Coupled Nanomechanical and Raman Microspectroscopic Investigation of Human Third Molar DEJ.

The dentino-enamel junction (DEJ) connects enamel, that covers the outer surface of a tooth, to a thicker underlying dentin. The DEJ is a critical interface that permits joining these materials that have widely dissimilar mechanical properties. AFM-based nanoindentation and Raman microspectroscopy were used to define the width and composition of human molar DEJ.

Mechanical properties of mineralized collagen fibrils as influenced by demineralization.

Dentin and bone derive their mechanical properties from a complex arrangement of collagen type-I fibrils reinforced with nanocrystalline apatite mineral in extra- and intrafibrillar compartments. While mechanical properties have been determined for the bulk of the mineralized tissue, information on the mechanics of the individual fibril is limited. Here, atomic force microscopy was used on individual collagen fibrils to study structural and mechanical changes during acid etching.

The aminobisphosphonate risedronate preserves localized mineral and material properties of bone in the presence of glucocorticoids.

Objective: Glucocorticoids (GCs) alter bone strength such that patients receiving these medications have a high rate of fragility-related fractures. The purpose of this study was to assess whether concurrent treatment with GCs (prednisolone) and risedronate (an aminobisphosphonate) would prevent the reduction in bone strength induced by GCs, in a mouse model of GC-induced bone loss and in patients enrolled in a clinical study.

Methods: We evaluated mice treated with prednisolone pellets alone, GCs plus risedronate, or placebo alone and iliac crest biopsy specimens obtained from patients who were treated with GCs plus placebo or GCs plus risedronate for 1 year.

The degree of bone mineralization is maintained with single intravenous bisphosphonates in aged estrogen-deficient rats and is a strong predictor of bone strength.

The treatment of osteoporotic women with bisphosphonates significantly reduces the incidence of bone fractures to a degree greater than can be explained by an increase in bone mineral density. In this study, 18-month Fischer 344 rats were ovariectomized and treated with a single dose of risedronate (intravenous, iv, 500 microg), zoledronic acid (iv, 100 microg) or continuous raloxifene (2 mg/kg, po, 3x/week). High resolution microCT was used to measure lumbar vertebral bone microarchitecture, the degree of bone mineralization (DBM) and the distribution of mineral.

Sequential treatment of ovariectomized mice with bFGF and risedronate restored trabecular bone microarchitecture and mineralization.

Basic fibroblast growth factor (bFGF), a potent mitogen, has been found to restore trabecular bone mass and connectivity in osteopenic rats. The purpose of this study was to determine how sequential treatment of ovariectomized (OVXed) mice with bFGF followed by risedronate would restore trabecular microarchitecture and improve bone strength through alterations in bone mineralization. Six-month old female Swiss-Webster mice were OVXed or sham-operated and left untreated for 4 weeks to develop osteopenia.

Effects of polar solvents on the fracture resistance of dentin: role of water hydration.

Although healthy dentin is invariably hydrated in vivo, from a perspective of examining the mechanisms of fracture in dentin, it is interesting to consider the role of water hydration. Furthermore, it is feasible that exposure to certain polar solvents, e.g.

Glucocorticoid-treated mice have localized changes in trabecular bone material properties and osteocyte lacunar size that are not observed in placebo-treated or estrogen-deficient mice.

Unlabelled: This study compares changes in bone microstructure in 6-month-old male GC-treated and female ovariectomized mice to their respective controls. In addition to a reduction in trabecular bone volume, GC treatment reduced bone mineral and elastic modulus of bone adjacent to osteocytes that was not observed in control mice nor estrogen-deficient mice. These microstructural changes in combination with the macrostructural changes could amplify the bone fragility in this metabolic bone disease.

TGF-beta regulates the mechanical properties and composition of bone matrix.

The characteristic toughness and strength of bone result from the nature of bone matrix, the mineralized extracellular matrix produced by osteoblasts. The mechanical properties and composition of bone matrix, along with bone mass and architecture, are critical determinants of a bone's ability to resist fracture. Several regulators of bone mass and architecture have been identified, but factors that regulate the mechanical properties and composition of bone matrix are largely unknown.

Local mechanical and optical properties of normal and transparent root dentin.

The mechanical and optical properties of healthy and transparent root dentin are compared using atomic force microscopy (AFM), micro-Raman and emission spectroscopies and fluorescence microscopy. The elastic modulus and hardness of intertubular and peritubular transparent and healthy dentin did not differ appreciably. The tubule filling material in the transparent zone, however, exhibited values between peritubular and intertubular dentin.

Amelogenin-guided crystal growth on fluoroapatite glass-ceramics.

The formation of aligned fibrous apatite crystals in enamel is predominantly attributed to the involvement of amelogenin proteins. We developed a model to study interactions of matrix proteins with apatite mineral in vitro and tested the hypothesis that amelogenin solubility affects the ability to induce protein-guided mineralization. Crystal growth experiments were performed on fluoroapatite (FAP) glass-ceramics in mineralizing solutions containing recombinant full-length amelogenin (rH174) at different concentrations.

Local properties of a functionally graded interphase between cementum and dentin.

The study of natural interfaces may provide information necessary to engineer functionally graded biomaterials for bioengineering applications. In this study, the mechanical, structural, and chemical composition variations associated with a region between cementum and dentin were studied with the use of nanoindentation, microindentation, optical microscopy, and Raman microspectroscopy techniques. Three-millimeter-thick transverse sections (N = 5) were obtained from the apical one-third of the roots of sterilized human molars.

Evaluation of a new modulus mapping technique to investigate microstructural features of human teeth.

Teeth contain several calcified tissues with junctions that provide interfaces between dissimilar tissues. These junctions have been difficult to characterize because of their small size. In this work a new technique using a combination of atomic force microscopy (AFM) and a force-displacement transducer was used to simultaneously study the surface topography and map mechanical properties of the junctions and adjacent hard tissues.

The effect of sample preparation technique on determination of structure and nanomechanical properties of human cementum hard tissue.

The mechanical properties of a tissue can be evaluated by determining the response of the structure to mechanical loading. This can be accomplished only when the tissue has been prepared with minimum to no artifacts, thus preserving its structure. In this study it was hypothesized that the structure of cementum is inhomogeneous, contributing to a significant variation in mechanical properties of cementum.

Micro-Raman spectroscopic investigation of dental calcified tissues.

The purpose of this study was to determine if dental calcified junctions (DEJs/CDJs) in human teeth contain different compositional phases compared to the adjacent dental calcified tissues. Peak positions and intensities were determined from micro-Raman spectra for PO(3-) (4) and the C--H modes and compared among the mineralized tissues and their junctions. Values of width were determined from the intersections of intensity regression lines through the junctions and in the adjacent tissues.

Ultrastructure and nanomechanical properties of cementum dentin junction.

The attachment between cementum and dentin has been given several definitions and nomenclature, including: interzonal layer, intermediate cementum, collagen hiatus, Hopewell-Smith's hyaline layer, and more commonly, cementum-dentin junction (CDJ). Understanding the attachment of two structurally dissimilar hard tissues such as cementum and dentin defined by a junction may provide information necessary to engineer functionally graded materials that can be used for efficient tooth restorations in clinical dentistry and other bioengineering applications. Hence, in this study, as a first step toward understanding the CDJ using a biomechanical approach, it was hypothesized that the CDJ between cementum and dentin is a wide zone with mechanical properties significantly lower than the neighboring tissues.

Both hPTH(1-34) and bFGF increase trabecular bone mass in osteopenic rats but they have different effects on trabecular bone architecture.

Unlabelled: Osteoporosis is a syndrome of excessive skeletal fragility that results from both the loss of trabecular bone mass and trabecular bone connectivity. Recently, bFGF has been found to increase trabecular bone mass in osteoporotic rats. The purpose of this study was to compare how trabecular bone architecture, bone cell activity, and strength are altered by two different bone anabolic agents, bFGF and hPTH(1-34), in an osteopenic rat model.

Optical spectroscopy and imaging of the dentin-enamel junction in human third molars.

A 351-nm laser excitation source was used to perform autofluorescence microscopy of dentin, enamel, and the dentin-enamel junction (DEJ) to obtain information regarding their morphology and spectral characteristics. The emission spectra of these calcified dental tissues were different from one another, and this enabled the DEJ to be imaged and dimensionalized. The DEJ displayed sharp and clearly delineated borders at both its enamel and dentin margins.

In situ atomic force microscopy of partially demineralized human dentin collagen fibrils.

Dentin collagen fibrils were studied in situ by atomic force microscopy (AFM). New data on size distribution and the axial repeat distance of hydrated and dehydrated collagen type I fibrils are presented. Polished dentin disks from third molars were partially demineralized with citric acid, leaving proteins and the collagen matrix.

Nanoindentation and storage of teeth.

This study determined changes in nanomechanical properties of dentin and enamel during storage in deionized water, calcium chloride buffered saline solution and Hank's balanced salts solution (HBSS). Atomic force microscopy based nanoindentation showed that storing teeth in deionized water or CaCl(2)-solution resulted in a large decrease in elastic modulus and hardness. At 1 day a decrease in the mechanical properties values of up to 20% and 30% was observed for enamel and dentin, respectively.

The functional width of the dentino-enamel junction determined by AFM-based nanoscratching.

The dentino-enamel junction (DEJ) constitutes a structurally unique interphase uniting two mineralized tissues with very different matrix composition and physical properties. Its excellent biomechanical properties have drawn interest as a biomimetic model for joining dissimilar materials. In order to characterize the functional width of the DEJ, nanoscratching experiments were performed on human third molars.

Nanomechanical properties of hydrated carious human dentin.

Most restorative materials are bonded to caries-affected dentin that has altered structure. We tested the hypothesis that hydrated dentin of the transparent zone did not have increased hardness or elastic modulus. Nanoindentation by modified AFM was used to determine site-specific elastic modulus and hardness for components of hydrated dentin from 8 carious and non-carious human teeth.

Mechanical properties of human dental enamel on the nanometre scale.

Atomic force microscopy (AFM) combined with a nano-indentation technique was used to reveal the structure and to perform site-specific mechanical testing of the enamel of third molars. Nano-indentations (size<500 nm) were made in the cusp area to measure the mechanical properties of single enamel rods at different orientations. The influence of etching on the physical properties was studied and etching conditions that did not significantly alter the plastic-elastic response of enamel were defined.

Mechanical properties of the dentinoenamel junction: AFM studies of nanohardness, elastic modulus, and fracture.

The dentinoenamel junction (DEJ) is a complex and poorly defined structure that unites the brittle overlying enamel with the dentin that forms the bulk of the tooth. In addition, this structure appears to confer excellent toughness and crack deflecting properties to the tooth, and has drawn considerable interest as a biomimetic model of a structure uniting dissimilar materials. This work sought to characterize the nanomechanical properties in the region of the DEJ using modified AFM based nanoindentation to determine nanohardness and elastic modulus.

Three-dimensional morphometry of the L6 vertebra in the ovariectomized rat model of osteoporosis: biomechanical implications.

This article summarizes the results of a three-dimensional study of changes in the morphology of the L6 rat vertebra at 120 days after ovariectomy (OVX), with estrogen replacement therapy used as a positive control. Synchrotron radiation microtomography was used to quantify the structural parameters defining trabecular bone architecture, while finite-element methods were used to explore the relationships between these parameters and the compressive elastic behavior of the vertebrae. There was a 22% decrease in trabecular bone volume (TBV) and a 19% decline in mean trabecular thickness (Tb.