Teeth Fluorescence
Melanie Ren
Introduction
Reflectance and fluorescence both affect how we perceive the appearance of an object when light falls upon it. Reflectance is the absorption of visible light (400-700nm) and spontaneous emission in the same wavelength region. People usually see objects based on the light that is reflected from the surface of the object. Fluorescence on the other hand, is the absorption of UV light (<=400nm) and spontaneous emission in a longer wavelength region such as 430-450nm. Human teeth exhibit a property known as autofluorescence, which is natural fluorescence by biological structures without the presence of any artificial fluorophores. This fluorescent property gives the teeth a look of vitality that we have grown accustomed to seeing. In the dentistry setting especially, it is important to understand more about teeth fluorescence to be able to properly "patch up" natural teeth with artificial components.
Background
Cavities and other forms of teeth damage and breakdown are common in our lives but people place high value their perfect smile. Dentists use a variety of artificial materials to amend damaged teeth but must take into account many factors in order to provide the best restoration for their patient. The composites need to appear to be the same color under various lightings (as was researched by a previous project) and also have similar fluorescence properties. These two phenomena are uncorrelated so the study discussed here is focused on finding the location of and peak intensities of teeth fluorescence so that we can get a better sense of what kind of materials to consider when picking a composite, since they must fluoresce in a similar manner with natural teeth. This is especially relevant in recent years since more artificial lighting with blue or UV components are now in use.
Some previous studies have been done on teeth fluorescence as well but most are studies in vitro, while ours is in vivo. In addition, most previous studies are performed with teeth that are heavily damaged whereas our study focuses on the average subject with generally healthy teeth. Previous studies also suggest that teeth fluorescence varies with age and that older teeth fluoresce at a longer wavelength (red-shift) and fluorescence peaks at the age of 26.5 and slowly declines thereafter. To see if we can validate this observation, we recorded the subjects' age information as well to see if there are any age-related trends.
Methods
For this study a Point Grey Camera (see image) was set up with two panels of LED lights. A total of 14 different LEDs (range 365nm - 940nm) were flashed onto the target surface in sequence and then captured through 8 different monochrome filters that limited the wavelength of the light detected by the camera. The first filter is a broadband filter that lets through the entire range of the LED wavelengths. Filters 2 through 8 are ranged between 437nm - 813nm.
We began each image capture session with white chalk as our target for calibration purposes and used the acquired images to normalize for the camera gain. After the white calibration, we captured images of teeth from 10 volunteers and then performed analysis using Matlab.
For our analysis we looked at the average intensity of the pixels after processing the image to account for camera gain, and filter and LED sensitivity differences. The processed image were displayed as a visual Donaldson Matrix where the rows correspond to the filter wavelengths (emissions) and columns correspond to LED channel wavelengths (excitation/absorption). The diagonal in the diagram is where the reflectances are and the region left of the diagonal is where the expected fluorescence signals will be. In the case where there is no fluorescence, the images will appear completely black except in the broadband filter and in the reflectance diagonal.
LED Channels/Light Absorbed
365nm 395nm 447nm 470nm 505nm 530nm 590nm 627nm 655nm 680nm 780nm 850nm 880nm 940nm
Filters/Light Emitted
broadband, 437 to 463nm, 487 to 513nm, 537 to 563nm, 587 to 613nm, 637 to 663nm, 687 to 713nm, 787 to 813nm
Results
Based on inspection of our visual Donaldson Matrix for all subjects, we decided to pursue data in the first 4 LED channels (365nm - 470nm) in the UV and blue range.
