Author

Yongji Fu

Date

March 2008

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Biomedical Engineering

Institution

Oregon Health & Science University

Abstract

Oral bacteria related disease such as periodontital disease and dental caries affects over 75% of adults over 35 years in the US. Resolving this issue becomes more difficult as antibiotic-resistance strains of bacteria in a biofilm pose an increasing challenge for dental care. Photodynamic therapy (PDT) is an antibiotic treatment that employs oxidation by a light-activated photosensitizer (PS) to kill targeted bacteria cells. PDT is a good alternative to regular antibiotics approaches because (1) the dual selectivity of PDT (PS can target to the bacteria cells and the illumination can be directed to the infected area), and (2) the difficulty for bacteria to develop resistance to PDT. The objective of this study is to understand the dosimetry of PDT for oral biofilm in order to design PDT protocols, using optical technologies. Research on this antibiotic effect of PDT is still in its early stage needs contributions from many different areas such as microbiology, biomedical optics, dentistry and biochemistry. This study presents the research using optical methods such as reflectance spectroscopy and confocal microscopy to monitor the uptake of photosensitizers (PS) into bacterial suspensions (planktonic state, using reflectance spectroscopy) and bacterial biofilms (biofilm state, using confocal reflectance) dosimetry. The threshold PDT dose (photons absorbed by PS per g of cells) was determined as 3.6x10[superscript 21] by cell survival studies following increasing light exposures, for both planktonic and biofilm states of bacteria. However the threshold radiant exposure H [subscript th] for biofilm (18 J/cm2) was about 10-fold higher than H [subscript th] in the planktonic state (1.3 J/cm2). This is because the photosensitizer concentration in the lower layer of biofilm is much less than the planktonic state photosensitizer concentration. The ability of treatment light to penetrate a tooth to achieve PDT both at surfaces and within the tooth, e.g., in cracks or fissures, was studied using a Monte Carlo program that simulates the structure of a tooth. In summary, three topics were addressed: (1) uptake of PS by planktonic and biofilm bacteria, (2) the threshold PDT dose required to kill planktonic and biofilm bacteria, and (3) a Monte Carlo simulation of the tooth to asses the ability of PDT treatment light to reach different parts of a tooth. The significance of this work is that the tools (optical assessment of PS uptake, Monte Carlo model for light delivery) and dosage information (PDT threshold lethal dose) are pertinent to design of PDT protocols for antibacterial effect on oral bacteria.

Identifier

doi:10.6083/M44T6G9F

School

OGI School of Science and Engineering

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