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Detecting Early Tooth Decay

February 22, 2011

PLM image of the occlusal surfaceBoth low-coherence light and ultrashort laser pulses can be used to measure internal structure in biological systems.  An optical signal that is transmitted through or reflected from a biological tissue will contain time-of-flight information, which in turn yields spatial information about tissue microstructure.” 

So began Huang et al. 20 years ago in the journal Science to describe their initial efforts to adapt a non-invasive fiberoptic imaging technique called optical coherence tomography, or OCT, to view tissues in the body.  In this case, they visualized the retina and coronary artery.  Five years later, Colston et al. applied OCT to the periodontal tissues of a pig, showing clearly the physical boundaries of the gingiva from the tooth and the tooth’s enamel from the cementum.  This study marked the first time that OCT had imaged a hard biologic tissue successfully. 

Since these groundbreaking papers, OCT is often employed with a polarization sensitive (PS) feature, creating the designation PS-OCT.  The PS feature eliminates reflection from the tissue surface and monitors changes to the incident polarized light due to structural changes in the tissue. 

This two-tiered approach has yielded a growing literature within the oral cavity, especially to image teeth.  A quick Pubmed search shows PS-OCT already has imaged the severity of caries lesions on smooth tooth surfaces, the extent of developmental enamel defects, and the demineralization under tooth restorations and sealants.  The device also has been used to monitor structural changes in enamel and dentin lesions as they undergo remineralization. 

Now, a team of NIDCR grantees shows for the first time in the December issue of the journal Lasers in Surgery and Medicine that PS-OCT can be used to assess early tooth demineralization.  In a study of 20 orthodontic patients, the researchers imaged pairs of structurally sound premolars that needed to be extracted.  The researchers found that they could measure early demineralization on both the buccal (facing the outside of the mouth) and occlusal surfaces (where the upper and lower teeth meet).  They explained that an area of demineralization produces a rise in reflectivity or intensity in the PS-OCT image.  This, in turn, causes a loss of intensity from the tooth’s lower layers, and the dentinal enamel junction may no longer be visible below the lesion area.  The extent of demineralization can be calculated by measuring the depth and intensity of the lesion area in the cross-polarization PS-OCT image. 

In most cases, the dentinal enamel junction was visible, indicating that PS-OCT penetrated sufficiently enough through the full thickness of the tooth enamel to acquire high quality images.  The researchers concluded, “We believe the ability to acquire complete 3D images and monitor the lesion development over longer periods of time will greatly facilitate these studies and we plan future studies along these lines.”


  • Louie T, Lee C, Hsu D, Hirasuna K, Manesh S, Staninec M, Darling CL, Fried D. Clinical assessment of early tooth demineralization using polarization sensitive optical coherence tomography, Lasers Surg Med. 2010 Dec;42(10):738-45.



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This page last updated: February 26, 2014