Light induced fluorescence evaluation: A novel concept for caries diagnosis and excavation.

In the era of minimal invasive dentistry, every effort should be directed to preserve the maximum tooth structure during cavity preparation. However, while making cavities, clinicians usually get indecisive at what point caries excavation should be stopped, so as to involve only the infected dentin. Apparent lack of valid clinical markers, difficulties with the use of caries detector dyes and chemo mechanical caries removal systems carve out a need for an improved system, which would be helpful to differentiate between the healthy and infected dentin during caries excavation. Light induced fluorescence evaluation is a novel concept implicated for caries detection and for making decisions while cavity preparation. This paper describes a few cases that explain the clinical applicability of this concept, using the SoproLife camera that works on this principle. Autofluorescence masking effect was found to be helpful for caries detection and the red fluorescence in the treatment mode was found helpful in deciding 'when to stop the excavation process.' Light induced fluorescence evaluation - Diagnosis - Treatment concept concept can be used as a guide for caries detection and excavation. It also facilitates decision making for stopping the caries excavation so as to involve infected dentin only.

INTRODUCTION

Once the caries has reached the cavitary stage, the only treatment option left is to restore the lesion, because of the irreversible nature of the disease. Till yester years, cavities were made using GV Black's principles that dictate extension for prevention. This classical approach to treat dentinal lesions mandates removing all the infected and affected dentin. However today, there is paradigm shift in the manner in which the cavitated dentinal lesions are handled.[1] With changes in the materials and restorative principles, the concept of ‘Minimally Invasive Dentistry (MID)’ has taken the lead. And, it is now well accepted to extend the cavities only to involve infected dentin and leaving the affected dentin as such.[23] However, while making cavities, it is usually difficult to know at what point caries excavation should be stopped, such as to involve only the infected dentin. This is due to the lack of valid clinical markers to differentiate between the infected and affected dentin.

Many subjective factors like consistency of the tissue and color are being used throughout to differentiate between the healthy and diseased dentinal tissue, and thus serve as a guide for the termination of the excavation process.[4] Other methods used to facilitate this excavation process include: use of caries detector dyes; use of chemo mechanical measures; smart prep burs,[5-8] etc. But there are concerns with their usage, like inadvertent cutting of sound dentin, increased time to excavate etc.[69] Fluorescence has also been used to guide the excavation process.[10-12] Based on the property of fluorescence of dental tissues, four different fluorescence visions can be observed: green fluorescence indicating healthy tissues; black green fluorescence indicating infected dentin; bright red colour indicting the margin of infected/affected dentin; and, acid green fluorescence indicating sound dentin at the end of excavation. These different fluorescence signals aid in caries detection and decision making during cavity preparation. This concept has been termed as Light Induced Fluorescence Evaluation – Diagnosis - Treatment concept (Life D.T concept).[1314]

Recently a new fluorescence based camera system that works on the principle of Life D.T has been launched to aid caries detection and to guide cavity preparation [SoproLife (Sopro, La Ciotat, France)]. The camera captures the images in three different modes that is, daylight, diagnosis and treatment mode.[13] Capturing in the day light provides a white light image with a magnification of more than 50 times than the tooth surface. The other two modes of the camera work on the principle of autofluorescence.[14] In the diagnostic mode, the camera uses a visible blue light frequency (wavelength 450 nm) to illuminate the surface of the teeth, and provides an anatomic image overlay of the green fluorescence image on the “white light” image. This green fluorescence is considered as an indicator of healthy dental tissues; while carious lesions could be detected by variation in the auto fluorescence of its tissues in relation to a healthy area of the same tooth.

In addition to the green fluorescence, red fluorescence may also be seen in some diagnostic mode images. This red fluorescence may represent deep dentinal caries; however, at the same time it might be a false signal coming from the organic deposits covering the tooth. Terrer E. et al. found a correlation between this red signal and organic deposits in the bottom of the groove.[13] Hence, if a red fluorescent signal is encountered in the diagnostic mode images, it needs to be validated. For validation, the area showing the red fluorescence should be washed off with sodium bicarbonate or pumice, and if the fluorescence persists, then only it is considered to be representative of infected dentin. The fluorescence would no longer be there, if the source is simply the organic deposits on the tooth surface.

The third mode is the treatment mode, and the red fluorescence captured in this mode is considered as an indicator to differentiate between infected and affected dentin.[1314]

The aim of this paper is to look upon the clinical applicability of the Life D.T concept for caries detection and excavation.

CASE REPORTS

In this paper we present clinical cases done using the principles of Life D.T concept, with SoproLife Camera system. The study involved human volunteers, and was approved by the institutional review board of Dayanand Anglo-Vedic Dental College Yamunanagar, India. An informed consent was sought from the volunteers for participation in the study. The caries in all the experimental teeth were diagnosed, and excavated applying the Life D.T concept, using different fluorescence signals. The clinical implications of the various fluorescence signals have been tabulated in Table 1. An assessment of caries excavation may be explained under following principles:

Table 1

Different fluorescence visions and its interpretations

Principle 1: Autofluorescence masking effect

Green fluorescence in the diagnostic mode of the camera is considered an indicator of healthy tooth and loss of green fluorescence (black green fluorescence) indicates infected dentin. This loss of green fluorescence is termed as ‘Autofluorescence masking effect’. In the first patient, the caries in tooth # 36 was scored as International Caries Assessment and Detection System 3 (ICDAS 3) [Figure 1a]; however. The pictures taken with SoproLife camera did show an autofluorescence masking effect in the disto-occlusal aspect of the tooth [Figure 1c], while only slight altered fluorescence was seen on the mesio-occlusal aspect [Figure 1c]. Using the Life D.T guidelines, this autofluorescence masking was indicative of deep dentinal caries. The caries was then excavated by the clinician who was blinded with the fluorescence signals. At the end of excavation, it was observed that a deep cavity had to be made in the Disto Occlusal aspect [Figure 1d]. Thus it might be concluded that “autofluorescence masking” effect can be used as an indicator to diagnose infected dentinal caries.

Figure 1

(a) White Light Image of 36, (b) Image showing loss in fluorescence on the Disto Occlusal aspect and green fluorescence on Mesio Occlusal aspect, (c) Image of cavity (A shallow cavity on the Mesio Occlusal aspect), Green fluorescence was achieved at the end of excavation, (d) Image of cavity (A deep cavity on Disto Occlusal aspect), (e) Image with validated red fluorescence. (Another patient), (f) Acid green fluorescence at the end of cavity

Principle 2: Excavate till acid green fluorescence is achieved

The second principle dictates that acid green fluorescence is to be achieved at the end of the excavation process, as this is considered as an indicator of sound dentin. In the second series of patients, the excavation was carried out in carious teeth without the guidance of a fluorescence camera. At the end of excavation, images were taken and acid green fluorescence was observed [Figure 1f] in a tooth which was suspected to have dentinal caries, owing to presence of validated red fluorescence, preoperatively [Figure 1e]. Similarly acid green fluorescence was also seen at the end of excavation in other patients [Figure 1b]

Thus, aiming to achieve acid green fluorescence might be used as a guideline for termination of excavation process.

Principle 3: Bright red fluorescence indicates infected/ affected dentin

This principle can only be applied when images are taken in the treatment mode. Terrer E. et al.. explained that in treatment mode images, sometimes red fluorescence may be seen at the end of excavation instead of acid green fluorescence, and this can be used as an indicator to differentiate between infected and affected dentin.[14] If bright red fluorescence is seen during cavity making and the area is soft to excavate, it indicates infected dentin, while the in areas which are hard to excavate, it indicates affected dentin. Third patient in our series was scored as ICDAS 3 both in the mesial and distal pits in tooth # 26. The diagnostic mode image showed red fluorescence in both the pits, which was validated even after washing with sodium bicarbonate, indicating infected dentin [Figure 2a]. During excavation, deep dentinal cavities was seen beneath both mesial and distal pits [Figure 2b], and at the end of cavity preparation, the treatment mode images were captured, and bright red fluorescence was seen in both the pits [Figure 2c]. This bright red fluorescence indicates infected/affected dentin to be confirmed using manual excavator. Applying the Life DT principles, only the areas that were “soft to excavate” were regarded as infected areas, while the "hard to excavate" was left as such. Conclusively, these principles might be helpful in guiding the clinicians to detect initial caries, and also useful to guide caries excavation by differentiating between the infected and affected dentin.

Figure 2

(a) Validated red fluorescence, (b) White light Image after caries excavation, (c) Image during cavity preparation showing bright red fluorescence

DISCUSSION

Though there is an increased focus on promoting the detection of non cavitated carious lesions, the irony is that in most of the clinical settings the lesions are detected at the cavitated stage only. And once caries is detected at the cavitation stage, restoration is the only viable option. While making dentinal cavities, clinicians frequently get confronted about where to stop the caries excavation process. Dentinal caries has an outer layer contaminated by bacteria forming a non-remineralizable necrotic collagen matrix, and an inner layer, having the potential to remineralize.[3]

In an ideal situation, only the layer of carious dentin, which is rich in bacteria, unremineralizable, and has necrotic tissue remaining on its surface, should be removed while leaving the inner remineralizable dentin (affected dentin) as such.[415] The inherent subjectivity in detecting this excavation boundary results in clinically significant differences in the quality and quantity of dentine removed by different operators. The need of the hour is to shift the restorative dentistry towards MID dentistry, and this requires promoting the use of novel diagnostic equipments, or other such aids that can help us to know ′where to stop the excavation process’. Various concepts that have been used in the past to guide the checkpoint for stopping the caries excavation include: use of caries detector dyes; use of chemomechanical means; and, Fluorescence Aided Caries Excavation. McComb D in a review article emphasized that though caries detector dyes are purported to aid the dentist in differentiation of infected/ affected dentin, these dyes cannot be concluded to be specific for infected dentin.[16] Literature also raises concerns that the use of these dyes frequently causes the staining of the Circumpulpal dentin or Dentino-enamel junction (DEJ), leading to unnecessary removal of sound tooth structure.[1617] Use of chemo-mechanical methods of removal of the caries is also increasing; however, these systems have been found to be much more time consuming than the conventional systems.[18] Authors have reported left-out carious dentin in DEJ regions when excavation is carried using chemo-mechanical caries removal methods.[6]

Fluorescence-aided caries excavation (F.A.C.E.) has also been used in past.[19] Lennon AM et al. in their study on F.A.C.E., caries detector, and conventional caries excavation in primary teeth concluded that excavation by using F.A.C.E. is more effective than conventional excavation in removal of the infected primary dentin.[12] In another study by Lennon et al., it was found that the excavation results on using F.A.C.E. are similar to Conventional excavation; and, superior to Caries Detector dyes and Chemo-mechanical excavation, however, these excavation procedures using F.A.C.E. required a significantly shorter excavation time as compared to the time required by conventional technique.[11] Life D.T is a novel concept based on the fluorescence property of dental tissues. It employs the priniciple that the fluorescence signals from the dental tissues can be used for caries detection and excavation, by differentiating between infected and affected dentin. SoproLife is a camera system that is based on Life D.T concept, and claims to help the clinician in diagnosing caries and in decision making during cavity preparation. Terrer E. et al. proposed that alteration in the green fluorescence should be considered as the indicator of caries.[13] This is similar to Quantitative light-induced fluorescence (QLF) system, in which, the loss of fluorescence has been shown to correlate with the degree of demineralization.[20]

In addition to the green fluorescence, red fluorescence is also observed in images captured in the diagnostic mode of the camera. The red fluorescence, in the diagnostic mode has been proposed to be either due to infected dentin, or as a false signal coming from organic tooth deposits. This initial red fluorescence needs to be validated. In the treatment mode, the red fluorescence is considered to arise from carious dentin and may be due to the breakdown of organic and inorganic constituents of dentin. This has been attributed to the Maillard reaction,[14] that is, a non-enzymatic browning reaction in carious dentin that results in the generation of advanced Maillard products (carboxymethyl lysine and pentoside).[1421] Terrer E. et al. explained this phenomenon to partially account for fluorescence variations due to suspected fluorophores in carious dentin, such as, dityrosine, pentoside and other Maillard reaction products.[14]

Our aim was to study the clinical applicability of Life D.T principles during caries excavation. The black green fluorescence (autofluorescence masking effect) was shown to be indicative of infected dentin while during cavity preparation, the bright red fluorescence was found to be indicative of infected/affected dentin. This junction was easily differentiated using a manual excavator and the areas which were hard to excavate, were left as such. Thus, different fluorescence signals were a helpful guide for caries detection and excavation. In vitro and in vivo studies are required both in unison and in comparison to other aids to validate the Life D.T concept.