Elbert De Josselin De Jong

Quantified light-induced fluorescence, review of a diagnostic tool in prevention of oral disease

Diagnostic methods for the use in preventive dentistry are being developed continuously. Few of these find their way into general practice. Although the general trend in medicine is to focus on disease prevention and early diagnostics, in dentistry this is still not the case. Nevertheless, in dental research some of these methods seem to be promising for near future use by the general dental professional. In this paper an overview is given of a method called quantitative light-induced fluorescence or (QLF) in which visible and harmless light excites the teeth in the patients mouth to produce fluorescent images, which can be stored on disk and computer analyzed. White spots (early dental caries) are detected and quantified as well as bacterial metabolites on and in the teeth. An overview of research to validate the technique and modeling to further the understanding of the technique by Monte Carlo simulation is given and it is shown that the fluorescence phenomena can be described by the simulation model in a qualitative way. A model describing the visibility of red fluorescence from within the dental tissue is added, as this was still lacking in current literature. An overview is given of the clinical images made with the system and of the extensive research which has been done. The QLF™ technology has been shown to be of importance when used in clinical trials with respect to the testing of toothpastes and preventive treatments. It is expected that the QLF™ technology will soon find its way into the general dental practice.

Lethal photosensitization of Porphyromonas gingivalis by their endogenous porphyrins under anaerobic conditions: An in vitro study

BACKGROUND Lethal photosensitization has been previously demonstrated in Porphyromonas gingivalis, but oxygen is considered to be essential to this process. However, since P. gingivalis is a periodontal pathogen which grows in the low oxygen conditions found in the subgingival crevice, it was considered prudent to study its photosensitivity in anaerobic conditions. METHODS A series of experiments were undertaken to attempt to induce lethal photosensitization in P. gingivalis (ATCC 33277) under strict anaerobic conditions using two different 405 nm light sources. Samples of P. gingivalis were grown on a blood-containing, solid growth medium before being suspended in saline and then exposed to 405 nm light delivered by either a hand-held light source (Toothcare™) (11.4 mW/cm(2)) or a laser pointer (328.5 mW/cm(2)). With the exception of the adjustment of the P. gingivalis suspensions to a fixed optical density, the experiments were carried out in their entirety within an anaerobic chamber. RESULTS The lowest Toothcare light dose tested (0.34 J/cm(2); 30s) yielded a statically significant kill of 63.4% which increased to 94.1% kill at higher light doses (3.42 J/cm(2); 300 s). The laser pointer similarly achieved kills of 90.2% at the lower light dose tested (9.86 J/cm(2); 30s) and 94.5% kill at the highest light dose (98.55 J/cm(2); 300 s). CONCLUSIONS Lethal photosensitization can be instigated in planktonic suspensions of P. gingivalis at 405 nm delivered by hand-held devices under anaerobic conditions. This suggests the possibility that lethal photosensitization occurred by the oxygen-independent type I pathway as oppose to the oxygen-dependent type II pathway.

A Monte Carlo simulation of the influence of sound enamel scattering coefficient on lesion visibility in light-induced fluorescence

Quantitative light-induced fluorescence (QLF) is based on the dark appearance of a white spot in otherwise highly fluorescent enamel. This can be explained by the increased scattering coefficient in the white spot compared with that of sound enamel. The aim of this study was to estimate the effect of different sound enamel scattering coefficients (s_SE) and enamel thickness d, caused by developmental enamel differences, on the fluorescence appearance of white-spot lesions. We ran a Monte Carlo simulation of a 4 × 4 mm² illuminated enamel slab on a highly fluorescent background. The slab had a 0.7 × 0.7 mm², 100-µm-deep, white spot in the center. Fluorescent and back-scattered photons re-emitted from the central 2 × 2 mm² were recorded. We found that the fluorescence photon excitance from the white spot (F_WS) was less than that of sound enamel (F_SE), with an optimum difference for S_SE between 20 and 80/mm. For s_SE <20/mm, both F_SE and F_WS decreased with d. We found no relation with d for s_SE >20/mm. The results indicate that for small s_SE, we are suffering from edge losses, which explains why the optimum for lesion visibility is not found at s_SE = 0/mm, as would be expected.

Application of biophysical technologies in dental research

There is a wealth of evidence to indicate that if dental caries can be recognized at an early stage, it is possible to halt its progression or even reverse it. This has led to an increased interest in the development of diagnostic techniques capable of visualizing caries at an early stage in addition to providing clinicians with an aid to diagnosis. Several techniques are available for research and clinical applications for detecting early demineralization. This manuscript has reviewed some of the techniques currently available to determine their advantages, whether they have any limitations and their applicability to dental research and clinical dentistry. Not one method is the perfect choice in all situations, but what is clear is that the development and application of biophysical technologies have allowed major advances to be made in dental research as well as in clinical dentistry. With continued developments these technologies will play an important role in the future management of dental disease.

A Preliminary Study of the Effects of pH upon Fluorescence in Suspensions of Prevotella intermedia

The quantification of fluorescence in dental plaque is currently being developed as a diagnostic tool to help inform and improve oral health. The oral anaerobe Prevotella intermedia exhibits red fluorescence due to the accumulation of porphyrins. pH affects the fluorescence of abiotic preparations of porphyrins caused by changes in speciation between monomers, higher aggregates and dimers, but this phenomenon has not been demonstrated in bacteria. Fluorescence spectra were obtained from suspensions of P. intermedia that were adjusted to pHs commensurate with the range found within dental plaque. Two fluorescent motifs were identified; 410 nm excitation / 634 nm emission (peak A) and 398 nm excitation / 622 nm emission (peak B). A transition in the fluorescence spectra was observed from peak A to peak B with increasing pH which was also evident as culture age increased from 24 hours to 96 hours. In addition to these ‘blue-shifts’, the intensity of peak A increased with pH whilst decreasing with culture age from 24 to 96 hours. A bacterium’s relationship with the local physiochemical environment at the time of image capture may therefore affect the quantification of dental plaque fluorescence.