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Quantitative Light-induced Fluorescence

QLF™ is a dental diagnostic tool for in-vivo and in-vitro quantitative

assessment of dental caries lesions, dental plaque, bacteria activity,

calculus, staining, and tooth whitening. With QLF™ real-time fluorescent

images are captured into the computer and stored in an image database.

Optional quantitative analysis tools enable the user to quantify parameterslike mineral loss, lesion depth, lesion size, stain size and severity with high

precision and repeatability . QLF™ can be used for purposes like product

testing, clinical practice, clinical education and of course research.

QLF™ Basic Principle 

QLF™ uses the principle of fluorescence to reveal dental caries. In the

images above the hardly distinguishable lesion in the image on the left

becomes very easy to observe in the QLF™ image. The contrast between

demineralised enamel and sound enamel has almost increased by a factor

ten. Also the absence of specular reflections in the QLF™ image makes it

much easier for the digital image processing system to calculate the size

and severity of the lesion.

With QLF™ other things can be detected and quantified also, like dental

plaque, calculus, and staining. The images below show at the far left a

clear example of dental plaque on the buccal surface of the 15 (red glow at

the mesial approximal area). The second image on the left shows even

more dental plaque at the interproximal area of the lingual surface of the

41, obviously due to the retainer wire. The second image on the right

shows calculus on the mesial surface of the 17. The image on the far right

shows plaque and calculus along the gingival margin of the 46. An

amalgam restoration is also clearly visible. [tooth numbering according to

Viohl's index]

HARDWARE

The QLF™ clinical system is a portable intra-oral camera device connected

to a computer with which initial enamel caries lesions on the lingual,

buccal and occlusal areas of tooth elements in-vivo can be quantified

longitudinally in time with respect to lesion depth and lesion size. The

teeth are illuminated with blue light and the images are captured with a

yellow filter. In this way the fluorescent images from the tooth elements

are grabbed. The fluorescence has the effect that white spot lesions areshown as dark spots. It has been shown that the difference between sound

and deficient enamel is significantly higher in the fluorescence image than

in the white light image. Also it has been shown that glossy reflections are

not visible in the fluorescence image, which makes computer calculations

more reliable. The method has been tested with in-vitro experiments with

TMR, LMR and with chemical analysis. A high correlational agreement was

found. The method is also used in modestly sized clinical trials where it

was shown that the technique is very sensitive to small changes in depth

and size of the lesions.

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The hardware of the intra-oral system

includes a measurement probe, a control

unit, and a computer fitted with a

framegrabber. The control unit consists of 

an illumination device and imaging

electronics. The light source is a specialarc-lamp based on Xenon technology. The

light from this lamp is filtered by a blue-

transmitting filter. A liquid light guide

transports the blue light to the teeth in the

mouth.

A dental mirror provides uniform illumination of the area to be recorded.

The recording of the fluorescence image is done with a yellow-transmitting

filter positioned in front of a color CCD-sensor. The blue- and yellow-filter

combination is optimized in such a way that the video image is completely

free of reflections. The image is digitized by the framegrabber and is

available for quantitative analysis with the QLF™ software.