Biomedical subjects

J H Kinney

Publications and source records attributed to J H Kinney.

50 records · Page 3Linked to original sources

PubMed1998

The relationship between three-dimensional connectivity and the elastic properties of trabecular bone.

A finite-element model was used to explore the relationship between connectivity density and the elastic modulus of trabecular bone. Six cubic specimens of trabecular bone, three prepared from human distal radii and three from L1 vertebrae, were imaged with synchrotron microtomography. The three-dimensional images were reconstructed into binary volumes of mineralized bone and soft tissue, and incorporated into the finite-element model. The relationship between three-dimensional connectivity and elastic modulus was explored by uniform thinning (atrophy) and thickening (recovery) of the trabecular bone. Though no functional relationship was found between connectivity and elastic modulus, there was a linear relationship, after a full cycle of atrophy and recovery, between the loss of elastic modulus and the overall loss of connectivity. The results indicate that recovery of mechanical function depends on preserving or restoring trabecular connectivity.

Aged↗

PubMed1998

Three-dimensional in vivo morphometry of trabecular bone in the OVX rat model of osteoporosis.

This paper describes the application of synchrotron radiation microtomography to osteoporosis research. By taking advantage of the high intensity, collimation, and monochromaticity of synchrotron radiation, we have been able to image the three-dimensional trabecular bone structure in living rats, thus providing serial data on the earliest architectural changes that occur with estrogen loss. Results from these in vivo animal experiments demonstrate that one of the earliest manifestations of estrogen loss, in addition to a decrease in the amount of trabecular bone, is decreased connectivity. We demonstrate that estrogen replacement therapy, when initiated soon after significant changes have occurred, restores bone mass to baseline levels but does not recover the trabecular connectivity. Even without an associated recovery in trabecular connectivity, finite element calculations on the three-dimensional images suggest that estrogen recovers the original structural modulus of elasticity. We believe the recovery of the elastic properties is due to an increase in trabecular thickness above baseline values.

Animals↗

PubMed1997

Dentin demineralization: effects of dentin depth, pH and different acids.

OBJECTIVES: This investigation sought to determine: 1) if dentin demineralization rates are proportional to acid concentration for demineralization in phosphoric acid (10% or 1.76 M, 0.025 M, 0.0001 M, with pH = 0.95, 2.0, 4.0 respectively); 2) if the etching characteristics are independent of dentin depth; and 3) if the etching characteristics for phosphoric acid were comparable to those for citric acid over a similar pH range. METHODS: Highly polished dentin disks from freshly extracted, non-carious, third molars were prepared with a reference layer. Samples were prepared from either superficial or deep coronal dentin. The samples were etched for periods of up to 30 min using phosphoric acid solutions (pH = 0.95, 2.0, 4.0) in a wet cell of an atomic force microscope (AFM). Depth changes with respect to the reference layer were determined for the intertubular and peritubular dentin to quantify structural changes. The results were compared with similar studies using citric acid (pH = 1.0, 2.15 or 3.4). Etching characteristics were statistically compared using 2-way repeated measures ANOVA at p < 0.05 and the Tukey's multiple comparison test. RESULTS: The relation between time and recession for peritubular dentin was initially linear. The intertubular dentin recession started rapidly but then reached a plateau within a very short interval for etching solutions at pH = 2.0 and 4.0. At the highest concentration, the recession decreased with time, but a clear plateau was not established. There was no statistical difference between peritubular etching rates of superficial and deep dentin surfaces with phosphoric acid at any concentration. There was also no difference in the intertubular dentin recession at the location of the plateau that depended on dentin depth. Etching rates increased dramatically with decreased pH for both phosphoric and citric acids, but were higher for citric acid than for phosphoric acid. SIGNIFICANCE: The AFM allowed quantification of changes during etching of wet dentin. Peritubular dentin etching rates increased with decreasing pH, as expected, but changes were not linear and were different for the two acids studied over a similar pH range. Intertubular dentin surface recession was small and plateaued for low concentrations. The peritubular etching rate and intertubular dentin recession did not depend on dentin depth.

Acid Etching, Dental↗

PubMed1997

The dentin substrate: structure and properties related to bonding.

OBJECTIVES: Dentin is a vital, hydrated composite material with structural components and properties that vary with location. These variations are reviewed along with alterations by physiological and pathological changes that allow classification into various forms of dentin. Structural characteristics and mechanical properties are reviewed and the limitations of our understanding of structure-property relationships for normal and modified forms of dentin are discussed with respect to their impact on dentin bonding. Recent progress in methods available to study dentin and its demineralization are emphasized with their promise to increase our understanding of dentin properties and structure. DATA SOURCES: Recent microstructural studies, focusing on scanning electron microscopy, atomic force microscopy and X-ray tomographic microscopy are included. A review of fundamental studies with emphasis on microstructurally sensitive methods, and prior reviews of basic mechanical properties are included with discussion of their correlation to composition and structure. STUDY SELECTION AND CONCLUSIONS: Emphasis in this work was placed on the major structural components of the tissue, including the collagen based organic matrix and its mineral reinforcement, the distribution of these components and their microstructural organization as related to mechanical properties and response to demineralization. Little information is included on biochemical and developmental studies or on non-collagenous proteins and other organic components for which limited understanding is available with respect to their role in structure-property relations and influence on bonding. In spite of the fact that the complexity of dentin precluded a comprehensive review, it is clear that local structural variations influence properties and impact nearly all preventive and restorative dental treatments. Much more work is needed in order to understand differences between vital and non-vital dentin, and dentin from extracted teeth. Although our knowledge is rudimentary in certain areas, increasingly sophisticated methods of studying dentin should provide the necessary information to model structure-property relations, optimize dentin bonding, and improve many aspects of preventive and restorative dentistry.

Apatites↗

PubMed1996

Hardness and Young's modulus of human peritubular and intertubular dentine.

A specially modified atomic-force microscope was used to measure the hardness of fully hydrated peritubular and intertubular dentine at two locations within unerupted human third molars: within 1 mm of the dentine enamel junction and within 1 mm of the pulp. The hardness of fully hydrated peritubular dentine was independent of location, and ranged from 2.23 to 2.54 GPa. The hardness of fully hydrated intertubular dentine did depend upon location, and was significantly greater near the dentine enamel junction (values ranged from 0.49 to 0.52 GPa) than near the pulp (0.12-0.18 GPa). A Nanoindenter was used to estimate the Young's modulus of dehydrated peritubular and intertubular dentine from the unloading portion of the load displacement curve. The modulus values averaged 29.8 GPa for the peritubular dentine (considered to be a lower limit), and ranged from 17.7 to 21.1 GPa for the intertubular dentine, with the lower values obtained for dentine near the pulp.

Analysis of Variance↗

PubMed1996

Atomic force microscope measurements of the hardness and elasticity of peritubular and intertubular human dentin.

An atomic force microscope was used to measure the hardness and elasticity of fully-hydrated peritubular and intertubular human dentin. The standard silicon nitride AFM tip and silicon cantilever assembly were replaced with a diamond tip and stainless steel cantilever having significantly higher stiffness. Hardness was measured as the ratio of the applied force to the projected indentation area for indentations with depths from 10-20 nm. The sample stiffness was measured by imaging specimens in a force-modulated mode. Hardness values of 2.3 +/- 0.3 GPa and 0.5 +/- 0.1 GPa were measured for the peritubular and intertubular dentin, respectively. Stiffness imaging revealed that the elastic modulus of the peritubular dentin was spatially homogeneous; whereas, there was considerable spatial variation in the elasticity of the intertubular dentin. The atomic force microscope can be used to measure the mechanical properties of fully hydrated calcified tissues at the submicron level of spatial resolution, thus augmenting more traditional depth sensing probes.

Dentin↗

PubMed1996

The threshold effects of Nd and Ho: YAG laser-induced surface modification on demineralization of dentin surfaces.

Laser irradiation alters the structure of dentin and produces surface layers that give the appearance of being more enamel-like. The laser-modified surface may be more resistant to demineralization; hence, many investigators are proposing continued development of the laser as a possible preventive treatment for caries. The purpose of this study was to explore the morphological changes that occur in dentin when treated at threshold illuminance with two clinically interesting laser wavelengths, and to evaluate the effectiveness of the laser-treated surface at resisting demineralization in an acid-gel solution. The Nd: YAG laser (wavelength 1060 nm) produced significant recrystallization and grain growth of the apatite, without the formation of second phases such as beta-tricalcium phosphate. This recrystallized surface layer showed resistance to demineralization; however, the layer did not provide protection of the underlying dentin from demineralization because of cracks and macroscopic voids that allowed for penetration of the demineralizing gel. The Ho: YAG laser-treated surface (wavelength 2100 nm) did not show significant evidence of recrystallization and grain growth, and only a trace amount of an acid-resistant layer was observed with demineralization. It is speculated that the Ho:YAG laser is coupling with absorbed water, and that the heat transfer from the water to the mineral phase is inefficient. For the purposes of creating a demineralization-resistant layer, threshold illuminance with both Nd: YAG and Ho: YAG was ineffective.

Absorption↗

PubMed1995

Atomic force microscopy of conditioning agents on dentin.

Dentin conditioners provide a microporous surface for penetration by bonding agents. This study used an atomic force microscope (AFM) to examine the initial steps in the conditioning process of dentin using three demineralizing agents, 0.5 M EDTA, and dilute solutions of phosphoric (3 mM, 6 mM) and citric (5 mM) acids, in order to establish the relationships between demineralization and changes in surface morphology. Polished dentin disks had a 10-nm-thick gold pattern applied which served as a height reference. Samples (n = 3/agent) were examined at baseline and at 2-s intervals for up to 120 s for each agent. EDTA (0.5 M) was used as received; other conditioners were diluted to slow the rats of demineralization for detailed study. The surfaces of the peritubular and intertubular regions were altered differently. Initially subsidence rates were equal and linear, but after a 100-nm depth change the intertubular rates decreased. For phosphoric acid and citric acid, the movement of the intertubular surface was uniform and the surfaces remained smooth. However, the intertubular surfaces were rough for the EDTA treatment. The surface subsidence reached a plateau after a depth change of about 0.5 microns, which resulted from a limit to the contraction of the demineralized and hydrated collagen scaffold.

Chelating Agents↗

PubMed1995

In vivo, three-dimensional microscopy of trabecular bone.

Osteoporosis, which is correlated with low bone mass and increased bone fragility, is responsible for about 1.2 million fractures per year in the United States. We have used the three-dimensional (3-D), X-ray tomographic microscope to image the trabecular bone architecture of the proximal tibias of six Sprague-Dawley rats in vivo. Three of these rats were then ovariectomized to induce estrogen depletion, and three remained as controls. Five weeks later, the tibias were reimaged. The ovariectomized rats lost approximately 65% of their trabecular bone volume as compared with an insignificant change in the control rats. The connectivity density of the trabecular bone, as measured by the Euler characteristic, was linearly correlated with trabecular bone volume, even in the ovariectomized rats. Hypoestrogenemic bone loss manifested itself in greatly reduced connectivity and fewer trabecular elements, but not in thinning of trabeculae. The ability to microscopically image sequential changes in the 3-D architecture of trabecular bone in vivo will allow exploration of the earliest stages of hypoestrogenemic bone loss and to more rapidly test the effectiveness of new clinical treatments for this major public health problem.

Animals↗

PubMed1995

Intermittent treatment with human parathyroid hormone (hPTH[1-34]) increased trabecular bone volume but not connectivity in osteopenic rats.

Previous studies have determined that intermittent parathyroid hormone (PTH) therapy increases bone mass and improves biomechanical strength in osteopenic animal models. The purpose of this investigation was to determine if intermittent human parathyroid hormone (hPTH[1-34]) therapy increased trabecular bone volume and connectivity in a rat model of established osteopenia using three-dimensional (3D) ex vivo in situ morphometry by X-ray tomographic methods (XTM). Six-month-old retired Sprague-Dawley breeder rats were used. Thirty animals were ovariectomized (OVX) and six were Sham operated. On day 56, post-OVX, a prePTH-treatment OVX groups was sacrificed. The remaining OVX animals were randomized into four groups of six animals each, given injections 5 out of every 7 days for 28 days of either vehicle or hPTH(1-34) at 4, 40, or 400 microg/kg of body weight (BW)/day and were sacrificed on day 84 post-OVX. At sacrifice, the left proximal tibias were harvested for XTM scans. hPTH(1-34) at medium and high doses significantly increased trabecular bone volume and trabecular thickness compared with ovariectomized animals treated with vehicle (p<0.05). The trabecular bone volume was equal to or greater than the Sham-operated animals in both hPTH(1-34) 40 and 400 microg/kg of BW treatment groups. Trabecular bone connectivity decreased by nearly 50% compared to the S ham-operated group at day 84 post-OVX and did not increase with any of the hPTH(1-34) treatments. Intermittent hPTH(1-34) treatment is osteopenic OVX rats increased trabecular bone volume to control levels or higher by thickening existing trabeculae. Human PTH(1-34) did not re-establish connectivity when therapy was started after 50% of the trabecular connectivity was lost. We hypothesize that to re-establish trabecular connectivity, a therapeutic intervention would have to be given before a significant distance between trabeculae has developed. Further studies will need to be done to refute or confirm our hypothesis.

Animals↗

PubMed1995

Mineral distribution and dimensional changes in human dentin during demineralization.

Many bonding agents require the dentin surface to be acid-etched prior to being bonded. Understanding the stability and morphology of the etched dentin surface is important for improving bond strength and reliability in these systems. In this study, the atomic force microscope was used to quantify dimensional changes that occur to fully hydrated dentin during demineralization with a pH 4.0 lactic acid gel. A high-resolution microtomography instrument, the x-ray tomographic microscope, was also used to quantify the mineral density distribution in the dentin as a function of etching time. The intertubular dentin surface shrank by less than 0.5 microns during etching, while the peritubular dentin receded at an initially rapid linear rate. The dentin surface retained its initial morphology, although it was more porous with the removal of the peritubular dentin. Beneath the etched surface, there were three major zones characterized by mineral density differences. The first zone was a fully demineralized collagen layer, subjacent to which was a partially demineralized zone of roughly constant mineral density. Immediately following the partially mineralized layer was normal dentin. The presence of the partially mineralized layer could be explained in terms of different transport rates in the peritubular and intertubular dentin.

Acid Etching, Dental↗

PubMed1994

Three-dimensional mapping of mineral densities in carious dentin: theory and method.

X-ray tomographic microscopy (XTM), a three-dimensional X-ray imaging technique, has been used to quantitatively map mineral concentrations in carious dentin. Data analysis from the XTM study indicates that variations in the mineral concentration surrounding the caries can be imaged in three dimensions with a spatial resolution that is sufficient to detect calcified and enlarged tubule spaces in the lesion. A three-dimensional image of the subsurface lesion indicates that lesion penetration is along the direction of the tubules. The mineral concentration in the uninfected dentin was measured by the XTM to be 1.29 +/- 0.14 g/cm3 based upon the tabulated X-ray attenuation coefficients for apatite. This value is in excellent agreement with averaged estimates for the mineral concentration in dentin (1.4 g/cm3). Furthermore, the mineral concentration determined using XTM varies from 2.25 g/cm3 in the remineralized dentin to as low as 0.55 +/- 0.17 g/cm3 in the demineralized tissue. The high concentration of mineral in the remineralized region suggests that organic matter is lost and mineral is deposited at some time during the caries process.

Dental Caries↗

PubMed1993

Atomic-force microscopic study of dimensional changes in human dentine during drying.

Six 1-mm thick sections of human dentine, three parallel to the occlusal surface and three perpendicular to the buccal surface, were prepared from non-carious third molars. The enamel was ground off, and the sections were polished with alumina powder to remove the smear layer. Each section was imaged by atomic-force microscopy with 20 nm horizontal and 0.1 nm vertical resolutions, initially while the samples were immersed in deionized water and then periodically during drying at room temperature. No dimensional changes over microscopic fields of view (scanned areas smaller than 50 x 50 microns) could be detected within the precision of the measurements (< 0.5%). Across the entire sample, however, vertical displacements of 10-20 microns were measured. Elasticity (Bernoulli beam) theory was used to calculate the engineering strain required to produce these displacements. The magnitude of the strain was 0.04% (SD = 0.01) in the buccal sections in the direction of the tubule axis and 0.09% (SD = 0.02) in the direction normal to the tubule axis. Also, the strain alternated between tension and compression across the samples. It was concluded that, as determined by using microscopic techniques, drying-induced strain is too small to require corrections for tubule size and tubule density.

Dental Stress Analysis↗

PubMed1993

Atomic force microscopy of acid effects on dentin.

Atomic force microscopy (AFM) was used in the examination of the early stages of acid treatment of dentin. Disks of highly polished dentin were initially examined under deionized water and following exposure to 0.025 M nitric acid for 20 s intervals from 0-100 s. Peritubular depth changes were linear (0.005 microns/s). The intertubular dentin surface initially moved at approximately 1/2 the peritubular rate and then reached a plateau as the demineralized collagen scaffold collapsed. There was no apparent difference in the tubule center-to-center distance during the treatment. Differences in the movement and morphology of the zones are of importance in dentin bonding applications relying on penetration of the demineralized dentin by adhesive monomers. The changes are probably related to the partial collapse of the collagen matrix. Alternatively, access to the apatite crystals and solubility may be higher in the peritubular zone. AFM appears to hold exceptional promise for the study of conditioning and priming agents for dentin bonding.

Acid Etching, Dental↗