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Optical Methods—Quantitative Light FluorescenceOral Health Research Institute, Indiana University School of Dentistry, Indiana University Emerging Technologies Center, Suite 222, 351 West Tenth Street, Indianapolis, IN 46202-4119; gstookey{at}iupui.edu
ABSTRACT Considerable research during the past two decades has focused upon the development of new technologies for the detection of dental caries. Of these technologies, the method that has been most extensively studied is based upon the indirectly assessed changes in the fluorescence of enamel associated with the loss of mineral. The purpose of this presentation was to review the available information regarding the use of this technology, commonly known as quantitative light fluorescence, for caries detection, particularly early caries detection, and the potential for the routine use of this technology in clinical caries trials. This technology is unique in its ability to measure small changes in the mineral content of enamel lesions quantitatively. The results of recent small-scale clinical trials have indicated that the impact of caries-preventive measures can be determined within a six-month period. With current hardware and software refinements and the results of long-term clinical validation studies that are in progress, it may be that this technology will be the future method of choice for caries clinical trials.
Key Words: caries • detection • quantitative light fluorescence BACKGROUND The need for a serious review of the methodologies used for clinical trials to assess the value of caries-preventive agents has been widely recognized for at least a decade. The pronounced decline in the prevalence, incidence, and patterns of caries in children during the 1970s and ’80s required significant changes in study designs, including marked increases in the number of subjects per group; use of populations with greater caries incidence rates; lengthened test periods; measures to closely monitor, supervise, or enhance treatments; measures to reduce and assess examiner error; utilization of more critical statistical analyses, and other procedural changes. The inevitable result of these changes in methodology was the pronounced decline in the number of clinical caries trials to evaluate new caries-preventive measures, due to various factors including the length of time required of clinical examiners, overall duration of clinical trials (about 4 years), and the rather incredible increase in cost from a few thousand to a few million dollars (Biesbrock, 2004). For many years, the loss of mineral from the enamel and dentin has been known to alter the optical properties, or visual appearance, of teeth; the commonly cited example of this is the so-called "white spot". During the 1960s and ’70s, there were a few scattered reports regarding the use of the optical properties of the teeth for diagnostic purposes. However, it was not until the early 1980s, when Swedish scientists (Bjelkhagen and Sundström, 1981; Bjelkhagen et al., 1982; Sundström et al., 1985) reported on the laser auto-fluorescence of enamel, that serious efforts began in this area. In 1981, these investigators reported on the use of laser auto-fluorescence for the qualitative assessment of mineral loss. These investigators noted that the use of laser fluorescence with the appropriate filters, rather than normal white light, enhanced the contrast between incipient lesions and sound enamel in vivo. Subsequent investigations (Hafström-Björkman et al., 1992) reported on the use of laser fluorescence for the development of a method for the quantitative assessment of enamel demineralization in vitro, and they noted that it compared favorably with longitudinal microradiography for the measurement of mineral changes in enamel in an in vitro caries model. Following these initial reports of the direct relationship between the mineral content of the enamel and the optical properties, particularly the fluorescence, substantial research was initiated by several groups of investigators to utilize this phenomenon to characterize the dental caries process using various in vitro, in situ, and in vivo models (Angmar-Månsson and ten Bosch, 1987, 1993; ten Bosch and Angmar-Månsson, 1991; Hafström-Björkman et al., 1992; Øgaard and ten Bosch, 1994; de Josselin de Jong et al., 1995; Angmar-Månsson et al., 1996, 2000; Emami et al., 1996; Al-Khateeb et al., 1997a,b, 1998a, 2000; Ando et al., 1997; Hall et al., 1997; Ferreira Zandoná et al., 1998a,b; Eggertsson et al., 1999; Lagerweij et al., 1999; Shi et al., 2001). The results of these studies clearly served to document the ability of laser or light fluorescence to quantify the amount of mineral loss associated with simulated and natural caries lesions of various sizes and to monitor changes in mineral content associated with both demineralization and remineralization. During the past few years, several in vivo and in situ studies have been conducted for further development of the quantitative light-induced fluorescence methodology in preparation for controlled clinical trials. However, relatively little information has been reported regarding the use of this methodology to monitor clinical caries or to validate the procedure clinically for the early detection of dental caries. This paper sets out to review the potential application of the method in the clinical trial setting, but technical descriptions of the methodology are outside the scope of this article. CLINICAL CARIES STUDIES In 1994, Øgaard and ten Bosch reported the results of an in vivo study in which caries lesions were induced on the buccal surfaces of vital premolars of seven orthodontic patients wearing orthodontic bands during a four-week period. The lesions were imaged at weekly intervals for 4 wks following the removal of the bands so that the fate of the lesions could be monitored with the use of light-scattering properties assessed by an optical caries monitor instrument. They noted that these early lesions regressed very rapidly following the removal of the microbial challenge and concluded that non-destructive quantitative methods could be useful for monitoring the fate of caries lesions. In 1995, de Josselin de Jong and co-workers reported a significant improvement in the instrumentation for determining quantitative laser fluorescence involving the use of a CCD microvideo camera and computerized image analysis. They also demonstrated the reproducibility of this technology for the investigation of caries lesions in situ. In 1997, Al-Khateeb and co-workers reported (1997a,b) on the use of laser fluorescence to quantify in situ effects of fluoride treatments on the remineralization of enamel lesions. Enamel specimens containing induced lesions were mounted on the buccal surfaces of maxillary first molars in 12 panelists at the initiation of each of three 35-day test periods involving different fluoride regimens. The specimens were removed at weekly intervals for imaging and replaced for continued exposure to the test regimens. From the results of the study, it was concluded that the laser fluorescence methodology permitted the detection of the amount of remineralization that occurred during the weekly intervals with each of the fluoride regimens and that the fluorescence results correlated very well with those observed with microradiography at the conclusion of the test periods. These investigators subsequently reported (Al-Khateeb et al., 1996, 1998a) the results of a pilot study using quantitative laser fluorescence to monitor changes in caries lesions in seven orthodontic patients with active lesions on the buccal surfaces of 15 teeth observed following the removal of the orthodontic brackets. The lesions were imaged in triplicate initially and at monthly intervals for 1 yr. During this period, the patients were provided instructions about dietary habits and effective oral hygiene, and they were provided a fluoride toothpaste for twice daily use. The results demonstrated that the area of the lesions decreased and that the fluorescence lost was partly regained, indicating that partial remineralization had occurred. These investigators concluded that quantitative laser fluorescence could be used to evaluate caries-preventive measures in caries-prone persons. Quite recently, the Karolinska team reported (Tranaeus et al., 2001b) on the use of the quantitative light-induced fluorescence method in a randomized six-month clinical trial to evaluate the effect of a fluoride varnish on the remineralization of white-spot lesions in 31 caries-active children from 13 to 15 yrs of age. The primary inclusion criterion was the presence of 2 or more white-spot lesions on the buccal surfaces of bicuspids and molars. Treatments consisted of professional tooth-cleaning at baseline and at six-week intervals throughout the test period. The fluoride varnish was applied to the designated patients at baseline, 1 wk, and each six-week visit. The selected lesions were examined by the fluorescence method at baseline and at six-week intervals. The results indicated that, while both regimens resulted in significant remineralization of the lesions, the fluoride varnish regimen was significantly more effective than the professional cleaning regimen alone. The investigators concluded that the quantitative light fluorescence method is a sensitive clinical method suitable for longitudinal quantification of incipient caries lesions on smooth surfaces. In February, 1998, we initiated a one-year pilot clinical study in 150 children from 9 to 12 yrs of age residing in a non-fluoridated community in Indiana, and the details of this study have been described previously (Ferreira Zandoná et al., 1999). The primary purpose of this pilot study was to obtain the necessary experiences with the then-available early prototype version of the quantitative light fluorescence (QLF) instrument to facilitate the appropriate design of future clinical trials as well as the further development of this instrumentation. All children were provided with a fluoride dentifrice and were instructed to maintain their normal oral hygiene procedures. Dental examinations were performed on all children at baseline, 4, 8, and 12 mos, with a small subset of children being examined monthly for 6 mos and bi-monthly thereafter. The children brushed their teeth with water immediately prior to each series of examinations. The series of examinations included QLF, an electrical conductance meter (ECM), a conventional clinical examination of assigned quadrants with or without the use of a dental explorer and loupes, digital radiography, and bitewing film radiography. Each type of examination was performed by a single examiner to avoid possible bias, and replicate examinations were randomly performed to assess error rates. In addition, exfoliated teeth were collected and subsequently examined by QLF prior to being sectioned for histologic, microradiographic, and polarized light analyses in 5 different laboratories. The results of these latter validation studies were reported previously (ten Cate et al., 1999).
The results from the QLF examinations (Ferreira Zandoná et al., 1999) are summarized in Fig. 1
Although the results of this pilot study were disappointing to some and did not achieve the optimistic expectations, in reality, the observations and experiences from this investigation were critical to the continued development of this methodology for several reasons. First, this was the very first time that the QLF technology had been used for the assessment of caries on occlusal surfaces. Previous studies at Indiana (Ferreira Zandoná et al., 1998a,b) had indicated that it was possible to use the QLF technology for the detection of caries in pits and fissures. Thus, occlusal surfaces were examined as well as buccal and lingual surfaces, and the results indicated that, in fact, the detection of incremental caries on occlusal surfaces was greater than that observed on buccal-lingual surfaces (Fig. 2  ). Considering the significant contribution of occlusal surfaces to the caries increments in clinical trials, this was an important advance of the technology.
Second, it was learned that the use of the QLF technology must be combined with a visual clinical examination. Since QLF actually detects any hypocalcified area, and this includes developmental defects, including dental fluorosis, it is essential to eliminate obviously non-carious hypoplastic areas with the visual clinical examination. Third, it was determined that the use of the QLF technology is a practical clinical examination procedure requiring about 15 min for an examination of all buccal, lingual, and occlusal tooth surfaces. Finally, it was found that there is a significant learning curve for a clinical examiner to achieve the necessary expertise for longitudinal clinical trials. In spite of significant practice for conducting the examinations prior to initiating this pilot clinical study, the examiners did not achieve the required level of expertise until about the four-month exam period and the completion of at least 200 examinations. In addition, several aspects of the QLF technology were identified that would greatly benefit from improvements in the methodology. These areas for further development and improvement included: (a) a visual light source within the handpiece to facilitate a visual examination of the tooth surfaces; (b) the need for an improved system for reproducibly capturing images of the suspicious areas of the tooth surfaces; (c) a method for determining whether the suspicious areas represent areas of active caries; and (d) the need for a more efficient and reproducible method for quantitatively analyzing the detected lesions. As is well-known, research on the further refinement of the QLF technology has continued, and significant improvements have been made since our 1998 pilot clinical study. A major advancement was the development of a markedly improved video repositioning system (de Josselein de Jong et al., 2000; van der Veen and de Josselin de Jong, 2001) for reproducibly capturing the desired images of lesions at subsequent examination periods. This advancement is now an integral part of the QLF instrumentation.
Recent reports (Al-Khateeb et al., 1998b; van der Veen et al., 1999; Ando et al., 2001a,b) have demonstrated the potential for using dehydration phenomena for determining whether enamel hypocalcifications detected by QLF are, in fact, active caries. Hypocalcified areas are inherently filled oral fluids, essentially water, and the presence of water alters the light-scattering properties of the area compared with sound enamel. Further, the presence of remineralization of the surface layer of an incipient enamel lesion (or white spot) retards the loss of fluid from the hypocalcified area. Since very early demineralized areas do not have a surface layer, it follows that the use of controlled dehydration will result in a rapid loss of fluid and an altered fluorescence pattern that will distinguish the lesion from both sound enamel and remineralized or arrested lesions. Fig. 3
CURRENT STATUS From these various studies, it is very clear that this technology can assess the ability of caries-preventive measures to arrest or remineralize caries lesions (van der Veen and de Josselin de Jong, 2000). Several investigations have reported the validity of this technology and its related ability to detect dental caries expressed in terms of sensitivity and specificity. As noted in recent reviews (Angmar-Månsson and ten Bosch, 2001; Tranaeus et al., 2002), the results of laboratory studies (Ferreira Zandoná et al., 1998a,b; Ando et al., 1999) as well as in vivo studies (ten Cate et al., 1999; Tranaeus et al., 2000, 2001a, Tranaeus et al., b) have demonstrated the significant potential for this technology to be used in both clinical research and clinical practice. In addition, we have reported (Ando et al., 2001c) that similar responses were observed in both deciduous and permanent teeth. Further, tests of the in vivo repeatability and reproducibility (Angmar-Mänsson and ten Bosch, 2001; Tranaeus et al., 2002) of both stages of the method (image capture and image analysis) showed excellent results, with intra-class correlation coefficients between 0.95 and 0.98 for image capture, and between 0.93 and 0.99 for image analysis. For this technology to become a viable and practical methodology for the detection and evaluation of caries in routine clinical trials, it appears that three major areas need to be addressed. First, the QLF technology requires further refinement, particularly in relation to the prototype instrumentation used in our initial pilot clinical study. As has been noted, much of this work has already been completed, and the remaining needs are presently being addressed. In terms of timing, it is realistic to believe that these efforts will be completed within the next 12 mos. Second, the ability of the QLF technology to detect and monitor early caries must be clinically validated (ten Bosch and Angmar-Månsson, 2000). In particular, it must be demonstrated that early lesions or demineralized areas detected by QLF will develop eventually into frank clinical caries, thereby confirming that these identified areas, or so-called early caries lesions, are truly caries, as has already been suggested from in vitro and in situ studies. Supported by a Program Project grant from NIH/NIDCR, clinical studies to address this matter with regard to both primary and secondary caries have been initiated during the past few months at the University of Iowa, Indiana University, and the University of Texas. These studies involve children from 8 to 12 yrs of age with examinations conducted at six-month intervals for at least 2 yrs. New technologies being evaluated are quantitative light fluorescence (QLF) and infra-red laser fluorescence (DIAGNOdent), with a conventional visual examination based on the present non-invasive (i.e., no dental explorer) European procedures. Exfoliated deciduous teeth are being collected for evaluation by polarized light microscopy to validate the caries detection methods. Third, new clinical test designs must be identified and validated (Kingman, 1999). These designs need to consider the use of incipient lesions or very early lesions as a starting point and acceptance of the quantitative assessment of the impact of a treatment procedure during a reasonable period of time, rather than accepting only frank cavitation as an end-point. As has been recently reported (Tranaeus et al., 2001b), with white-spot lesions as a starting point, it was possible to demonstrate a significant benefit from treatments with a fluoride varnish within 6 mos—in fact, within 6 wks—using only 13 patients with 32 lesions. Not only did this study confirm the benefits that have repeatedly been reported with the use of conventional caries clinical procedures, but also the magnitude of the benefit observed with QLF was comparable with that reported previously. The use of patients with the disease under investigation and the specific assessment of the impact of the treatment on these identified lesions are procedures used in medical research to identify effective treatment procedures. Coupling this test design with the inclusion of initially non-carious but high-caries-risk tooth surfaces would permit the assessment of caries-preventive measures as well as caries treatment measures. A clinical pilot study to test and perfect this study design related to fluoride dose response is presently being initiated at Indiana University with Government support. CONCLUSIONS In summary, it is apparent that the new instrumental methods for the detection of dental caries have been developed, and their use is on the immediate horizon. Primarily because of extensive laboratory and clinical research demonstrating its ability to quantify the extent of demineralization and to monitor changes in the mineral content of lesions following treatment, Quantitative Light Fluorescence is the most likely technology for future use in clinical trials. In spite of the progress that has been made in the development of this technology, it appears that it will take two to three years to complete the necessary research for the routine use of QLF for clinical caries trials.
FOOTNOTES Presented at the International Consensus Workshop on Caries Clinical Trials, Glasgow, Scotland, January 7–10, 2002 REFERENCES
Journal of Dental Research, Vol. 83, No. suppl 1,
C84-C88 (2004) This article has been cited by other articles:
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