Fundamentals and Applications of Biophotonics in Dentistry Anil Kishen Anand Asundi Imperial College Press Vol.4 Series on Biomaterials and Bioengineering Fundamentals and Applications of Biophotonics in Dentistry SERIES ON BIOMATERIALS AND BIOENGINEERING Series Editors: A W Batchelor (Monash Univ. Sunway Campus Malaysia Sdn Bhd) J R Batchelor (UK) Margam Chandrasekaran (Singapore Institute of Manufacturing Technology, Singapore) Vol. 1: An Introduction to Biocomposites by Seeram Ramakrishna (National University of Singapore, Singapore), Zheng-Ming Huang (Tongji University, China), Ganesh V Kumar (National University of Singapore, Singapore), A W Batchelor (Monash University Malaysia, Malaysia) Joerg Mayer (TECIM, Switzerland) Vol. 2: Life-Enhancing Plastics: Plastics and Other Materials in Medical Applications by Anthony Holmes-Walker (Biolnteractions Ltd, UK) Vol. 3: Service Characteristics of Biomedical Materials and Implants by Andrew W Batchelor (Monash University Malaysia, Malaysia) and Margam Chandrasekaran (Singapore Institute of Manufacturing Technology, Singapore) Vol.4 Series on Biomaterials and Bioengineering Fundamentals and Applications of Biophotonics in Dentistry Anil Kishen National University of Singapore, Singapore Anand Asundi Nanyang Technological University, Singapore Imperial College Press Jft^ Published by Imperial College Press 57 Shelton Street Covent Garden London WC2H 9HE Distributed by World Scientific Publishing Co. Pte. Ltd. 5 Toh Tuck Link, Singapore 596224 USA office: 27 Warren Street, Suite 401-402, Hackensack, NJ 07601 UK office: 57 Shelton Street, Covent Garden, London WC2H 9HE British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. FUNDAMENTALS AND APPLICATIONS OF BIOPHOTONICS IN DENTISTRY Series on Biomaterials and Bioengineering — Vol. 4 Copyright © 2007 by Imperial College Press All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the Publisher. For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to photocopy is not required from the publisher. ISBN 1-86094-704-2 Printed by Fulsland Offset Printing (S) Pte Ltd, Singapore PREFACE Biophotonics is revolutionizing the field of medicine, biology and chemistry and creating a new breed of medical engineers while at the same time getting engineers a taste of medicine. From an engineer's perspective, biophotonics is the application of photonics - the technology of generating and harnessing packet of light energy called photons - to image, detect and manipulate biological materials. In biology the understanding of molecular mechanisms, function of proteins and molecules has seen great new advances. In biomedical engineering detection, diagnoses and treatment targeting both macro-objects like the teeth or bone as well as micro-objects such as bacteria have seen better understanding through the development of new tools. There is another school of thought, albeit much smaller that defines biophotons as a quantum of light that is permanently and continuously emitted by all living systems. For example, humans emit radiation similar to a blackbody with maximum power being emitted at a wavelength of about 10 um. Regardless of definition, biophotonics is a multi-disciplinary field that bridges engineering, the sciences and medical fields. This diversity of sciences and technologies usually makes for challenging and interesting projects - that could be driven by engineers and clinicians alike. However, there is still the need that clinicians understand some concepts in photonics while engineers get a feel for medical and bio-chemical sciences. Towards this end, this book is written by persons from different fields such as engineering, sciences and medical field. The book is roughly divided into two sections - the first introduces the readers to some basic concepts in the field of biophotomechanics. As the name suggests, this topic looks at the use of optical methods (photo) for the study of mechanical behaviour (mechanics) of biological objects v VI Preface in the macro-scale such as teeth and bone. The next chapter introduces some recent techniques on bioimaging such as fluorescence microscopy and optical coherence tomography amongst others. Chapter 4 introduces spectroscopy - a erstwhile tool in biophotonics while chapter five deals with lasers and laser tissue interaction. Finally Chapter 6 provides an introduction to Photodynamic therapy a growing technology for targeted application of photonic radiations. The second half of the book applies some of these basic concepts to the field of dentistry to highlight some of the features and adaptation of photonics in this area. Dental photomechanics provides an understanding of mechanical and thermal characteristics of dentine and permits a better understanding of the causes of damage and failure of certain treatments. Chapter 8 uses spectroscopic methods specifically Micro-Raman spectroscopy for a better understanding of the materials aspects of dentine and adhesives. The next chapter on Dental and Oral Optics describes tools and techniques for imaging and optical properties of dentine and enamel. The final chapter on fiber optic sensors explores new sensor development for effective and fast ways of detecting and diagnosing oral bacteria. We, as editors, feel that the book would be just as informative for final year undergraduate, graduate students in bioengineering as it would to clinicians and dental surgeons to gain a better understanding of a process or treatment. Anil Kishen and Anand Asundi CONTENTS Preface FUNDAMENTALS Chapter 1 Introduction 1.1. Introduction 1 1.2. Definition and Significance 2 1.3. Classification of Biophotonics in Dentistry 3 1.3.1. Diagnostic 3 1.3.2. Therapeutic 4 1.3.3. Research 5 1.4. Future Opportunities 7 1.5. Scope of this Book 8 Chapter 2 Photomechanics 2.1. Introduction to Mechanics 9 2.1.1. Force and Stress 10 2.1.2. Deformation and Strain 13 2.1.3. Stress-Strain Equations 16 2.2. Basic Optical Engineering 16 2.2.1. Geometric Optics 17 2.2.2. Physical (Wave) Optics 19 2.2.3. Photonics 27 2.3.. Photomechanics 30 2.3.1. Moire and Grid Methods 31 2.3.2. Speckle Methods 40 2.3.3. Photoelasticity 46 2.3.4. Holography 54 2.3.5. Digital Photomechanics 58 2.4. Concluding Remarks 60 VI! Vlll Contents Chapter 3 Biomedical Imaging 3.1. Introduction 64 3.2. Non-Linear Optical Microscopy (NLOM): 65 Multiphoton Excited Fluorescence (MPEF) and Second Harmonic Generation (SGH) 3.2.1. Principles of NLOM 66 3.2.2. Development and Applications 69 of NLOM 3.2.3. NLOM in Dentistry 72 3.3. Optical Coherence Tomography (OCT) 73 3.3.1. Principles of OCT 74 3.3.2. Developments and Applications 75 of OCT 3.3.3. OCT in Dentistry 80 3.4. Coherent Anti-Stokes Raman Scattering 82 (CARS) and Modulated Imaging (MI) 3.5. Fluorescence Contrast Enhancement 85 3.6. Concluding Remarks 87 Chapter 4 Spectroscopy 4.1. Introduction 93 4.2. Molecular Orbitals and Transitions 94 4.3. Transition Dipole Moment 99 4.4. Spin Selection Rule 100 4.5. Franck-Condon Principle 102 4.6. Jablonski Diagram 104 4.7. Stokes Shift 107 4.8. Spectrophotometry 108 4.9. Fluorescence Intensity and Lifetime 110 4.10. Spectrofluorimetry 112 4.11. Fluorescence Quenching 115 4.12. Fluorescence Resonance Energy Transfer 116 (FRET) 4.13. Fourier Transform Infrared (FTIR) 117 Spectroscopy 4.14. Concluding Remarks 120 Contents IX Chapter 5 Lasers and Laser Tissue Interaction 5.1. Introduction 123 5.2. Laser Basics 124 5.2.1. Characteristics of Lasers 126 5.3. Light Propagation in Tissue 128 5.4. Optical Imaging and Diagnosis 131 5.4.1. Optical Imaging 131 5.4.2. Optical Spectroscopic Diagnosis 133 5.5. Optical Processing of Tissue 141 5.5.1. Photothermal Effects 142 5.5.2. Photomechanical Effects 144 5.5.3. Photochemical Effects 144 5.5.4. Applications of Laser Processing 145 of Tissue 5.6. Concluding Remarks 148 Chapter 6 Mechanisms and Applications of Photodynamic Therapy 6.1. Historical Background 154 6.2. Photosensitizers 155 6.3. Light Applicators 156 6.4. PDT Mechanisms 161 6.4.1. Photophysics and Photochemistry 161 6.4.2. Biological Effect 162 6.5. PDT Dosimetry 166 6.6. Progress in Clinical Application 167 6.6.1. Non-Malignant Diseases 168 6.6.2. Malignant Diseases 169 6.7. PDT in Dentistry 175 6.7.1. Technical Challenges 175 6.7.2. Current Status 176 6.8. Concluding Remarks 177