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Title: Quantitative image processing as an objective alternative to dental clinical indices
Author: Taylor, Andrew
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2010
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Most research in dentistry is based on clinical assessment by dentists. This is naturally subjective and qualitative. The most common means of standardising this assessment is to use a clinical index, which lays out clear criteria against which to make the assessment. This works well, but lacks the precision and objectivity of an automated, quantitative method. The increased statistical power offered by quantitative methods allows more research to be done more quickly, cheaply and safely, and the objectivity makes inter-study comparisons more valid and can help improve blinding. The use of imaging methods offers the chance to archive large amounts of information for alternative analysis later. An algorithm was developed to automatically assess caries penetration in micro- CT scans of extracted teeth. This was tested against Quantitative Light-Induced Fluorescence (QLF), an Electric Caries Meter (ECM), Fibre-Optic Transillumination (FOTI) examination and histological assessments, and found to be effective in measuring depth in dentine (ICC = .822 with histology; N = 45, p < .001), but insufficient supporting evidence was found to recommend its use in measuring enamel caries. Further work, with higher-resolution scans and a healthier sample space, would be required to establish a suitable micro-CT-based gold standard for enamel caries. Automated planimetry already offers objective quantification of dental plaque; however, all present systems use extra-oral photography and measure only or principally the buccal surfaces of anterior teeth. Due to physical and chemical differences between different areas of the mouth, this may not be sufficient to assess treatment effects throughout the mouth. Therefore two versions of an intra-oral planimetry system were developed and trialled by comparing known-antibacterial cetylpyridinium chloride to placebo. The first uses a standard QLF imaging system with red disclosing agent, while the second uses an illuminant with 470nm peak wavelength to excite fluorescein dye. It was found, using the QLF system, that statistically significant (p = .032) whole-mouth effects did not appear on anterior buccal surfaces (p = .526), showing that intra-oral planimetry is required to fully evaluate product effects. The fluorescein-based system did not separate the products. This is believed to be because of compliance issues. Objective quantification of stain covering an entire tooth surface is well established, but discrete patches of dark stain must still be measured using indices such as Lobene. Here, an algorithm is developed to measure the area of such stain using QLF, and it is tested in a six-week stain-growth study comparing stannous fluoride, chlorhexidine and a control. This was found to correlate well with clinical assessments (Pearson's = .835) and separate groups (p < .001). It is clear from this work that quantitative methodologies have a role in the areas tested here. The methodologies are in their early stages and should be refined before routine use.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available