Detection of Subgingival Calculus by Optical Methods

Fardad Shakibaie (2011). Detection of Subgingival Calculus by Optical Methods PhD Thesis, School of Dentistry, The University of Queensland.

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Author Fardad Shakibaie
Thesis Title Detection of Subgingival Calculus by Optical Methods
School, Centre or Institute School of Dentistry
Institution The University of Queensland
Publication date 2011-06
Thesis type PhD Thesis
Supervisor Professor Laurence J Walsh
Professor Halina Rubinsztein-Dunlop
Total pages 432
Total colour pages 209
Total black and white pages 223
Subjects 11 Medical and Health Sciences
Abstract/Summary Abstract The central hypothesis of this thesis is that calculus can be identified based on its unique optical properties (reflection and fluorescence). Detection of subgingival calculus using conventional tactile senses has limited sensitivity and specificity. Light-induced fluorescence methods and optical imaging are promising optical technologies for differentiating subgingival calculus from a healthy root surface and from materials which may be present in the subgingival environment. Fluorescence as an optical method is explored in the first part of the thesis. Information on potential fluorophores obtained from a comprehensive review of the available literature was supplemented by systematic analysis of the fluorescing components of calculus and other root surface materials using chemometric analysis. This approach identified a number of fluorescing compounds, which were then compared to a library comprising 20 fluorophores as pure standards. Whole samples as well as organic and inorganic extracts of samples, and pure fluorophores were examined at 230-265 nm excitation wavelengths, and the emissions recorded from 285-800 nm. The specific excitation wavelengths of 230 and 265 nm were shown to identify calculus based on the presence or absence of fluorescence emissions in the ultraviolet and visible blue regions, allowing discrimination from sound dentine, root caries, saliva and blood. To confirm the presence and concentration of key fluorophores, data obtained from analysis of individual fluorophores was used to deconvolute fluorescence curves from clinical samples and their extracts. This chemometric analysis revealed that tryptophan was a key diagnostic fluorophore for distinguishing calculus from other root-surfaces when using UV fluorescence at 265-310 nm. Differences in blue fluorescence (420-500 nm) arising from analogues of tyrosine, collagens or an unknown fluorophore also discriminated calculus from dentine. From these findings, the recommended configuration was excitation at 230-265 nm combined with a 310 nm short-pass filter. The second part of the thesis addressed optical imaging methods for calculus detection. The design of a slim intra-oral camera handpiece able to view subgingival calculus within narrow periodontal pockets is presented. The benefits of an additional fluorometer calibration scale display are then examined, since such a device could not only view subgingival calculus but also verify its existence based on standardized numerical information. Such fluorometer calibration can be achieved either through a conventional ratio fluorometer or by a new photometric fluorometer, the design of which is presented. Such fluorometers can be integrated into an intra-oral camera to allow specific detection of subgingival calculus on the root-surface. The third part of the thesis explores the use of visible light for calculus detection, employing a mixture of fluorescence and reflection approaches. Microscopic digital photography was undertaken using various light sources to illuminate samples, with various colour filters applied in front of the objective lens. Analysis of reflectance standardization (calibration) ratios determined that violet + blue or blue light sources used in combination with red or orange filters were useful for identifying dental calculus. A violet + blue light source used with a red filter was able to successfully identify all subgingival calculus samples because of greater mean red fluorescence than other root-surface components. In contrast, blue light combined with a red filter could discriminate calculus from most other samples in one of the three RGB luminosities. Such light-filter combinations could be used in an intra-oral camera employing a ratio fluorometer to detect only subgingival calculus. In contrast, in a laboratory trial of an intra-oral camera (Durr VistaCam) with a 405 nm light emitted diode, this commercial system performed poorly and was unable to discriminate subgingival calculus from other materials. To explore the effect of possible confounding factors on reflectance and fluorescence, the effect of covering the root surface with saliva or blood was assessed. Saliva did not affect the reflection and fluorescent luminosities of the root compared with its dry state, whereas blood reduced light luminosities compared to either saliva-coated or dry surfaces. Further aspects of this work confirmed the viability of new photometric fluorometer equations, for reproducing a standard luminosity for each particular object, despite variations in the image data caused by changes in camera-aperture, exposure-time, final magnification, and the intensity of the light source, with a demonstrated accuracy of 88.66%. Overall, the work undertaken in this thesis has documented the light absorbing and emitting properties of components of subgingival calculus, mapped the major optical properties of interest, and identified appropriate wavelengths to differentiate subgingival calculus from other root-surface components. It also provides a foundation for future studies where these principles and optical techniques could be used to develop novel devices in clinical dental practice.
Keyword Detection
Optical imaging
Laser fluorescence
Subgingival calculus
Additional Notes The colour pages for s33503732_PhD_resubmission.pdf are: 28, 31, 34-35, 37-39, 67-70, 91, 97, 101-105, 107-108, 111-112, 114, 122, 124, 126-156, 160-170, 172-177, 180, 182-191, 222-226, 233-284, 286-311, 313-324, 326-331 Please Print all pages of the following files in colour pages: Figures 3.2 to 3.5.pdf (2 colour pages), Figures 3.16 to 3.19.pdf (2 colour pages), Figures 3.29 to 3.32.pdf (2 colour pages), Figures 3.39 to 3.42.pdf (2 colour pages), Figures 3.52 to 3.55.pdf (2 colour pages), Figures 3.67 to 3.70.pdf (2 colour pages), Figures 3.76 to 3.79.pdf (2 colour pages), Figures 3.90 to 3.93.pdf (2 colour pages), Figures 3.100 to 3.103.pdf (2 colour pages), Figures 3.109 to 3.112.pdf (2 colour pages), Figures 3.124 to 3.127.pdf (2 colour pages), Figures 3.138 to 3.141.pdf (2 colour pages)

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Created: Wed, 06 Jul 2011, 15:17:59 EST by Fardad Shakibaie on behalf of Library - Information Access Service