Changing Paradigm: A Different View of Caries Lesions
In the past decade advanced technologies have been developed to detect and quantify noncavitated carious lesions and aid in the objective monitoring of therapeutic or preventive treatments. While these are powerful tools in detecting early stages of demineralization, they are also important in determining lesion activity by enabling monitoring of lesions over time.
However, because caries rates in the United States have fallen and caries progression rates have slowed, the indiscriminant use of these technologies will likely result in a high number of false-positive caries calls. This could then, depending on how the instrument’s “caries” call is interpreted by the user, lessen the number of teeth that could benefit from more conservative caries interventions. Therefore, in general, the information obtained from technology-based caries detection methods requires a certain level of expertise for use and interpretation (ie, a learning curve). This implies that the untrained clinician is likely to have a high error rate in the interpretation of data provided by these technologies, which will include a high percentage of false-positive diagnoses.
Examples of technology-based methods for caries detection available in the US market that will be discussed, including their indications, advantages, and limitations, are listed in Table 1. There are other methods available in practice that are not listed (eg, luminescence and heat-based Canary System™[Quantum Dental Technologies, www.thecanarysystem.com], digital radiography), and many others not yet available in practice for caries detection (eg, ultrasonic methods, multiphoton imaging, optical coherence tomography, micro CT). As these methods are rapidly evolving and new ones are constantly appearing on the market, the competent user of any technology-based caries detection instrument should always understand the strength of the supporting evidence, be able to interpret the data obtained, and, of course, follow the manufacturer’s indications, contraindications, and instructions regarding proper use of the instrument.
Transillumination
Detection of a carious lesion is based on changes in scattering and absorption of light photons traveling through the carious lesion that can be observed by the clinician as a dark shadow. While the operatory light can be used for some lesions in anterior teeth, a more intense light using fiber-optic technology greatly enhances detection ability. Methods using this intense light source are referred to as FOTI (fiber-optic transillumination) or DiFOTI (digital imaging FOTI), which operates under the same principle as FOTI but allows for the saving of digital images of the transilluminated tooth. In the literature, most studies have focused on transillumination as a method to replace radiographs with varying performance.
For example, Vaarkamp1 et al concluded that FOTI is as specific as bitewing radiography for detecting approximal caries, but less sensitive. On the other hand, Schneiderman et al2 concluded DiFOTI had higher sensitivity than visual examination for detection of lesions more than half way through the enamel on occlusal and smooth surfaces, and higher sensitivity than radiographic examination for approximal lesions. In general, detection in posterior teeth is low for approximal enamel lesions but improves when lesions have reached dentin (comparable to radiographs).
Fluorescence Methods
Dental hard tissues fluoresce naturally with a variety of emission spectra depending on the wavelength used for excitation.3 Fluorescence-based caries detection instruments use different excitation wavelengths to elicit fluorescence of dental tissues and/or bacterial byproducts to detect and assess caries lesions. Examples are discussed in the following paragraphs.
Blue-Green Light-Induced Fluorescence
An example of a blue-green light-induced fluorescence instrument is the Quantitative Light Induced Fluorescence™(QLF) (Inspektor, www.inspektor.nl), which uses light with 290-nm to 450-nm wavelengths for caries detection (blue-green light). The fluorescence from the tooth is collected through a long pass filter (540 nm). Under these conditions a caries lesion will appear darker than the surrounding healthy tissue.4 However, if anything disrupts the path of the excitation light or the light emitted back from the tooth to the viewer/camera (demineralized crystals, a crack, hypomineralized crystals, fluorotic tissue, etc), the area will look darker. In order to accurately quantify the caries lesion, it is essential that the surface be clean and dry.
There are several blue-green light fluorescence instruments on the market. Some allow only for image acquisition (useful for patient education), while others also allow for image quantification (important for lesion and treatment monitoring). Some also allow for monitoring of other fluorescent entities, such as dental plaque, using other light wavelengths. Some of these are stand-alone instruments, while others can be easily connected to a computer. The cost is thus influenced by all these factors.
In general, instruments such as the QLF that allow for lesion quantification (eg, size, intensity of fluorescence loss) will enable easier monitoring of lesion activity and changes over time. The QLF can be used on any kind of caries lesion (ie, coronal, root, primary, secondary, smooth surface, approximal surface) as long as the surface of the lesion is accessible to the camera.
Infrared Laser Fluorescence
This technology includes the DIAGNOdent and DIAGNOdent pen (KaVo Dental, www.kavousa.com), which use pulsed diode portable lasers that emit light at 655 nm to excite fluorescence. The signal is likely derived from bacterial byproducts (porphyrins) in the lesion; therefore, it is generally secondary to the caries process itself.5 This also helps to explain the many possible causes for false-positive results using this technology, as positive readings can be obtained in response to stain in fissures (eg, tea), calculus and plaque, and some dental materials (eg, some sealants).
With these instruments, a caries lesion will provide a higher reading (higher fluorescence) than the surrounding sound tissue (the instruments give readings on a 0 to 99 scale). The DIAGNOdent has two types of probe tips (ie, smooth surfaces, and pits and fissures), while in the DIAGNOdent pen the probe tip is a wedge-shaped single sapphire fiber that rotates around its axis. This makes it possible to use the pen in interproximal spaces to monitor approximal lesions. Comparisons between the DIAGNOdent and DIAGNOdent pen have shown similar validity for both instruments.6
To decrease false-positive readings it is essential to have a clean and dry tooth surface. During scanning of pits and fissures it is important to rotate the probe, as caries lesions do not develop uniformly. To ensure reproducibility the user should be properly trained. It may also help to wait to record a value for a surface until it has been repeated at least once by the same operator. Although recommendations have been suggested of what the values in the scale represent along with possible associated treatments,7 it is important to remember that these instruments are all aids to clinical examination, and thus clinical judgment should always take precedent.
Light-Reflection Methods
Caries detection is achieved using the difference in reflective properties of sound and caries lesion structure (ie, carious tooth structure increases light scattering). For example, the Midwest Caries I.D.™(DENTSPLY Professional, www.cariesid.com) emits a soft light-emitting diode (LED) light (635 nm and 880 nm with an intensity between 4 µW and 80 µW) and captures the resulting reflection and refraction from the tooth surface (backscattering). One advantage of this method is that the tooth can be examined under wet conditions. Presence of a red light and audible tones indicate a positive finding.
However, as with other methods, the instrument is not a diagnostic stand-alone method. Interference in readings can come from stain, blood, plaque, calculus, some dental materials, and intense ambient light. There is also an increased chance of false positives in the presence of atypical morphology of the tooth or thin enamel. The instrument can be used to detect occlusal (as with DIAGNOdent, a rotating motion is needed during scanning) and approximal lesions (in this case the probe is placed occlusally on the marginal ridge following the angle of the approximal surface). With DIAGNOdent, there is no image that can be stored over time.
Electrical Conduction and Resistance
The principle of electrical conductance for caries detection is based on the fact that sound enamel has little porosity and a low amount of fluid, and thus it is a poor conductor. When a caries lesion develops, there is increased porosity and fluid in the lesion, creating a greater potential for electrical conductance. A variety of electrical conductance-resistance-based methods have been developed in recent decades for caries detection. An example is the CarieScan (CarieScan, LLC, www.cariescan.com), an instrument now available in the United States that is based on AC impedance. Impedance is the measure of the degree to which an electric circuit resists electric current flow when a voltage is impressed between two electrodes. In direct current circuits (DC) impedance corresponds to resistance. In alternating current systems (AC), impedance is a function of the resistance, inductance, and capacitance.
By measuring impedance at a range of AC frequencies (electrical impedance spectroscopy) a better picture of the electrical behavior of the tissue being studied is obtained. Every material has different impedance levels, with carious tissues having a lower electrical impedance (or higher conductivity) than sound tooth surfaces. Immature enamel is more conductive than matured enamel, and dentin is more conductive than enamel.
The CarieScan is a point system, which means the probe does not move from a particular point during scanning. The tooth should be clean and dry. A score and color reading is given between 0 (green = sound) and 100 (red = lesion cavitation) to identify different stages of noncavitated lesions. The higher the values, the more advanced are the lesions (ie, lower impedance).8 The scoring system is based on in vitro research with permanent teeth, thus the scale may not be applicable to primary teeth. The instrument cannot be used to monitor cavitated lesions or root caries lesions, as these expose dentin, which has high conductivity and low resistance, and thus would always read 100. It should not be used to detect secondary caries lesions, as there is potential for interference with some dental materials. The probe can be used on areas to which it has direct access: occlusal and smooth surfaces. The manufacturer states that the instrument should not be used on patients with fitted cardiac pacemakers.
Conclusion
In recent decades dentistry has come to recognize that caries is generally a slowly progressing disease process, and that caries lesions can progress, regress, or arrest at any point in time. Caries management should always be patient-centered and based on risk.
There is also a great emphasis on therapies that successfully allow for nonsurgical management of noncavitated lesions. These noninvasive treatments need to be monitored over time, and this is where new technology-based caries detection methods play a role. They provide the dentist with a tool to more objectively, and sometimes more precisely, monitor lesions over time and thus help determine “lesion activity” and effectiveness of treatment. They allow dentists to “see” much more than they had been able to see before (ie, better detection and assessment of earlier stages of demineralization). But this comes at a price: a high level of false-positive calls, which may lead to overtreatment. Thus, these methods require expertise and training for correct use and data interpretation. They are not stand-alone diagnostic methods, but aids to clinical decision-making.
References
1. Vaarkamp J, ten Bosch JJ, Verdonschot EH, Bronkhoorst EM. The real performance of bitewing radiography and fiber-optic transillumination in approximal caries diagnosis. J Dent Res. 2000;79(10):1747-1751.
2. Schneiderman A, Elbaum M, Shultz T, et al. Assessment of dental caries with Digital Imaging Fiber-Optic Transillumination (DIFOTI): in vitro study. Caries Res. 1997;31(2):103-110.
3. Bjelkhagen H, Sundström F, Angmar-Månsson B, Rydén H. Early detection of enamel caries by the luminescence excited by visible laser light. Swed Dent J. 1982;6(1):1-7.
4. Sundström F, Fredriksson K, Montán S, et al. Laser-induced fluorescence from sound and carious tooth substance: spectroscopic studies. Swed Dent J. 1985;9(2):71-80.
5. König K, Flemming G, Hibst R. Laser-induced autofluorescence spectroscopy of dental caries. Cell Mol Biol (Noisy-le-grand). 1998;44(8):1293-1300.
6. Lussi A, Hellwig E. Performance of a new laser fluorescence device for the detection of occlusal caries in vitro. J Dent. 2006;34(7):467-471.
7. Lussi A, Megert B, Longbottom C, et al. Clinical performance of a laser fluorescence device for detection of occlusal caries lesions. Eur J Oral Sci. 2001;109(1):14-19.
8. Pitts NB, Longbottom C, Hall AF, et al. Diagnostic accuracy of an optimised AC impedance device to aid caries detection and monitoring. Caries Res. 2008;42(3):211.
About the Author
Margherita Fontana, DDS, PhD
Associate Professor
Department of Cariology
Restorative Sciences and Endodontics
University of Michigan School of Dentistry
Ann Arbor, Michigan
Carlos Gonzalez-Cabezas, DDS, MSD, PhD
Associate Professor
Department of Cariology
Restorative Sciences and Endodontics
University of Michigan School of Dentistry
Ann Arbor, Michigan
