A human has naturally 32 teeth in their mouth and, as with all aspects of the human body, these can be subject to disease. Despite significant advances since the wide spread adoption of fluoride dental decay is still the second most common disease around the world, after the common cold, as ranked by the World Health Organisation. Detection methods for early disease are, however, very crude. The major tool is the dentist's eyes where he is initially looking for a white spot on a white background. As the lesions develop they can be seen on x-rays but at this stage the loss of material from the tooth is normally such that "drilling and filling" is the only option. The challenge in this research is to develop new methods to detect disease in its earliest stages, when through, careful cleaning and high fluoride doses, the teeth can be persuaded to re-mineralise, frequently then being stronger than before the outbreak of the disease.
The methods explored include Multiphoton Imaging, Fibre Optic Confocal, OCT, Fluorescence Spectroscopy, Dual Wavelength Spectrophotometry, Ultra-sound. Prof Girkin is currently leading an EPSRC based project to build a clinical instrument based upon infrared imaging supported by a granted patent.
The work started when Prof Girkin lead the applications team at the Institute of Photonics, Strathclyde University where Dr Simon Poland (now at KCL) and Dr David Hughes (now at Dundee University) gained their PhDs working in this area. External collaborators include in Dundee Prof Nigel Pitts, Dr Andrew Hall, Dr Chris Longbottom, Dr Sandy Cochran IMSAT Dundeefor the ultra-sound work, Prof Anderson Gomes, Universidade Federal de Pernambuco, Brazil, Prof Denise Zezell IPEN, Sao Paulo, Brazil, Prof Maria Simionato, Dr Adriana Riberio University of Sao Paulo, Department of Microbiology . As stated above light has always been a major tool for the dentist and the research has been based upon this premise only using modern optical technologies to enhance the information being supplied to the examiner (See Ref1). The aim is not a "go/no go" instrument but something that provides additional information for the skilled user.
The initial work was based around the use of multiphoton microscopy (internal link to MP page) to build up a three dimensional image of the tooth (see Ref 2,3 ) This revolutionary technique enables the dentist to see right into the tooth but is complex to use and not suitable for general dental practitioners. The image shows an area of disease given a false colour of green with health tissue appearing as blue.
Fibre optic confocal microscopy (FOCOM)
By using conventional confocal microscopy techniques, optical slices of materials can be obtained, incorporating fibre optics in to the system allows portability of the scan head. FOCOM has been demonstrated previously in the department (Ref 4,5,6) as an exciting method of detecting dental caries. By scanning a micro-optic after the fibre depth profiles through the tooth can be recorded with the separation between peaks giving the depth of the lesion. The work is now concentrating on creating the first hand held FOCOM device for in-vitro detection.
Optical coherence tomography (OCT)
OCT is a relatively new technology which modifies the standard Michelson interferometer in order that depth profiles can be recorded of an object. OCT has been demonstrated for use with dental samples (Ref 7) and the work here concentrates on creating a suitable clinical device for monitoring dental erosion.
Although the fibre optic and OCT methods provide a way of measuring the depth of the lesion or erosion we have also been exploring the use of dental fluorescence in an attempt to provide some diagnostic information in a single visit. Clinicians divide the so called “white spot lesions” into three classes, shiny, dull and brown and we have been using spectroscopic analysis of fluorescence excited with a blue laser diode to explore options for aiding the dentist in this matter (see Ref 8). We have found that by examining the correct spectral region we are able to quantify the disease process (see Ref 9,10,11). We have also be examining the use of time resolved imaging methods to obtain further information from samples (Ref 12).
Dual Wavelength Photospectroscopy (DWPS)
As a further advance on the spectroscopic theme we have been examining ways of determine the tooth’s vitality. Most people who have had the misfortune to go to hospital will no doubt have had their blood oxygen levels monitored using a pulse oximeter. Such a device uses DWPS to calculate levels of oxygenated and de-oxygenated blood through the absorption of light at different wavelengths. This technology has been approached for use in testing pulp vitality of teeth however a proven technology has not yet been produced.
Ultrasound has been used as a method for the inspection of materials since the start of the last century, and as a non-invasive medical tool since the 1950's. However, it has never matured as a technology for dental diagnosis, even though there have been studies carried out in to this since the late 1960's. By using novel top of the range high frequency transducers, the work carried out here has broke through resolution barriers previously noted. Due to the high resolution, three dimensional images of the inner macro-structure of the tooth have been rendered as well as thickness measurements (useful for erosion studies) (Ref 13).
Replacement of Dental Curing Lights
In some earlier work the team also developed a blue curing light based upon the then new InGaN LEDs (see Ref 14,15 ). This device had several advantages over the more conventional halogen sources and a commercial product was available shortly afterwards.
The work has been reported on national television and radio and formed a display under the title of the "Dental Detectives" in the Science Museum in London in 2004.
1. "A review of other potential diagnostic modalities for caries" A Hall, J M Girkin Journal of Dental Research 83 89-94 (2004)
2. "Two-photon Imaging of Intact Dental Tissue", J M Girkin, A F Hall, S Creanor, Dental Caries 2 317-325 (2000)
3. "Macroscopic multiphoton biomedical imaging using semiconductor saturable Bragg reflector modelocked lasers", J.M. Girkin, D. Burns, and M.D. Dawson, Proc. SPIE, 3616 , 92 (1999 )
4. " Application of a Novel Confocal Imaging Technique for the Early Detection of Dental Decay" Christel Rousseau , John M. Girkin, Shilpa Vaidya, Andrew F. Hall, John C. Whitters and Steve L. Creanor Proc SPIE 3064 p212-218 (2002)
5. "Fibre Optic Confocal Microscopy of Early Caries Lesions" J M Girkin, A Hall, R Strang, S Creanor, C J Whitters, C Rousseau, accepted for Early Detection of Caries 3 June (2003)
6. "Development of fibre-optic confocal microscopy for detection and diagnosis of dental caries" C. Rousseau, S Poland, A. F. Hall and C. J. Whitters and J. M. Girkin Caries Research 41 245-251 (2007)
7. "Evaluation of Enamel Dental Restoration Interface by Optical Coherence Tomography" L. S. A. de Melo, R. E. de Araujo, A. Z. Freitas, D. Zezell, N. D. Vieira-Jr, J. Girkin, A. Hall, M. T. Carvalho and A. S. L. Gomes, Journal of Biomedical Optics 10(6), 064027, (2005)
8. "The effect of dentine on fluorescence measurements of enamel lesions in vitro" C Rousseau, S Vaidya, SL Creanor, AF Hall, JM Girkin, CJ Whitters, R Strang Caries Research 36 381-385 (2002)
9. "Fluorescence spectroscopy of natural carious lesions", AF Hall, A CRibeiro, JM Girkin, R Strang, SL Creanor, CJ Whitters, C Rousseau, Early Detection of Caries 3 June (2003)
10. "A preliminary investigation of a spectroscopic technique for the diagnosis of natural caries lesions" Adriana Ribeiro , Christel Rousseau , John Girkin , Andrew Hall , Ronald Strang, C John Whitters , Stephen Creanor, Anderson S.L. Gomes Accepted Journal of Dental Research 33, 73, (2005)
11. "Blue laser diode excited fluorescence spectroscopy of natural carious lesions" J M Girkin, C Rousseau, A F Hall, R Strang, C J Whitters, S L Creanor, A CRibeiro PROC SPIE April (2004)
12. Time-correlated single-photon counting fluorescence lifetime confocal imaging of decayed and sound dental structures with a white-light supercontinuum source G. McConnell, J.M. Girkin, S. M. Ameer-Beg, P.R. Barber, B. Vojnovic, Avijit Banerjee, Timothy Watson, Richard Cook Journal of Microscopy 225, 126-136 (2007)
13. "Investigation of dental samples using a 35 MHz focussed ultrasound piezocomposite transducer" D.A. Hughes, J.M. Girkin, S. Poland, C. Longbottom, T.W. Button, J. Elgoyhen, H. Hughes, C. Meggs, S. Cochran, , Ultrasonics 49, 212, (2008)
14. "Curing of Dental Composites by use of InGaN Light-emitting Diodes", C J Whitters, J M Girkin, J J Carey Optics Letters 24 67-68 (1999)
15. "In vitro evaluation of the InGaN LED as a dental curing device" J C Whitters, R Strang, J M Girkin, J J Carey, J Dent Res 78 1073-1075 (1999)