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Recent Aids in diagnosis of dental caries

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Recent Aids in Diagnosis of Dental Caries

RECENT AIDS IN DIAGNOSIS OF DENTAL CARIES
Various methods are being used for diagnosis of dental caries 1] Radiographic techniques a) Digital b) Xeroradiography 2] Electronic caries monitor (ECM) 3] Detection systems based on electrical current

measurement 4] Optical caries detection techniques a) Optical coherence tomography (OCT) b) Polarized Raman Spectroscopy (PRS) 5] Enhanced visual techniques a) Fiber-Optic TransIllumination (FOTI) b) Digital (DIFOTI) 6] Fluorescent techniques a) Visible light fluorescence - QLF b) Laser fluorescence — DIAGNODent c) Infrared fluorescence. 7] Transillumination with Near -Infrared light. 8] Near-Infrared reflectance imaging. 9] Terahertz Pulse Imaging. 10] Multiphoton Imaging. 11] Time-Correlated Single- Photon counting fluorescence Lifetime Imaging Imaging Fiber-Optic TransIllumination

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Caries diagnosis is the art or act of identifying a disease from its signs and symptoms.

TO DIAGNOSE OR TO DETECT? The art of diagnosis rests on the assumption that diseases can be identified from their signs and symptoms. Diagnostic reasoning is an extremely complex process that involves elements of simple and pattern recognition,

probabilistic

considerations

hypothetico -deductive

thinking. Diagnostic decision making is a balancing act. The clinician must not overlook diseases in need of treatment, and, at the same time, he must not make a diagnosis when it is not warranted. The inherent complexity of the diagnostic process explains why nobody has ever been able to unveil how clinicians think when they examine their patients and seek the right diagnosis. During the diagnostic process the clinician attempts to assign a label to a set of signs and symptoms brought together from various sources (e.g. interview, clinical examination and

supplementary tests). This information is used to assess the probability that the patient has a certain condition. In medicine the diagnosis is a pivotal step for making treatment decisions. Therefore, the diagnostic step has sometimes been referred to as ‗a me ntal resting place on the way to intervention‘. Figure 8.1 illustrates the classical diagnostic decision process as outlined above. 2 6

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FIG 8.1: THE CLASSICAL DIAGNOSTIC DECISION PROCESS

Our understanding of the caries process has continued to advance, with the vast majority of evidence supporting a dynamic process which is affected by numerous modifiers tending to push the mineral equilibrium in one direction or another, i.e. towards remineralisation or demineralisation. With this greater understanding of the disease, comes an opportunity to promote ‗preventative‘ therapies that

encourage the remineralisation of non -cavitated lesions resulting in inactive lesions and the preservation of tooth structure, function and aesthetics. Central to this v ision is the ability to detect caries lesions at an early stage and correctly quantify the degree of mineral loss, ensuring that the correct intervention is instigated. The failure to detect early caries, leaving those detectable only at the deep enamel, or cavitated stage has resulted in poor results and outcomes for remineralisation therapies. A range of new detection systems have been developed and are either

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currently available to practitioners or will shortly be made so. These detection systems are the refore aimed at

augmenting the diagnostic process by facilitating either earlier detection of the disease or enabling it to be quantified in an objective manner.

Visual inspection, the most ubiquitous caries detection system, is subjective. Assessment of features such as colour and texture are qualitative in nature. These assessments provide some information on the severity of the disease but fall short of true quantification. They are also limited in their detection threshold and their ability to detect early, non cavitated lesions restricted to enamel is poor. It is this ability to quantify and/or detect lesions earlier that the novel diagnostic systems offer to the clinician.

Novel

diagnostic

systems

are

based

upon

the

measurement of a physical signal — these are surrogate measures of the caries process. Examples of the physical signals that can be used in this wa y include X-rays, visible light, laser light, electronic current, ultrasound, and

possibly surface roughness. For a caries detection device to function, it must be capable of initiating and receiving the signal as well as being able to interpret the strength of the signal in a meaningful way. Table 2 demonstrates the physical principles and the detection systems that have taken advantage of them. 2 7

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CLINICAL METHODS: Visual detection of caries was described as early as 1801, in a book entitled ―Skinner: A Treatise of Human Teeth.‖ One of the most important early contributions to diagnosis of dental caries came from G.V. Black. Black was among the first to describe, in explicit detail, methods of visual and tactile detection of dental caries as part of an oral examination, including the cleaning and drying of teeth and the use of explorers, that still are in use 100 years later. For detection of proximal caries, Black de scribed the use of separators to directly visualize areas of concern and the use of ligatures (dental floss) passed through the contact point to detect surface roughness and breakdown. Black‘s

diagnostic methods laid the groundwork for future criteria for the detection of dental caries. Radike described detailed criteria for the visual and tactile detection of dental caries that until recently were used widely in epidemiologic and

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clinical research. They relied heavily on an explorer ―catch‖ for detection o f caries on occlusal surfaces and recorded cavitated lesions, but not noncavitated lesions. Since the days of Black, our diagnostic understandings have been far more advanced than simply diagnosing caries at the level of cavitation. The latest contribution to visual diagnostic criteria for caries is the International Caries Detection development and of Assessment which Criteria a (ICDAS), joint effort the of

involved

international cariologists. ICDAS was designed to facilitate the standardized diagnosis of caries on all tooth surfaces at all stages of severity. An updated version of ICDAS (ICDAS II) has been well accepted and been used in clinical studies with as good well intraexaminer as and interexaminer sensitivity and

agreement, specificity 2 8 .

satisfactory

[1] RADIOGRAPHIC METHODS: Less than six months after W.C. Roentgen‘s discovery of the x-ray, William J. Morton, a New York physician, was one of the first to report that x -rays could have dental applications. More recent developments include higher speed film and digital radiography. Current digital imaging technologies generate images whose diagnostic yield may equal, but not necessarily exceed, that of images obtained by using conventional film 2 8 .

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A] DIGITAL RADIOGRAPHS Digital radiography has offered the potential to

increase the diagnostic yield of dental radiographs and this has manifested itself in subtraction radiography. A digital radiograph (or a traditional radiograph that has been digitised) is comprised of a number of pixels. Each pixe l carries a value between 0 and 255, with 0 being black and 255 being white. The values in between represent shades of grey, and it can be quickly appreciated that a digital radiograph, with a potential of 256 grey levels has significantly lower resolution than a conventional

radiograph that contain millions of grey levels. This would suggest that digital radiographs would have a lower diagnostic Research yield has than that of traditional with radiographs. and

confirmed

this;

sensitivities

specificities of digital radiographs being significantly lower than those of regular radiographs when assessing small proximal lesions.

However, digital radiographs offer the potential of image enhancement by applying a range of algorithms, some of which enhance the white end of the grey scale (such as Rayleigh and hyperbolic logarithmic probability) and others the black end (hyperbolic cube root function). When these enhanced radiographs are assessed their

diagnostic performance is at least as good as conventional radiographs, with reported values of 0.95 (sensitivity) and 0.83 (specificity) for approximal lesions. See Fig. 8.2 for an example of this enhancement. When these findings are
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considered, one must remember that digital radiographs offer a decrease in radiographic dose and thus offer additional benefits than diagnostic yield. Digital images can also be archived and replicated with ease. 2 7

FIG 8.2: COMPARISON OF REGULAR AND ENHANCED DIGITAL RADIOGRAPHS. (A) DIGITAL RADIOGRAPH, (B) ENHANCED RADIOGRAPH WHERE THE

INTERPROXIMAL LESIONS BETWEEN FIRST MOLAR AND SECOND PREMOLAR CAN BE SEEN MORE

CLEARLY.

As described above, using digital radiographs offers a number of opportunities for image enhancement, processing and manipulation. One of the most promising technologies in this regard is that of radiographic subtraction which has been extensively evaluated for both the detection of caries and also the assessment of bone loss in periodontal studies. To perform subtraction radiography the images should be taken using either a geometry stabilising system (i.e. a bitewing holder) or software has been employed to register

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the images together, then any differences in the pixel values must be due to change in the object .

Two radiographs of the same object can be compared using their pixel values.

The value of the pixels from the first object is subtracted from the second image.

If there is no change, the resultant pixel will be scored 0; any value that is not 0 must be attributable to either the onset or progression of demineralisation, or regression.

Subtraction images therefore emphasise this change and the sensitivity is increased. It is clear from this description that the radiographs must be perfectly, or as close to perfect as possible, aligned. Any discrepancies in alignment would result in pixels being incorrectly

represented as change. Several studies have demonstrated the power of this system, with impressive results for primary and secondary caries. However, uptake of this system has been low, presumably due to the need for well aligned images. Recent advances in software have enabled two images with moderate alignment to be correctly aligned and then subtracted. This may facilitate the introduction of this technology into mainstream practice where such

alignment algorithms could be built into practice software currently used for displaying digital radiographs. An example of a subtraction radiograph is shown in Fig. 8.3. 2 7

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FIG. 8.3: EXAMPLE OF A SUBTRACTION OF TWO DIGITAL RADIOGRAPH BITEWING SHOWING RADIOGRAPHS. PROXIMAL LESION (A) ON

MESIAL SURFACE OF FIRST MOLAR, (B) FOLLOW UP RADIOGRAPH TAKEN 12 MONTHS LATER, (C) THE AREAS OF DIFFERENCE BETWEEN THE TWO FILMS ARE SHOWN AS BLACK, I.E. IN THIS CASE THE PROXIMAL LESION HAS BECOME MOR E

RADIOLUCENT AND HENCE HAS PROGRESSED

B] XERORADIOGRAPHY: Mechanism : Xeroradiography is an electrostatic

process which uses an amorphous selenium photoconductor material, vacuum deposited on an aluminium substrate, to form a plate. The plate, enclosed in light tight cassette, may be likened to films used in halide-based technique. The key functional steps in the process involve the sensitization of the photoconductor plate in the charging station by

depositing a uniform positive charge on its surface with a
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corona-emitting device called scorotron. That is, the

uniform electrostatic charge placed on a layer of selenium is in electrical contact with a grounded, conductive

backing. In the absence of electroma gnetic radiation, the photoconductor remains nonconductive and with its uniform electrostatic charge when radiation is passed through an object which will vary the intensity of the radiation, observed Rawls and Owen. The photoconductor will then conduct its electrostatic charge into the grounded base in proportion to the intensity of the exposure. After charging, the cassette is inserted into a thin polyethylene bag to protect the cassette and plate from saliva. The generated latent image is developed using throu gh liquid an toner. electrophoretic The process

development

process

involves the migration to and subsequent deposition of toner particles suspended in a liquid onto an image reception under the influence of electrostatic field forces. That is, by applying negatively charged powder (toner) which is attracted to the residual positive charge pattern on the photoconductor, the latent image is made visible and the image can be transferred to a transparent plastic sheet or to paper. The toner is thereafter fixed to a receiver sheet onto which a permanent record is made. The plate is then cleaned of toner for reuse. 3 0

POSSIBLE ADVANTAGES OF XERORADIOGRAPHY ELIMINATION OF ACCIDENTAL FILM EXPOSURE : the reasons being that large light intensity is required for photoconduction and even when there is exposure, the
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charged area intrinsically gets erased. As a result, there is minimal need for storage for film protection during processing.

HIGH

RESOLUTION :

Xeroradiography

has

excellent

characteristics of the forces around the electrostatic charges which form the latent image. The strengths of the fields are smaller at the centre of charged ones than at the edge, resulting in a greater number of powder pa rticles

collections peripherally than in central charged areas. This greatly enhances local contrast which, in turn, improves resolution and image quality.

SIMULTANEOUS TISSUES

EVALUATION

OF

MULTIPLE

EASE OF REVIEWING USE OF REFLECTED OR TRANSMITTED LIGHT is allowed by xeroradiography. This is because the image can be mounted either in a transparent plastic sheet or on opaque paper.

HIGHER LATITUDE OF EXPOSURE FACTORS : little image quality change in xeroradiography will require large kilo-voltage variations. The end point is that chances of incorrect exposure and retakes are highly slim.

BETTER

EASE

AND

SPEED

OF

PRODUCTION

EECONOMIC BENEFIT REDUCED EXPOSURE TO RADIATION HAZARDS WIDE APPLICATIONS
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POSSIBLE DISADVANTAGES OF XERORADIOGRAPHY: TECHNICAL DIFFICULTIES : Both the amount of

radiation exposure and the thickness of xeroradiographic plate are linearly proportional. An increased thickness of the plate will increase the speed, because of the greater likelihood that the x-rays passing through the photo conducting layer will interact.

FRAGILE SELENIUM COAT : the amorphous selenium photoconductor However, the is a layer highly is electrically quite stable layer.

easily

scratched.

Notwithstanding, it has been observed that the surface shows good resistance to scratching, chipping and abrasion. As a result, placement and retention in confined area like the mouth would possibly be difficult.

SLOWER SPEED : comparatively, xeroradiography has a lower speed than halide radiographs. This can be signific ant when dealing with intraoral films.
30

[2] ELECTRONIC CARIES MONITOR (ECM): MECHANISM: The ECM device employs a single, fixed frequency alternating current which attempts to measure the ‗bulk resistance‘ of tooth tissue (see Fig. 5). This can be undertaken at either a site or surface level. When measuring the electrical properties of a particular site on a tooth, the ECM probe is directly applied to the site, typically a fissure, and the site measured. During the 5 s measurement
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cycle, compressed air is expressed fro m the tip of the probe and these results in a collection of data over the

measurement period, described as a drying profile that can provide useful information for characterising the lesion. An example of this is shown in Fig. 8.4 While it is generally accepted that the increase in porosity associated with caries is responsible for the mechanism of action for ECM, there are some points to consider: (1) Do electrical measurements of carious lesions measure the volume of the pores, and if so, is it the total pore volume or just a portion, perhaps the superficial portion, that is measured? (2) Do electrical measurements measure pore depth? If this is the case, what happens during remineralisation where the superficial layer ma y

remineralise, leaving a pore beneath? (3) Is the morphological complexity of the pores a factor in the measurement of conductivity? There are also a number of physical factors that will affect ECM results. These include such things as the temperature of the tooth, the thickness of the tissue, the hydration of the material (i.e. one should not dry the teeth prior to use) and the surface area. 2 7

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FIG. 8.4: A DEMONSTRATION OF AN ECM PROFILE OBTAINED FROM A PRIMARY ROOT CARIES LESION IN VITRO DEMONSTRATING THE SITES ASSESSED.

FIG.8.5 – THE ECM DEVICE (VERSION 4) AND ITS CLINICAL APPLICATION. (A) THE ECM MACHINE, (B) THE ECM HANDPIECE, (C) SITE SPECIFIC

MEASUREMENT TECHNIQUE, (D) SURFACE SPECIFIC MEASUREMENT TECHNIQUE.

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The reproducibility of the device has been assessed in a number of publications and has been rated as good to excellent for both measurement techniques. A clinical trial has been undertaken using the ECM device on root caries, and the successful outcome of this study suggests t hat dentine may be a more suitable tissue for ECM. The study assessed the effect of 5000 ppm fluoride dentifrice against 1100 ppm on 201 subjects with at least 1 root caries lesion. These were site specific measurements taken using the airflow function of the ECM unit. After 3 and 6 months, there was statistical difference between the two groups, with the higher fluoride group showing a better

remineralising capability than the lower fl uoride paste users21 (see Fig 8.6). This is good evidence to suggest that ECM is capable of longitudinal monitoring and that clinicians may be able to employ the device to monitor attempts at remineralising, and thus potentially arresting, root caries lesions in their patients. 27

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FIG. 8.6: ECM VALUES FROM A ROOT CARIES STUDY USING HIGH AND LOW CONCENTRATIONS THE INCREASING OF ECM

FLUORIDE

DENTIFRICES.

VALUES RELATE TO A REDUCTION IN POROSITY AND INCREASE IN ELECTRICAL RESISTANCE.

A further application of electronic monitoring of caries is that of Electrical Impedance Spectroscopy or EIS. Unlike ECM which uses a fixed frequency (23 Hz), EIS scans a range of electrical frequencies and provides information on capacitance and impendenc e among others. This process provides the potential for more detailed analysis of the structure of the tooth to be developed, including the presence and extent of caries.
27

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[3] DETECTION SYSTEMS BASED ON ELECTRICAL CURRENT MEASUREMENT : Every material possesses its own electrical signature; i.e. when a current is passed through the substance the properties of the material dictate the degree to which that current is conducted. Conditions in which the material is stored or physical changes to the structure of the material will have an effect on this conductance. Biological

materials are no exception and the concentration of fluids and electrolytes contained within such materials largely govern their conductivity 2 7 .

For example, dentine is more conductive than enamel. In dental systems, there is generally a probe, from which the current is passed, a substrate, typically the tooth, and a contra- electrode, usually a metal bar held in the patient‘s hand. Measurements can be taken either from ena mel or exposed dentine surfaces. In its simplest form, caries can be described as a process resulting in an increase in porosity of the tissue, be it enamel or dentine. This increased porosity results in a higher fluid content that sound tissue and this difference by can be detected electrical by electrical or

measurement impedance 2 7 .

decreased

resistance

[4] OPTICAL CARIES DETECTION TECHNIQUES: Optical caries detection methods are based on

observation of the interaction of energy which is applied to the tooth, or the observation of energy which is emitted
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from the tooth. Such energy is in the form of a wave in the electromagnetic spectrum. In its simplest form, caries can be described as a process resulting in structural changes to the dental hard tissue. The diffusion of calcium, phosphate, and carbonate out of the tooth, the demineralisation process, will result in loss of mineral content. The r esultant area of demineralised tooth substance is filled mainly by bacteria and water. The porosity of this area is greater than that of the surrounding structure. Increased scattering of incident light due to this structural change appears to the human eye as a so called white spot. Hence, the caries process leads to distinct optical changes that can be measured and quantified with advanced detection methods based on light that shines on and interacts with the tooth 2 9 .

SCATTERING : Scattering is the process in which the direction of a photon is changed without loss of energy. The incident light is forced to deviate from a straight path when it interacts with small particles or objects in the medium through which the light passes. In physical terms scattering is regarded as a material property. A glass of milk is seen as white because incident light on the milk is scattered in all directions, leaving the milk without absorption. Snow appears white because light incident in the snow is scattered in all directions by the small ice crystals. Light of all visible wavelengths Scattering is exits snow without suffering sensitive,

absorption.

highly

wavelength

shorter wavelengths scatter much more than longer ones. Therefore, caries detection methods employing wavelengths
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in the visible range of the electromagnetic spectra (400 nm to 700 nm) are highly limited by scattering. An early enamel lesion looks whiter than the surrounding healthy enamel because of strong scattering of light within th e lesion. Methods measuring lesion severity are based on differences enamel 2 9 . in scattering between sound and carious

ABSORPTION WITH FLUORESCENCE: Absorption is the process in which photons are stopped by an object and the wave energy is taken in by th e object. The energy lost is mostly converted into heat or into another wave which has less energy and hence longer wavelengths. In physical terms absorption is also regarded as a material property. The previous analogy of the glass of milk appearing white can be extended to a cup of tea; the tea is seen as transparent because it does not scatter light, but it looks brown because much of the light is absorbed by the tea. Likewise, mud and pollution in white snow can be seen as dark spots because certain wav elengths are absorbed by these polluted spots. Absorption of light in tissue is strongly dependent on the wavelength. Water is an example of a strong absorber in the infrared range. After absorption the energy can be released by emission of light at a long er wavelength, through the process of fluorescence.

Fluorescence occurs as a result of the interaction of the wavelength illuminating the object and the molecule in this object. The energy is absorbed by the molecule with subsequent electronic transition to the next state, to a
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higher level state where the electrons remain for a short period of time. From here the electrons may fall back to the ground state and release the gained energy in terms of longer wavelength and colour, which is related to the energy given off and fluorescent light can be emitted. Autofluorescence, the natural fluorescence of dental hard tissue without the addition of other luminescent substances has been known for a long time. Demineralisation will result in loss of autofluorescence which can be quantified using caries detection methods based on the differences in fluorescence between sound and carious enamel. 2 9

[A] OPTICAL COHERENCE TOMOGRAPHY (OCT): OCT can be defined as optical inferometric technique to create cross sectional images of scattering media. There are various functional techniques developed in OCT. They are 1) Polarisation sensitive Optical coherence

tomography (PSOCT) 2) Doppler OCT 3) Wave length dependent OCT

Among these PS-OCT is popular. Studies of light propagation in dental tissue using PS -OCT revealed strong birefingence in enamel and anisotropic light propagation through dentinal tubules. Amaechi et al used the area under the LCI signal as a measure of the degree of refle ctivity of the tissue and showed that this area is related to the amount of mineral loss, and increases with increasing

demineralization time. Hence, OCT could possibly be used
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to quantitatively monitor the mineral changes in a caries lesion. In the early investigations, birefringence induced artefacts in the enamel OCT image. These were eliminated by measuring the polarization state of the returned light. Birefringence detected by PS -OCT, however, has been shown to be useful as a contrast agent indicating precarious or carious lesions in both enamel and dentin 29 .

Baumgartner et al showed that PS -OCT can provide additional information related to the mineralization status and/or the scattering properties of the dental materials. The studies demonstrated that PS-OCT is well suited for the imaging of interproximal and occlusal caries, early root caries, and for imaging decay under composite fillings. Longitudinal measurements of the reflected light intensity in the orthogonal polarization state from the area o f simulated caries lesions linearly correlated with the square root of time of demineralization indicating that PS -OCT is well suited for monitoring changes in enamel mineralization over time. OCT provides high resolution morphological depth imaging of incipient caries. With OCT, early lesions can be readily identified as regions of high light

backscattering with depth into the enamel as compared to healthy sound enamel. From the OCT images, the lesion depth can be approximated to provide clinically useful information to guide treatment decisions. In addition, there is a derived parameter known as the optical attenuation coefficient in order to distinguish sound from carious enamel non-subjectively. OCT is being combined with
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Polarized Raman Spectroscopy (PR S) since regions of high light backscattering not related to caries development can lead to false-positive results. PRS provides biochemical specificity along with molecular structural/orientational information. With PRS, the Raman depolarization ratio calculated from the main phosphate vibration at ~959 cm -1 from parallel- and crosspolarized Raman spectra allows discrimination between sound and early developing caries. In combination, OCT and PRS have potential for detecting and monitoring early lesions wi th high sensitivity and high specificity. 2 9

[B] POLARIZED RAMAN SPECTROSCOPY (PRS): OCT imaging in regions of hypocalcification can sometimes show increased light back -scattering at the surface, which could be misinterpreted as signs of early caries. To help rule out such false -positive readings and increase the specificity of this method, OCT and PRS have been coupled of to obtain caries. biochemical PRS (e.g., provides collagen information details in on for the vs.

confirmation molecular

composition

dentin

predominantly inorganic apatite in enamel) and molecular structure of cells and tissues. Like OCT, PRS measures light scattering. Although most scattered photons have the same energy and wavelength as the incoming excitation light, about 1 in 107 photons scatter at energy different from that of the incoming light. This energy difference is proportional to the vibrational energy of the scattered molecules within the sample and is known as the Raman
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Effect. As with other emerging optical methods, the properties of the scattered light within sound or porous carious regions are being explored to determine their use in caries detection. In fluorescence-based techniques, there are a limited number of intrinsic fluorophores that can provide diagnostic information without the addition of external dyes. In contrast, PRS can provide information not only about bacterial porphyrins leached in to carious regions, but also about the primary mineral matrix and, thus, the state of demineralization or remineralisation of the tooth. This information is gathered without the need to add extrinsic dyes or agents. PRS provides information on the

composition, crystallinity and orientation of the mineral matrix, all of which are affected in caries formation or remineralization. 4

[5] ENHANCED VISUAL TECHNIQUES [A] FIBRE OPTIC TRANSILLUMINATION (FOTI) : The basis of visual inspection of caries is based upon the phenomenon of light scattering. Sound enamel is comprised of modified hydroxyapatite crystals that are densely packed, producing an almost transparent structure. The colour of teeth, for example, is strongly influenced by the underlying dentin shade. Wh en enamel is disrupted, for example in the presence of demineralisation, the

penetrating photons of light are scattered (i.e. they change direction, although do not loose energy) which results in an optical disruption. In normal, visible light, this appear s as a ‗whiter‘ area— the so called white spot. This appearance is
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enhanced if the lesion is dried; the water is removed from the porous lesion. Water has a similar refractive index (RI) to enamel, but when it is removed, and replaced by air, which has a much lower RI than enamel, the lesion is shown more clearly. This demonstrates the importance of ensuring the clinical caries examinations are undertaken on clean, dry teeth. Fibre optic transillumination takes advantage of these optical properties of enamel and enhances them by using a high intensity white light that is presented through a small aperture in the form of a dental hand piece. Light is shone through the tooth and the scattering effect can be seen as shadows in enamel and dentine, with the device‘s strength the ability to help discriminate between early enamel and early dentine lesions (see Fig. 7). A further benefit of FOTI is that it can be used for the detection of caries on all surfaces; and is particularly useful at proximal lesions 2 7 .

The diagnosis of approximal carious lesions has been primarily through visual clinical examination. However, in situations where the teeth are normally in anatomical contact with others, it is a very difficult task for the dentist to detect caries in posterior teeth by that exam, re sulting in a high proportion of false negative decisions. Conventional bitewing radiography remains the most common diagnostic aid because it has been shown to enhance the detection of approximal lesions. However, there are some problems associated horizontal with this technique, is for example, if the of

angulation

incorrect,

overlapping

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approximal surfaces will occur on the radiograph. Other problem is the incapacity of method to distinguish Fibre -optic

noncavitated

from

cavitated

lesions.

transillumination (FOTI) has been investigated as an alternative method for the detection of approximal carious lesions. In this method, a white light from a cold -light source is passed through a fibre to an intraoral fibre-optic light probe that is placed on the buccal or lingual side of the tooth and the surfaces are examined through transmitted light, which is viewed from the occlusal surface. A carious lesion has a lowered index of light transmission and so appears as a darkened shadow when transilluminated. FOTI is a simple, non-invasive, and painless procedure that can be used repeatedly with no risk to the patient. In the literature, the validity of diagnoses made with FOTI has usually been assessed by comparison with the radiographic diagnosis of the same surface, although it is well known that radiography itself is not an accurate method 2 9 .

Fibre optic consists of a halogen lamp and a rheostat to produce a light of variable intensity. Two attachments are used; a plane mouth mirror mounted on a steel cuff and a fibre optic probe of 0.5 mm diameter so that it can be placed in embrasure region. It produces a narrow beam of light for transillumination. The rheostat is set to give a light of maximum intensity. For examination the tip of the probe is placed in the embrasure immediately beneath the contact point of the proximal surface to be examined either on the buccal or lingual surface depending on the tooth. The
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marginal ridge is viewed from the occlusal surface. A shadow extending to the dentinoenamel junction beneat h the marginal ridge may be evident if there is a break in the integrity of the enamel of marginal ridge. 4

One

would of

expect occlusal

that

FOTI to

would be

enable improved

discrimination

lesions

(particularly dentine lesions), as well as detection of proximal lesions (in the absence of radiographs) to be higher. As a technique FOTI is an obvious choice for translation into general practice; the equipment is

economical, the learning curve is short and the procedure is not time consuming. However with the simplicity of the FOTI system come limitations; the system is subjective rather than objective, there is no continuous data outputted and it is not possible to record what is seen in the form of an image. In order to address some of these concerns, an imaging version of FOTI has been developed; digital imaging FOIT (DiFOTI). 2 7

[B]

DIGITAL

IMAGING

FIBER

OPTIC

TRANSILLUMINATION (DIFOTI) This is a relatively new methodology tha t was adopted in an attempt to reduce the perceived shortcomings of FOTI by combining FOTI and a digital charge -coupled device (CCD) camera. Digital Imaging Fiber -Optic

TransIllumination (DIFOTI) has been introduced to improve early detection of carious su rfaces. DIFOTI uses fiber -optic transillumination of safe visible light to image the tooth.
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DIFOTI uses visible light and not the ionising radiation and is approved by US food and drug administration for caries detection on approximal smooth and occlusal s urface as well as recurrent caries. DIFOTI uses scattering of light by carious tissue as a method of distinguishing it from healthy enamel the carious part of the tooth appears to be dark against the light background of healthy tooth. 2 9

Light delivered by a fiber-optic is collected on the other side of the tooth by a mirror system and fed to a digital electronic CCD.

Then the acquired data are sent to a computer for analysis with dedicated algorithms, which produce digital images that can be viewed by the clinician and patient in real time or stored for later use.

Schneiderman et al.24 found that DIFOTI technique has superior sensitivity over conventional radiographic methods for detection of approximal, occlusal, and smooth surface caries, and specificity was slightly less in general. It has all the advantages of FOTI and also it has overcome the disadvantage of FOTI as images in this technique can be stored for future reference.
29

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FIG. 8.7: FOTI EQUIPMENT

FIG. 8.8:

EXAMPLE OF FOTI ON A TOOTH. (A)

NORMAL CLINICAL VISION, (B) WITH FOTI.

[6] FLUORESCENT TECHNIQUES [A] VISIBLE LIGHT FLUORESCENCE — QLF: Quantitative light-induced fluorescence (QLF) is a visible light system that offers the opportunity to detect early caries and then longitudinally monitor their

progression or regression. Using two forms of fluorescent detection (green and red) it may also be able to determine if a lesion is active or not, and predict the likely progression of any given lesion. Fluorescence is a phenomenon by which an object is excited by a particular wavelength of light and the fluorescent (reflected) light is of a larger wavelength. When the excitation light is in the visible
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spectrum, the fluorescence will be of a different colour. In the case of the QLF the visible light has a wavelength (l) of 370 nm, which is in the blue region of the spectrum. The resultant auto-fluorescence of human enamel is then

detected by filtering out the excitation light using a band pass filter at l > 540 nm by a small intra -oral camera. This produces an image that is comprised of only green and red channels (the blue having been filtered out) and the predominate colour of the enamel is green.

Demineralisation of enamel results in a reduction of this auto-fluorescence. This loss can be quantified using

proprietary software and has been shown to correlate well with actual mineral loss. The source of the autofluorescence is thought to be the enamel dentinal junction — the excitation light passes through the transparent enamel and excites fluorophores contained within the EDJ. Studies have shown that when underlying dentine is removed from the enamel, fluorescence is lost, although only a small amount of dentine is required to produce the fluorescence seen. Decreasing the thickness of enamel results in a higher intensity of fluorescence. The presence of an area of demineralised enamel reduced the fluo rescence for two main reasons. The first `is that the scattering effect of the lesion results in less excitation light reaching the EDJ in this area, and the second is that any fluorescence from the EDJ is back scattered as it attempts to pass through the lesion. 2 7

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The QLF equipment is comprised of a light box containing a xenon bulb and a hand piece, similar in appearance to an intraoral camera, [see Fig. 8]. Light is passed to the hand piece via a liquid light guide and the hand piece contains the band pass filter. Live images are displayed via a computer and accompanying software enables patient‘s details to be entered and individual images of the teeth of interest to be captured and stored. QLF can image all tooth surfaces except inter - proximally. [See Fig.8.9] for an example of QLF images that have been merged to create a montage on the anterior teeth

demonstrating resolution of buccal caries over a 1 month period following supervised brushing. Once an image of a tooth has been captured, the next stage is to analyse any lesions and produce a quantitative assessment of the demineralisation status of the tooth. This is undertaken using proprietary software and involves using a patch to define areas of sound enamel around the lesion of interest. Following this the software uses the pixel values of the sound enamel to reconstruct the surface of the tooth and then subtracts those pixels which are considered to be lesion. This is controlled by a threshold of fluorescence loss, and is generally set to 5%. T his means that all pixels with a loss of fluorescence greater than 5% of the average sound value will be considered to be part of the lesion. Once the pixels have been assigned ‗‗sound‘‘ or ‗‗lesion‘‘ the software then calculates the average fluorescence l oss in the lesion, known as %DF, and then the total area of the lesion in mm2, a the multiplication of these two variables
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results in a third metric output, DQ. See Fig. 8.10 for an example of the analysis and the resultant lesion. When examining lesions longitudinally, the QLF device employs a video repositioning system that enables the precise

geometry of the original image to be replicated on subsequent visits. QLF has been employed to detect a range of lesion types. Smooth surfaces, secondary caries and demineralisation adjacent to orthodontic brackets have all been examined. The reliability of both stages of the QLF process; i.e. the image capture and the analysis; have been examined and has been shown to be substantial. The QLF system offers additional benefits beyond those of very early lesion detection and quantification. The images acquired can be stored and transmitted, perhaps for referral purposes, and the images themselves can be used as patient

motivators in preventative practice .

FIG. 8.8: QLF EQUIPMENT. (A) THE QLF UNIT LIGHT BOX, DEMONSTRATING THE HANDPIECE AND

LIQUID LIGHT GUIDE; (B) A CLOSE-UP OF THE INTRA-ORAL CAMERA FEATURING A DISPOSABLE MIRROR TIP THAT ALSO ACTS AS AN AMBIENT LIGHT SHIELD.

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For clinical research use, the ability to remotely analyse lesions enables increased legitimacy in trials; permitting, for example, a repeat of the analyses to be conducted by a third-party. QLF is one of the most promising technologies in the caries detec tion stable at present, although further research is required to

demonstrate its ability to correctly monitor lesion changes over time. There is also a great deal of interest in red fluorescence, and whether or not this can be a predictor of lesion activity and again, research is currently being undertaken in this area.
27

FIG.8.9: EXAMPLE OF QLF IMAGES. (A) WHITE LIGHT IMAGE OF EARLY BUCCAL CARIES EFFECTING THE MAXILLARY TEETH, (B) QLF IMAGE TAKEN AT THE SAME TIME AS (A), NOTE THE IMPROVED

DETECTION OF LESIONS AS A RESULT OF THE INCREASED CONTRAST BETWEEN SOUND AND

DEMINERALISED ENAMEL, (C) 6 MONTHS AFTER THE INSTITUTION OF AN ORAL HYGIENE THE LESIONS HAVE RESOLVED. 2 7 PROGRAMME,

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FIG. 8.10: AN EXAMPLE OF LESION ANALYSIS USING QLF. (A) LESION ON THE OCC LUSAL SURFACE OF A PREMOLAR PATCH IS IDENTIFIED ON AND THE ANALYSIS (B) THE

PLACED

SOUND

ENAMEL,

RECONSTRUCTION

DEMONSTRATES

CORRECT

PATCH PLACEMENT AS THE SURFACE NOW LOOKS HOMOGENOUS, (C) THE ‗SUBTRACTED‘ LESION IS DEMONSTRATED IN FALSE COLOUR INDICATING THE SEVERITY OF THE DEMINERALISATION, (D) THE QUANTITATIVE OUTPUT FROM THIS ANALYSIS AT A VARIETY OF FLUORESCENT THRESHOLD LEVELS. 2 7
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[B] LASER FLUORESCENCE — DIAGNODENT: The DIAGNODent (DD) instrument (KaVo , Germany) is another device employing fluorescence to detect the presence of caries. Using a small laser the system produces an excitation wavelength of 655 nm which produces a red light. This is carried to one of two intra -oral tips; one designed for pits and fissures, and the other for smooth surfaces. The tip both emits the excitation light and collects the resultant fluorescence. Unlike the QLF system, the DD does not produce an image of the tooth; instead it displays a numerical value on two LED displ ays. The first displays the current reading while the second displays the peak reading for that examination. A small twist of the top of the tip

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enables the machine to be reset and ready for another site examination and a calibration device is supplied wit h the system. There has been some debate over what exactly the DD is measuring; it is not employing the intrinsic changes within the enamel structure in the same way as QLF; this has been demonstrated by the inability of DD to detect artificial lesions in in-vitro settings. Instead the system is thought to measure the degree of bacterial activity; and this is supported by the fact that the excitation wavelength is suitable for inducing fluorescence from bacterial

porphyrins; a by product of metabolism (Fig 8.11). Initial evaluations of the device suggest that it may be a promising tool for clinical use. However, the device is not without its confounders, and, like many novel caries detection devices, requires teeth to be clean and dry. The presence of stain, calculus, plaque and, when used in the laboratory, the storage medium, have all be shown to have an adverse effect on the DD readings. Most confounders tend to cause an increase in the DD reading, leading to false -positives. The literature surrounding the DD device was recently assessed in a systematic review. The authors found that, for dentinal caries, the DD device performed well, although there was a great deal of heterogeneity in the studies and they were all undertaken in vitro. The authors stated th at these results could not be extrapolated into the clinical setting and then detected a worrying trend for the device to produce more false-positives than traditional diagnostic systems. Their conclusion was therefore that there was insufficient evidence to support the use of the device as a
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principle means of caries diagnosis in clinical practice. It should be noted that the DD device has not been employed in a clinical trial, so there are no data indicating that the system can detect a dose response. 2 7

FIG 8.11: THE DIAGNODENT DEVICE.

[C] INFRARED FLUORESCENCE: In theory, the tooth is exposed to light (irradiation) with a wavelength of between 700 and 15,000 nm. Barrier filters are used to observe any resulting fluorescence. Studies by Alfano et al. mention exposure of teeth to wavelengths exceeding 700 nm, but the results were not presented. Longbottom Unpublished suggest reports the commented technique is upon able by to

that

discriminate between sound and carious enamel and dentin. Further work is required to determine if the fluorescence signal from exposure to infrared irradiation is greater than that from other wavelengths. Additionally, any heating
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effects from absorption of infrared irradiation may have potentially damaging effects on t he dental pulp, given the increased penetration and decreased scattering of the longer wavelength. Specific coherent sources of such irradiation have been relatively difficult to acquire, and detection involves the use of infrared-sensitive detectors as CCDs or film 2 9 .

[7] TRANSILLUMINATION WITH NEAR-INFRARED LIGHT: The caries lesion may also be examined by shining white light through the tooth. Wavelengths in the visible range (400 – 700 nm) are limited by strong light scattering, making it difficult to image through more than 1 mm or 2 mm of tooth structure. Therefore , methods employing wavelengths in the visible range of the electromagnetic spectra (400 –700 nm) such as QLF (λ > 520 nm), LF (λ = 655 nm), and Digital Imaging Fibre-Optic

Transillumination (DIFOTI) which uses high intensity white light, are highly limited by scattering. Methods that use longer wavelengths, such as in the NIR spectra (780 -1550 nm), can penetrate the tissue more deeply. This deeper penetration is crucial for the transillumination (TI) method. Research has shown that enamel is highly transpar ent in the NIR range (750 nm-1500 nm) due to the weak scattering and absorption in dental hard tissue at this wavelengths. 2 9

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FIG 8.12: TRANSILLUMINATION (TI) WITH NEAR INFRARED (NIR) LIGHT. EXPERIMENTAL SET -UP OF THE TI SYSTEM. THE TOOTH IS ILLUMINATED W ITH NIR LIGHT. POLARIZERS ARE USED TO

EXPERIMENTALLY BLOCK OUT THE AMBIENT LIGHT FROM SATURATING THE DETECTOR, A CHARGE COUPLE DEVICE (CCD). 3 0

[8] NEAR-INFRARED REFLECTANCE IMAGING: In this technique, the tooth is exposed to light (irradiation) with a wave length of between 700 and 1500 nm. Light scattering in sound dental enamel decreases markedly in the NIR region and studies have shown that enamel has the highest transparency near 1310 nm. At this wavelength, the attenuation coefficient is only 2 to 3 cm−1, which is a factor of 20 to 30 times lower than in the visible region. At longer wavelengths, water absorption increases significantly and reduces the penetration of the NIR light . Even though the light scattering for sound enamel is at a minimum in the NIR, the light scattering coefficient of enamel increases by 2-3 order of magnitudes upon

demineralization due to the formation of pores on a similar size scale to the wavelength of the light that act as Mie scatterers. Therefore, caries lesions can be imaged with optimal contrast at 1310 nm. And detection is done by
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infrared sensitive detectors as CCD or film. According to Christian Zakian et al a sensitivity of > 99% and a

specificity of 87.5% for enamel lesions and a sensitivity of 80% and a specificity > 99% for dentine lesions. The nature of the technique offers significant advantages, including the ability to map the lesion distribution rather than obtaining single point measurements, it is also non-invasive,

noncontact, and stain insensitive. These results suggest that NIR spectral imaging is a potential clinical technique for quantitative caries diagnosis and can determine the presence of occlusal enamel and dentin lesions. 2 9

[9] TERAHERTZ PULSE IMAGING: This method uses waves with tetrahertz frequency (=1012 Hz or a wavelength of approximately 30μm) for an image to be obtained by tetrahertz irradiation, the object is placed in the path of the beam. It is possible to record tetrahertz images using CCD detector. It has no adverse thermal effects, it is non ionising low signal to noise ratio, but the cost of equipment is high, and careful interpretation is required. Dental Applications for this technique have been limited but promising. Longitudinal sections through three teeth have demonsrated increased terahertz absorption by early occlusal discriminate dental caries and an apparent ability to enamel

caries

from

idiopathic

hypomineralisation. Work in progress to image intact te eth with early carious lesion. 2 9

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[10] MULTIPHOTON IMAGING: Infra red light of 850 nm has been used for

multiphoton imaging of teeth. In conventional fluorescence imaging (QLF), a single blue photon is used to excite a fluorescent compound in the tooth. In the multiphoton technique two infrared photons (with half the energy of blue photon) are absorbed simultaneously. With this

technique, sound tooth tissue fluoresces strongly, whereas carious tooth tissue fluoresces to a much lesser extent. In practice, by using motors with micron accuracy, one can move the plane of focus through the tissue and record the sectional images from the tooth to form a 3D image. Caries will appear as a dark form with in a brightly fluorescing tooth. To highlight the diseased tissue, the image may be displayed in its negative form so that caries appear bright with in dark tooth. 2 9

[11]

TIME-CORRELATED

SINGLE-PHOTON

COUNTING FLUORESCENCE: LIFETIME IMAGING: It has also been demonstrated that fluorescence lifetime imaging microscopy (FLIM) has the ability to distinguish the carious region from sound dental tissue. Optical band pass interference filters were then applied to this broad-bandwidth source to select the 488 nm excitation wavelength required to perform TCSPC FLIM of dental structures. The white-light generation source provides a flexible method of producing variable -bandwidth visible and ps-pulsed light for TCSPC FLIM. The results from the dental tissue indicate a potential method of discriminating
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diseased tissue from sound, but stained tissue, which could be of crucial importance in limiting tissue resection during preparation for clinical restorations. 2 9

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