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 parameters like 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™ theory

O47000A O27000A O17000A O15000A

The QLF™ method is based on the auto-fluorescence of teeth. When teeth are illuminated with high intensity blue light they will start to emit light in the green part of the spectrum. The fluorescence of the dental material has a direct relation with the mineral content of the enamel. The Basic principle of dental fluorescence is described in more detail below. The QLF™ system consists of hardware (a handpiece and a controlbox), a Windows PC and  QLF™ software.

There is extensive scientific literature available on QLF™. Click here for an overview.



QLF™ technical specifications

QLF™ camera in mouth QLFTM\CLIN system
QLF™ parameters
QLFTM\CLIN software
QLF™ clinical trial software



QLF™ Results

The most important features of the QLF™ measuring system are: acquiration of measurement results with high precision and repeatability; easy use, reliable software measurement cycles, the potential to shorten up clinical trials.



QLF™ Basic Principle

premowl.bmp premolf.bmp
tooth image without QLF™ tooth image with QLF™


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]


B15 L41 B17 L46
B15 L41 B17 L46



QLF™ Software

The QLF™ software makes it possible to capture in-vivo images of the tooth elements in the computer. Live images are displayed in real-time on the monitor screen of the computer. Using an optimized capturing sequence, assessment of all tooth-surfaces in the mouth is a matter of minutes. A semi-automatic technique is used to quantify the lesion size and depth and volume from the image of the tooth. The software is equipped with several tools to manage very large databases of multiple patients.
The most important parameters produced by the software are:
Lesion Area (Area in mm2)
Lesion depth expressed in percentual fluorescence loss (DF in %)
Lesion volume (DQ in mm2.%)



QLF™ Hardware

front_lijntekening.gif (4246 bytes)
handstuk_lijntekening.gif (2123 bytes)


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 are shown 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.
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 special arc-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. qlf measurement probe
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.



Some QLF™ Research results

9 months.gif (25992 bytes)
Images and data  courtesy of S. Al-Khateeb, Karolinska Institutet, Stockholm, Sweden


Another typical QLF™ result as presented in the QLF™ software. The occlusal surface of the second upper premolar at different timepoints with 3 months intervals. The QLF™ system shows here a slow progression of a caries lesion in a stage where clinical intervention (drilling) is not necessary (click the screendump to show at higher resolution). QLF screendump 1


A white spot lesion as seen with QLF™. By clicking on one of the links you can follow the remineralization process over a period of 100 days. lestwo.gif (4488 bytes)
AVI   QuickTime


More information

If you would like to receive more information about QLF™ by mail please fill out the following .



Please look at our references page. You will find a number of scientific publications about the QLF™ method and measuring system here.



Copyright 2000-2006 Inspektor Research Systems BV (tel: +31 20 676 49 88) Please read our legal notice. For site related questions and remarks please contact our webmaster.