The detection and treatment of dental caries has not changed radically since the time of G. V. Black. Detection of caries depended upon locating mineral loss on bite wing radiographs, examining stain and discoloured areas on the tooth surface or probing lesions with a sharp explorer. All these techniques depended upon the interaction of two parts of the electromagnetic spectrum; visible light or x-rays. Radiographs and visual examination can detect caries but at a much later stage in the disease process so treatment involves operative techniques to restore tooth structure that has been destroyed. Restorations have become more conservative with the introduction of bonding but detection and treatment is done once the lesion is fairly large. There are a number of new technologies that can locate and monitor early small carious lesions using different forms of light or energy. When one combines early detection with new technologies for remineralization we can treat, stabilize or remineralize carious lesions without the need for surgical intervention.
These diagnostic techniques focus light or energy on a tooth surface and examine the interaction with tooth structure. The interactions are classified in figure 1 from work published by Hall and Girkin in 2004.1 X-Rays involve both transmission and scattering. The scattering occurs when they encounter calcified tissue and restorations. Visual examination is looking at reflection of light from the tooth surface along with some backscattering from areas just below the surface. The newer technologies are combinations of these various phenomena including fluorescence, absorption with heat production etc.
There are a number of other factors that influence the sensitivity of the detection system such as the wavelength of light, the resolution and sensitivity of the detection system and the distance of the detector from the tooth surface. Longer wavelengths will penetrate deep into tooth structure but may miss small areas of decay. One needs to consider all these factors when harnessing light and energy for caries detection. The final consideration is the location being studied and the presence of existing restorations. Early interproximal lesions and caries around restorations present major challenges for any diagnostic system.
Dental caries arises from an overgrowth of specific bacteria that can metabolize fermentable carbohydrates and generate acids as waste products of their metabolism. Streptococci mutans and Lactobacillus are the two principal species of bacteria involved in dental caries and are found in the plaque biofilm on the tooth surface.2,3,4 When these bacteria produce acids, the acids diffuse into tooth enamel, cementum or dentin and dissolve or partially dissolve the mineral from crystals below the surface of the tooth. If the mineral dissolution is not halted or reversed, the early subsurface lesion becomes a “cavity”.
The tooth surface undergoes demineralization and remineralization continuously, with some reversibility. When exposed to acids, the hydroxyapatite crystals dissolve to release calcium and phosphate into the solution between the crystals. These ions diffuse out of the tooth leading to the formation of the initial carious lesion. The reversal of this process is remineralization. Remineralization will occur if the acid in the plaque is buffered by saliva, allowing calcium and phosphate present primarily in saliva to flow back into the tooth and form new mineral on the partially dissolved subsurface crystal remnants.5 The new “veneer” on the surface of the crystal is much more resistant to subsequent acid attack, especially if it is formed in the presence of sufficient fluoride. The balance between demineralization and remineralization is determined by a number of factors. Featherstone describes this as the “Caries Balance”, or the balance between protective and pathological factors (see figure 2).6
These early lesions (both enamel and root surface) typically have an intact hard outer surface with subsurface demineralization. The tooth surface remains intact because remineralization occurs preferentially at the surface due to increased levels of calcium and phosphate ions. Figure 37 shows a cross-section of an early carious lesion using polarising light microscopy. The line drawing in Figure 4 shows the various layers in an early lesion.8 The clinical characteristics of these early carious lesions include:
Loss of normal translucency of the enamel resulting in a chalky white appearance particularly when dehydrated,
Fragile surface layer susceptible to damage from probing, particularly in the pits and fissures,
Increased porosity, particularly of the subsurface, with increased potential for uptake of stain,
Reduced density of the subsurface, which may be detectable radiographically (depending upon mineral loss and location) or with transillumination (depending upon location and loss of mineral),
Potential for remineralization with increased resistance to further acid challenge particularly with the use of enhanced remineralization treatments.9
Radiographic and visual examination are satisfactory if there is a substantial cavitated carious lesion. Detecting early pit and fissure caries is challenging. Radiographic imaging is of minimal diagnostic value because of the large amounts of surrounding enamel.10,11 A number of studies have found the dental explorer inefficient for the diagnosis of occlusal caries.12,13 There are a number of the concerns with the use of the explorer in detecting pit and fissure caries:
Since cavitation in pit and fissure caries occurs late in the disease process, using an explorer stick to detect caries only finds larger lesions,
Probing an occlusal pit or fissure could convert a small lesion into a larger one,14
The probing could produce irreversible traumatic defects in areas that have the potential to remineralize,
Probing can inoculate the fissure with microorganisms from other intraoral sites,15,16
A stick or catch with an explorer may be due to fissure morphology or probe pressure rather than a carious lesion.
Radiographs do perform well in detecting carious lesions in interproximal areas, especially if the area of decay is at least half way through the enamel or into dentin In terms of early lesion detection, radiographs are not able to detect small lesions in the order of 50 – 100 (microns) in the interproximal areas, which could remineralize if detected early and suitable preventive measures instituted.17 An extensive review of the literature by Dove18 found that “overall the strength of the evidence for radiographic methods for the detection of dental caries is poor for all types of lesion on proximal and occlusal surfaces”. He further stated that “it is beneficial only if the intervention is the surgical removal of tooth structure and detrimental if it is used for non-invasive remineralization methods”. Pretty and Maupome in their review of radiographic diagnostic procedures concluded that “for interproximal lesions a clinician using radiographs can be very certain of the lack of disease in apparently sound surfaces (97% specificity) but not as certain that disease is indeed present in suspect interproximal surfaces (54% sensitivity)”.19 Radiographs and visual examination are valid diagnostic tool for the detection of larger lesions but there is need for more sensitive methods.
DIAGNODent20,21 uses laser excitation to distinguish between carious and healthy tooth structure. The device is based upon the fluorescence caused by porphyrins (chromophores or coloured protein molecules) present i
n carious tissue and not the amount of enamel demineralization.22 Porphpyrins are also found in a number of oral bacteria but not the prime bacteria found in dental caries (Strep mutans and Lactobacilli).23 Porphyrin fluorescence can lead to false positives since porphyrins are also found in stained, healthy fissures.24,25 A number of studies have been performed to assess the feasibility of using this device,26,27 and they have concluded there is potential to improve occlusal caries assessment compared to visual examination and radiographs. Nevertheless, a validity study involving the DIAGNOdent concluded that it was not statistically significantly different from visual inspection.28 DIAGNOdent is suitable for detecting small superficial lesions, rather than deep dentinal lesions.29 There are various sensitivity and specificity values obtained for the DIAGNOdent and they differ widely among different researchers, 0.76 ~ 1.00 for the sensitivity and 0.47 ~ 0.94 for the specificity.30,31,32,33,34
Ongoing research discovered that certain dental polishing pastes that became trapped in the occlusal grooves also luminesced when exposed to the DIAGNODent light creating a false positive signal35 In addition, plaque, calculus and composites also created a false signal.36 Work just published by Karlson and others found that DIAGNODent is not suitable as a diagnostic tool for root caries, a common problem in older patients.37 Fluorescence especially at this particular wavelength may not provide the most accurate tool for early caries diagnosis since it is monitoring porphyin fluorescence and is not linked to the status of the enamel crystal.
QLF or Quantitative Light-Induced Fluorescence was developed by Inspektor Research in the Netherlands and is now distributed in North America by 3M. With QLF, real-time fluorescent images are captured into the computer and stored in an image database. Proprietary software developed by Inspektor Research enables the user to quantify parameters like mineral loss, lesion size, stain size and severity with precision and repeatability. Several studies have demonstrated the ability of the QLF system to detect and monitor caries over time, both in children and adults.38,39,40 The principle behind it relies on the fact that the enamel surface will fluoresce under certain optical excitation conditions.41 If the enamel is demineralized, the enamel fluoresces less and this loss of fluorescence is detected and quantified by QLF.42,43
QLF is more accurate than visual examination44 or radiographs, DIAGNODent or DIFOTI.45 QLF is very promising but there is need to develop the capability to probe lesion depths. It may not be able to detect interproximal lesions deep within the contact area. QLF has also been adopted by other manufacturers but it may not be as sensitive as the Inspektor Research version due to differences in software analysis and image capture technology. QLF examines the changes in fluorescent images of a tooth surface and is able to provide an accurate assessment of changes in mineral content of the tooth.46
The Caries ID from Midwest detects reflected infra-red and red light from the tooth surface. Using an incident beam from an LED, the device measures the reflectance. Healthy enamel is more translucent than demineralized enamel so the device is able to measure and quantify the change in reflectance. Caries ID is able to detect early caries on smooth surfaces, interproximal areas and occlusal fissures. There may be false positives associated with the following conditions:47
teeth with growth malformations in enamel or dentin such as amelogenesis imperfecta
teeth with dark stains
hypermineralization
hypocalcification
dental fluorosis
The Caries ID may generate false positives in these situations:48,49
on or at the interface of dental restorations or for residual drilling caries detection
on buccal and lingual areas of anterior and posterior teeth
on dark brown stains, calculus and intense plaque,
on restorations and sealants
on primary teeth due to thin enamel
if there is very intense ambient light
on dry teeth.
Since the technology is based upon reflectance and not luminescence the device cannot detect lesions below the surface and can be fooled by dark stain and surface topography. The technology was just introduced in 2006 with very little published background research initially. Caries ID may be more accurate than visual or radiographic examination for pit and fissure caries but it has a number of limitations and can not be used to assess ongoing remineralization or demineralization.
The Canary System developed by Quantum Dental Technologies takes a different approach to light interacting with teeth. The Canary, using the same type of near Infra-Red laser as DIAGNODent or Caries ID, rapidly pulses the laser and looks at the interaction of the laser light when the laser is turned off. When pulses of laser light are focused on a tooth, the tooth glows and releases heat. The analysis of the re-emitted radiation (luminescence) and the thermal behavior of the emitted infrared photons, provides very accurate information about the condition of the tooth. As a lesion grows, there is a corresponding change in the signal. As remineralization progresses, a signal reversal indicates an improvement in the condition of the tooth. The temperature rise in the tooth is no more than 1-2 degrees Celsius which patients can not detect. There is no alteration of any of the tissues and no safety issues such as those associated with dental x-rays.
The Canary System is able to see down about 4-5 millimetres (the average depth of tooth enamel), by changing the cycle or frequency of the laser pulse. Low frequencies about 5 Hertz, are deep probes because the heat that is generated pulses up and down very slowly and so it penetrates very deeply into the tooth. High frequencies, around 1,000 Hertz are shallow probes.
Research has shown that PTR-LUM technology used in The Canary System can detect:
Occlusal Pit and fissure caries 50,51,52
Smooth Surface Caries53,54
Acid Erosion Lesions55
Root Caries56,57
Interproximal carious lesions58,59
Demineralization and Remin-eralization of early carious lesions60
PTR-LUM has demonstrated that it is able to detect small early lesions in order of 50 microns in depth, even in the interproximal regions of teeth. The Canary System is currently undergoing clinical trials which should be completed by the time this article is published.
This is one of the most challenging clinical situations for all these new technologies. Restorative materials including amalgam and composite resin, at times, mask the ability of laser light or other forms of energy to penetrate the material. Radiographs can show us defects along the gingival seats of Class II restorations but they cannot examine the walls of the restorations nor the occlusal surfaces. DIAGNODent, D-Carie and QLF have problems with caries detection although QLF is able to monitor the margins of composites and sealants on the occlusal, buccal and lingual surfaces. The Canary System using PTR-LUM has shown in preliminary studies the ability to detect lesions around the visible margins of composites.61
Light, energy and teeth allow for some very interesting interactions. Using low power las
ers, x-rays, visible light and other modalities we can explore and detect caries and other defects in teeth. Each modality has its strengths and weaknesses but the new and emerging technologies will allow clinicians to non-invasively detect and monitor tooth decay. Developing sensitive monitoring systems means we can create unique remineralization programs for our patients and change the way we treat dental caries. Waiting for cavitation may not be optimal treatment. Early detection and remineralization will emerge as the standard approach to treating dental caries. oh
Disclosure
Dr. Stephen Abrams is CEO of Quantum Dental Technologies, which has developed The Canary Dental Caries Detection System. He has not received any compensation for the preparation of this article.
Stephen Abrams is the founder of Four Cell Consulting, Toronto Ontario, Canada, which provides consulting services to dental companies in the area of new product development and promotions. Dr. Abrams recently founded Quantum Dental Technologies, a company developing laser-based technology for the early detection and ongoing monitoring of dental caries. He developed the “Triple Laminate Technique” for utilizing soft tissue undercuts when fabricating complete and partial dentures. Dr. Abrams was awarded the Barnabus Day Award from the Ontario Dental Association for 20 years of distinguished service to the dental profession. He is one of the founding board members of ACCERTA Claim Corporations, a dental and pharmacy claims management company. He can be contacted at (416)-265-1400 or e mail; dr.abrams4cell@sympatico.ca
Oral Health welcomes this original article.
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