Fluorescence-Enhanced Theragnosis: A Novel Approach to Visualize, Detect, and Remove Caries

While most dental practices operate under a surgical model, caries management by risk assessment (CAMBRA) encourages a medical model of disease prevention and management to control the manifestation of the disease or keep the oral environment in a state of balance between pathological and preventive factors.¹ Early detection, diagnosis, and prediction of lesion activity are of great interest and may change traditional operative procedures substantially. Fluorescence tools with high levels of magnification and observational capacity have the ability to guide clinicians toward a more preventive and minimally invasive treatment strategy. Based on the fluorescence principle, light-emitting diode (LED) cameras may combine magnification, fluorescence, image acquisition, and an innovative therapeutic concept called light-induced fluorescence evaluator for diagnosis and treatment (LIFEDT). It provides strategies according to light emission and color coding, guiding decisions on preventive measures or procedural techniques that remove only the infected tissues and maintain what can be preserved.

New, proven, and evidence-based devices have been developed that are aimed at ensuring that the diagnostic process is able to gather all needed information related to any given caries lesion in question to grant a minimally invasive treatment option, leaving as much tooth structure intact as possible and, thereby, facilitating restorative material choice in accordance with the diagnosed caries specificity. "Theragnosis" is a term that combines therapy and diagnosis through fluorescence-enhanced magnification, making true minimally invasive caries management possible.²

Bioluminescence is visible light generated by a living organism through a chemical reaction. One type of chemical, luciferin, is acted on by another type of chemical, an enzyme called luciferase, in the presence of oxygen. The energy produced by this reaction takes the form of photons, or units of light. Bioluminescent organisms occur in a wide variety of habitats and include varied creatures such as beetles, fungi, plankton, and bacteria.³

Fluorescence, a type of luminescence, occurs in a gas, liquid, or solid chemical system, being a process that can cause things to emit light. Things that fluoresce absorb light of shorter wavelength and re-emit it as longer-wavelength light. This changes the color, such as from blue to red.⁴ Fluorophores are excited by a range of wavelengths, and also emit over a broad range. Thus, for any fluorophore there will be some overlap between its absorption (excitation) spectrum and its emission spectrum.⁵

Fluorescence spectroscopy and microscopy are commonly used methods in biological and chemical sciences and are established tools in bacterial biofilm analysis and detection.^6,7

Light sources used for fluorescence must produce light within the absorption region of the fluorophore of interest, at sufficient intensity. Until recently, the types of UVA light sources used included nitrogen lasers, helium cadmium lasers, high-pressure mercury lamps, high-pressure xenon lamps, and metal-halide arc lamps, which are large and expensive and have limited lifespans. LED technology, UVA-emitting LEDs, have been developed and facilitate UVA use. To observe fluorescence, optical filters are used, which pass the fluorescence wavelengths but not the excitation wavelengths. These filters can range from colored glass or polymers (such as colored spectacles) to more expensive interference filters made by depositing layer upon layer of dielectric materials onto a glass surface, each of which has different refractive indices.⁵

König et al studied spectral autofluorescence characteristics of dental caries.⁸ A wide range of carious lesions revealed characteristic emission of endogenous fluorophores with strong fluorescence bands in the red spectral region when excited with 407 nm line radiation of a krypton ion laser. Healthy hard dental tissue exhibited no emission bands in the red. The fluorescence spectra of carious lesions were typical for fluorescent porphyrins, mainly protoporphyrin IX. A possible source of these porphyrins within carious tissues is bacterial biosynthesis.

Mature plaque produces red autofluorescence when illuminated with blue light at 405 nm.^9,10 Such red autofluorescence has been observed in the fluorescence images of teeth coated with plaque or calculus.¹¹ This extrinsic red autofluorescence is formed in the dental plaque^8,11,12 and is particularly found on active caries.^13,14 Little is known about the exact origin of this autofluorescence, but the red autofluorescence is assumed to originate from specific bacterial metabolites formed in the oral biofilm, such as protoporphyrin IX.¹⁵ If red autofluorescence correlates with disease-associated plaque, this autofluorescence could serve as an indicator of plaque-induced diseases.

Composition of the growth medium has the ability to influence the way bacteria display red-fluorescing metabolic products. To identify the source of the clinically observed red autofluorescence, the rapidly changing conditions within the mouth must be considered. Bacteria related to dental caries and periodontal disease exhibit red autofluorescence. In studies, the autofluorescence characteristics of tested strains depended on the nutrients present, such as metalloporphyrins, suggesting that the metabolic products of the oral biofilm could be responsible for red autofluorescence.^16,17

Streptococcus mutans induces enamel and dentin lesions and modifies the fluorescence in the red and green spectral regions, with a stronger signal in the red region, due to porphyrin gradient signals. The presence of S. mutans may be a prerequisite for the emission of fluorescence from carious lesions, and some interactions of S. mutans with exposed tooth matrix elements may also be required for the generation or unmasking of fluorophores.¹⁸

Current available techniques are mainly handheld devices or cameras (eg, DOE Dental Oral Exam System, DentLight Inc, dentlight.com; K-Lite, Smile Line USA, smilelineusa.com). However, some devices have the advantage of employing an ultraviolet headlight and filtered loupes, leaving the hands free for operator usage. For example, the REVEAL^™ system (Designs for Vision, designsforvision.com) has loupes that are customized to the operator's ocular specificities (Figure 1). Magnification of 2.5x empowers objective valuation ability by overcoming limitations in visual, tactile, and radiological caries diagnosis. Also, the system influences treatment selection by enabling clearer identification of resin degradation, bacterial contamination, and differentiation of infected versus affected tissue. It empowers minimal caries intervention with targeted treatment delivery and management. Finally, the hands-free device provides treatment guidance for the entire process from diagnosis to differentiation of diseased and non-diseased tissue, to identification until treatment completion.

Theragnosis is the blend of therapy and diagnosis. It is applied when a product, device, or technology is used both to aid the diagnosis and as a therapeutic mode in one or more health issues. It allows improvement in cost-effectiveness and encourages the development and application of precision medicine and dentistry.^2,19 As translational research evolves in dentistry, it is expected that theragnostic modalities will be enhanced, especially as technology available for various health modalities grows in usage in the dental field.

Figure 2 provides a clinical view with the REVEAL system. Areas with orange fluorescence indicate mature biofilm. Caries detection is demonstrated on an extracted and sectioned third molar. Under daylight, brownish areas indicate arrested demineralizations (Figure 3). A caries detection dye (Sabel^™ Seek^™, Ultradent, ultradent.com) clearly penetrated into areas that were not affected by caries (Figure 4). When viewed with the dental fluorescence device, orange and brown staining indicated active caries (Figure 5).

Application of the fluorescence-enhanced theragnosis concept is illustrated with a clinical case in Figure 6 through Figure 13. While brown discolorations of fissures were visible in daylight (Figure 6), further diagnosis was necessary. With the aforementioned dental fluorescence headlight-and-loupe system, active caries lesions could be detected and differentiated from inactive caries as they were indicated by red fluorescence (Figure 7 and Figure 8). Active caries was selectively and carefully removed with an air-abrasion unit and respective powders (Sylc^® SmarTip CR and Sylc^® Caries Removal Powder, Denfotex Research Ltd, denfotexresearch.com) while brownish dentin that did not reveal active caries was preserved (Figure 9 and Figure 10). The prepared lesions were restored with composite resin (Figure 11). Figure 12 shows the postoperative situation. Care was taken to avoid any occlusal and functional contacts on the restorations (Figure 13).

Theragnosis, which combines diagnosis and therapeutics through fluorescence, allows enhancement of clinical decision-making and provision of minimally invasive interventions toward dental caries, improving precision for the dental surgeon and prevention of healthy tooth structure for the patient.

As the inventor and patent holder of REVEAL^™, Dr. Steier receives royalties from Designs for Vision.

Liviu Steier, DMD, PhD
Clinical Professor, Department of Preventive and Restorative Sciences, University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania

José Antonio Poli de Figueiredo, BDS, MSc
Professor of Oral Biology and Endodontology, Vice-Provost (Research), Federal University of Rio Grande do Sul, Porto Alegre/RS, Brazil

Markus B. Blatz, DMD, PhD
Professor of Restorative Dentistry and Chairman, Department of Preventive andRestorative Sciences, Assistant Dean for Digital Innovation and Professional Development,University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania