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  • Strain-guided mineralization in the bone-PDL-cementum complex of a rat periodontium. Bone reports Grandfield, K., Herber, R. P., Chen, L., Djomehri, S., Tam, C., Lee, J., Brown, E., Woolwine, W. R., Curtis, D., Ryder, M., Schuck, J., Webb, S., Landis, W., Ho, S. 2015; 3: 20–31

    Abstract

    OBJECTIVE: The objective of this study was to investigate the effect of mechanical strain by mapping physicochemical properties at periodontal ligament (PDL)-bone and PDL-cementum attachment sites and within the tissues per se.DESIGN: Accentuated mechanical strain was induced by applying a unidirectional force of 0.06N for 14 days on molars in a rat model. The associated changes in functional space between tooth and bone, mineral formation and resorbing events at the PDL-bone and PDL-cementum attachment sites were identified by using micro-X-ray computed tomography (micro-XCT), atomic force microscopy (AFM), dynamic histomorphometry, Raman microspectroscopy, AFM-based nanoindentation technique, and were correlated with histochemical stains specific to low and high molecular weight GAGs, including biglycan, and osteoclast distribution through tartrate-resistant acid phosphatase (TRAP) staining.RESULTS: Unique chemical and mechanical qualities including heterogenous bony fingers with hygroscopic Sharpey's fibers contributing to a higher organic (amide III - 1240 cm-1) to inorganic (phosphate - 960 cm-1) ratio, with lower average elastic modulus of 8 GPa versus 12 GPa in unadapted regions were identified. Furthermore, an increased presence of elemental Zn in cement lines and mineralizing fronts of PDL-bone was observed. Adapted regions containing bony fingers exhibited woven bone-like architecture and these regions rich in biglycan (BGN) and bone sialoprotein (BSP) also contained high-molecular weight polysaccharides predominantly at the site of polarized bone growth.CONCLUSIONS: From a fundamental science perspective the shift in local properties due to strain amplification at the soft-hard tissue attachment sites is governed by semiautonomous cellular events at the PDL-bone and PDL-cementum sites. Over time, these strain-mediated events can alter the physicochemical properties of tissues per se, and consequently the overall biomechanics of the bone-PDL-tooth complex. From a clinical perspective, the shifts in magnitude and duration of forces on the periodontal ligament can prompt a shift in physiologic mineral apposition in cementum and alveolar bone albeit of an adapted quality owing to the rapid mechanical translation of the tooth.

    View details for PubMedID 26636129

  • Mineral Density Volume Gradients in Normal and Diseased Human Tissues PLOS ONE Djomehri, S. I., Candell, S., Case, T., Browning, A., Marshall, G. W., Yun, W., Lau, S. H., Webb, S., Ho, S. P. 2015; 10 (4): e0121611

    Abstract

    Clinical computed tomography provides a single mineral density (MD) value for heterogeneous calcified tissues containing early and late stage pathologic formations. The novel aspect of this study is that, it extends current quantitative methods of mapping mineral density gradients to three dimensions, discretizes early and late mineralized stages, identifies elemental distribution in discretized volumes, and correlates measured MD with respective calcium (Ca) to phosphorus (P) and Ca to zinc (Zn) elemental ratios. To accomplish this, MD variations identified using polychromatic radiation from a high resolution micro-computed tomography (micro-CT) benchtop unit were correlated with elemental mapping obtained from a microprobe X-ray fluorescence (XRF) using synchrotron monochromatic radiation. Digital segmentation of tomograms from normal and diseased tissues (N=5 per group; 40-60 year old males) contained significant mineral density variations (enamel: 2820-3095 mg/cc, bone: 570-1415 mg/cc, cementum: 1240-1340 mg/cc, dentin: 1480-1590 mg/cc, cementum affected by periodontitis: 1100-1220 mg/cc, hypomineralized carious dentin: 345-1450 mg/cc, hypermineralized carious dentin: 1815-2740 mg/cc, and dental calculus: 1290-1770 mg/cc). A plausible linear correlation between segmented MD volumes and elemental ratios within these volumes was established, and Ca/P ratios for dentin (1.49), hypomineralized dentin (0.32-0.46), cementum (1.51), and bone (1.68) were observed. Furthermore, varying Ca/Zn ratios were distinguished in adapted compared to normal tissues, such as in bone (855-2765) and in cementum (595-990), highlighting Zn as an influential element in prompting observed adaptive properties. Hence, results provide insights on mineral density gradients with elemental concentrations and elemental footprints that in turn could aid in elucidating mechanistic processes for pathologic formations.

    View details for DOI 10.1371/journal.pone.0121611

    View details for Web of Science ID 000352588500024

    View details for PubMedID 25856386

    View details for PubMedCentralID PMC4391782

  • The narwhal (Monodon monoceros) cementum-dentin junction: A functionally graded biointerphase PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE Grandfield, K., Chattah, N., Djomehri, S., Eidelmann, N., Eichmiller, F. C., Webb, S., Schuck, P., Nweeia, M., Ho, S. P. 2014; 228 (8): 754–67

    Abstract

    In nature, an interface between dissimilar tissues is often bridged by a graded zone, and provides functional properties at a whole organ level. A perfect example is a "biological interphase" between stratified cementum and dentin of a narwhal tooth. This study highlights the graded structural, mechanical, and chemical natural characteristics of a biological interphase known as the cementum-dentin junction layer and their effect in resisting mechanical loads. From a structural perspective, light and electron microscopy techniques illustrated the layer as a wide 1000-2000 μm graded zone consisting of higher density continuous collagen fiber bundles from the surface of cementum to dentin, that parallels hygroscopic 50-100 μm wide collagenous region in human teeth. The role of collagen fibers was evident under compression testing during which the layer deformed more compared to cementum and dentin. This behavior is reflected through site-specific nanoindentation indicating a lower elastic modulus of 2.2 ± 0.5 GPa for collagen fiber bundle compared to 3 ± 0.4 GPa for mineralized regions in the layer. Similarly, microindentation technique illustrated lower hardness values of 0.36 ± 0.05 GPa, 0.33 ± 0.03 GPa, and 0.3 ± 0.07 GPa for cementum, dentin, and cementum-dentin layer, respectively. Biochemical analyses including Raman spectroscopy and synchrotron-source microprobe X-ray fluorescence demonstrated a graded composition across the interface, including a decrease in mineral-to-matrix and phosphate-to-carbonate ratios, as well as the presence of tidemark-like bands with Zn. Understanding the structure-function relationships of wider tissue interfaces can provide insights into natural tissue and organ function.

    View details for DOI 10.1177/0954411914547553

    View details for Web of Science ID 000342058800002

    View details for PubMedID 25205746

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