Browsing by Subject "Crack"

Now showing 1 - 4 of 4
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    Assessing the Accuracy and Reliability of Root Crack and Fracture Detection in Teeth Using Sweep Imaging with Fourier Transform (SWIFT) Magnetic Resonance Imaging (MRI)
    (2017-08) Schuurmans, Tyler
    Introduction: Magnetic Resonance Imaging (MRI) has the potential to aid in determining the presence and extent of cracks/fractures in teeth due to more advantageous contrast, without ionizing radiation. An MRI technique called Sweep Imaging with Fourier Transform (SWIFT) has overcome many of the inherent difficulties of conventional MRI with detecting fast-relaxing signals from densely mineralized dental tissues. The objectives of this in vitro investigation were to develop MRI criteria for root crack/fracture identification in teeth and to establish intra- and inter-rater reliabilities and corresponding sensitivity and specificity values for the detection of tooth-root cracks/fractures in SWIFT MRI and limited field of view (FOV) CBCT. Materials and Methods: MRI-based criteria for crack/fracture appearance was developed by an MRI physicist and 6 dentists, including 3 endodontists and 1 Oral and Maxillofacial (OMF) radiologist. Twenty-nine human adult teeth previously extracted following clinical diagnosis by a board-certified endodontist of a root crack/fracture were frequency-matched to 29 non-cracked controls. Crack/fracture status confirmation was performed with magnified visual inspection, transillumination and vital staining. Samples were scanned with two 3D imaging modalities: 1) SWIFT MRI (10 teeth/scan) via a custom oral radiofrequency (RF) coil and a 90cm, 4-T magnet; 2) Limited FOV CBCT (1 tooth/scan) via a Carestream (CS) 9000 (Rochester, NY). Following a training period, a blinded 4-member panel (3 endodontists, 1 OMF radiologist) evaluated the images with a proportion randomly re-tested to establish intra-rater reliability. Overall observer agreement was measured using Cohen’s kappa and levels of agreement judged using the criteria of Landis and Koch. Sensitivity and specificity were computed with 95% confidence interval (CI); statistical significance was set at 0.05. Results: MRI-based crack/fracture criteria were defined as 1-2 sharply-delineated, high-signal (bright/white) line shape(s) that must be visible on multiple contiguous image slices. The line shape(s) must present as: single entities, or parallel pairs in close proximity, or pairs in close proximity exhibiting convergence or divergence extending from the external boundary of the tooth to the pulpal cavity. Intra-rater reliability for MRI was fair-to-almost perfect (κ=0.38-1.00) and for CBCT was moderate-to-almost perfect (κ=0.66-1.00). Inter-rater reliability for MRI was fair (κ=0.21; 95%CI:0.10-0.31; p< 0.001) and for CBCT was moderate (κ=0.45; 95%CI:0.34-0.56; p<0.001). Sensitivity: MRI=0.59 (95% CI:0.39-0.76; p=0.46); CBCT=0.59 (95% CI:0.59-0.76; p=0.46). Specificity: MRI=0.83 (95% CI:0.64-0.94; p<0.01); CBCT=0.90 (95% CI:0.73-0.98; p<0.01). Conclusions: Education and training for both imaging modalities is needed to improve reliabilities for the identification of tooth-root crack/fractures. Despite the advantages of increased contrast and absence of artifact from radio-dense materials in MRI, comparable measures of sensitivity and specificity (in relation to CBCT) suggest quality MRI improvements are needed, specifically in image acquisition and post-processing parameters. Given the early stage of technology development and multiple available pathways to optimize MR imaging of teeth, there may be a use for SWIFT MRI in detecting cracks and fractures in teeth.
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    Crack and concrete deck sealant performance
    (2013-05) Johnson, Karl Andrew
    The research objective of this project was to define the current state-of-the-art regarding the use of bridge deck sealants and crack sealers to extend the life of reinforced concrete bridge decks. The role of deck sealants and crack sealers is to prevent chloride ion ingress, originating from deicing materials spread on the road, from penetrating into the concrete bridge deck and corroding the reinforcing steel bars. The report includes the information generated from a literature review and survey. The literature review focused on current and significant studies in the field of deck and crack sealing. The intent of the survey is to determine common practices for the use and application of these sealers in different states throughout the United States. After all of the information is collected and compiled from the literature review and the survey, the best materials and practices are recommended for use in Minnesota and throughout the Midwest.
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    Durability of high density polyethylene for potable hot water applications: crack propagation.
    (2012-09) Singh, Gyanender P.
    Polyethylene (PE) pipes, are used for water delivery, are susceptible to oxidation. As a result of oxidation PE becomes brittle and brittle pipes/tubes crack under the influence of tensile loads. These cracks initially propagate slowly and later on grow quickly becoming unstable. The focus of this study is slow crack growth in high density polyethylene (HDPE). Crack propagation experiments were conducted to determine the dependence of crack growth on degradation and stress levels. HDPE samples, with 0.3mm thickness, were exposed to 80°C chlorinated water (5-8 ppm) for up to 65 days. Thin samples were selected to ensure uniform degradation through the thickness. Although the brittleness of the polymer can be evaluated using strain-at-failure, the drawback of this method is that it destroys the sample. The Carbonyl Index (CI) obtained by Fourier Transform Infrared (FTIR) spectroscopy was established as a nondestructive measure of the degradation level. CI ranged from 35 to 93. A higher value of carbonyl index represents a greater extent of degradation. The relationship between CI and loss of mechanical performance was validated by strain-at-failure. Crack propagation tests were conducted were conducted on degraded polymer samples at constant load. The load (stress level) ranged from 5.1 to 9.2 MPa. In all 5 samples were tested. It was found that the crack propagation rate ranged from 6.31 x 10-10 to 1.26 x 10-2 m/s while the stress intensity factor ranged from 0.91 to 4.07 MPa√m. For a single degradation level, regardless of stress, the data when converted to log scale, and fit with the linear elastic fracture mechanics (LEFM) relationship = CKn. As the degradation increased the crack propagation rate increased such that all data were fit by the relationship = C(CI)Kn such that the exponential parameter ‘n’ was a constant for all the samples regardless of the level of degradation. The LEFM model fit to the data was best for moderate and high levels of degradation corresponding to CI of 55 and 90. Scanning Electron Microscopy (SEM) images show minimal deformation in the region around the crack tip, and ductile fibril stretching in the process zone. While the polymer had become brittle upon oxidation, there is local ductility in the process zone. An LEFM approach is typically applied to brittle materials, while the SEM results show that crack propagation is a combination of brittle and ductile behavior. Future studies should consider other modeling approaches that allow for ductile behavior in the process zone.
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    Field And Laboratory Evaluation of Asphalt Crack Sealant Performance
    (2020-05) Munch, Jared
    Crack sealing on hot-mix asphalt (HMA) pavement roads is a pavement maintenance technique used to limit the intrusion of water into the pavement structure, and thereby, delay additional distresses. There are two commonly used methods of crack sealing in Minnesota: (i) clean-and-seal, and (ii) rout-and-seal. Since roads in Minnesota are extremely susceptible to cracking in the transverse direction, the goal of this study was to provide insight to the most effective method of crack sealing on asphalt pavements. Based on the field performance results, this study compared the abovementioned two methods for difference scenarios and developed a decision tree to identify the most effective crack sealing method for a given condition of pavement and traffic. As an additional component to the primary study, a new testing procedure for evaluating the adhesiveness between the sealant material and the HMA matrix was developed. This procedure tests sealant materials in tension to produce a stress/strain curve of the sealant as it fails.