DENTAL HEALTH
Using Near-Infrared Light to Detect Decay and Fast Pulses to Remove It
By Dana Talesnik National Institutes of Health
Advances in laser and light-based imaging technologies may soon change the face of modern dentistry . Tooth enamel is almost transparent at longer wavelengths , making it possible to shine near-infrared light on a tooth to detect dental decay .
“ You can see right into the tooth ,” says Dr . Daniel Fried , professor , University of California , San Francisco School of Dentistry . “ The enamel looks almost like an ice cube .”
Light-based imaging is minimally invasive , providing a safer alternative to an X-ray ’ s ionizing radiation , explains Fried . His team is also researching laser technology that can remove dental decay and composite fillings , bonding and adhesives , which could mean less painful visits to the dentist .
There ’ s long been a need for more reliable methods to diagnose tooth decay , adds Fried . Most cavities form on the occlusal surfaces of teeth . Dentists visually inspect teeth for decay , which can lead to false-positives and overtreatment . Even X-rays are not sensitive enough to detect early occlusal cavities .
“ Many lesions in the mouth have been re-mineralized and ... no longer need intervention ,” says Fried . “ Dentists have trouble telling the difference between active and arrested lesions ; this new technology has the potential of differentiating them .”
Light-Based Imaging More Precise
Fried ’ s research focuses on two kinds of light-based imaging that provide a more precise picture than X-rays and therefore could help diagnose and treat tooth decay much earlier . Near-infrared imaging is sensitive enough to detect early demineralization and can screen many teeth at once . Optical coherence tomography ( OCT ), similar to an ultrasound , shows cross-sections and can image deep into the tooth .
“ OCT [ already ] has changed the practice of ophthalmology ,” explains Fried . “ It ’ s been very successful for retinal imaging ... and it ’ s also very promising for dentistry .”
Capable of imaging through composites and sealants , OCT is particularly useful for assessing lesion severity and activity .
“ If the dentist doesn ’ t know if [ a lesion ] is active or arrested ,” says Fried , “ with OCT , you can actually see the lesion structure , how deep it is and if it has a definitive surface zone suggesting that remineralization has occurred .”
Tomography is especially suited for clinical trials as it can track changes over time . In OCT clinical trials , Fried ’ s lab has detected significant demineralization that wasn ’ t spotted visibly . He recalled that their first studies in 2010 were encumbered by slow technology . Now , they ’ ve acquired a new system that uses a scanning device on a chip capable of taking entire 3-D images in a second .
“ One of the most exciting things we can do with OCT is monitor the changes in lesions as we re-mineralize them ,” says Fried . “ With nonsurgical intervention , you can treat [ the tooth ] with fluoride and re-mineralize lesions ... That ’ s important for assessing lesion activity ” and whether intervention is necessary .
In a demineralized tooth , the decay reflects a lot of light and appears white against the healthy enamel , which looks dark in the near-infrared spectrum .
“ Tooth enamel is almost transparent at longer wavelengths , making it possible to shine nearinfrared light on a tooth to detect dental decay .”
“ We get the highest contrast at these longer wavelengths , significantly higher than other imaging technologies ,” says Fried . And there ’ s another benefit to near-infrared imaging . “ Stains , which are responsible for a lot of false-positives , don ’ t absorb at these longer wavelengths , so you can image just the demineralization without the stain .”
A recent clinical study found a dramatic difference between near-infrared imaging and X-rays , reports Fried . In 26 lesions seen at the near-infrared spectrum that penetrated the dentin , only one of them showed up on X-ray .
Lasers Can Remove Cavities .
You may know the drill . Now meet the new lasers that can selectively remove cavities . Compact and precise , these infrared lasers scan the tooth ’ s surface and emit tiny , fast pulses to remove decay selectively without overly impacting healthy tooth structure .
Dr . Daniel Fried
Fried ’ s research focuses on light-based imaging that provide a more precise picture than X-rays and therefore could help diagnose and treat tooth decay much earlier . These technologies complement each other . First , a near-infrared image is taken and Fried ’ s team has an algorithm to convert it to pixels . Then the highspeed laser scans the surface and removes decay , followed by an OCT scan that checks how much was removed .
“ You can also use the near-infrared to enhance visibility of composites ,” says Fried . “ Dentists spend more time removing existing composites and restorations than putting in new ones . If the composite is color-matched to the tooth , it ’ s hard to see where it is ,” and that makes it tough to remove without damaging nearby healthy enamel .
Spectral-guided ablation can be used to selectively remove composite from tooth surfaces . When a laser strikes material , some of it vaporizes and the plume looks different when it strikes enamel vs . composite , explains Fried .
Using spectral-guided ablation , it ’ s possible to see the calcium lines of enamel to make sure the laser is only striking composite . In a current clinical study , Fried ’ s lab is removing small composite restorations in less than a minute .
The combination of these laser and lightbased technologies could lead to earlier and better detection and intervention of dental decay .
— Adapted from the NIH Record , 2019 .
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