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Optical Spectroscopy Study of Transparent Non-Carious Human Dentin and Dentin-Enamel Junction

Description: Improving our knowledge of the morphology, composition and properties of the dentin, enamel, and the dentin-enamel junction (DEJ) is vital for the development of improved restorative materials and clinical placement techniques. Most studies of dental tissues have used light microscopy for characterization. In our investigation, the spectroscopic properties of normal and non-carious transparent human root dentin, and the dentin-enamel junction were investigated using emission imaging microscopy, and micro-spectroscopy. Experimental results reveal new information on the structural and biochemical characteristics of these dental tissues.
Date: December 14, 1999
Creator: Marshall, G.W.; Marshall, S.J.; Gallagher, R.R. & Demos, S.
Partner: UNT Libraries Government Documents Department

On the fracture of human dentin: Is it stress- orstrain-controlled?

Description: Despite substantial clinical interest in the fractureresistance of human dentin, there is little mechanistic information inarchival literature that can be usefully used to model such fracture. Infact, although the fracture event indent in, akin to other mineralizedtissues like bone, is widely believed to be locally strain-controlled,there has never been any scientific proof to support this belief. Thepresent study seeks to address this issue through the use of a novel setof in vitro experiments in Hanks' balanced salt solution involving adouble-notched bend test geometry, which is designed to discern whetherthe critical failure events involved in the onset of fracture are locallystress- or strain-controlled. Such experiments are further used tocharacterize the notion of "plasticity" in dentin and the interaction ofcracks with the salient microstructural features. It is observed thatfracture in dentin is indeed locally strain-controlled and that thepresence of dentinal tubules does not substantially affect this processof crack initiation and growth. The results presented are believed to becritical steps in the development ofa micromechanical model for thefracture of human dentin that takes into consideration the influence ofboth the microstructure and the local failure mode.
Date: February 1, 2006
Creator: Nalla, R.K.; Kinney, J.H. & Ritchie, R.O.
Partner: UNT Libraries Government Documents Department

Role of Alcohol on the Fracture Resistance of Dentin

Description: Healthy dentin, the mineralized tissue that makes up the bulk of the tooth, is naturally hydrated in vivo; however, it is known that various chemical reagents including acetone and ethanol can induce dehydration and thereby affect its properties. Here, we seek to investigate this in light of the effect alcohol can have on the mechanical properties of dentin, specifically by measuring the stiffness, strength and toughness of dentin in simulated body fluid and scotch whisky. Results indicate that chemical dehydration induced by the whisky has a significant beneficial effect on the elastic modulus, strength and fracture toughness of dentin. Although this makes teeth more resistant to fracture, the change in properties is fully reversible upon rehydration. This effect is considered to be associated with increased cross-linking of the collagen molecules from intermolecular hydrogen-bonding where water is replaced with weaker hydrogen-bond forming solvents such as alcohol.
Date: May 1, 2006
Creator: Nalla, Ravi K.; Kinney, John H.; Tomsia, Antoni P. & Ritchie,Robert O.
Partner: UNT Libraries Government Documents Department

On the fracture of human dentin: Is it stress- orstrain-controlled?

Description: Despite substantial clinical interest in the fracture resistance of human dentin, there is little mechanistic information in archival literature that can be usefully used to model such fracture. In fact, although the fracture event indent in, akin to other mineralized tissues like bone, is widely believed to be locally strain-controlled, there has never been any scientific proof to support this belief. The present study seeks to address this issue through the use of a novel set of in vitro experiments in Hanks' balanced salt solution involving a double-notched bend test geometry, which is designed to discern whether the critical failure events involved in the onset of fracture are locally stress- or strain-controlled. Such experiments are further used to characterize the notion of ''plasticity'' in dentin and the interaction of cracks with the salient microstructural features. It is observed that fracture in dentin is indeed locally strain-controlled and that the presence of dentinal tubules does not substantially affect this process of crack initiation and growth. The results presented are believed to be critical steps in the development of a micromechanical model for the fracture of human dentin that takes into consideration the influence of both the microstructure and the local failure mode.
Date: February 1, 2006
Creator: Nalla, R.K.; Kinney, J.H. & Ritchie, R.O.
Partner: UNT Libraries Government Documents Department

On the Increasing Fragility of Human Teeth with Age: ADeep-Ultraviolet Resonance Raman Study

Description: Ultraviolet resonance Raman spectroscopy (UVRRS) using 244nm excitation was used to investigate the impact of aging on humandentin. The intensity of a spectroscopic feature from the peptide bondsin the collagen increases with tissue age, similar to a finding reportedpreviously for human cortical bone.
Date: July 14, 2006
Creator: Ager III, J.W.; Nalla, R.K.; Balooch, G.; Kim, G.; Pugach, M.; Habelitz, S. et al.
Partner: UNT Libraries Government Documents Department

On the in vitro fracture toughness of human dentin

Description: The in vitro fracture toughness of human dention has been reported to be of the order of 3 MPa sqrt m. This result, however is based on a single study for a single orientation, and furthermore involves notched, rather than fatigue precracked, test samples.
Date: February 5, 2002
Creator: Imbeni, V.; Nalla, R.K.; Bosi, C.; Kinney, J.H. & Ritchie, R.O.
Partner: UNT Libraries Government Documents Department

Aging and Fracture of Human Cortical Bone and Tooth Dentin

Description: Mineralized tissues, such as bone and tooth dentin, serve as structural materials in the human body and, as such, have evolved to resist fracture. In assessing their quantitative fracture resistance or toughness, it is important to distinguish between intrinsic toughening mechanisms which function ahead of the crack tip, such as plasticity in metals, and extrinsic mechanisms which function primarily behind the tip, such as crack bridging in ceramics. Bone and dentin derive their resistance to fracture principally from extrinsic toughening mechanisms which have their origins in the hierarchical microstructure of these mineralized tissues. Experimentally, quantification of these toughening mechanisms requires a crack-growth resistance approach, which can be achieved by measuring the crack-driving force, e.g., the stress intensity, as a function of crack extension ("R-curve approach"). Here this methodology is used to study of the effect of aging on the fracture properties of human cortical bone and human dentin in order to discern the microstructural origins of toughness in these materials.
Date: May 7, 2008
Creator: Ager, Joel; Koester, Kurt J.; Ager III, Joel W. & Ritchie, Robert O.
Partner: UNT Libraries Government Documents Department

On the development of life prediction methodologies for the failure of human teeth

Description: Human dentin is known to be susceptible to failure under cyclic loading. Surprisingly, there are few reports that quantify the effect of such loading, considering the fact that a typical tooth experiences a million or so loading cycles annually. In the present study, a systematic investigation is described of the effects of prolonged cyclic loading on human dentin in a simulated physiological environment. In vitro stress-life (S/N) data are discussed in the context of possible mechanisms of fatigue damage and failure.
Date: September 18, 2002
Creator: Nalla, R.K.; Imbeni, V.; Kinney, J.H.; Marshall, S.J. & Ritchie, R.O.
Partner: UNT Libraries Government Documents Department

Science and Technology Review January/February 2008

Description: This month's issue has the following articles: (1) The Edward Teller Centennial--Commentary by George H. Miller; (2) Edward Teller's Century: Celebrating the Man and His Vision--Colleagues at the Laboratory remember Edward Teller, cofounder of Lawrence Livermore, adviser to U.S. presidents, and physicist extraordinaire, on the 100th anniversary of his birth; (3) Quark Theory and Today's Supercomputers: It's a Match--Thanks to the power of BlueGene/L, Livermore has become an epicenter for theoretical advances in particle physics; and (4) The Role of Dentin in Tooth Fracture--Studies on tooth dentin show that its mechanical properties degrade with age.
Date: November 14, 2007
Creator: Chinn, D J
Partner: UNT Libraries Government Documents Department

On the mechanistic role of the dentin-enamel junction in preventing the fracture of human teeth

Description: The dentin-enamel junction (DEJ), which is the interface between the dentin and outer enamel coating in teeth, is known for its unique biomechanical properties that provide a crack-arrest barrier for flaws formed in the brittle enamel. In this work, we re-examine how cracks propagate in the proximity of the DEJ, and specifically quantify, using interfacial fracture mechanics, the fracture toughness of the DEJ region. Additionally, we show that the vital function of the DEJ, in preventing cracks formed in enamel from traversing the interface and causing catastrophic tooth fractures, is not necessarily associated with the crack-arrest capabilities of the DEJ itself, but rather with the development of crack-tip shielding, primarily from uncracked-ligament bridging, in the mantle dentin adjacent to the DEJ. Measurements of the toughness of the DEJ region give estimates of G{sub c} {approx} 115 J/m{sup 2}, i.e., {approx}5 to 10 times higher than enamel and {approx}75 percent of that of dentin.
Date: September 1, 2004
Creator: Imbeni, V.; Kruzic, J.J.; Marshall, G.W.; Marshall, S.J. & Ritchie, R.O.
Partner: UNT Libraries Government Documents Department

Effect of orientation on the in vitro fracture toughness ofdentin: The role of toughening mechanisms

Description: A micro-mechanistic understanding of bone fracture thatencompasses how cracks interact with the underlying microstructure anddefines their local failure mode is lacking, despite extensive research nthe response of bone to a variety of factors like aging, loading, and/ordisease.
Date: January 28, 2003
Creator: Nalla, R.K.; Kinney, J.H. & Ritchie, R.O.
Partner: UNT Libraries Government Documents Department

Biomolecular Origin of The Rate-Dependent Deformation of Prismatic Enamel

Description: Penetration deformation of columnar prismatic enamel was investigated using instrumented nanoindentation testing, carried out at three constant strain rates (0.05 s{sup -1}, 0.005 s{sup -1}, and 0.0005 s{sup -1}). Enamel demonstrated better resistance to penetration deformation and greater elastic modulus values were measured at higher strain rates. The origin of the rate-dependent deformation was rationalized to be the shear deformation of nanoscale protein matrix surrounding each hydroxyapatite crystal rods. And the shear modulus of protein matrix was shown to depend on strain rate in a format: G{sub p} = 0.213 + 0.021 ln {dot {var_epsilon}}. Most biological composites compromise reinforcement mineral components and an organic matrix. They are generally partitioned into multi-level to form hierarchical structures that have supreme resistance to crack growth [1]. The molecular mechanistic origin of toughness is associated with the 'sacrificial chains' between the individual sub-domains in a protein molecule [2]. As the protein molecule is stretched, these 'sacrificial chains' break to protect its backbone and dissipate energy [3]. Such fresh insights are providing new momentum toward updating our understanding of biological materials [4]. Prismatic enamel in teeth is one such material. Prismatic microstructure is frequently observed in the surface layers of many biological materials, as exemplified in mollusk shells [5] and teeth [6]. It is a naturally optimized microstructure to bear impact loading and penetration deformation. In teeth, the columnar prismatic enamel provides mechanical and chemical protection for the relatively soft dentin layer. Its mechanical behavior and reliability are extremely important to ensure normal tooth function and human health. Since enamel generally contains up to 95% hydroxyapatite (HAP) crystals and less than 5% protein matrix, it is commonly believed to be a weak and brittle material with little resistance to fracture [7]. This study is aimed at exploring the effect of the weak amelogenin-rich protein ...
Date: July 5, 2006
Creator: Zhou, J & Hsiung, L
Partner: UNT Libraries Government Documents Department

Age estimation in forensic sciences: Application of combined aspartic acid racemization and radiocarbon analysis

Description: Age determination of unknown human bodies is important in the setting of a crime investigation or a mass disaster, since the age at death, birth date and year of death, as well as gender, can guide investigators to the correct identity among a large number of possible matches. Traditional morphological methods used by anthropologists to determine age are often imprecise, whereas chemical analysis of tooth dentin, such as aspartic acid racemization has shown reproducible and more precise results. In this paper we analyze teeth from Swedish individuals using both aspartic acid racemization and radiocarbon methodologies. The rationale behind using radiocarbon analysis is that above-ground testing of nuclear weapons during the cold war (1955-1963) caused an extreme increase in global levels of carbon-14 ({sup 14}C) which have been carefully recorded over time. Forty-four teeth from 41 individuals were analyzed using aspartic acid racemization analysis of tooth crown dentin or radiocarbon analysis of enamel and ten of these were split and subjected to both radiocarbon and racemization analysis. Combined analysis showed that the two methods correlated well (R2=0.66, p < 0.05). Radiocarbon analysis showed an excellent precision with an overall absolute error of 0.6 {+-} 04 years. Aspartic acid racemization also showed a good precision with an overall absolute error of 5.4 {+-} 4.2 years. Whereas radiocarbon analysis gives an estimated year of birth, racemization analysis indicates the chronological age of the individual at the time of death. We show how these methods in combination can also assist in the estimation of date of death of an unidentified victim. This strategy can be of significant assistance in forensic casework involving dead victim identification.
Date: November 2, 2009
Creator: Alkass, K; Buchholz, B A; Ohtani, S; Yamamoto, T; Druid, H & Spalding, S L
Partner: UNT Libraries Government Documents Department

THz near-field imaging of biological tissues employing synchrotron radiation

Description: Terahertz scanning near-field infrared microscopy (SNIM) below 1 THz is demonstrated. The near-field technique benefits from the broadband and highly brilliant coherent synchrotron radiation (CSR) from an electron storage ring and from a detection method based on locking onto the intrinsic time structure of the synchrotron radiation. The scanning microscope utilizes conical wave guides as near-field probes with apertures smaller than the wavelength. Different cone approaches have been investigated to obtain maximum transmittance. Together with a Martin-Puplett spectrometer the set-up enables spectroscopic mapping of the transmittance of samples well below the diffraction limit. Spatial resolution down to about lambda/40 at 2 wavenumbers (0.06 THz) is derived from the transmittance spectra of the near-field probes. The potential of the technique is exemplified by imaging biological samples. Strongly absorbing living leaves have been imaged in transmittance with a spatial resolution of 130 mu-m at about 12 wave numbers (0.36 THz). The THz near-field images reveal distinct structural differences of leaves from different plants investigated. The technique presented also allows spectral imaging of bulky organic tissues. Human teeth samples of various thicknesses have been imaged between 2 and 20 wavenumbers (between 0.06and 0.6 THz). Regions of enamel and dentin within tooth samples are spatially and spectrally resolved, and buried caries lesions are imaged through both the outer enamel and into the underlying dentin.
Date: December 23, 2004
Creator: Schade, Ulrich; Holldack, Karsten; Martin, Michael C. & Fried,Daniel
Partner: UNT Libraries Government Documents Department

LLE Review quarterly report, January--March 1995. Volume 62

Description: This volume of the LLE review, covering the period of January-March 1995, contains articles on the evaluation of the mechanism for laser damage in OMEGA UV multilayer coatings using a combination of conventional laser-damage characterization methods and atomic force microscopy; a dual-amplitude, fiber-coupled waveguide integrated-optic modulation device for generating temporally shaped optical pulses in OMEGA-, a proposal for modifying the indirect-drive irradiation geometry of the National Ignition Facility (NIF) to provide the additional flexibility for performing direct-drive experiments; direct measurements of terminal-level lifetime in several different Nd:YLF laser media; an overview of the materials science issues, basic mechanisms, and potential device applications for light-emitting porous silicon; and a study of the time-dependent reflection and surface temperatures for laser-irradiated dental hard tissue at two CO{sub 2} laser wavelengths.
Date: July 1, 1995
Partner: UNT Libraries Government Documents Department