Elsevier

Journal of Dentistry

Volume 38, Issue 10, October 2010, Pages 788-795
Journal of Dentistry

Occlusal caries detection by using thermal imaging

https://doi.org/10.1016/j.jdent.2010.06.010Get rights and content

Abstract

Objectives

To explore the applicability of thermal changes associated with dehydration for the detection and quantification of early tooth decay on occlusal surfaces using infrared imaging.

Methods

A total of 72 sites on 25 human teeth with various degrees of natural demineralisation have been used. Continuous evaporation of water inside the pores by pressurised air-drying is used to produce a thermodynamic response on the tooth surface. The temporal profile of the temperature will depend on the amount of water at each position and this is studied in relation to the degree of porosity and the lesion severity. The area enclosed by the time–temperature curve, ΔQ, was then used for quantification of the lesion.

Results

Maps of ΔQ were obtained and histological examinations were performed for all teeth. A detection sensitivity of 77% and specificity of 87% for areas that are either sound or have a histological E1 lesion, 87% and 72% for areas that have either an E2 or EDJ lesion, and 58% and 83% for areas that have a lesion reaching the dentin was found using this method.

Conclusions

Thermal imaging shows the ability to discriminate, in vitro, between (a) either areas that are sound or with a lesion on the outer half of the enamel and (b) areas with a lesion extending to the middle of the enamel or deeper. However, variations of the temperature in an open mouth and humidity due to respiration can potentially challenge the ability of using this technique in vivo and this requires further investigation.

Introduction

Dental caries is a dynamic disease that is still amongst the most prevalent diseases in the world. It is characterised by tooth demineralisation that initially leads to increased surface enamel porosity. Leaving these lesions untreated can result in the formation of cavities that can reach the dentin and pulp and eventually cause tooth loss. Occlusal and aproximal surfaces are amongst the most susceptible sites of demineralisation due to acid attack from bacterial by-products in the biofilm.1

The use of preventive agents to inhibit or reverse the demineralisation process is advised on the detection of lesions at an early stage.2, 3, 4, 5 It is therefore desirable to identify and manage incipient caries on time in order to avoid invasive clinical intervention. However, detecting early lesions is a difficult diagnostic task and quantitative techniques assisting in the decision-making are required. Monitoring of therapeutic success after interventions is also challenging requiring relatively large changes in lesions before they can be reliably detected using most of the currently available diagnostic aids.

The initial stage of the disease is characterised by dissolution of hydroxyapatite and this leads to a non-uniform mineral loss and an increase in enamel porosity—this is commonly known as a white spot lesion.5 Therefore, estimating the amount of enamel surface porosity or mineral loss can assist in the detection and quantification of early tooth demineralisation non-invasively.

Radiographical methods are not ideal due to the patient exposure to ionising radiation and their lack of sensitivity at very early stages of the disease.6, 7, 8 Electrical caries’ monitoring has demonstrated good performance for single point measurements9; however, imaging methods have the advantage of being more illustrative and allow performing relative measurements with respect to other sites within the same tooth. Current imaging methods are based on the observation of changes in the light transport within the tooth, namely absorption, scattering10, 11, 12 and fluorescence.10, 11, 12 In general, porous media scatters away more light than uniform media and stain within the tooth tends to absorb light; stain is therefore a strong confounding factor in caries detection with visible imaging techniques. This is of particular interest when looking at occlusal surfaces where uptake of stain may be an indicative of lesion arrest.

Continuous evaporation of water accumulated inside the pores produces a thermodynamic transient on the tooth surface that will last until a new thermal equilibrium is reached when the tooth dries. The temporal profile of the temperature will depend on the amount of water stored inside the lesion as well as the shape of the lesion and can therefore contain information related to its degree of porosity and severity. Thermal imaging for caries’ detection has been little explored in the past. Kaneko et al.13 reported a method to quantify tooth decay on flat tooth surfaces using an infrared camera; the method was tested with a set of 18 extracted incisors with artificial lesions. Their method relies on sensing the temperature time-decay due to water evaporation from the tooth surface as it is dried by an air-jet. A similar study was reported a year later using thermal imaging to look at the temperature time-decay immediately after a pulse of heat delivered onto flat tooth surfaces using a xenon flash light; 19 incisors with artificial lesions were used in these experiments.14, 15 Such artificial lesions may exhibit greater porosity than natural lesions where the dynamic process of de- and re-mineralisation has occurred.

Recently, another technique was proposed to identify dental carious tissues using frequency-domain laser infrared photothermal radiometry (PTR).16, 17, 18 PTR uses the optical to thermal energy conversion resulting from tooth laser absorption and studies the changes observed in the thermal wave diffusion inside teeth with various degrees of demineralisation. The technique appears promising for the detection of pit and fissure caries up to 5 mm below the surface; however, according to the authors, it is less appropriate for imaging.

Although thermography has shown to be useful in the evaluation of smooth surface caries, no evidence is found of such evaluation at occlusal surfaces. The purpose of this study is to assess the performance of thermal imaging for quantifying natural demineralisation, both early and advanced, on occlusal surfaces.

Section snippets

Teeth

A set of 25 extracted teeth (premolars and molars) with different natural lesion severities were used for this study. In order to have independent measures at a tooth level, a uniform distribution of lesion severities across the 25 samples used in this experiment was selected based on their ICDAS code; having 5 teeth per codes 1–5. The teeth were collected from the Oral Health Centre of the University of Indiana, USA. Soft tissues were removed from the collected teeth and the teeth were

Results

Infrared video sequences were obtained from a total of 25 teeth. In addition, a total of 72 histological slices with different lesion severities were selected and lesions were identified as either from the surface or the fissure pattern. Note that lesions reaching the dentin were only in the fissures. Two random groups of 48 samples were then formed, both balanced for severity and location of the lesion by sorting the data from the tooth slices ascending in histological score and divided per

Discussion

Every object above zero Kelvin will radiate infrared (IR) electromagnetic energy as described by the black-body radiation theory.19 This energy can be detected with an IR camera and temperature measurements can be performed. Models describing the thermodynamics of the drying process of porous media have been reported in the past.20, 21

Tooth temperature will be influenced by a number of factors such as ambient and body temperature, breath and moisture. The amount of water stored inside the tooth

Conclusions

Our investigations demonstrate that thermal imaging has the ability to discriminate between (a) areas that are either sound or with an early lesion on the outer half of the enamel and (b) areas with lesions extending to the middle of the enamel or deeper. This could potentially be useful for in vitro measurements where other methods such as radiography have low sensitivity to early tooth decay but high sensitivity to decay at E2 level and above. However, the viability of taking in vivo

Acknowledgements

The authors would like to acknowledge access to the infrared camera used for the experiments to Dr. Mark Dickinson and Dr. David Binks from the Photon Science Institute at the University of Manchester. We thank Prof. Kim Ekstrand and Prof. David Ricketts for scoring the histological slices. We also thank Prof. Helen Worthington for useful discussions on statistical analysis. Dr. Iain Pretty is funded by a NIHR Clinician Scientist Award.

References (21)

  • C.A. Murdoch-Kinch et al.

    Minimally invasive dentistry

    The Journal of the American Dental Association

    (2003)
  • E.A.M. Kidd et al.

    What constitutes dental caries? Histopathology of carious enamel and dentin related to the action of cariogenic biofilms

    Journal of Dental Education

    (2004)
  • K.J. Anusavice

    Present and future approaches for the control of caries

    Journal of Dental Education

    (2005)
  • L.J. Walsh

    The current status of low level laser therapy in dentistry. Part 2. Hard tissue applications

    Australian Dental Journal

    (1997)
  • A. Fejerskov et al.
  • A. Wenzel et al.

    Accuracy of visual inspection, fiber-optic transillumination, and various radiographic image modalities for the detection of occlusal caries in extracted non-cavitated teeth

    Journal of Dental Research

    (1992)
  • V. Machiulskiene et al.

    A comparison of clinical and radiographic caries diagnoses in posterior teeth of 12-year-old Lithuanian children

    Caries Research

    (1999)
  • D.F. Côrtes et al.

    An in vitro comparison of the ability of fibre-optic transillumination, visual inspection and radiographs to detect occlusal caries and evaluate lesion depth

    Caries Research

    (2000)
  • R.P. Ellwood et al.

    In vitro assessment of methods of applying the electrical caries monitor for the detection of occlusal caries

    Caries Research

    (2004)
  • E. de Josselin de Jong et al.

    A new method for in vivo quantification of changes in initial enamel caries with laser fluorescence

    Caries Research

    (1995)
There are more references available in the full text version of this article.

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