Twenty years ago, in the journal Science, Huang, et al described their initial efforts to adapt a noninvasive fiber-optic imaging technique called optical coherence tomography (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 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 2-tiered approach has yielded a growing literature within the oral cavit, especially to image teeth. A 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 National Institute of Dental and Craniofacial Research (NIDCR) shows for the first time that PS-OCT can be used to assess early tooth demineralization in a study published in the December 2010 issue of Lasers in Surgery and Medicine.
In the 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 and occlusal surfaces. 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 dental enamel junction (DEJ) 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 DEJ was visible, indicating that PS-OCT penetrated sufficiently enough through the full thickness of the tooth enamel to acquire high quality images. They concluded that they believe the ability to acquire complete 3-dimensional images and monitor the lesion development over longer periods of time will greatly facilitate these studies and plan future studies.
(Source: NIDCR, Science News in Brief, February 22, 2011)