue available for evaluation, past work has been largely based on indentation methods. In this investigation we have evaluated the resistance to fracture of human enamel using a conventional fracture mechanics approach and incremental crack growth. We compared the fracture resistance of cuspal enamel obtained from the teeth of representative "young" and "old" donor groups. Our results show that there is a substantial reduction in the resistance to fracture with age, that it is anisotropic, and that the degradation is more severe than that which occurs to dentin. As such, we feel this work is a significant contribution to the field.
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http://dx.doi.org/10.1016/j.actbio.2015.12.038DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4754146PMC
March 2016

The role of organic proteins on the crack growth resistance of human enamel.

Acta Biomater 2015 Jun 22;19:33-45. Epub 2015 Mar 22.

Department of Material Science and Engineering, University of Washington, Seattle, WA, USA; Department of Restorative Dentistry, School of Dentistry, University of Washington, Seattle, WA, USA. Electronic address:

With only 1% protein by weight, tooth enamel is the most highly mineralized tissue in mammals. The focus of this study was to evaluate contributions of the proteins on the fracture resistance of this unique structural material. Sections of enamel were obtained from the cusps of human molars and the crack growth resistance was quantified using a conventional fracture mechanics approach with complementary finite element analysis. In selected specimens the proteins were extracted using a potassium hydroxide treatment. Removal of the proteins resulted in approximately 40% decrease in the fracture toughness with respect to the fully proteinized control. The loss of organic content was most detrimental to the extrinsic toughening mechanisms, causing over 80% reduction in their contribution to the total energy to fracture. This degradation occurred by embrittlement of the unbroken bridging ligaments and consequent reduction in the crack closure stress. Although the organic content of tooth enamel is very small, it is essential to crack growth toughening by facilitating the formation of unbroken ligaments and in fortifying their potency. Replicating functions of the organic content will be critical to the successful development of bio-inspired materials that are designed for fracture resistance.
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http://dx.doi.org/10.1016/j.actbio.2015.03.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4499056PMC
June 2015

On the Mechanics of Fatigue and Fracture in Teeth.

Appl Mech Rev 2014 May 30;66(3):0308031-3080319. Epub 2014 Apr 30.

Department of Materials Science and Engineering, University of Washington , Seattle, WA 98195;

Tooth fracture is a major concern in the field of restorative dentistry. However, knowledge of the causes for tooth fracture has developed from contributions that are largely based within the field of mechanics. The present manuscript presents a technical review of advances in understanding the fracture of teeth and the fatigue and fracture behavior of their hard tissues (i.e., dentin and enamel). The importance of evaluating the fracture resistance of these materials, and the role of applied mechanics in developing this knowledge will be reviewed. In addition, the complex microstructures of tooth tissues, their roles in resisting tooth fracture, and the importance of hydration and aging on the fracture resistance of tooth tissues will be discussed. Studies in this area are essential for increasing the success of current treatments in dentistry, as well as in facilitating the development of novel bio-inspired restorative materials for the future.
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http://dx.doi.org/10.1115/1.4027431DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4240032PMC
May 2014

Fatigue of the resin-enamel bonded interface and the mechanisms of failure.

J Mech Behav Biomed Mater 2013 May 1;21:121-32. Epub 2013 Mar 1.

Department of Mechanical Engineering, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA.

The durability of adhesive bonds to enamel and dentin and the mechanisms of degradation caused by cyclic loading are important to the survival of composite restorations. In this study a novel method of evaluation was used to determine the strength of resin-enamel bonded interfaces under oth static and cyclic loading, and to identify the mechanisms of failure. Specimens with twin interfaces of enamel bonded to commercial resin composite were loaded in monotonic and cyclic 4-point flexure to failure within a hydrated environment. Results for the resin-enamel interface were compared with those for the resin composite (control) and values reported for resin-dentin adhesive bonds. Under both modes of loading the strength of the resin-enamel interface was significantly (p≤0.0001) lower than that of the resin composite and the resin-dentin bonded interface. Fatigue failure of the interface occurred predominantly by fracture of enamel, adjacent to the interface, and not due to adhesive failures. In the absence of water aging or acid production of biofilms, the durability of adhesive bonds to enamel is lower than that achieved in dentin bonding.
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http://dx.doi.org/10.1016/j.jmbbm.2013.02.017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3653582PMC
May 2013

Fatigue of the resin-dentin interface: a new approach for evaluating the durability of dentin bonds.

Dent Mater 2013 Apr 21;29(4):437-49. Epub 2013 Feb 21.

Adhesive Dentistry Research Group, Department of Cariology, Institute of Dentistry, University of Turku, Turku, Finland.

Unlabelled: There are concerns regarding the longevity of resin composite restorations and the clinical relevance of in vitro bond strength testing to the durability of dentin bonds in vivo.

Objective: The objectives of this investigation were to: (1) develop a new method of experimental evaluation for quantifying the durability of dentin bonds, (2) apply this method to characterize the interfacial strength of a selected commercial system under both monotonic and cyclic loading, and (3) distinguish mechanisms contributing to the interface degradation and failure.

Methods: A new method for fatigue testing the resin-dentin interface was developed based on a four-point flexure arrangement that includes two identical bonded interfaces. Cyclic loading of specimens comprised of coronal dentin bonded to a commercial resin composite and controls of resin composite was performed to failure within a hydrated environment. Scanning electron microscopy and nanoscopic dynamic mechanical analysis were used to evaluate failure mechanisms.

Results: The fatigue strength of the resin-dentin interface was significantly lower (p≤0.0001) than that of the resin composite and reported for dentin over the entire finite life regime. Defined at 1×10(7) cycles, the apparent endurance limit of the resin-dentin interface was 13MPa, in comparison to 48MPa and 44MPa for the resin composite and dentin, respectively. The ratio of fully reversed endurance limit to ultimate strength of the interface (0.26) was the lowest of the three materials.

Significance: The proposed approach for characterizing the fatigue strength of resin-dentin bonds may offer new insights concerning durability of the bonded interface.
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http://dx.doi.org/10.1016/j.dental.2013.01.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3602384PMC
April 2013

On the fatigue behavior of resin-dentin bonds after degradation by biofilm.

J Mech Behav Biomed Mater 2013 Feb 17;18:219-31. Epub 2012 Nov 17.

Adhesive Dentistry Research Group, Institute of Dentistry, University of Turku, Turku, Finland.

The durability of resin-dentin bonds is a growing concern in the placement of composite restorations. Most reported evaluations concerning the mechanical behavior of the bonded interface are conducted using static loading to failure only. They also do not account for the acid production of biofilms, which is one of the most common contributors to interfacial failures in vivo. In this investigation resin-dentin bonded interface specimens were exposed to S. mutans for 14 days and then subjected to quasi-static or cyclic four-point flexure to failure. Control specimens (without biofilm) were evaluated after aging for one and fourteen days. While no significant difference in flexure strength resulted from the duration of water aging (66.2 MPa vs. 56.9 MPa), biofilm exposure caused a significant reduction in strength (29.3 MPa; p ≤ 0.000). After water aging for one and fourteen days the apparent endurance limits were 13.0 MPa and 13.1 MPa, respectively. Biofilm treatment caused a significant (p ≤ 0.001) reduction in fatigue resistance of the interface, and the endurance limit was reduced to 9.9 MPa. Fatigue failure of the control specimens initiated within the resin composite adjacent to the interface, whereas failure of the biofilm treated specimens initiated within the hybrid layer and appeared attributed to the localized demineralization of dentin. Biofilm degradation is an important consideration in assessing the durability of resin-dentin bonds.
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http://dx.doi.org/10.1016/j.jmbbm.2012.10.019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3557748PMC
February 2013
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