Dr. Annie Shrestha Profile

Dr. Annie Shrestha

Post-doctoral fellow at Univ of Toronto

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Proceedings Article | 25 March 2013 Paper

Photodynamic therapy for inactivating endodontic bacterial biofilms and effect of tissue inhibitors on antibacterial efficacy

Annie Shrestha, Anil Kishen

Proceedings Volume 8566, 85660G (2013) https://doi.org/10.1117/12.2007985

KEYWORDS: Photodynamic therapy, Tissues, Tissue optics, Bacteria, Biological research, Oxygen, Laser scanners, Confocal microscopy, Proteins, In vitro testing

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Complex nature of bacterial cell membrane and structure of biofilm has challenged the efficacy of antimicrobial photodynamic therapy (APDT) to achieve effective disinfection of infected root canals. In addition, tissue-inhibitors present inside the root canals are known to affect APDT activity. This study was aimed to assess the effect of APDT on bacterial biofilms and evaluate the effect of tissue-inhibitors on the APDT. Rose-bengal (RB) and methylene-blue (MB) were tested on Enterococcus faecalis (gram-positive) and Pseudomonas aeruginosa (gram-negative) biofilms. In vitro 7- day old biofilms were sensitized with RB and MB, and photodynamically activated with 20-60 J/cm². Photosensitizers were pre-treated with different tissue-inhibitors (dentin, dentin-matrix, pulp tissue, bacterial lipopolysaccharides (LPS), and bovine serum albumin (BSA)) and tested for antibacterial effect of APDT. Microbiological culture based analysis was used to analyze the cell viability, while Laser Scanning Confocal Microscopy (LSCM) was used to examine the structure of biofilm. Photoactivation resulted in significant reduction of bacterial biofilms with RB and MB. The structure of biofilm under LSCM was found to be disrupted with reduced biofilm thickness. Complete biofilm elimination could not be achieved with both tested photosensitizers. APDT effect using MB and RB was inhibited in a decreasing order by dentin-matrix, BSA, pulp, dentin and LPS (P< 0.05). Both strains of bacterial biofilms resisted complete elimination after APDT and the tissue inhibitors existing within the root canal reduced the antibacterial activity at varying degrees. Further research is required to enhance the antibacterial efficacy of APDT in an endodontic environment.

Proceedings Article | 13 July 2007 Paper

Optical sensor based system to monitor caries activity

A. Shrestha, R. Tahir, A. Kishen

Proceedings Volume 6633, 663317 (2007) https://doi.org/10.1117/12.729438

KEYWORDS: Dental caries, Optical sensors, Absorption, Sensors, Ocean optics, Teeth, Biomedical optics, Spectroscopy, Bacteria, Spectrophotometry

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The aim of the study is to evaluate the ability of a visible light based spectroscopic sensor system to monitor caries activity in saliva. In this study an optical sensor is utilized to monitor the bacterial-mediated acidogenic profile of stimulated saliva using a photosensitive pH indicator. Microbiological assessment of the saliva samples were carried out using the conventional culture methods. In addition, the shifts in the pH of saliva-sucrose samples were recorded using a pH meter. The absorption spectra obtained from the optical sensor showed peak maxima at 595nm, which decreased as a function of time. The microbiological assessment showed increase in the bacterial count as a function of time. A strong positive correlation was also observed between the rates of decrease in the absorption intensity measured using the optical sensor and the decrease in pH measured using the pH meter. This study highlights the potential advantages of using the optical sensor as a sensitive and rapid chairside system for monitoring caries activity by quantification of the acidogenic profile of saliva.

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