Laser Fluorescence and Quantitative Light Fluorescence


Fluorescence is a phenomenon by which the wavelength of light emitted from a fluorescing material that has been illuminated by laser light is changed into a larger wavelength.

Chromophores are molecules that selectively absorb light at particular wavelengths. The chromophores causing fluorescence in dental hard tissues have not been clearly identified. Blue fluorescence has been attributed to dityrosine, yellow fluorescence likely due to structural proteins in hard tissues and red to a protoporphyrin product of bacterial breakdown. Carious lesions, plaque and microorganisms also contain fluorescent substances.

It is possible to utilize the properties of light in dental diagnosis.
The difference between fluorescence of healthy tooth structure and carious lesions can be made visible by two technologies that use light for diagnosis but utilize different principles, namely, Laser Fluorescence and Quantitative Light Fluorescence (QLF).

The difference between these two technologies is that laser fluorescence aims to detect fluorescence due to bacterial byproducts while QLF aims to detect demineralized enamel.

Laser Fluorescence

Brief Description

Laser fluorescence is a relatively new technology. The basis of laser fluorescence would be to measure the fluorescence level of bacterial products such as porphyrins within carious lesions.

The best known manufacturer of laser diagnostic dental tools would be KavoUSA, which manufactures the DiagnoDent line of laser tools.


Fig 1. The KaVo DIAGNOdent

These include portable pen versions.

DiagnoDent Pen
Fig 2. The KaVo DIAGNOdent Pen Version

Working Principle

These tools utilize a small 656nm red diode laser that "supports the detection of noncavitated, occlusal pit-and-fissure caries as well as smooth surface caries at the earliest possible stage" (Sanchez -Figueras, 2004)
This light is carried to one of two intra-oral tips of the device, one which is designed for pits and fissures and one designed for smooth surfaces.

This tip emits the light and receives the resultant fluorescence. It is placed against the tooth surface and the laser light penetrates the tooth. The tip for approximal surfaces is constructed in a way that it is able to reflect the light of excitation and detection laterally.

The DiagnoDent then displays a numerical value on the two LED displays. The first display shows the current reading while the second shows the peak reading during the exam.

The intensity of the fluorescence can indicate the depth of the carious lesion, and is displayed as a number ranging from 0 - 99, with 99 the maximum.

Effectiveness, Sensitivity and Specificity

Many studies have investigated this method of caries detection.

'The threshold between occlusal caries limited to enamel and caries into dentin was found to be around 18 under humid conditions. Clinically visible white spot lesions are measurable with this device. However, very initial lesions with no fluorophores from bacteria present, are not captured by the DiagnoDent.' (Lussi et al., 1999, 2001; Shi et al., 2000)

The DiagnoDent is also unable to detect artificial lesions under in-vitro settings due to the absence of bacterial porphyrins.

Proponents of laser fluorescence claim that it has the ability to detect enamel defects that are too small for typical methods of diagnosis, such as radiography, as these are more effective when the caries has progressed to a significantly severe stage. Hence, laser diagnosis has the benefit of allowing dental caries to be treated at a very early stage. Problems of traumatic damage due to explorer probing can also be avoided.

The DIAGNOdent may have a slight tendency for false positive readings, due to contaminants.
'The presence of stain, calculus, plaque and, when used in the laboratory, the storage medium, have all be shown to have an adverse effect on the DD readings. Most confounders tend to cause an increase in the DD reading, leading to false-positives.' (Pretty, 2006)

It was concluded that DiagnoDent is more sensitive for detecting caries based on systematic reviews (Bader and Shugars, 2004; Lussi et al., 2004; Ricketts, 2005)

Quantitative Light Fluorescence (QLF)

Brief Description

QLF is another cutting edge technology available. The basis of QLF depends on the fact that enamel in teeth naturally fluoresces under certain conditions. Demineralized regions of enamel do not fluoresce as much.

Working Principle

'Laser light was used to induce fluorescence of enamel in a sensitive, non-destructive diagnostic method for caries detection. The tooth was illuminated with a broad beam of blue-green light from an argon laser, producing diffuse mono-chromatic light with a wavelength of 488nm. The fluorescence of the enamel occurring in the yellow region was observed through a yellow (520nm) high-pass filter which filters out all reflected and back-scattered light.' (Bjelkhagen & Sundstrom, 1981 ; Bjelkhagen et al., 1982)

This property of enamel has been further developed with the use of fluorescent dyes and color microvideo Charge-Coupled Devices (CCDs) to capture the diagnostic images.

To calculate fluorescence loss from the lesion, the fluorescence of the lesion is subtracted from the fluorescence of the surrounding sound tissue. The difference is found. Three lesion quantities may be obtained from this: Percentage Mean Fluorescence Loss over the lesion, Percentage Maximum Fluorescence Loss in the lesion and the area of the lesion in square millimeters.

To facilitate clinical studies at different locations, a small, portable system for intraoral use was developed with a regular non-coherent light source and filter system to replace the laser source.

Effectiveness, Sensitivity and Specificity

The portable QLF device was validated against chemical analysis and microradiography, and it was concluded that QLF was a sensitive, reproducible method for quantification of enamel lesions but limited to a depth of about 400um. (Al-Khateeb et al., 1997b)


Fig 3. Hidden Demineralisation of Tooth

Note that in the photo above, the darkened region indicates demineralized enamel.

QLF Lesion Analysis
Fig 4. An example of lesion analysis using QLF
(Pretty, 2006)

In the photo above, the red regions are due to fluorescing plaque.

Light scattering in the lesion acts as a barrier for excitation light to reach the underlying fluorescent sound tooth tissues and as a barrier for fluorescent light from the layers below the lesion to reach the tooth surface. Hence, QLF has limited depth detection.

QLF has been proven more sensitive than electrical conductance for the measurement of shallow occlusal lesions but not discrimination of deeper lesions. (Tranaeus et al. 1997b; Gonzales-Cabezas et al., 2003; Pretty et al., 2003b)

Quick Links
Homepage| Contents Page | Introduction | Visual-Tactile Caries Diagnosis | Radiography| Fiber-Optic Transillumination (FOTI)
Electrical Conductance | Laser Fluorescence And QLF | Towards The Future: Other New And Emerging Technologies | A Summary



1) Fejerskov, O., & Kidd, E. (2008), Dental Caries: The Disease and Its Clinical Management 2nd edition. Wiley-Blackwell..

2) Lussi, A., Hibst, R., & Paulus, R. (2004). DIAGNOdent: an optical method for caries detection. J Dent Res, 83 Spec No C, C80-83.

3) Pretty, I. A. (2006). Caries detection and diagnosis: novel technologies. J Dent, 34(10), 727-739.

4) Sanchez-Figueras A (2006). Laser Fluorescence Detection of Dental Caries. Retrieved October 01, 2009 from

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