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PubMed1999

Orientation variance as a quantifier of structure in texture.

I consider how structure is derived from texture containing changes in orientation over space, and propose that multi-local orientation variance (the average orientation variance across a series of discrete images locales) is an estimate of the degree of organization that is useful both for spatial scale selection and for discriminating structure from noise. The oriented textures used in this paper are Glass patterns, which contain structure at a narrow range of scales. The effect of adding noise to Glass patterns, on a structure versus noise task (Maloney et al., 1987), is compared to discrimination based on orientation variance and template matching (i.e. having prior knowledge of the target's orientation structure). At all but very low densities, the variance model accounts well for human data. Next, both models' estimates of tolerable orientation variance are shown to be broadly consistent with human discrimination of texture from noise. However, neither model can account for subjects' lower tolerance to noise for translational patterns than other (e.g. rotational) patterns. Finally, to investigate how well these structural measures preserve local orientation discontinuities, I show that the presence of a patch of unstructured dots embedded in a Glass pattern produces a change in multi-local orientation variance that is sufficient to account for human detection (Hel Or and Zucker, 1989). Together, these data suggest that simple orientation statistics could drive a range of 'texture tasks', although the dependency of noise resistance on the pattern type (rotation, translation, etc.) remains to be accounted for.

Computer Simulation↗
PubMed1997

Local and global orientation in visual search.

Six experiments investigated the role of global (shape) and local (contour) orientation in visual search for an orientation target. Experiment 1 demonstrated that search for a conjunction of local contours with a distinct global orientation was less efficient than search for a target featurally distinct in terms of both global and local contour orientation. However, Experiments 2 and 4 demonstrated that the presence of a unique line contour was neither sufficient nor necessary to allow efficient search. Experiment 5 found that search for a local orientation difference was strongly impeded by irrelevant variation in global orientation, arguing for a preeminent role for global orientation. Finally, Experiment 6 demonstrated that the orientation search asymmetry holds for the global orientation of stimuli. Taken together, the results are consistent with visual search processes guided predominantly by a representation of global orientation.

Adult↗
PubMed1986

Human orientation discrimination: changes with eccentricity in normal and amblyopic vision.

The authors measured orientation discrimination of a single line as a function of eccentricity, line length, and standard orientation. Orientation discrimination improved with increasing line length at all eccentricities. The shortest length at which orientation discrimination was optimal increased with eccentricity. When a line length was used for which discrimination was optimal at all eccentricities, it was found that orientation discrimination performance changed little with increasing eccentricity. Under the same conditions, the oblique effect in orientation discrimination decreased with increasing eccentricity. Similar results were also obtained in both eyes of strabismic amblyopes. The difference between the just noticeable differences in orientation of the amblyopic and nonamblyopic eye decreased with increasing line length for central vision. This interocular difference also decreased with increasing eccentricity. The absence of the oblique effect in orientation discrimination at large eccentricities support the hypothesis that the area 17 S-cell orientation anisotropy underlies the oblique effect in orientation discrimination of long lines since this sensorial anisotropy is limited to the central visual field.

Adult↗
PubMed1998

Contrast-invariant orientation tuning in cat visual cortex: thalamocortical input tuning and correlation-based intracortical connectivity.

The origin of orientation selectivity in visual cortical responses is a central problem for understanding cerebral cortical circuitry. In cats, many experiments suggest that orientation selectivity arises from the arrangement of lateral geniculate nucleus (LGN) afferents to layer 4 simple cells. However, this explanation is not sufficient to account for the contrast invariance of orientation tuning. To understand contrast invariance, we first characterize the input to cat simple cells generated by the oriented arrangement of LGN afferents. We demonstrate that it has two components: a spatial-phase-specific component (i.e., one that depends on receptive field spatial phase), which is tuned for orientation, and a phase-nonspecific component, which is untuned. Both components grow with contrast. Second, we show that a correlation-based intracortical circuit, in which connectivity between cell pairs is determined by the correlation of their LGN inputs, is sufficient to achieve well tuned, contrast-invariant orientation tuning. This circuit generates both spatially opponent, "antiphase" inhibition ("push-pull"), and spatially matched, "same-phase" excitation. The inhibition, if sufficiently strong, suppresses the untuned input component and sharpens responses to the tuned component at all contrasts. The excitation amplifies tuned responses. This circuit agrees with experimental evidence showing spatial opponency between, and similar orientation tuning of, the excitatory and inhibitory inputs received by a simple cell. Orientation tuning is primarily input driven, accounting for the observed invariance of tuning width after removal of intracortical synaptic input, as well as for the dependence of orientation tuning on stimulus spatial frequency. The model differs from previous push-pull models in requiring dominant rather than balanced inhibition and in predicting that a population of layer 4 inhibitory neurons should respond in a contrast-dependent manner to stimuli of all orientations, although their tuning width may be similar to that of excitatory neurons. The model demonstrates that fundamental response properties of cortical layer 4 can be explained by circuitry expected to develop under correlation-based rules of synaptic plasticity, and shows how such circuitry allows the cortex to distinguish stimulus intensity from stimulus form.

Animals↗
PubMed1999

Sexual orientation and risk of suicide attempts among a representative sample of youth.

OBJECTIVE: To examine whether sexual orientation is an independent risk factor for reported suicide attempts. DESIGN: Data were from the Massachusetts 1995 Centers for Disease Control and Prevention Youth Risk Behavior Survey, which included a question on sexual orientation. Ten drug use, 5 sexual behavior, and 5 violence/ victimization variables chosen a priori were assessed as possible mediating variables. Hierarchical logistic regression models determined independent predictors of suicide attempts. SETTING: Public high schools in Massachusetts. PARTICIPANTS: Representative, population-based sample of high school students. Three thousand three hundred sixty-five (81%) of 4167 responded to both the suicide attempt and sexual orientation questions. MAIN OUTCOME MEASURE: Self-reported suicide attempt in the past year. RESULTS: One hundred twenty-nine students (3.8%) self-identified as gay, lesbian, bisexual, or not sure of their sexual orientation (GLBN). Gender, age, race/ethnicity, sexual orientation, and all 20 health-risk behaviors were associated with suicide attempt (P<.001). Gay, lesbian, bisexual, or not sure youth were 3.41 times more likely to report a suicide attempt. Based on hierarchical logistic regression, female gender (odds ratio [OR], 4.43; 95% confidence interval [CI], 3.30-5.93), GLBN orientation (OR, 2.28; 95% CI, 1.39-3.37), Hispanic ethnicity (OR, 2.21; 95% CI, 1.44-3.99), higher levels of violence/ victimization (OR, 2.06; 95% CI, 1.80-2.36), and more drug use (OR, 1.31; 95% CI, 1.22-1.41) were independent predictors of suicide attempt (P<.001). Gender-specific analyses for predicting suicide attempts revealed that among males the OR for GLBN orientation increased (OR, 3.74; 95% CI, 1.92-7.28), while among females GLBN orientation was not a significant predictor of suicide. CONCLUSIONS: Gay, lesbian, bisexual, or not sure youth report a significantly increased frequency of suicide attempts. Sexual orientation has an independent association with suicide attempts for males, while for females the association of sexual orientation with suicidality may be mediated by drug use and violence/victimization behaviors.

Adolescent↗
PubMed2001

Binding and orientation of fibronectin on surfaces with collagen-related peptides. Student Research Award in the Masters Science Degree Candidate category, 27th annual meeting of the Society for Biomaterials, St. Paul, MN, April 24-29, 2001.

Although fibronectin (FN) has been used in a variety of in vitro studies to enhance cell and bacteria adhesion, relatively little is known about the molecular interactions of FN with surfaces, particularly the interactions that can control the binding, conformation, and functionality of FN on these surfaces. Even less is known about approaches needed to control binding, orientation, and functionality of FN bound on surfaces. To begin to fill this gap in our knowledge, we hypothesized that functional FN can be bound and specifically oriented on polystyrene surfaces with FN-specific collagen-related peptides (CRPs). We further hypothesized that monoclonal antibodies that react with specific epitopes on FN can be used to quantify both FN binding and orientation on these surfaces. On the basis of these hypotheses, we initiated a systematic investigation of the binding and orientation of FN on polystyrene surfaces with CRPs. To bind FN to surfaces, we used two different CRPs: CRP-I (TLQPVYEYMVGV) and CRP-II (TGLPVGVGYVVTVLT). The binding and orientation of the FN molecule to these immobilized CRPs was quantified with (125)I-FN and monoclonal antibodies. Monoclonal antibodies used for this study were reactive with specific regions of the FN molecule, that is, the amino (N) terminus (anti-N antibodies) and carboxyl (C) terminus (anti-C antibodies). The results of our studies demonstrated that although CRP-I and CRP-II could be bound directly to polystyrene, these directly immobilized CRPs failed to bind (125)I-FN . Thus, to facilitate FN binding to the CRPs, we used bovine serum albumin (BSA) as a spacer to physically elevate the CRPs away from the polystyrene surface. Thus, CRP-I and CRP-II were covalently linked to BSA via the N and C termini of each CRP (CRP-I-BSA and CRP-II-BSA). (125)I-CRP-BSAs were all found to bind to equivalent levels on polystyrene (1.60-2.60 microg/cm2). When CRP-BSAs were immobilized on polystyrene, they all successfully bound (125)I-FN in a range of 34-72 ng/cm2 (mean). Using monoclonal antibodies to FN to characterize the orientation of FN bound to the various CRP-BSAs, we demonstrated that (1) FN consistently bound to either CRP-I-BSA or CRP-II-BSA; (2) bound FN reacted significantly more with anti-C antibodies than with anti-N antibodies; and (3) the increased reactivity of bound FN to anti-C antibodies was consistent, whether FN was bound by CRP-I or CRP-II or the CRPs were bound to BSA by the C or N termini. These data demonstrated an enhanced binding of anti-C antibodies to immobilized CRP-BSA relative to anti-N antibodies. We interpreted the data to be the result of FN binding in an oriented fashion with N termini of FN bound tightly to the BSA-polystyrene surface. In this position, the C termini of FN are exposed and available for binding by the anti-C antibodies. Alternatively, in this orientation the N termini of the FN would not be available to bind the anti-N antibodies, thereby explaining the decreased reactivity of the CRP immobilized FN to the anti-N antibodies. These studies not only demonstrate the utility of peptides in binding and orienting large molecular weight proteins such as FN on surfaces but underscore the need for well-characterized reagents (e.g., monomeric/functional FN and antibodies) to specifically bind, orient, and characterize large molecular weight proteins immobilized on various surfaces.

Animals↗
PubMed1986

Orientation measurements of microsphere doublets and metaphase chromosomes in flow.

Obtaining information about the shape of particles from slit-scan profiles is facilitated if the particles are oriented. Elongated particles orient in the nozzle of flow cytometers, but orientation may be disrupted before the particles get to the point of measurement. We have used our slit-scan flow cytometer to investigate the orientation of microsphere doublets in a liquid jet in air, in flow across a glass surface, and in a 200-microns-square capillary tube as a function of distance from the flow chamber nozzle. Particles were classified as being oriented if there was a centrally located dip in the slit-scan profile. Essentially all the doublets in the jet were oriented, and no disorientation was noted over the distances measured (up to 10 mm from the nozzle). Particle orientation was maintained for 80 microns in flow across a glass surface. In the capillary-type flow chamber, essentially all of the particles were oriented at the tube entrance and for several millimeters into the tube. There then occurred a region where particle tumbling started and progressively fewer doublets met the orientation criteria. The distance to where tumbling began could be estimated by calculating the length required to establish the parabolic flow profile in the tube. Finally, the fraction of oriented particles reached a constant value that did not change with increased distance into the tube. When sample was injected off axis (i.e., halfway between the chamber center and the chamber walls), particle tumbling began closer to the tube entrance.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Line↗
PubMed2005

Uniaxial drawing of poly[(R)-3-hydroxybutyrate]/cellulose acetate butyrate blends and their orientation behavior.

Miscible blends of PHB and CAB were prepared by the solvent-casting method with various blend compositions, and their orientation behavior was investigated during uniaxial drawing. X-ray analysis revealed that the orientation of the crystallizable PHB component in the drawn PHB/CAB blends was changed from c-axis-orientation to a-axis-orientation with increasing CAB content. The a-axis-orientation was a result from the a-axis-oriented crystal growth caused by the intramolecular nucleation and the confined crystal growth. For quantitative assessment of the chain orientation, the Hermans orientation functions of the two respective components were obtained from the polarized FT-IR measurements. The orientation function of pure PHB stretched to 5 times of its initial length was approximately 0.8. However the value decreased rapidly with increasing CAB content, and it turned to a negative value from 30 wt.-% CAB content. This indicates that the PHB chains were aligned perpendicular to the drawing direction. On the contrary, the value of the CAB component remained almost unchanged at about 0.1 regardless of the blend composition and the annealing time, indicating that the CAB chains were constantly oriented parallel to the drawing direction without any chain relaxation. In addition, SAXS analysis suggested that the lamellar stacking direction also changed from parallel to perpendicular in the stretching direction with increasing CAB content.

Algorithms↗
PubMed1998

Multiple-step method for making exceptionally well-oriented liquid-crystalline sols of macromolecular assemblies.

X-ray fiber diffraction is potentially powerful in solving the atomic structure of filamentous assemblies of macromolecules, as demonstrated for tobacco mosaic virus. However, it requires extremely well-oriented sols to allow for extraction of intensities on closely located layer-lines. A high degree of orientation requires a high filament concentration to restrain the orientational freedom, but orienting concentrated sols is hampered by their high viscosity. Here, we report a systematic method that reproducibly produces extremely good orientation, which involves three steps; liquid crystallization, centrifugation and magnetic orientation. We found that a slow centrifugation can trigger a dynamic self-orientation process to form perfectly homogeneous liquid-crystalline sols, and further centrifugation to concentrate sols followed by magnetic orientation produces exceptionally well-oriented sols. The best-oriented flagellar sol showed a disorientation angle of 0.6 degrees as 1sigma of its Gaussian distribution. The new method has been successfully applied to many other systems, such as tobacco mosaic virus and F-actin.

Actins↗
PubMed1992

Orientation and segregation of a micromanipulated multivalent: familiar principles, divergent outcomes.

We studied the orientation and segregation of a particular quadrivalent in living grasshopper spermatocytes. Quadrivalents were detached from the spindle by micromanipulation, then placed and bent as desired. The detached quadrivalents reattach and orient on the spindle. Their orientation is determined by the same principles that apply to ordinary chromosomes in mitosis and meiosis, but the outcome is different. Certain characteristics of the quadrivalent lead to a variety of orientations rather than the single one typical of ordinary chromosomes. Two kinetochores in the quadrivalent are linked to the others by unusually long, flexible chromosome arms. These kinetochores may face either the same pole or opposite poles and tend to orient initially to the pole toward which they face. Consequently, the initial orientation of the flexibly linked kinetochores is variable, and, moreover, they frequently reorient. In contrast, the other two kinetochores are as rigidly connected as those in a small bivalent and so display the typical back-to-back arrangement. Usually, this arrangement leads quickly to a stable orientation of the two kinetochores to opposite poles. Sometimes, however, the back-to-back arrangement changes to a side-by-side arrangement so that the orientation of both kinetochores to the same pole is favored. The combined effect of this diverse behavior is that the quadrivalent has four stable orientations, each leading to a different distribution of chromosomes in anaphase. The result is genetic chaos. Ironically, this chaos is produced by the same mechanisms that, in ordinary bivalents and mitotic chromosomes, produce a single stable orientation and genetically appropriate chromosome distribution.

Aneuploidy↗
PubMedDate not supplied

The effect of managed care on hospital marketing orientation.

Marketing is a central activity of modern organizations. To survive and succeed, organizations must know their markets, attract sufficient resources, convert these resources into appropriate services, and communicate them to various consuming publics. In the hospital industry, a marketing orientation is currently recognized as a necessary management function in a highly competitive and resource-constrained environment. Further, the literature supports a marketing orientation as superior to other orientation types, namely production, product and sales. In this article, the results of the first national cross-sectional study of the marketing orientation of U.S. hospitals in a managed care environment are reported. Several key lessons for hospital executives have emerged. First, to varying degrees, U.S. hospitals have adopted a marketing orientation. Second, hospitals that are larger, or that have developed strong affiliations with other providers that involve some level of financial interdependence, have the greatest marketing orientation. Third, as managed care organizations have increased their presence in a state, hospitals have become less marketing oriented. Finally, contrary to prior findings, for-profit institutions are not intrinsically more marketing oriented than their not-for-profit counterparts. This finding is surprising because of the traditional role of marketing in non-health for-profit enterprises and management's greater emphasis on profitability. An area of concern for hospital executives arises from the finding that as managed care pressure increases, hospital marketing orientation decreases. Although a marketing orientation is posited to lead to greater customer satisfaction and improved business results, a managed care environment seems to force hospitals to focus more on cost control than on customer satisfaction. Hospital executives are cautioned that cost-cutting, the primary focus in intense managed care environments, may lead to short-term gains by capturing managed care business, but may not be sufficient for long-term success and survival. Understanding consumer needs and perceptions, and using appropriate marketing strategies to ensure greater customer satisfaction and repeat business, will be among the key tasks for hospital executives in the future.

Bed Occupancy↗
PubMedDate not supplied

Biased cell migration of fibroblasts exhibiting contact guidance in oriented collagen gels.

We present here the first quantitative correlation for cell contact guidance in an oriented fibrillar network in terms of biased cell migration. The correlation is between the anisotropic cell diffusion parameter, DA = Dx/Dy, and the collagen gel birefringence, delta n, a measure of axially biased collagen fibril orientation in the x-direction. The cell diffusion coefficients, Dx and Dy, measure the dispersal of cells in the directions coincident with and normal to the axis of fibril orientation, respectively. Three essential methodological components are involved: (i) exploiting the orienting effect of a magnetic field on collagen fibrils during fibrillogenesis to systematically prepare uniform axially oriented collagen gels; (ii) using a microscope/image analysis workstation with precise, computer-controlled rotating and translating stages to automate birefringence measurement and, along with rapid "coarse optical sectioning" via digital image processing, to enable 3-D cell tracking of many cells in multiple samples simultaneously; and (iii) employing a rigorous statistical analysis of the cell tracks to estimate the magnitude and precision of the direction-dependent cell diffusion coefficients, Dx and Dy, that define DA. We find that this measure of biased migration in contact guidance (DA) increases with increasing collagen fibril orientation (delta n) due mainly to a rapid enhancement of migration along the axis of fibril orientation at low levels of fibril orientation, and to a continued suppression of migration normal to the axis of fibril orientation at high levels of fibril orientation.

Anisotropy↗
PubMed2005

Sex differences in the flexibility of sexual orientation: a multidimensional retrospective assessment.

The flexibility of sexual orientation in men and women was examined by assessing self-reported change over time for three dimensions of sexual orientation (sexual fantasy, romantic attraction, and sexual behavior) across three categorical classifications of current sexual orientation (heterosexual, bisexual, and gay). The primary purpose of the study was to determine if there were sex differences in the flexibility (i.e., change over time) of sexual orientation and how such differences were manifested across different dimensions of orientation over the lifespan. Retrospective, life-long ratings of sexual orientation were made by 762 currently self-identified heterosexual, bisexual, and gay men and women, aged 36 to 60, via a self-report questionnaire. Cumulative change scores were derived for each of the three dimensions (fantasy, romantic attraction, and sexual behavior) of orientation by summing the differences between ratings over consecutive 5-year historical time periods (from age 16 to the present). Sex differences were observed for most, but not all, classification groups. There were significant sex differences in reported change in orientation over time for gays and heterosexuals, with women reporting greater change in orientation over time than did men. Bisexual men and women did not differ with respect to self-reported change in orientation.

Adaptation, Psychological↗
PubMed1982

The orientation and direction selectivity of cells in macaque visual cortex.

Quantitative data are presented on the orientation and direction specificity of the responses of cells in macaque monkey striate cortex. There is a bimodal distribution of direction-specific and nondirection-specific cells, with similar orientation tuning in each class. Cells range in orientation bandwidth at half amplitude from 6 degrees to 360 degrees (i.e. no orientation tuning), with a median near 40 degrees. Foveal-parafoveal and simple-complex subsamples show similar ranges of orientation bandwidths as well as similar medians (the bandwidths being somewhat broader than those found in cat cortex). The foveal subsample and a high-spatial-frequency subsample have more horizontal and vertical optimal orientations than oblique ones. Most cells show inhibition to some orientations, as well as excitation to others. Minimum-response orientations are generally less than 90 degrees from the optimal orientation--indicating maximum inhibition adjacent to the excitatory orientations. Three simple receptive field models are shown to differ in their abilities to account for these results.

Animals↗
PubMed1993

Dynamics of orientation tuning in the cat striate cortex neurons.

Dynamics of orientation tuning was studied by a flashing light bar in 233 single units of cat primary visual cortex. Orientation tuning was plotted by the criterion of spike number in successive fragments of responses with a step of 10 or 20 ms. Preferred orientation and the width of orientation tuning were measured for each of such curves. It was found that successive dynamic change of preferred orientation during response was typical for 63% of units under study, while such change of orientation tuning width was typical for 93%. Neurons with or without shift in preferred orientation differed in their response characteristics: latency and duration of discharge, its frequency and response rise time, as well as quality of orientation tuning. Possible functional significance of two groups of cortical units, "scanners" (with systematic preferred orientation shift) and "timers" (without it), is discussed in accordance with the idea of spatiotemporal orientation coding in the primary visual cortex.

Animals↗
PubMed2003

Cellulose orientation at the surface of the Arabidopsis seedling. Implications for the biomechanics in plant development.

In diffuse growing cells the orientation of cellulose fibrils determines mechanical anisotropy in the cell wall and hence also the direction of plant and organ growth. This paper reports on the mean or net orientation of cellulose fibrils in the outer epidermal wall of the whole Arabidopsis plant. This outer epidermal wall is considered as the growth-limiting boundary between plant and environment. In the root a net transverse orientation of the cellulose fibrils occurs in the elongation zone, while net random and longitudinal orientations are found in subsequent older parts of the differentiation zone. The position and the size of the transverse zone is related with root growth rate. In the shoot the net orientation of cellulose fibrils is transverse in the elongating apical part of the hypocotyl, and longitudinal in the fully elongated basal part. Leaf primordia and very young leaves have a transverse orientation. Throughout further development the leaf epidermis builds a very complex pattern of cells with a random orientation and cells with a transverse or a longitudinal orientation of the cellulose fibrils. The patterns of net cellulose orientation correlate well with the cylindrical growth of roots and shoots and with the typical planar growth of the leaf blade. On both the shoot and the root surface very specific patterns of cellulose orientation occur at sites of specific cell differentiation: trichome-socket cells complexes on the shoot and root hairs on the root.

Anisotropy↗
PubMed1993

Orientational behavior of phosphatidylcholine bilayers in the presence of aromatic amphiphiles and a magnetic field.

A number of aromatic-containing additives which can influence the orientation of fragments of lipid bilayer membranes by a magnetic field have been investigated. Two properties of these additives prove important: (1) sufficient detergency to facilitate reorganization of bilayer components and (2), sufficient anisotropy in magnetic susceptibility the preferred direction of fragment orientation. Triton X-100 is identified as effective in terms of facilitating magnetic field ordering of bilayer fragments but does not alter the preferred direction of orientation. A combination of the detergent CHAPSO (3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate) and the aromatic alcohol 1-naphthol facilitates both ordering and alters the preferred direction of bilayer orientation. As mixtures of dimyristoylphosphatidylcholine (DMPC) and CHAPSO, which orient with bilayer normals perpendicular to the magnetic field, were titrated with 1-naphthol, the assemblies underwent transitions, first to random orientation, and then to an orientation with bilayer normals parallel to the field. Based on temperature-induced phase transitions and the extent of motional averaging of the 31P shielding tensor of the DMPC headgroup, the DMPC in these oriented samples appears to maintain a bilayer morphology during transitions. The insight provided in this study regarding factors which influence fragment stability and orientation lays the groundwork for the design of improved field-oriented media for spectroscopic investigation of membrane components.

Biophysical Phenomena↗
PubMed1996

Dentin shear strength: effects of tubule orientation and intratooth location.

OBJECTIVES: Dentin has a highly oriented tubule structure, and the tubule number density and area fraction of intertubular dentin vary with distance from the pulp. This investigation sought to determine the influence of tubule orientation on shear strength of dentin from samples derived at various intratooth locations. METHODS: Third molars were sectioned and prepared to provide samples from two locations (center and cusp) and with one of three specific tubule orientations. In series 1, matched pairs of midcoronal samples were tested using two tubule orientations. A paired t-test was used for statistical analysis. In series 2, three samples from central and cuspal areas were tested using three different tubule orientations. A two-day ANOVA was used for statistical analysis. Each sample had dimensions of approximately 1 x 1 x 5 mm and was tested in a hydrated state by a single plane lap shear method. RESULTS: The paired dentin samples of the midcoronal dentin in the two orientations had shear strengths of 72.4 +/- 15.6 MPa and 78.4 +/- 13.2 MPa, and were not significantly different (p > 0.05; paired t-test). In the second series, samples from the center location with tubules parallel to the shear plane with applied force in directions rotated by 90 degrees did not exhibit a significant difference (p > 0.05), with an average value of 53.5 +/- 9.5 MPa. Samples oriented with tubules along the long axis of the specimen and tested with shear force applied perpendicular to the tubule direction had significantly higher (p < 0.05; two-way ANOVA) shear strength (78.0 +/- 8.5 MPa). The specimens from the cusp area did not exhibit a statistically significant difference (p > 0.05; two-way ANOVA) with respect to the three orientations (83.6 +/- 8.4; +/- 13.8; 91.8 +/- 12.7 MPa). Cuspal areas were stronger than central areas in two of the three orientations tested. SIGNIFICANCE: Results indicated that the shear strength differs in central and cusp areas and is dependent on dentin tubule orientation in the central area. Shear strengths were much larger than values reported in shear bond strength tests. This suggests that dentin shear strength is far in excess of dentin bond strengths using shear tests, and that fractures through dentin in such result from flaws or stress concentration in the dentin.

Analysis of Variance↗