Recent Aids in diagnosis of dental caries

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 Imaging Fiber-Optic TransIllumination

(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

Current Concepts In Cariology Page 121


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 pattern recognition,

probabilistic considerations and 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 mental resting place on the

way to intervention’. Figure 8.1 illustrates the classical

diagnostic decision process as outlined above. 26



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 vision 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



currently available to practitioners or will shortly be made

so. These detection systems are therefore 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 way 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. 27



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 described 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



clinical research. They relied heavily on an explorer “catch”

for detection of 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 and

Assessment Criteria (ICDAS), the development of which

involved a joint effort of 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 good

intraexaminer and interexaminer agreement, as well as

satisfactory sensitivity and specificity 28.

[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 28.

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 pixel

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 yield than that of traditional radiographs.

Research has confirmed this; with sensitivities and

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

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. 27

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

the images together, then any differences in the pixel values

must be due to change in the object.



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. 27

FIG. 8.3: EXAMPLE OF A SUBTRACTION OF TWO

DIGITAL BITEWING RADIOGRAPHS. (A) RADIOGRAPH

SHOWING PROXIMAL LESION ON MESIAL SURFACE


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.


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 MORE 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

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 electromagnetic 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 through an electrophoretic

development process using liquid toner. The 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. 30

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

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 particles

collections peripherally than in central charged areas. This

greatly enhances local contrast which, in turn, improves

resolution and image quality.

SIMULTANEOUS EVALUATION OF MULTIPLE

TISSUES

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



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 is a highly electrically stable layer.

However, the layer is quite 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 significant

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



cycle, compressed air is expressed from 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 may

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. 27

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.

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 that

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 fluoride 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

FIG. 8.6: ECM VALUES FROM A ROOT CARIES STUDY

USING HIGH AND LOW CONCENTRATIONS OF

FLUORIDE DENTIFRICES. THE INCREASING ECM

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 impendence 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

[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 27.

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 enamel 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 can be detected by electrical measurement by

decreased electrical resistance or impedance 27.

[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

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 resultant

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 29.

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 exits snow without suffering

absorption. Scattering is highly wavelength sensitive,

shorter wavelengths scatter much more than longer ones.

Therefore, caries detection methods employing wavelengths

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 the

lesion. Methods measuring lesion severity are based on

differences in scattering between sound and carious

enamel29.



ABSORPTION WITH FLUORESCENCE: Absorption is

the process in which photons are stopped by an object and

the wave energy is taken in by the 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 wavelengths 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 longer 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 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. 29

[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 reflectivity 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

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 of

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

Polarized Raman Spectroscopy (PRS) 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 with high sensitivity and high

specificity. 29

[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 to obtain biochemical information for

confirmation of caries. PRS provides details on the

molecular composition (e.g., collagen in dentin vs.

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

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 into 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. When 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 appears as a

‘whiter’ area—the so called white spot. This appearance is

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

lesions27.

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, resulting 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 with this technique, for example, if the

horizontal angulation is incorrect, overlapping of

approximal surfaces will occur on the radiograph. Other

problem is the incapacity of method to distinguish

noncavitated from cavitated lesions. Fibre-optic

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 29.

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

marginal ridge is viewed from the occlusal surface. A

shadow extending to the dentinoenamel junction beneath the

marginal ridge may be evident if there is a break in the

integrity of the enamel of marginal ridge. 4

One would expect that FOTI would enable

discrimination of occlusal lesions to be improved

(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). 27

[B] DIGITAL IMAGING FIBER OPTIC

TRANSILLUMINATION (DIFOTI)

This is a relatively new methodology that 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 surfaces. DIFOTI uses fiber-optic

transillumination of safe visible light to image the tooth.

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 surface 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. 29



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

FIG. 8.7: FOTI EQUIPMENT


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.


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

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 auto-

fluorescence 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 fluorescence 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.27

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%. This 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 loss in

the lesion, known as %DF, and then the total area of the

lesion in mm2, a the multiplication of these two variables

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.

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 detection 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 PROGRAMME,

THE LESIONS HAVE RESOLVED. 27



FIG. 8.10: AN EXAMPLE OF LESION ANALYSIS USING

QLF. (A) LESION ON THE OCCLUSAL SURFACE OF A

PREMOLAR IS IDENTIFIED AND THE ANALYSIS

PATCH PLACED ON SOUND ENAMEL, (B) THE

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. 27



[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 displays. 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

enables the machine to be reset and ready for another site



examination and a calibration device is supplied with 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 that

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

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. 27

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. Unpublished reports commented upon by

Longbottom suggest that the technique is able to

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

effects from absorption of infrared irradiation may have

potentially damaging effects on the 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

film29.

[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 transparent in the NIR range (750 nm-1500

nm) due to the weak scattering and absorption in dental

hard tissue at this wavelengths. 29

FIG 8.12: TRANSILLUMINATION (TI) WITH NEAR-

INFRARED (NIR) LIGHT. EXPERIMENTAL SET-UP OF

THE TI SYSTEM. THE TOOTH IS ILLUMINATED WITH

NIR LIGHT. POLARIZERS ARE USED TO



EXPERIMENTALLY BLOCK OUT THE AMBIENT LIGHT

FROM SATURATING THE DETECTOR, A CHARGE

COUPLE DEVICE (CCD). 30

[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

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. 29

[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 caries and an apparent ability to

discriminate dental caries from idiopathic enamel

hypomineralisation. Work in progress to image intact teeth

with early carious lesion. 29

[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. 29

[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

diseased tissue from sound, but stained tissue, which could

be of crucial importance in limiting tissue resection during

preparation for clinical restorations. 29


Documents

Recent Aids in diagnosis of dental caries